genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
of North America. It is known from the type species, ''A. ursidens'', a second species, ''A. cultridens'', and a possible third, ''A. nexus''. Initially believed to be a relative of '' Phenacodon'', it was subsequently found to be an arctocyonid, possibly related to '' Claenodon''. ''Anacodon'' was extremely robust compared to other members of its family, and may have been capable of climbing and digging like modern bears.
Taxonomy
Early history
The first specimens of ''Anacodon'' to be discovered were a pair of mandibular rami, apparently from different individuals. In 1882, they were described by
Edward Drinker Cope
Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
. Cope assigned the new genus to
Phenacodontidae
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the “wastebasket taxon” Condylarthra, which may instead represent early-stage perissodactyls. They lived from the late early Paleocene to early middle ...
. Ten years later, in 1892,
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. (August 8, 1857 – November 6, 1935) was an American paleontologist, geologist and eugenics advocate. He was professor of anatomy at Columbia University, president of the American Museum of Natural History for 25 y ...
and Jacob Lawson Wortman instead assigned it to the family
Arctocyonidae
Arctocyonidae (from Greek ''arktos'' and ''kyôn'', "bear/dog-like") is an extinct, possibly polyphyletic family of placental mammals which lived from the late Cretaceous to the early Eocene. They were initially regarded as creodonts, though ha ...
. In 1915, a second species of ''Anacodon'', ''A. cultridens'', was named by Walter Granger and
William Diller Matthew
William Diller Matthew FRS (February 19, 1871 – September 24, 1930) was a vertebrate paleontologist who worked primarily on mammal fossils, although he also published a few early papers on mineralogy, petrological geology, one on botany, one on ...
. In 1937,
George Gaylord Simpson
George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...
suggested that ''Anacodon'' may have represented a late-surviving member of an arctocyonid lineage deriving from '' Claenodon''. A second mandible, considerably smaller than ''A. ursidens'', was later recovered in the Buckman Hollow locality of Wyoming's
Almy Formation
The Almy Formation is a geologic formation in Wyoming. It preserves fossils dating back to the Paleogene period.
See also
* List of fossiliferous stratigraphic units in Wyoming
* Paleontology in Wyoming
Paleontology in Wyoming includes resea ...
, and in 1956, it was formally described by Charles Lewis Gazin. He tentatively assigned it to ''Anacodon'', assigning to it the binomial name ''Anacodon''? ''nexus'', though noted that it may have been a species of ''Claenodon''. In 2006, it was tentatively reassigned to ''Arctocyon''. Postcranial remains of ''Anacodon'' have since been recovered from the
Willwood Formation
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.
Description
The holotype of ''Anacodon'', consisting of two mandibular rami, preserves only the
molars
The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...
, with the exception of what may represent the fourth
premolar
The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
on the more damaged mandible; the other premolars are not preserved. The overall morphology of the teeth resembles modern
bears
Bears are carnivoran mammals of the family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout most o ...
, being flatter and more crenulated than in other arctocyonids. ''Anacodon'' may have been trending away from carnivory and towards a more herbivorous diet. ''Anacodon'' is unusually robust by arctocyonid standards, to the point where the remains of its postcranial skeleton were initially mistaken for those of a
taeniodont
Taeniodonta ("banded teeth") is an extinct order of eutherian mammals, that lived in North America and Europe from the late Cretaceous (Maastrichtian) to the middle Eocene.
Taeniodonts evolved quickly into highly specialized digging animals, and ...
. In many respects, it resembles a larger version of the related '' Chriacus''. The forelimbs were extremely robust, more so than the hind limbs, with curved ungual phalanges. A small spur on the
tibia
The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...
interlocked with the
astragalus
Astragalus may refer to:
* ''Astragalus'' (plant), a large genus of herbs and small shrubs
*Astragalus (bone)
The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...
, restricting mediolateral (side-to-side) movement of the foot. The
calcaneus
In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel; : calcanei or calcanea) or heel bone is a bone of the Tarsus (skeleton), tarsus of the foot which constitutes the heel. In some other ...
of the foot is unusual in that it is strongly arched, a morphology otherwise only seen in certain
hominids
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...
, ursids, and the
giant anteater
The giant anteater (''Myrmecophaga tridactyla'') is an Insectivore, insectivorous mammal native to Central America, Central and South America. It is the largest of the four living species of anteaters, which are classified with sloths in the or ...
. Its overall morphology suggests that it may have been analogous to bears, being partly
arboreal
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
and
fossorial
A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...