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CREODONTS AND DOGS
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. In the past, there
were other groups of carnivorous mammals.
As already mentioned, South
A third group of
carnivorous mammals were the creodonts--a group of carnivorous mammals
apart from the Order Carnivora to which all
modern carnivores belong. They
may or may not have had a common ancestor with carnivores.
They were not as intelligent as the carnivores and were probably
slower and clumsier. In the Oligocene,
the herbivores evolved to become faster and more specialized which may
have contributed to the demise of the creodonts.
After the Eocene, creodonts were extinct from
|In the late Eocene and early Oligocene of North America, the only carnivores which could reach (and exceed) 100 kg were the creodonts Hemipsalodon and Hyaenodon. A few nimravid cats approached this size (Hunt, 2002). Over 50 genera of creodonts are known, including Sarkastodon which grew to 3 meters and was larger than bears.|
THE ORDER CARNIVORA
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).
|Many primitive carnivores are classified as “miacoids”.|
Only a few modern mammals (several shrews, Solenodon, and the platypus) produce venom. A small Paleocene eutherian mammal which may be a relative of carnivores possessed grooves in its canines, probably as a means of injecting venom (Fox, 2005).
|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.
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,
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
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
|The amphicyonid Ysengrinia resembled bears in some aspects of its legs although its lower legs were longer than found in living bears (Hunt, 2002).|
Bears have been known
since the small Oligocene genus Ursavis which weighed
10 kg. Arctodus measured almost 5 feet
at the shoulder (while on all fours), Agriotherium measured over three feet at the shoulder (on all
fours), and the European cave bear Ursus spleaeus was about the size of the Alaskan brown bear.
The giant pandas were an early offshoot of bears and were first known
The genus Ursavus may be ancestral to all modern bears. Two fossil species of small black bears may be the ancestors of the black bears of North American and Asiatic black bears (Kurten, 1980).
The earliest fossils of the modern giant panda are the small Pleistocene species Ailuropoda microta. The teeth of this species are intermediate between the crushing teeth of modern pandas and those of the Late Miocene bear considered to be ancestral to pandas, Ailurarctos (which evolved from an earlier Miocene ursid, Ursavus). Ailurarctos had developed a precursor to crushing teeth by 7 million years ago and Ailuropoda microta was probably feeding on bamboo by 2 million years ago, given modifications of its teeth. Another Pleistocene panda, Ailuropoda baconi was larger than the modern giant panda, Ailuropoda melanoleuca (Jin, 2007).
The following photo compares the sizes of a wolf and black bear skull to that of a cave bear.
The European cave bear had very blunt teeth and was fed primarily on plant matter (Kurten, 1988).
One group of bears, the tremarctine bears, are only known from the New World. Although they evolved in North America, their only living descendant is the South American Andean bear. Other extinct species of this group included the Florida cave bear which could reach 600 pounds and was probably a vegetarian, primarily. A relative of Andean bears, Arctodus simus, is the largest known bear and may have weighed 1,500 pounds. It had unusually short faces, skulls with more cat-like proportions, long legs, and light-built bodies (Kurten, 1988). Giant pandas are modified bears, forming a sister group relationship to Indarctos and Agriotherium (Salesa, 2006).
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). 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 and black bears are known (Kurten, 1988).
The procyonids (raccoons and their relatives) have been known since the early Oligocene. Lesser pandas evolved in the Miocene. 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.
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 (the group that includes the modern raccoon and red panda) are known from the Early Oligocene (Kurten, 1980).
| One group of
carnivores, the mustelids include skunks, otters, and weasels. A giant mustelid Megalictis ferox once lived in