In the modern world, there is only one significant group ...
REPTILES
While some classify Nanchangosaurus as a thecodont which became similar to ichthyosaurs in its adaptations to aquatic life, others feel that it might be a primitive ichthyosaur intermediate between terrestrial thecodonts and later aquatic groups (Carroll, 1998).
Askeptosaurus was an aquatic diapsid (thallatosaur) which measured 2 meters (Carroll, 1998).
Australia’s fossil fauna included a lizard (goanna) which reached 4 to 5 meters in length (Dawson, 1995).
EARLY MAMMALS
Although the brains of the early mammals are larger than those of cynodonts, they retained primitive cynodont features (Kielan-Jaworowska, 2004).
Although the quadrate, articular, and angular were attached to the lower jaw in cynodonts, they probably already contributed to hearing (Kielan-Jaworowska, 2004).
Meckel’s cartilage and its associated elements are initially attached to the lower jaw of marsupial embryos (Kielan-Jaworowska, 2004).
Hadroconium is the earliest known mammal which lacks a groove in the lower jaw for Meckel’s cartilage. This groove was present in early mammals such as Sinoconodon, Morganucodon, and Haldanodon (Kielan-Jaworowska, 2004).
Sinoconodon is considered as the sister group to all other mammals. Mammalian tooth patterns evolved slowly. While SInoconodon possessed advanced features such as a distinction between premolars and molars and a single replacement of premolars, incisors and canines were replaced multiple times. It had not yet achieved consistent occlusion. Incisors and canines were only replaced once in Morganucodon, Haldanodon, and Gobiconodon. Morganucodon was the first to undergo determinate skull growth, unlike the indeterminate skull growth observed in Sinoconodon (Kielan-Jaworowska, 2004).
A separate interclavicle bone (typical of reptiles) was present in some mammals before being lost in higher mammal groups (Kielan-Jaworowska, 2004).
Docodonts were group of extinct mammals closer to crown mammals than were morganucodonts. They were typically the size of a mole or smaller (Kielan-Jaworowska, 2004).
A number of fossil mammals are classified with the monotremes. Shuotherium is the most primitive member of this clade. Several primitive monotremes are known including mammals which were quite large for Mesozoic mammals and fossil monotremes which possessed teeth (Kielan-Jaworowska, 2004).
MAMMALS:
The feature which defines mammals is a jaw joint consisting of a dentary condyle and a fossa of the squamosal (part of the temporal bone in higher mammals) and other features of the temporal bone. The only other group to possess contact between the dentary and the squamosal is the group of cynodonts thought to be most closely related to mammals, the tritheledontids. In this group, the dentary lacks a condyle and there is no clear fossa of the squamosal, indicating that their jaw joint condition was intermediate between mammals and other cynodonts (Kielan-Jaworowska, 2004).
MORGANUCODONTIDS AND CROWN MAMMALS
The common ancestor of morganucodontids and crown mammals are characterized by a single tooth replacement (although Sinoconodon replaced its premolars only once), tooth occlusion, and features of the braincase (Kielan-Jaworowska, 2004).
DOCODONTS AND CROWN MAMMALS
The common ancestor of docodonts and crown mammals evolved better tooth occlusion and additional features of the braincase (Kielan-Jaworowska, 2004).
HADROCONIUM AND CROWN MAMMALS
The common ancestor of Hadroconium and crown mammals enlarged its brain and lost the postdentary trough for ancestral bones (although a number of mammals in various lineages would possess a trough, perhaps because of reversion) (Kielan-Jaworowska, 2004).
CROWN MAMMALS
The common ancestor of modern mammals evolved better tooth occlusion, a longer cochlea, and a modified ankle (Kielan-Jaworowska, 2004).
Eutriconodontans, multituberculates, symmetrodontans, eupantotherians, and tribotherians are among the groups which are typically classified as more closely related to therian mammals than montremes, forming a nested hierarchy of clades (Kielan-Jaworowska, 2004).
Of the three mammalian fossils known from Africa during the enteri Mesozoic, two date from the Triassic (Maglio, 1978).
The triconodont Repenomamus giganticus represents the largest known Mesozoinc mammal, weighing perhaps 12-14 kg and being about 50% larger than its opossum-sized relative R. robustus. Its teeth were modified in a way that would adapt if for carnivory and remains of a young dinosaur (psittacosaur) were found in its stomach (Hu, 2005).
Hu, Yaoming. Large Mesozoic mammals fed on young dinosaurs. Nature 433: 149-52, 2005.
INSECTIVORES
Insectivores have not always existed. Insectivores are primitive placental mammals and significant variations have evolved in some of their lineages. Although most shrews are the size of mice, an island species can reach a meter in length (Prothero, 2002). Elephant shrews weigh between 50 and 540 g (Oduor-Okelo). In some insectivores, the zygomatic arch is interrupted and the jugal bone may even be absent. In some, it is possible that the only bone in the arch is the maxillary (although the nature of this bony process is still debated) (MacPhee, from Szalay, 1993). Unlike most insectivores, some species in the family Chrysochloridae and 1 genus of tenrec retain contact between the palatine and the frontal bones in the orbit (MacPhee, from Szalay, 1993).
Although all moles have the same carpal bones, they vary in sesamoid bones and the fusion of carpal bones (such as the scaphoid and lunate). Some possess a prepollex ( a radial sesamoid) in the hand and a prehallux (a tibial sesamoid) in the foot) (Sanchez-Villagra, 2005). Significant modification of the humerus occurred in some moles as an adaptation for a digging lifestyle.
The diversification of African insectivores occurred in two major waves, the first of which occurred in the Oligocene and whose lineages are mostly extinct (Maglio, 1978). [pic]
Some members of the insectivore family Talpidae have a reduced pubic symphysis while in others it is absent (although it is present in embryos). Those which lack a pubic symphysis may have a “secondary pubic symphysis” formed by the ilium (MacPhee, from Szalay, 1993).
In the insectivore family Talpidae, there are known examples of both endotheliochorial and epitheliochorial placentas (MacPhee, from Szalay, 1993)
CARNIVORES
In the modern world, there is only one significant group of carnivorous mammals, the Order Carnivora, which includes dogs, cats, bears, otters, skunks, hyenas, etc. Not a single carnivore fossil is known prior to the Cenozoic Era, indicating that these prominent species were absent from most of earth’s history. Even once carnivorous mammals are known from the fossil record, tens of millions of years pass before modern genera are known and many of the early groups (miacids, nimravid cats, “bear-dogs” and others) became completely extinct. The carnivore fossil record does not support the creationist claim that modern kinds of organisms originated in the first week of life on earth.
Modern carnivores certainly have a wide range of anatomical and physiological features which adapt them for their predatory lifestyle. Does the complexity of carnivores indicate that they were intelligently designed? No. There are many ways to be a predator and a great diversity of organisms which can be preyed on. Invertebrates such as spiders, centipedes, praying mantises, wasps, octopi, squid, and lobsters prey on other animals. Among vertebrates, fish, frogs, salamanders, turtles, snakes, lizards, crocodiles, and birds can prey on other animals. A great diversity of extinct animals were also carnivorous.
In the past, there were other groups of carnivorous mammals. South America and Australia possessed large marsupial predators, including some which resembled bears, coyotes, and saber-tooth cats. Among placental mammals, a group the called mesonychians evolved into the largest terrestrial mammalian predators in history but were more closely related to modern cows than to modern carnivores. Dolphins and many whales are carnivores. The extinct creodonts were a group of carnivorous mammals apart from the Order Carnivora. Some resembled cats and others were bear-sized. Many primates incorporate other animals into their diets. Creodonts survived in Africa longer than on other continents, perhaps because of the late arrival of dogs in Africa (Maglio, 1978).
As a result, there is no body design that modern carnivorous mammals had to possess. Ancestral carnivores did not have to evolve the only possible set of anatomical structures which would allow a predatory lifestyle, they simply had to evolve one of many possible designs. After the extinction of the dinosaurs, ancestral carnivores were able to diversify and fill empty ecological niches. Even once carnivores began to develop adaptations for a predatory lifestyle, some reworked this “design” for herbivory (such as the giant panda).
GROUPS
In the creationist model, carnivores The Order Carnivora (containing the modern carnivores) evolved in the Paleocene. The first carnivores, such as Procitis below, were weasel-like (Flynn, 1982). The order Carnivora is a monophyletic group given molecular analyses and anatomical evidence (Bininda-Emonds, 1999).
There are two suborders in the Order Carnivora: Feliformia and Caniformia. Feliformia includes the most primitive Paleocene forms (such as Procitis), a number of extinct groups, and modern forms such as cats, hyenas, and viverrids. The first hyena from the Miocene, Ictitherium, still retained many primitive features. Hyenas diversified into a number of species, such as the hunting hyena below (Flynn, 1982). Some hyenas (such as Lycyaena) possessed teeth which were not specialized for crushing bone and were more similar to those of cats. One hyena, Chasmaporthetes, is known from North America (Kurten, 1988).
Felids and hyena lineages separated from the line which led to modern herpestids and viverrids.
The suborder Caniformia includes dogs and bears. Canids were the first branch to separate from others in this lineages, followed by bears, seals, raccoons, and mustelids (Bininda-Emonds, 1999).
The miacid carnivores of the Upper Eocene and Lower Oligocene show a relationship to canids. The family Canidae seems to have originated in North America in the Oligocene after which time they spread to the Old World. The fox-sized Hesperocyon is the earliest known dog relative. Among other Late Oligocene to Miocene species (such as Mesocyon, Tephrocyon, and Tomarctus), the fossil species Leptocyon may be ancestral to the genus Canis. The first members of the genus Canis are known from the Pliocene and the first wolves of the species Canis lupus are known from the Pleistocene. (Other wolves were known which were not ancestral to dogs such as the largest Pleistocene wolf, the dire wolf). (Olsen, 1985).
The small Early Oligocene species Hesperocyon was the first known member of the group which would include bears and dogs; Cynodictis and Daphoenodon would be its descendants in the Miocene.
Osteoborus was a wolf that might have been a scavenger since its teeth would have been capable of crushing bone. Dire wolves were large with large heads, thick teeth, and short legs. The wolf-sized Borophagus possessed short legs and a large skull whose short jaws included its thick, bone-crushing teeth (Kurten, 1988).
A variety of species of the family Canidae are known in North America during 30 million years. About 3 million years ago, a coyote species existed in North America which was ancestral to both the modern coyote and to an extinct European form (Kurten, 1988).
Small wolves have been found in association with Homo erectus sites in China (dated between 500,000 and 200,000 years old) and short faced wolves thought to be related to dogs are known from mammoth-hunters of the Ukraine. A number of dog fossils have been found associated with human populations including sites dated at 12,000 years (Iraq), 11,000 to 12,000 years (North America), 10,500 years (Siberia), 7,300 years (China), and 3,000 years (Australia) (Olsen, 1985). Domestic dogs evolved from wolves (they are genetically distinct from jackals and coyotes). Domestic dogs had multiple origins with occasional interbreeding between populations (Hunt, from Szalay, 1993; Vila, 1997; Morell, Olsen, 1985).
There are about 400 breeds of dog. Many of them have undergone population bottlenecks in the evolution of their breed and, as a breed, show a higher frequency of certain genetic disorders (Lindblad-Toh, 2005).
The ancestral members of the family Canidae seem to have evolved in North America about 10 million years ago and the gray foxes are the most primitive canids alive today. The next lineage to diverge included red foxes, arctic foxes, raccoon dogs, bat-eared foxes, and fennec foxes. Of the two most derived groups, one group contains the crab eating fox, short-eared dog, maned wolf, and bush dog. Of the wolf-like canids, side-striped and black backed jackals were the earliest branch of this group followed by African wild dogs, dholes, Ethiopian wolves, golden jackals, coyotes, grey wolves and domestic dogs (Lindblad-Toh, 2005).
A number of early Tertiary carnivores, such as nimravid cats and creodonts, became largely extinct in the Oligocene of North America. By the mid-Miocene, creodonts were rare species restricted to Eurasia and Africa and of the nimravid cats, only the saber-toothed Barbourofelinae survived in North America. These carnivores in North America were replaced by amphicyonine beardogs (which had existed in North America since the Eocene) and hemi-cyonine bears which would be the major Holarctic carnivores until their extinction at the end of the Miocene. They were eventually replaced by bears, wolves, hyenas, and true cats (Hunt, 2002).
Amphicyonid carnivores, the “bear dogs”, ranged in size from under 2-4 kg to over 200 kg that are known from North America, Europe, and Africa. The earliest known genus in North America was Daphoenus whose smallest species D. lambei (2-4 kg) is probably ancestral to the later fox and wolf-sized members of the genus. Paradaphoneus was probably omnivorous and might also have climbed trees (Hunt, 2001). Amphicyonid carnivores were not as digitigrade as are modern cats and dogs (their feet were not as elongated so that only the toes touched the ground; Hunt, 2002a). Amphicyon had an alveolus for a vestigial upper first premolar whose root measured only 3 mm (Cook, 1926).
The amphicyonid Ysengrinia resembled bears in some aspects of its legs although its lower legs were longer than found in living bears (Hunt, 2002).
In the modern world, there is only one significant group of carnivorous mammals, the Order Carnivora, which includes dogs, cats, bears, otters, skunks, hyenas, etc. Modern carnivores vary in size from the least weasel (45 grams) to the Alaskan brown bear (1500 pounds). Amphicyonid carnivores, the “bear dogs”, ranged in size from under 2-4 kg to over 200 kg that are known from North America, Europe, and Africa.
Cats, modern and fossil, have varied greatly in their size.
The cougar is classified in the same genus (Felis) as the domestic cat.
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Dogs obviously vary enormously in size. While St. Bernards and great danes can approach the size of small bears, others are considerably smaller. American hairless terriers stand 5-13 inches tall at the shoulder and hairless Chinese crested dogs stand about 12 inches and weigh 5 to 7 pounds (De Prisco, 1990).
The small ursid Ursavus weighed 10 kg (Hunt, from Szalay, 1993).
BEAR DIVERSITY
There is no support for the creationist claim that modern bears have always existed. Bears are absent from almost all of earth’s history. The first bears appeared in the Oligocene (the genus Ursavus, which may be ancestral to all modern bears) and modern lineages of bears aren’t known until far more recent times. Brown bears evolved a million years ago and polar bears evolved from ancestral brown bears by a hundred thousand years ago (Feazel, 1990).
Anatomical and molecular evidence indicates that all modern bears are related. The three subfamilies of bears include the giant panda, spectacled bear, and ursine bears. Although the relationships of pandas were once questioned, anatomical and genetic evidence clearly identify them as bears, are the sister group of other ursids (Lindberg, 2004; Zhang, 1993; Peng, 2007). Of the ursine bears, the sloth bear is the most primitive lineage followed by the sun bear (Fulton, 2006; Yu, 2004).
When considering the diversity of modern and fossil bears, it is often greater than that which would have separated ancestral bears from other primitive carnivores of their suborder.
The earliest bears weighed 10 kg. A relative of modern Andean bears, Arctodus simus, is the largest known bear and may have weighed 700 kg. While modern sun bears can weigh 30 kg, polar and brown bears can weigh more than 500 kg. Pleistocene polar bears were larger than the modern specie and may have stood 13 feet tall (Feazel, 1990).
The earliest bears were apparently adapted to spend much of their time in trees. The Malaysian sun bear is the smallest modern bear and is the most arboreal. It possesses limb modifications which adapt it for tree climbing. The panda also climbs well and possesses limb adaptations for climbing (Sasaki, 2005). In contrast, tremarctine bears had unusually short faces, skulls with more cat-like proportions, long legs, and light-built bodies. They probably depended more on a cursorial lifestyle (Kurten, 1988).
The modern polar bear depends primarily on meat. Other bears have a much more varied diet consuming meat, insects (such as ants), and plant matter (such as berries). Sloth bears feed primarily on insects (Lindberg, 2004). Most of the diet of modern pandas consists of bamboo. The European and Florida cave bears had very blunt teeth, suggesting that they fed primarily on plant matter (Kurten, 1988).
MUSTELIDS
The earliest mustelid fossils are known from the Late Eocene, marten-like animals are known from the Oligocene, and martens, weasels, otters, badgers, and skunks are known from the Miocene. The earliest fossils of procyonids are known from the Early Oligocene (Kurten, 1980).In North America, the modern species of badger seems to have arisen 3 million years ago while the long-tailed weasel, spotted skunk, striped skunk, and bobcat were present by 2 million years ago. Shortly afterwards, wolverines are known (Kurten, 1988).
In two separate lineages of modern carnivores, the giant pandas which are bear relatives and the red pandas which are relatives of skunks and raccoons, a carpal bone (the radial sesamoid) has become longer and modified so that it can function as an opposable "false thumb". Although the structure is structurally different in the two pandas (as are the muscles which move it), originally its presence was used to classify giant pandas and red pandas as close relatives. A fossil relative of red pandas, the puma sized Simocyon batalleri, also possessed this structure, reinforcing other data which suggest that giant pandas and red pandas are not closely related. Since the fossil species was arboreal but carnivorous, the false thumb of the red panda seems to have originated as an adapation to arboreal life rather than for feeding on bamboo. The back of Simocyon was adapted to permit galloping (like that of some smaller relatives like weasels), making it the largest relative of bears to move this way (Salesa, 2006). Pandas related to the modern red panda were once found throughout all the northern continents (Kurten, 1988). Genetic evidence indicates that red pandas are mustelids, rather than bears (Flynn, 2000).
Mustelids have diversified to a greater extent in norther continents while viverrids have diversified moreso on southern continents. Viverrids are the only carnivores in Madagascar (Maglio, 1978).
Fifteen of the eighteen viverrid genera are endemic to Africa (Keast, 1972).
Tail length in bats varies greatly. Some animals have even lost their tails such as some mice, some dogs, Manx cats, etc. Longtail weasels have from 19 to 33 vertebrae in their tails (King, 1989).
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PINNIPEDS
Walruses and sea lions have been known since the Late Oligocene. The earliest members have flippers but their teeth resemble terrestrial carnivores. Seals are first known with Potamotherium from the Early Miocene, which was similar to marine otters. Semantor had a form intermediate between Potamotherium and modern seals but it lived too late to be directly ancestral to them.
True seals are the sister group to fur seals, sea lions, and the walrus (Fulton, 2006).
The Caniformia suborder is divied into two infraorders: the Canoidea (which includes the family Canidae) and the Arctoidea (which includes bears (ursidae), pinnipeds, and mustelids) (Fulton, 2006).
Pinnipeds monophyletic with Phocidae split from walruses and sea lions. The earliest fossils are known from the coasts of North America, of pinnipeds are represented by phocids in the Atlantic and otaroids of the Pacific, suggesting a North American origin of the group (Arnason, 2006).
There are 21 genera of pinnipeds which can be divided into 3 families: Otariidae (sea lions and fur seals), Odobenidae (walrus), and Phocidae (all other seals) (Scheffer, 1958).
The northern fur seal may spend 6-8 months at sea during which time it may cover 10,000 miles. In contrast, other seals (such as the harbor seal) frequently go onto land (Scheffer, 1958).
Size can differ significantly in the family Phocidae ranging from the less than 5 foot long ringed seal which can weigh 200 pounds to the 21 foot long southern elephant seal which weigh eight thousand pounds (Scheffer, 1958).
While many pinnipeds have a varied diet, some have specialized on prey as diverse as crabs (such as the crabeater seal) and birds and other seals (the leopard seal). Walruses can even prey on whales (Scheffer, 1958).
Miocene pinnipeds possessed some primitive features (such as dental characteristics) (Scheffer, 1958).
Genetic and anatomical evidence indicates that pinnipeds are a monophyletic of bears (Vrana, 1994).
Unlike other pinnipeds, true seals (Phocidae) cannot swing their hindlimbs forward for locomotion on land and they lack external ears (Coffey, 1977).
Caspian and ringed seals measure 1.5 meters while male southern elephant seals can measure up to 6 meters (Coffey, 1977).
KANGAROOS[pic]
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Modern marsupials are not known from the fossil record during the majority of the history of life on earth, the majority of history of life on land, and even the majority of mammalian history. The most advanced modern marsupials (such as kangaroos) evolved long after the first primitive marsupials. The earliest marsupials are known from the Upper Cretaceous of North America and were probably in living in South America at this point as well. Marsupials were already diverse in South America by the Paleocene. These North American fossils belong to the group Didelphoidea, an early group that contains the modern opossum and survived in North America through the Miocene. Marsupials migrated from North America to Europe (with one specimen known from Asia as well) and all became extinct in the Miocene. Marsupials migrated from South America to Antarctica (by the Eocene) and then to Australia (by the Oligocene). Marsupial success was limited throughout most of the world because of the great diversification of placental mammals. Two southern continents, South America and Australia, were isolated from the centers of placental evolution for much of the Cenozoic Era and offered marsupials an opportunity to diversify that they lacked elsewhere.
If the adaptation to a specific environmental niche required an intelligent design because of the complexity of the required adaptations, it is not expected that completely unrelated lineages could evolve similar adaptations. In contrast, it appears that the potential for variability is such that groups which are unrelated can adapt to similar environments in similar ways. There are marsupials which have evolved adaptations which are similar to rodents, moles, flying squirrels, saber tooth cats, wolverines, and coyotes. It is not expected that an intelligent designer would produce two completely different designs which result in similar products. Anatomical and genetic evidence indicates that marsupial and placental mammals each form separate clades despite the similar adaptations possessed by members of these groups.
Many fossil marsupials were highly modified from their ancestral lineages. In South America, the microbiotherids were marsupials which were very different from other groups and had a huge bony case around their ear bones. The borhyaeinoidea included at least 35 genera which evolved from the didelphids. They were carnivores that bore superficial similarities to medium sized placental carnivores. Borhyaena resembled a wolf, Thylacosmilus a tiger sized “saber tooth cat”, and one was bear-sized. Lycopsis was a coyote-sized predator (de Mulzon, 1997). Caenolestids were small insectivorous/omnivorous animals and the most abundant marsupials of Miocene. South America possessed a burrowing marsupial Necrolestes. Marsupials of the family Groeberiidae were rodent-like with enlarged incisors. Marsupials of the family Argyrolagidae hopped bipedally like kangaroo rats and jerboas (Keast, 1972). In Australia, fossil dasyurids included mouse-sized insectivorous species and dog-sized carnivorous species. Marsupial moles, anteaters, weasel-like (Keast, 1972). Gliding marsupials, which resemble the flying squirrels in placental lineages, are known in three separate genera of the Phalangeroidea (Keast, 1972).
In Australia, marsupials are first known from Late Oligocene. Since they were already diverse by this point, they probably arrived earlier. The Dasyuroidea are small to mid sized insectivores, omnivores, and carnivores that evolved from the didelphids (Akotarinja was very similar to the didelphids). There are 14 modern genera (including the Tasmanian devil, the Tasmanian wolf Thylacynus which became extinct in 1934, and the numbat or Australian anteater). There are 6 fossil genera. The group Perameloidea includes modern bandicoots and some fossil species. They actually have a placenta but the young are still born very immature and must mature in the mother’s pouch.
Diprotodon (below) measured 10 foot long and was the largest known marsupial. Simostenurus was an unusual kangaroo which had only one toe on each foot. The fossil kangaroo Procoptodon stood 2.6 m (8 ft.)
Significant variation occurs in the family Didelphidae. The number of vertebrae varies from 47 to 63 and the number of teats from 7 to 25. This family of marsupials varies in the presence of the pouch: he pouch is present in some genera (such as Caluromys, Chironectes, and Didelphis) while a pair of skin folds which enclose the nipples exist in other genera (such Marmosa, Monodelphis, and Philander).
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The same type of placenta which defines placental mammals has evolved within marsupial lineages. Placental mammals are given their name because of the chorioallontoic placenta which forms during fetal development. There are 3 marsupials in which the allantois fuses with the chorion to produce a chorioallantoic placenta: Perameles, Isoodon, and Echymipera (Mossman, p. 54).
The 62 species of kangaroos are classified in the superfamily Macropoidea. The 6 largest members of this superfamily are called kangaroos while the others are called wallabies (although there is some size overlap between the smallest female kangaroos and the largest male wallabies) (Dawson, 1995). If creationists are correct, then modern marsupials (such as kangaroos and wallabies) have always existed. There is no evidence to support this claim. If kangaroos are intelligently designed, it would be hard to define what the ancestral design actually was, given the great variation which can occur in the group.
By 25 million years ago, 4 families of rat kangaroos had evolved (which are represented by modern potoroos and bettongs). In general, rat kangaroos have a body length of about a foot to a foot and a half with a tail which measures about a foot long. Some weigh as much as 5 pounds. The musky rat kangaroo is the smallest, measuring less than a foot (with a 6 inch tail) and weighing slightly more than a pound. Rat kangaroos can hop on their hind legs in a manner similar to larger kangaroos. Some rat kangaroos have prehensile tails. The musky rat kangaroo (Hypsiprymnodon) is intermediated between kangaroos and phalangers (Keast, 1972).
Later fossil forms include carnivorous species and Procoptodon which could reach a height of 2 ½ meters and a weight of 200 kg. Some extinct kangaroos were four-toed while others were one toed. Dendrolagus was an extinct, short-faced species of kangaroo (Keast, 1972). The earliest species of the group which includes modern kangaroos were rat-sized. As grasslands spread throughout Australia, kangaroos diversified to include large, browsing species (some of which became extinct just as aborigines arrived in Australia). An extinct relative of the modern gray kangaroo could weigh up to 150 kg (Dawson, 1995).
Kangaroos and wallabies have a decreased tooth count, and their high crowned teeth are located more anteriorly in the mouth (Keast, 1972). Kangaroos molars move forward in their mouths before being lost. In old age, kangaroos may be left with only one molar on each side of their jaws (Dawson, 1995).
Chromosome numbers can vary within families of marsupials such as Didelphidae (14, 18, 22), Phalangeridae (14, 20), Petauridae (10,26, 18, 20, 22), and Macropodidae (12, 14, 16, 20, 22, 24, 32). Different molecular mechanisms exist for sexual determination in the family Macropodidae including species in which males have 11 chromosomes and females have 10 and others in which males have 13 and females 12 (Stonehouse, 1977). Some (but not all) kangaroos can undergo diapause in which embryonic development is paused at an early embryonic age (Dawson, 1995).
The 78 modern species and additional extinct members of the marsupial group Phalangeroidea are divided in the families Phalangeridae (possums and gliders), Tarsipedinae (honey possums), Phascolarctinae (koalas), Thylacoleoninae (extinct lion-like forms), Macropodidae (rat kangaroos, wallabies, and kangaroos), Diprotodontidae (large, extinct herbivores), and Vombatidae (womabats) (Keast, 1972). Superspecies resulting from interspecific matings are known in marsupial groups Phalangeridae and Perameloidea (Keast, 1972).
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??? Genetic and anatomical similarities (such as the synovial joints between accessory processes on vertebrae) link edentates as a clade.
Similar processes have been observed in cats, the rodent Geomys, and the creodont Patriofelis (Rose, from Szalay, 1993). Armadillo scales are bony scutes covered with horny keratin.
XENARTHANS
Anteaters, armadillos, tree sloths, and giant ground sloths (edentates or xenarthans) would not have to share any similarities based on their significant differences in ecological niches. However, genetic and anatomical similarities (such as the synovial joints between accessory processes on vertebrae, vestigial enamel and the articulation between the ischium and the vertebral column) link edentates as a clade (Simpson, 1980; Delsuc, 2001). The modern diversity of edentates represents only a fraction of their past species richness. Although modern xenarthans are limited to 13 genera, more than 215 genera are recognized from the fossil record. Most genera became extinct relatively recently, within the last 10,000 years (Delsuc, 2001).
The primitive armadillo Utaetus possessed primitive features such as enamel on its teeth but the all modern species and most fossil groups lost the enamel on their teeth. (Keast, 1972).
Significant variations are known in edentate groups. Tree sloths vary in the number of cervical vertebrae: 5-8 in Coloepus and 8-9 in Bradypus. The number of sacral vertebrae varies in edentates from 4-6 in anteaters and 7-13 in armadillos (with 17 known in extinct glyptodonts). This variation results from caudal vertebrae (and in some, one lumbar vertebrae) into the sacrum (Rose, from Szalay, 1993). The fusion of the caudal vertebrae with the ischium resembles the synsacrum in birds; such ossification is lacking in one anteater. Sacroischial fusion also occurs in some moles, a rodent, and a bat. The number of vertebrae with accessory processes and joints varies in anteaters (four to at least 10) and in armadillos. (Rose, from Szalay, 1993).
Armadillos vary. The number of teeth in armadillos varies from 7-9 in Dasypus to 25 in Priodontes. The only armadillos which possesses teeth in the premaxillary bone are in the genus Euphractus (and possess a pair of teeth). The fossil anteater Stegotherium possessed jaws like an anteater while Peltephilus was horned and its teeth suggest that it was either a carnivore or a scavenger (Simpson, 1980). Large canines in the armadillo Macroeuphractus may indicate scavenging. Armadillos of the subfamily Pampatherinae were almost as large as glyptodonts (Keast, 1972). Glyptodonts were the heaviest of all armored mammals measuring up to 12 feet, although the earliest species were small and had little armor (Keast, 1972; Simpson, 1980).
Fossil anteaters possesses shorter snouts than modern species (Keast, 1972). Unlike the giant anteater, the pygmy anteater and tamandua are arboreal and possess prehensile tails (Simpson, 1980). Anteaters have lost teeth entirely.
Pangolins, like anteaters, have lost their teeth (Delsuc, 2001).
CL: therians, Afrotheria, xenartha (Delsuc, 2001).
CL: anteaters form a group while anteaters and sloths form another—what is Cyclopes? It is sister group of anteaters (Delsuc, 2001).
The European fossil Eurotamandua lacks teeth but does not seem to be related to anteaters. (Instead, it seems to be related to palaeoanodonts, an extinct group of digging mammals with reduced teeth.) (Delsuc, 2001).
Pangolins lack teeth (Maglio, 1978).
Order Xenartha includes an extinct North American group known as the Palaeodonta which may be related to pangolins.
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The two subfamilies of sloths differ in the width of their snouts (Keast, 1972).
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TETHYTHERES
AFROTHERIA
The superordinal clade Afrotheria is composed of elephant shrews, elephants, sea cows, hyraxes, aardvark, golden moles and tenrecs. Molecular evidence demonstrates their relationship and they share a number of anatomical features including a large yolk sac and allantois (Oduor-Okelo, 2004; Madsen, 2001). Some of the groups within Afrotheria are more closely related to each other, forming the group Tethytheria.
TETHYTHERIA
The name Tethytheria is the name given to a group of related mammals: elephants (Proboscidea), sirens (Sirenia) and an extinct group of mammals called the Demostylia. The first members of this group seem to have been semi-aquatic, including the ancestors of elephants. (Gaeth, 1999).
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Elephant tusks are actually elongated teeth. There has been considerable variation in teeth during the evolution of elephants.
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The 3 modern species of elephants (proboscideans) represent only a small fraction of the diversity of this group whose fossil lineages include at least 40 genera and 164 species and subspecies. These fossil forms include mastodons, mammoths, deinotheres and moeritheres, gomphotheres, and the ebrithopods. Elephants of the past have included some forms the size of pigs (such as the earliest known proboscidean from the late Paleocene, Phoshatherium) and other which were larger than modern elephants. Dwarf elephants from the genera Elephas, Mammuthus, and Hesperoloxodon are known from islands of the Mediterranean and off the coast of California. Those from California range from 1.05 to 2.43 meters at the shoulder while mainland species of these genera reached up to 4 meters (Prothero, 2002). The various species of Barytheres varied in size from that of a tapir to that of a small elephant.
Moeritherium was an early proboscidean which seems to have possessed a small trunk. Wooly mammoths, unlike other species of mammoths, evolved a thick coat of hair as an adaptation for glacial environments. Ear size varies in both fossil and modern lineages.
As elephant lineages evolved, modifications of the jaws included significant variations in the numbers of teeth: anthracobunes had a tooth formula of 3,1,4,3/3,1,4,3 (incisors, canines, premolars, and molars in the upper/and lower jaws). This tooth formula was modified to 3,1,3,3/2,0,3,3 in Moeritherium 2,0,3,3/2,0,3,3 in barytheres, 0,0,2,3/1,0,2,3 in deinotheres. Different lineages modified different teeth into tusks: some possessed tusks on their upper jaws, some on their lower jaws, and some possessed both. Upper and lower jaw tusks could be straight or curved. Some gomphotheres such as Platybelodon and Ambeledon had shovel-like inferior incisors. Tooth shape varied significantly and the ancestral shape adapted for browsing on leaves was modified as grasslands spread for a grazing lifestyle.
THe first hyraxes were rabbit sized. They later diversified to produce browsing and grazing species. Some had longer legs adapted for running and one group, the pliohyraxes, became horse-sized. Their diversity declined after bovids arrived in Africa (Prothero, 2002; Maglio, 1978).
About a dozen genera of sirens were known in the Miocene (Maglio, 1978). Although modern sirens are aquatic animals, the fossil Pezosiren was a pig-sized walking siren which possessed legs and feet and was capable of locomotion on land (Prothero, 2002). Other fossil sirens retained small hind limbs. The paddles of modern sirens are comprised of 5 digits (which may retain nails in some manatees). Unlike other sirens, manatees possess 6 cervical vertebrae. Dugong males possess tusks composed of enlarged incisors (Coffey, 1977). The Steller’s sea cow could reach 10 tons in weight.
ARTIODACYTLS
Are terrestrial herbivores designed? If there was only one possible suite of adaptations which would allow an animal to feed on plant material, it would be much less likely that herbivorous animals could evolve. If herbivory were an example of “irreducible complexity” in which intermediate stages would serve no adaptive function, then it could be argued that the inherent complexity of multiple adaptations would make the evolution of herbivory unlikely. A survey of amniotes indicates that a great diversity of independent lineages have become modified in a great variety of different ways to incorporate plant material in their diets. In order to evolve a herbivorous lifestyle, ancestral forms do not have to evolve the only set of anatomical and physiological mechanisms which will allow this lifestyle, they simply have to evolve one of many possible modes. Intermediate forms do not have to be able to digest all types of plant matter, they can begin with the simpler material. Some of the most difficult plants to digest, such as grasses, did not reach their current distribution throughout the world overnight. Grasses gradually became more prevalent over tens of millions of years, giving herbivorous mammals tens of millions of years to gradually adapt to them.
Although the first anapsid reptiles were carnivorous, anapsid lineages produced a variety of herbivores, such as pareisasaurs.
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A number of separate lineages of turtles have modified the ancestral diet to include large amounts of plant matter such as box turtles, wood turtles, and a wide variety of tortoises.
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Some lineages of lizards, such as the iguanas, modified the ancestral lifestyle to become herbivorous.
Some archosaurs, such as aetosaurs, became adapted for herbivory.
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Although the first dinosaurs were carnivorous, dinosaurs produced a variety of independent lineages which adapted to herbivory in different ways.
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The modifications of the mouth, teeth, and jaw muscles needed to accommodate chewing tough fibrous materials evolved gradually through transitional forms in independently lineages, such as the ornithopods and ceratopsians.
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Even the theropod dinosaurs included some forms which apparently modified the ancestral carnivorous diet to include more plant material, such as the segnosaurs.
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Many birds have adapted to feed on plants, including algae and aquatic plants,
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leaves,
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fruits,
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seeds
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nectar,
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and sap.
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In the lineage which would lead to mammals, herbivory evolved independently numerous times. Although the first synapsid reptiles were carnivorous, some pelycosaurs modified the ancestral diet to become herbivorous.
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Although the earliest therapsids were carnivorous, a diversity of herbivorous lineages evolved.
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Although the earliest cynodonts were carnivorous, a diversity of herbivorous lineages evolved.
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Many of the lineages of primitive Mesozoic mammals became specialized to feed on plants.
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Although the first marsupials were omnivores/carnivores, some lineages evolved specializations for herbivory including kangaroos and hippo-sized Diprotodon.
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In placental mammals, diverse lineages adapted to feeding on plants. Although the Order Carnivora includes most carnivorous mammals, giant pandas and red pandas are two lineages which adapted to herbivory independently. Many primates have specialized in feeding on plants, including gorillas. Plant material makes up a large percentage of the diet of rodents although different rodents have specialized to feed on leaves, seeds, bark, and other plant parts.
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Elephants adapted to a variety of diets including browsing and grazing.
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South American sloths and armadillos adapted for herbivory.
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Most large, herbivorous mammals are ungulates. A diversity of extinct lineages evolved in the past.
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A great diversity of modern ungulates exist and have adapted to herbivorous lifestyles in a wide variety of different ways. These diverse lineages include camels, pigs, pronghorns, giraffes, hippos, bison, yaks, cows, sheep, goats, antelope, horses, tapirs, and rhinos.
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When studying the great variety of herbivorous animals in the modern world and throughout the fossil record, a number of conclusions become clear. First, there is not one single way to feed on plants. A great variety of very different animals can all excel at being herbivores. Second, adaptations for herbivory have occurred in a wide variety of amniote groups. Given enough time and opportunity, it seems that almost any lineage could produce species which have some specializations to feed on plants. Finally, herbivory can be acquired in stages. Some plant material (such as fruit and succulent leaves) can be digested with fewer specializations than other parts (such as grass and wood). Many modern animals include some plant material in their diet but are not completely dependent on plants (e.g. humans, black bears, many rodents, opossums, etc.). Early members of many fossil lineages were herbivores but lacked many of the adaptations possessed by later members of these lineages. As a result, it does not seem as if the adaptations which allow an animal to feed on plants require an intelligent design. Through natural variation, a diversity of different types of animal can adapt to herbivory if given time and opportunity.
UNGULATES
EARLY
Modern groups of herbivorous mammals known has ungulates (cattle, goats, pigs, camel, hippos, deer, giraffes, horses, rhinos) have not always existed. The majority of the history of life on earth, the majority of the history of vertebrates, the majority of the history of vertebrate life on land, and the majority of the history of mammals passed without a single fossil of an ungulate. After the extinction of the dinosaurs, a very primitive group of herbivorous ungulates evolved known as condylarths. These condylarths possessed traits which linked them both to Cretaceous mammals and to the ungulates which descended from them (Archibald, 1996). Chriacus was an unspecialized condylarth from the Early Paleocene which has traits which link it to Diacodexis (Hunt, 1997).
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In many parts of the world, primitive ungulates evolved in isolation. In South America, one group of colonizing ungulates evolved into 6 ungulate orders (including horselike and camel-like forms) which were unique to South America and left no living descendants. Many became extinct following the immigration of more advanced mammals (deer, horses, elephants, camels, wolves, bears, and cats) after North America and South America fused at the end of the Cenozoic.
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Because there were no large mammalian predators of the Early Paleocene (creodonts appear in the Late Paleocene and carnivores appear later), a group of condylarths evolved into predators in the Early Paleocene. Although condylarths were to evolve into many groups of herbivores, the earliest forms lacked many of the later specializations so that this change in lifestyle did not require as many modifications as might be thought. The mesonychians evolved from the condylarths but were carnivorous, not herbivorous like all of the other condylarth descendants. Some mesonychids had hooves. (Prothero, from Szalay, 1993)
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For much of the Early Cenozoic Era, Africa was separated from Europe and Asia by the ancient Tethys Sea which allowed its ungulates to evolve in isolation until a faunal interchange in the Miocene following African contact with Asia. North American ungulates (horses, camels) evolved in isolation for much of the Cenozoic until land bridges allowed migration into Asia and South America. Europe had unique herbivores which became extinct in the Eocene (Prothero, 2002).
The archaic ungulates of the Paleocene had evolved into primitive artiodactyls and perissodactyls by the Early Eocene. The earliest artiodactyls and perissodactyls were primitive and retained many traits of the condylarths. For example, the early Eocene fossil Diacodexis was a rabbit-sized condylarth whose modified leg and ankle identify it as an ancestor of the artiodactyls. Other than these features, it is similar to other condylarths and may be descended from the Lower Paleocene Chriacus (Hunt, 1997).
As these lineages became more specialized, they adapted to a herbivorous lifestyle in different ways. Hindgut fermenters such as perissodactyls (and elephants) ferment plant material in terminal portions of the digestive tract (such as the large intestine) and have an advantage when processing high fiber, low quality food. They are able to use 45% of the cellulose in their food and require 48 hours for the food to pass through the digestive tract. Ruminants have modified their stomachs to ferment plant material in separate chambers. Although ruminants can diverse plant materials, they prefer young shoots. They can process 60% of the fiber in their diet but food requires 80 hours to pass through their digestive tract (Prothero, 2002). In addition ruminants don’t excrete urea and instead use nitrogen to supply their gut organisms. As a result, they need to drink less which is an advantage in arid environments. The disadvantage is that if their food is nutrient rich, the excess gas from its fermentation can cause so much bloating that it is fatal. Because of the heat associated with foregut fermentation, ruminants are limited in size (Prothero, 2002).
Horns evolved several times. True horns (such as in cattle and antelopes) form from bone and are never shed. Giraffe horns form from cartilage which is converted into bone (and are called ossicones). Pronghorns make horns which have a keratin sheath which is shed once a year. Antlers are composed of bone without keratin and are shed once a year. They occur only in deer. Other hornlike structures include the cemented hair of rhinos, the bony knobs of brontotheres, the horn on the pig Kubanochoerus, the horns of some oreodonts, protoceratids, and some groups of deer (Prothero, 2002).
In the Mid to Late Eocene, artiodactyls lineages began to specialize and separate into three main lineages: pigs (and hippos), tylopods (camels, oreodonts, and other extinct groups), and ruminants (deer, cattle, sheep, goats, antelope, giraffes; Prothero, 2002).
PIGS
The lineage which led to hippos and pigs diverged early from ancestral artiodactyls and modern species lack many of the adaptations of the more derived lineages (Hunt, 1997). Hippos evolved from late Eocene anthracotheriids which gradually increased their size, modified their body for aquatic environments, and modified their teeth (Hunt, 1997). The earliest pig, Propalaeochoerus, is known from the Early Oligocene and pigs were a diverse lineage as of the Miocene. The anatomy of pig does not seem to require a specific design since a number of separate lineages evolved piglike specializations independently. These groups evolved including cebuochoerids and choeropotamids in Europe, helohyids, entelodonts, and anthracotheres in Asia, and helohyids and the hippo-like Achaenodon in North America. Pigs and their relatives could be quite diverse. The entelodont Daenodon coule reach 8 feet in height at the shoulder with a body 11 feet long and skull five feet long (Prothero, 2002). Dinohyus stood 6 feet tall at the shoulder. Pigs are classified into two families: Suidae and Tayassuidae which have been separate lineages since the Late Oligocene. Species of the family Tayassuidae are known only from the New World. Different lineages of pigs adapted their teeth to include more grass in their diets and raised the positions of their orbits to enhance vision in grasslands (Maglio, 1978). The North African pig Kubanochoerus possessed a single horn on its forehead.
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Tetraconodon had thick teeth that might have been used for scavenging. An extinct warthog stood a meter tall and other extinct warthogs were more adapted for grazing. (Prothero, 2002). Modern species can vary significantly. Warthogs possess a modified head with tusks and the Asian babirusa possesses long curved tusks from the lower jaw. While the modern pygmy hog weighs 9 kg, the giant forest hog weighs 275 kg (Prothero, 2002).
The extinct family Anthracotheriidae of piglike animals ranged in size from small dogs to that of a hippo. Some possessed elongated snouts. Some feel that hippos evolved from anthracotherids (Maglio, 1978). The earliest hippos, Hexaprotodon, diversified into a number of extinct species. Hippos migrated from Africa to Europe and Asia , (Maglio, 1978). Hippos have existed since the Miocene and earlier hippo species had primitive tooth counts and slender limbs. The fossil record includes dwarf hippos which were the sizes of small pigs (Prothero, 2002).
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Anatomical, fossil, and genetic evidence conclude that whales evolved from amphibious artiodactyls most closely related to hippos.
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CAMELS
Camels had a very diverse fossil record. Camels were in North America since the mid Eocene and for 40 million years their distribution was limited to North America; in the Pliocene they migrated to Eurasia. The earliest camels were rabbit sized and were followed by goat-sized species. Camels evolved from small animals like Poebrodon which gradually became larger, lengthened their necks, replaced their hooves with pads, and modified their legs (became digitgrade, reduced several toes, and fused limb bones). Some developed a protective postorbital bar around their eyes (Hunt, 1997). One camel group (floridatragulines) possessed a long, thin snout. North American relatives of llamas possessed longer legs for a running lifestyle. Camelops was 20% larger than the modern dromedary. The giraffe-like camel Aepycamelus would have stood about 8 feet at the shoulder. They evolved high crowned teeth adapted for eating grass with the evolution of grassland in North America, just as the horses did. In the Pliocene, camels migrated to South America and were the ancestors of llamas. (Caroll, 1988;Prothero, 2002).
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Protoceratids were an extinct group related to camels. Although the first protoceratids lacked horns, a great diversity of horn structures evolved in the group.
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OREODONTS
Oreodonts (such as Merycodon) were primitive artiodactyls which retained five fingers. They were quite diverse including pig-and hippo-like forms, some species whose nasal position suggests a short trunk, and several with high crowned teeth (Prothero, 2002).
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RUMINANTS
Today, ruminants are represented by the 65 modern genera that include deer, giraffes, cattle, sheep, goats, antelopes, and their relatives. The first ruminants were rabbit sized and similar to deer superficially and possessed four toes. Ruminants evolved from primitive forms like mid-Eocene Homacodon and other dichobunids and Late Eocene Mesomeryx. The earliest ruminants of the Late Eocene (Hypertragulus, Indomery) were in the process of reducing the number of toes, fusing their fibula to the tibia, and modifying their teeth. They retained 5 toes on their front legs and 4 on their hind legs (Hunt, 1997). In addition to a number of extinct species with a variety of primitive features, the late Eocene-early Oligocene ruminants included ancestral deer (which became increasingly deerlike over time and developed short antlers by the Miocene). From ancestral deer evolved giraffes (beginning with short-necked Miocene genera Climacoceras, Canthumeryx, Paleomeryx, and Palaeotragus). Bovids are first known from the Late Oligocene and had produced sheep and gazelles by the Late Miocene and cattle by the early Pliocene (Hunt, 1997).
GIRAFFES
Giraffes possess a four-chambered stomach, as is typical of ruminants and seem to be most closely related to deer. (For example, deer lack a gall bladder which most ungulates possess. Giraffes possess them as fetuses but typically lack them as adults.) Although their body form has been highly modified, they possess the same number of vertebrae as cows and the same number of neck vertebrae as virtually all mammals (seven) (Spinage, 1968). When girafffes first appeared in Upper Eocene, the elements of the foot had begun to fuse and the postorbital bar was still incomplete. They still had 5 fingers and 4 toes but lateral digits were reduced. In later species, lateral toes were gradually reduced until there were 2 primary toes. Giraffes from the mid-Miocene possessed a normal neck and legs, with a body form similar to that of the modern okapi. Sivantherium was a giant ox-like giraffid from India which had huge mooselike ossicones which resembled antlers superficially (Prothero, 2002; Spinage, 1968). Birgerbohlinia, a relative of giraffes, stood almost 6 feet at the shoulder. The extinct giraffe Palaeotragus germani apparently evolved elongated neck and limbs separately from the lineage which led to modern giraffes. Small giraffes species stood 2 m tall at the shoulder (Maglio, 1978).
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DEER
Primitive cervoids which seem to be ancestral to deer, pronghorns, and moschids are known from the Oligocene. They were superficially similar to Chinese water deer, the most primitive lineage of modern deer. The second-most primitive group of modern deer, the muntjacs, possess simple antlers with a single fork, like species known from the Miocene (Prothero, 2002).
Modern chevrotains (family Tragulidae) or “mouse deer” are a very primitive lineage which is similar to these ancestral forms. Modern mouse deer satand 8 to 11 inches at the shoulder and weigh 2-5 kg (Prothero, 2002). In contrast, the largest deer, the Irish elk possessed antlers which could span 3.5 meters and weigh 45 kg.. Modern moose stand 9 feet at the shoulder and weigh 1,750 pounds (Prothero, 2002). The earliest deer possessed large canines which were lost in most modern lineages of deer (Maglio, 1978). The fossil record includes a variety of deer, such as the “brush-antlered deer”.
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Pronghorns were once very diverse. They are relatives a true deer (Prothero, 2002).
One North American group of diomomerycids or “pseudo-deer” varied significantly in their antlers. They had true horns rather than antlers in that they were not shed. Some had horns on the back of their heads, in addition to those over the eyes (Prothero, 2002).
BOVIDS
Bovids are the most diverse ungulates. They possess 4 chambered stomach and most possess 2 horns (although Tetracerus possesses four). Fossils from the Early Miocene may represent basal hornless bovids; true primitive bovids are recognized from the mid-Miocene which possessed small, 3 inch horns. Basal Miocene bovids are survived from two lineages in India (the four-horned antelope and nilgai). The genus Bos was domesticated from the wild species Bos primigenius, the auroch. Yaks and other Asian species are also wild species of Bos. The Indian gaur measure 2 meters at the shoulder and weigh 900 kg. An extinct relative of the Cape buffalo (Peloiovis) possessed horns which measured 4 meters (and possibly 5 meters with its keratin tips) and has been found with early hominids (Prothero, 2002). African species of the family Bovidae can be divided into a series of related tribes. A number of superspecies complexes are known within Bovidae; both species and genera are known to interbreed (Keast, 1972). The European wisent is related to the American bison. The bison came to North America about 500,000 years ago (Prothero, 2002).
The subfamily Caprinae includes goats, sheep, musk ox. Primitive species from the Miocene possessed short, curved horns. Musk ox stand 1.5 meters at the shoulder and weigh 400 kg (Prothero, 2002). A number of mammals have evolved reduced brain sizes. An extinct island species of bovid genus Myotragus reduced its brain size by half compared to other living and fossil bovids (Niven, 2005).
Antelopes are diverse ruminants of the tribe bovini. Duikers have a larger brain size to body size ratio compared to other antelopes and lack horns. Impalas can achieve jumps of 9 meters in length. Dwarf antelopes stand 25 cm at the shoulder and weigh 3 kg. The eland is the largest antelope which stands 2 meters at the shoulder and weighs 990 kg. Kudus measure 1 meter (Prothero, 2002).
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One of the arguments which could be made against design in artiodactyls is that, given the variation within groups of artiodactyls, it would be hard to argue that any particular group was designed for a particular lifestyle. Although most artiodactyls have been herbivores, one group evolved into formidable predators and include the largest terrestrial land predator in mammalian history. Although most artiodactyls have been terrestrial, some (such as modern hippos and a number of extinct forms) have adapted to an amphibious lifestyle and one lineage evolved into whales, the mammals which are most specialized for aquatic life. Given that the first artiodactyls and the first members of each lineage (camels, ruminants, giraffes, etc.) were small and primitive, many of the most complex aspects of the “design” of modern animals resulted from evolution within lineages rather than being an essential design element present from the start. Many traits, such as large size, tooth modifications to digest grass, and horns, evolved independently multiple times in separate lineages. Each lineage produced a variety of forms. Pigs produced a variety of forms which varied in diet, limb structure, the presence of horns, and size (from forest hogs of 9 kg to extinct forms 11 feet long and 8 feet tall at the shoulder with a 5 foot head). Hippos have included species the size of small pigs and others with more slender legs for running. Camels have ranged from primitive rabbit-sized species to giant forms with giraffe-like necks. Many of the most complex traits in camels (for feeding and locomotion, for example) evolved within lineages rather than being present in an ancestral design. The complexity of protoceratid horns evolved within protoceratids and was not evident in the early hornless species. Fossil giraffes includes small, okapi-like animals, giant oxlike forms, and a considerable variety of horn (ossicone) shapes. The most specialized traits of modern giraffes evolved within giraffe lineages and were not part of an ancestral design. Deer and bovids have varied considerably in size and the complement of horns or antlers.
PERISSODACTYLS
Perissodactyls have a diverse fossil record although there are only 6 modern genera of horses, tapirs, and rhinos. Perissodactyls are easily recognized by their odd number of toes, unlike the artiodactyls which possess an even number of toes. The primitive arctocyonids evolved into the condylarth family Phenacodontidae that included Early Eocene forms like Loxolophus which had a short diastema behind the first premolar and Karagalax, a tapiroid. In Phenacodus, digits I and V are reduced on both hands and feet. Tetraclaenodon was closer to horse ancestry. Homogalax was the ancestor of tapirs, including basal species of tapir such as Heptodon, Helates (Eocene), and Prototapir (Oligocene) (Maas, 2001).
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Hyracodon of the Eocene was ancestral to the various groups of rhinos. They were common and diverse in the Northern Hemisphere during the Oligocene and Miocene but became extinct in North America after the Pliocene. Teloceras is an American hornless rhinocerous. While some indricotheres were cow-sized, Paraceratherium (also known as Balucitherium and Indricotherium) was the largest terrestrial mammal that ever lived, standing 18 feet at the shoulder and weighing 44,000 pounds.
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The oldest species of the family Rhinocerotidae from the Eocene possessed tusks. Many were semi-aquatic, some were hippo-like and some probably possessed a proboscis. By the Oligocene, horns evolved and Menoceras possessed paired horns. Elasmotherium was elephant sized with a 1.2 meter skull and a 2 meter horn. The modern Sumatran rhino belongs to the same group as Elasmotherium and wooly rhinos. Many rhinos lacked horns (Prothero, 2002).
The brontotheres were an extinct group of rhinos that had become dog-sized, hornless species (such as Eotitanops) by the Oligocene and rhino-sized species by the Miocene. The largest bronthothers stood 2.5 meters at the shoulder. Some species possessed solid horns unlike the typical branched ones. Brontotheres became extinct at the end of the Eocene (Prothero, 2002).
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The horses present an excellent set of transitional fossils with over 40 genera and 100 species. The first horses (equids) evolved from phenacodontid condylarths in the Late Paleocene which had already evolved a specialization of limbs for running and specializations for chewing plant material (molar cusp patterns, jaw musculature). The teeth of the first horses were still generalized enough that they might have been omnivores rather than full-fledged herbivores. In the Late Eocene and Oligocene, the climate of North America became drier. The type of plant life in North America changed and many previous inhabitants of North America (such as a diversity of primitive primates) became extinct. Grasses evolved in this drier climate and horses became adapted to these new environments.
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Miohippus was still a browser of woodland and forest plant material. Its side toes were still important—in forests, agility (the ability to leap to the side suddenly) can be more important than speed in a single direction. In the Miocene, Miohippus evolved into a number of horse groups: pygmy horses, browsing horses which migrated to Eurasia and became successful there, and horses which were now adapted to life on North American plains with specialized teeth for grinding grasses and leg modifications for greater speed. This last group maintained three toes on each foot and included Merychippus
In the Late Miocene, Merychippus species evolved into a number of successful species including smaller horses, 3 toed browsing hipparion horses, and one toed horses. The Hipparion horses in Eurasia were successful and were able to adapt to a wide variety of habitats, ranging from steppe to forest. A long nasal region of Hippidion suggests a proboscis. Hipparion horses survived for quite some time in Africa, but competition from an ever-increasing number of bovid species (such as antelopes) probably contributed to their demise. The one-toed horses were better adapted to grassland while the side toes of hipparion horses gave them advantages in savannas. While the side toes of the hipparion horses would only touch the ground when the full weight of the body was placed on the foot, these toes were important when making sudden changes of direction (which is important in savannas where there are still trees to hide predators) (Forsten, 1982;
Stirton, 1955; Hulbert, 1982; Webb, 1977; Garces, 1977; Prothero, 2002).
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The majority of the fossil genera of horses have had lateral toes. These toes were gradually reduced in the lineage which led to modern horses. Modern horses still retain bony splints as the last vestiges of these lateral toes and occasional horses with lateral toes have been born in modern times.
The variability of perissodactyls undermine design arguments. Perissodactyls are classified together because of shared anatomical and genetic features. However, the differences between the simple ancestral species and the descendent lineages which include horses, rhinos, tapirs, brontotheres, and chalicotheres is considerable. Each of these lineages has also varied significantly. Horses have ranged from cat-sized, multi-toed browsers to large, one-toed grazers. Rhinos have included hornless and horned species, terrestrial and amphibious species, hairless and wooly species, small species and the largest land mammals in history (standing more than 20 feet at the shoulder). Brontotheres included small, hornless animals and giant horned forms. The most complex aspects of the “design” of specialized perissodactyls evolved gradually within groups rather than appear suddenly in a finished form in the early members of a group.
HUMMINGBIRDS
Pectoral muscles in hummingbirds comprise a quarter of the total body weight (Stokes, 1989).
Fossils of the stem penguin Waimanu are known from the Paleocene Epoch, 60 million years ago, shortly after the extinction of the dinosaurs. Although their bodies were shaped like those of modern comorants, their wings were modified as swimming flippers (Fordyce, 2007)
BATS
One third of all of the species of mammals are bats. Bats have a number of characteristics (both genetic similarities and anatomical traits such as the unique innervation of the wing by the facial nerve) which indicate that they descended from a common ancestor. Although bats share these similarities, such as adaptations to flight, there are significant anatomical variations within the bats (Hand, 2003). Pteropus is the largest modern bat with a body length of one foot (406 mm) and a wingspan of almost 5 feet (Dobson, p. 16). The smallest bats measure 25 mm in length (Walker, p. 184). The Thai bat Craeonycteris thonglongyai weighs 1.6 g while Pteropus edulis can weigh 1.5 kg, a difference of about 1,000 fold (Maina, 2000). Megachiropterans vary from 10 to 1,5000 grams in weight with forearm lengths which vary between 36 and 228 mm. Microchiropterans vary from 2 to 196 grams in weight with forearm lengths of 22 to 115 mm (Nowak, 1994).
There is considerable variation in specific anatomical bat features, such as the size and shape of the skull in bats.
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Bats vary significantly in their teeth. The greatest number of teeth in bats is 38 (2,1,3,3/3,1,3,3) although many have fewer than this. In Desmodontes, the dental formula is 1,1,2,0/2,1,3,0 for a total of 20 teeth. (Dobson, p. xx). Some megachiropterans (such as Rousettus, Pteropus, and Eidolon) possess 34 teeth while others (Nyctimene and Paranyctimene) possess 24 teeth (Baron, 1966).
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Bats vary in their hands and feet. In most bats (some Megachiropterans and almost all Microchiropterans) the second finger possesses a rudimentary phalanx. Some Microchiropterans lack a second phalanx. (Dobson, p. xii). The first toe of Cheiromeles is thumblike in its appearance (Dobson, p. xvi). Many bats possess an additional element of their foot to support the wing membrane known as a calcar. The calcar may be composed of cartilage, calcified cartilage, or bone. It is present in most, but not all, of bats in both suborders. In some Microchiropterans, it forms a basket for catching insects. It begins its development as a piece of cartilage near but separate from the calcaneus. Of the three fossil bats (Adams, p. 321-7). Microchiropterans possess a claw on their second finger while most megachiropterans retain it (Walker, p. 187). Members of the subfamily Macroglossinae vary in the presence/absence of a tail (Baron, 1966).
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BRAINS
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In bats, the telencephalon is proportionately larger in the Megachiropterans and the medulla, cerebellum and midbrain are proportionately larger in the Microchiropterans. The encephalization quotient varies from .52 to 1.23 in Microchiropterans and .95 to 1.37 in Megachiropterans. The olfactory bulb is large in most Megachiropterans but small in most Microchiropterans. The accessory olfactory bulb is absent in Megachiropterans but is present in some Microchiropterans. Some bats retain their vomeronasal organ; the family Phyllostomidae possesses a vomeronasal nerve. In Desmodus, the hypoglossal nerve is very large. Megachiropterans have larger cerebullums and cerebrums, both with gyri and sulci while Microchiropterans have smaller and smooth cerebellums and cerebrums. In Megachiroptera, the pons is larger and the there is a clearer division between the medulla and spinal cord. In Microchiropterans, the paraflocculus dorsalis is evident and the inferior colliculus may be very large. The midbrain is exposed in Microchiropterans, unlike Megachiropterans. There are variations in brain structure between families of bats. For example, the anterior rhinal and hippocampal sulci are more developed in Phyllostomidae, the medial geniculate nucleus in Noctilionidae, the rostral and sylvian sulci in Miniopterinae, the dorsal cochlear nucleus in Megadermatidae. (Adams, p. 106-114). In the image below, the brain of the bat Taphozous retains the primitive condition of midbrain exposure while in the brain of Pteropus, the cerebrum and cerebellum have expanded and cover the midbrain. A similar result occurred during primate evolution.
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Relative brain length and height of the cerebral hemispheres can vary by a factor of more than 1.6. Megachiropterans possess a longer corpus callosum than microchiropterans and the difference in relative length is about 12.3 times between the largest and shortest species. Although bat brains possess few sulci, there are variations in the patterns of sulci between different groups of bats. The olfactory bulbs vary in their size, shape, and their connections to the rest of the cerebrum. The midbrain exposure (ranging from completely covered to completely exposed) varies among bats and considerable variation can exist within a species. While the cerebellum of some bats are essentially smooth others are more convoluted.
Among megachiropterans, brain weight varies from .48 g to 10.45 g and among microchiropterans it varies from .07 g to at least 2.59 g.
The encephalization indices of bats range from 83 (in Tylonycteris) to 271 (in Macroglossinae), 279 (Brachyphyllinae), and 375, 394, and 404 (Pteropodinae). The species of Murininae often have a brain size 2.3 times larger than those of Tylonycteris (Baron, 1966).
The percentage of the total brain composed by individual regions of the brain vary in different bat species. The percentage of the total brain composed by the medulla can vary from 5.3-19.7%, midbrain 4.2-14.6%, cerebellum 11.5-28.9%, and telencephalon 37.7-70.2%. In humans, the telencephalon composes 85% of the total brain (Baron, 1966).In microchiropterans, the size of the medulla can vary by a factor of 2.2, the midbrain by a factor of 2.7, the telencephalon by a factor of 5.3. The largest variation between brain regions in microchiropterans was that of cerebellum which varies 5.1 times between Vampyrops brachycephalus and Tylonycteris pachypus (Baron, 1966).Among bats, there is a difference of 7.1 times in the size of the telencephalon, and a difference of 5.1 times in the size of the diencephalon (between Pteropus lylei and Tylonycteris pachypus). Among bats there is a difference of 7.6 in the size of the striatum, 5.1 in the size of the septum, 7.2 in the size of the hippocampus, and 9.2 in the size of the neocortex (Baron, 1966).
The accessory olfactory bulb is present in some bats while it is reduced and absent in others and varied by a factor of more than 26 between Vampyrum spectrum and Sphaeronycteris toxophyllum (members of the same family). The main olfactory bulb in microchiropterans varies by a factor of more than 30 (between Phylloderma stenops and Cyttraops alecto). The paleocortex size in microchiropterans varies by a factor of 9.3 (between Phylloderma stenops and Cyttraops alecto), the amygdala by a factor of 2.8, the hippocampus by a factor of 6.1, and the neocortex by a factor of 6.3 (Vampyrops vittatus and Tylonycteris pachypus) (Baron, 1966). Reduction of brain size has occurred in multiple species in at least 8 families of bats (Niven, 2005).
The pineal gland varies considerably in bats. Pteropus tonganus possess a greatly increased vascular supply to the pineal, forming a vascular cuff around it. The pineal gland is largest in Dobsonia praedatrix in which it reaches the brain surface and covers the anterior potion of the cerebellum. The reduction of the ependymal lining of the third ventricle allows the pineal to contact CSF. The pineal of D. praedatrix (in subfamily Pteropodinae) is .56% of the brain’s weight, which is 50 times larger than the expected value for the bats in the related subfamily Macroglossinae. Unlike most other bats, major pineal arteries actually enter the organ (Bhatnagar, 1990).
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In bats, ears are more variable than in other group of mammals and can reach the largest size (relative to body size) in mammals. In most Microchiropterans, the ears are longer than the head. (Dobson, p. xix) Most bats have a prominent ear lobe called the tragus (Walker, p. 184). The number of cochlear turns is 1.75 in Pteropus and 3.5 in Rhinolophus. The size of the cochlea of fossil bats is small and overlaps the megachiropterans (Adams, p. 143-5). The noses of certain families of bats (Rhinolopidae, Nycteridae, and Phyllostomidae) are unique among mammals. They are composed both of an elaborate nasal integument and glandular structures. Among other functions, they are very sensitive to touch (Dobson, p. xix).
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Bat sounds can be produced by oral or nasal echolocation pulses. Those which use nasal pulses possess a curvature in the skull skull to adapt to change in nasopharynx. Both molecular and anatomical evidence support that nasal emission seems to have evolved twice in bats. (Teeling, 2002). The Megachiropteran bats do not perform echolocation except for Rousettus which uses tongue clicking (Adams, p. 17). Bats are not the only animals to evolve the ability to use echolocation: sonar is used by South American oil birds, southeast Asian swiftlets, porpoises, dolphins, and the fish Gymnarchus.
The mouth is located more inferiorly in some bats. In Pteropus, the large intestine is so prominent that it appears similar to the large intestine. In many Microchiropterans, the stomach is so small that it simply seems to be an expansion of the esophagus (Dobson, p. xx-xxii). There is considerable stomach variation in bats; in vampire bats the stomach forms a long tube. The bat Desmodus possesses a pouch at the distal end of its stomach which holds the ingested blood (Weichert, 1970, p. 183).
The clitoris is almost as long as the penis in the bat genus Noctilio. In Noctilio and Cheiromeles, the urethra passes through the clitoris in females. The uterus may be simplex or bicornuate in bats (Dobson, p. xxiv, xxx). Most females have two mammary glands but some have four. In some bats, the testes only descend during breeding season into a temporary sac (Walker, p. 184). There are four variations in amnion formation known in bats. The allantois is of moderate size in most bats but it is small to nearly absent in others. At the limb bud stage, embryos utilize both a choriovitelline and a chorioallantoic placenta (Adams, p. 71-6).
Megachiropterans predominantly feed on fruit although some feed on fruit and nectar and some feed on nectar and pollen. A few may include some leaves and buds in their diet. In general, the megachiropterans do not feed on insects, although Epomophorus wahlbergi may feed on beetles when flowers are not available (Baron, 1966).Bats of the family Phyllostomidae have adapted to a variety of diets such as insects taken in flight, insects gleaned from surfaces, fruit and flowers, small vertebrates (some feeding on frogs and lizards, others feeding on birds, bats, and rodents), nectar and pollen, omnivorous diets, and blood (Baron, 1966).
Bats of the subfamily Glossophaginae (Family Phyllostomidae) possess a long, extendible tongue covered with bristle-like papillae which is adapted for feeding on nectar. The more a species feeds on plants, the longer the snout tends to be. These species rely less on echolocation, depending on the pale color of flowers and the musky smell of the flowers (Baron, 1966).Vampire bats of the family Desmodontidae vary in the animals they prey on for blood meals. Some feed primarily on mammals, others exclusively on birds, and others feed on both birds and mammals. (Baron, 1966).
Rousettus is the only megachiropteran which can fly in complete darkness (Baron, 1966). Some bats can hover while others (the larger megachiropterans) can use air currents to soar (Maina, 2000). Some bats are solitary most of the time while Tadarida brasilensis may live in groups of estimated size 30 to 50 million (Adams, p. 362).
There is an incredible amount of variation which occurs within bats and this variation undermines the argument of design. If bats were designed, what were they designed for? Some use vision to fly during the day to find fruit while others use echolocation to find insects at night. Their skulls and brains show an incredible degree of intergroup variation—more variation than what separates humans from chimps, for example. Although the sensory systems (including the ears, nose, and the ability to perform echolocation) can be quite complex, these features are much simpler in the more primitive bats. In other words, the most complex features of bats were not part of an original design but rather a specialization which occurred later in bat evolution. Echolocation, for example, seems to have evolved twice in bats (and several additional times in other groups). If only a fraction of this variability was present in the ancestors of bats, there is no reason to think that a small arboreal ancestor could not have been modified over time for gliding and eventually flying.
Large variations in the size of the cerebellum are known in mammalian groups, especially in bats, insectivores, whales, primates, and elephants (Weaver, 2005).
RODENTS
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About half of all modern species of placental mammals are rodents (and an additional third are bats). More than 1700 species are existed since the Paleocene and 1/4 of the known rodent families are now extinct. The earliest rodents (family Ischyromyidae) are known from North America and Europe and they lack the feeding specializations that characterize later rodents. The order Rodentia includes rabbits, which are distantly related to the other groups. The Oligocene rodent Anagale still retained many primitive features (for example, it lacked a postorbital bar but a postorbital process was present). The Eurymyloidae was a Paleocene group that shared characteristics with both rodents and rabbits and was close to the ancestry of rodents. Rabbits have been known since the Paleocene.
The first squirrels are known from the Late Oligocene of North America and Europe. In the Miocene, there was a great radiation of squirrels, including a variety of flying squirrels in Europe (Black, ). Some flying squirrels have a piece of cartilage from the arm which supports their gliding membrane. Some modern squirrels are the size of mice.
Modern rodents range in size from the harvest mouse (Micromys minutus) which weighs 6 grams to the pig-sized modern capybaras (weighing up to 80 kg). Size can vary significantly within rodent families. Family Sciuridae includes woodchucks, squirrels, and chipmunks in addition to rodents which do not live in Orange County such as prairie dogs. There are more than 260 species known worldwide which range in size from the African pygmy squirrel weighing 10 grams to the marmots which can weigh 7.5 kg (Alderton, 1996). Myomorph rodents include mice and rats, composing more than one quarter of all mammalian species. The harvest mouse can weigh as little as 6 grams and the Phillipine slender tailed cloud rat can weigh 2 kg.
Some fossil rodents achieved considerable size. Fossil relatives of capybaras, such as Neochoerus were 40% larger. The pig-sized modern capybaras are the largest rodents but their fossil relatives, such as Neochoerus were 40% larger. The fossil beaver Castoroides of North America could reach ten feet in length (including a 3 foot tail). The fossil rodent Telicomys was about the size of a hippo, measuring more than 2 meters in length. Protohydrochoerus in South America could reach the size of a tapir. Horned gophers such as Ceratogaulus measured 2 feet and had horns. The fossil beaver Paleocastor could dig burrows 2.5 meters deep (and the remains of these burrows have been called ‘Devil’s Corkscrews’). Fossil guinea pigs could reach 10 feet in length and weights of 1,500 pounds. The early rodent Epigaulus hatchery possessed a pair of horns (Giant Guinea pig, 2004; Alderton, 1996).
The Pliocene rodent Actenomys possessed arms intermediate between burrowing and non-burrowing rodents and flared zygomatic arches (Fernandez, 2000).
Teeth can vary among rodents. The Australian water rat possesses only 12 teeth as an adaptation for feeding on aquatic animals in a semi-carnivorous lifestyle. The African silvery mole rat possesses 28 teeth (Alderton, 1996). Mutant mice can produce vestigial premolars which have been absent in the rodent lineage for 50 million years (Peterkova, 2005).
The cranium within related groups of rodents (such as the squirrels pictured below) can vary considerably in size and shape.[pic]
Some rodents are unique to Africa and some are similar to South American caviamorphs (Maglio, 1978).
Patagonian hares may resemble rabbits in some of their body features but they are actually an unrelated group of rodents.
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Some rodents have evolved scales on their tails, such as some porcupines and squirrels. Porcupines have obviously specialized some of their hairs to function as defensive quills. Some porcupines have more quills than others.
The majority of rodents have reduced the number of toes on their front feet to four, although some have five (such as the brown rat) while others have three (such as guinea pigs). Many rodents possess dexterous front limbs which can hold and manipulate food. Jerboas have toes whose metatarsals are fused to form a single bone.
Some rodents, such as naked mole rats, have lost their fur (Alderton, 1996). In comparison to closely related rats, naked mole rats possess a greatly enlarged somatasensory cortex which occupies the majority of the cerebral cortex usually devoted to vision. Almost 1/3 of the somatosensory cortex is devoted to interpreting sensations detected by the incisors (Catania, 2002).
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In female hyenas, the clitoris resembles a penis and the urethra passes through it. In some rodents, the urethra passes through the clitoris (Weichert, p. 302).
PRIMATES
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Eocene primates developed a more grasping foot. Proconsul, New World monkeys, some Old World monkeys, and gibbons possess a prehallucial bone. (Isidro, 2002). Lemurs related to the modern indrids adapted to diverse habitats. Archaeolemur possessed the least curved phalanges, indicating a terrestrial lifestyle. Modern indrids live in trees and have greater phalangeal curvature. A group of extinct sloth lemurs (Mesopropithecus, Babakotia, Palaeopropithecus, and Archaeoindris) have highly curved phalanges, even more curved than that in spider monkeys and gibbons. They were one of the most suspensory primates in history, perhaps second only to orangutans (Jungers, 1997). Oreopithecus’ hand was not only modified to allow a precision grip, but it also could exert force in its grip that is only seen in hominids (Moya-Sola, 1999).
Most cebid monkeys have a fairly flat face (except in Alouatta) and a rounded skull without an occipital projection (except in Saimiri) (Anderson, 1987).
Occasionally in humans postpermanent teeth have been observed (Weichert, 1970, p. 172).
Mouse lemurs vary in their dental formulas. One species possesses a conical molar with one cusp as opposed to the normal triangular teeth with three cusps. Another possesses an extra molar (Cuozzo, 2003). Modern old world monkeys and apes (including humans, depicted below) possess one premolar fewer than New World monkeys and ancestral primates. In some New World monkeys the last molar is reduced and may even be absent (as in the lower jaws of Xenothrix and in 15% of Ateles specimens) (Anderson, 1987).
The flying lemur also glides (Keast, 1972).
Folding of the cerebrum occurs in some marsupials. While the majority of placental mammals possess gyri and sulci on the surface of the cerebrum, smooth cerebrums are known in some rodents, insectivores, and prosimians (Ariens, p.1518). There is also considerable brain variation observed in related primates. The dwarf lemur possesses a smooth cerebrum while that of another lemur, the sifaka, is convoluted with gyri and sulci. Among New World monkeys, some such as the pygmy marmoset possess a smooth cerebrum while the majority possess gyri and sulci. There are other groups of mammals, such as insectivores and rodents, in which the cerebrum may be smooth or wrinkled, depending on the species.
Some lemurs are among the smallest mammals in the world, while some subfossil forms reached five feet in length. Gigantopithecus is known from the Middle Miocene to Pleistocene from Asia.
From its teeth and mandibles, it is the largest ape that ever existed (since teeth are twice the size of gorilla teeth, it may have reached 11-12 feet in height).
Oreopithecus was a bipedal ape outside the hominid lineage although it would have been capable only of a very slow gait. It was found on the island of Tuscany and perhaps went extinct with the arrival of mainland predators. The hominid primates such as Australopithecus, Kenyanthropus, and Sahelanthropus walked upright. Although creationists argue that these were simply apes and not human ancestors, nevertheless they were bipedal apes. A number of mammals have evolved some degree of bipedal locomotion. Some, including bears, gorillas, chimps, extinct ground sloths, extinct chalicotheres can/could walk on their hind legs at least over short distances. A lemur named the sifaka spends most of its life in trees but when it comes to the ground it leaps on its hind feet. Some rodents such as jerboas hop on their hind legs as do kangaroos.
Species of the Family Callitrichidae (one of two families of New World Monkeys) possess 7 cervical vertebrae, 11-13 thoracic vertebrae, 6-8 lumbar vertebrae, 2-3 sacral vertebrae, and 25-33 caudal vertebrae. Species of the family Cebidae possess 7 cervical vertebrae, 12-15 thoracic vertebrae, 5-8 lumbar vertebrae, 2-5 sacral vertebrae, and 17-34 caudal vertebrae
(Anderson, 1967).
Extinct apes of the family Hylobatidae include the small genera Aeolopithecus and Dendropithecus (Maglio, 1978).
Australopithecus crassidens was a South African australopithecine whose cranial capacity measured 530 cc (Maglio, 1978).
Delsuc, Frederic. The evolution of armadillos, anteaters, and sloths depicted by nuclear and mitochondrial phylogenies. Proc. R. Soc. Lond B 268: 1605-15, 2001.
Maglio, Vincent (ed.) Evolution of African Mammals. Harvard University Press, Cambridge, 1978.
Kielan-Jaworowska, Zofia. Mammals from the age of dinosaurs. Columbia University Press, New York, 2004.
Stonehouse, Bernard. The Biology of Marsupials. University Park Press, Baltimore, 1977.
Maglio, Vincent. Evolution of African mammals. Harvard University Press, Cambridge, 1978.
Hunt, Kathleen. Transitional Vertebrate Fossils FAQ Part 2C. Talk.Origins Archive, 1997.
Simpson, George. Splendid Isolation. Yale University Press, New Haven, 1980.
Prothero, Donald. Horns, tusks, and flippers: the evolution of hoofed mammals. Johns Hopkins University Press, Baltimore, 2002.
Keast, Allen. Evolution, Mammals, and Southern Continents. State University of New York Press, Albany, 1972.
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