Coryphodon

''Coryphodon'' (from Greek κορῦφὴ, "point", and ὀδοὺς, "tooth", meaning ''peaked tooth'', referring to "the development of the angles of the ridges into points n the molars") is an extinct genus of pantodonts of the family Coryphodontidae.

''Coryphodon'' was a pantodont, a member of the world's first group of large browsing mammals. It migrated across what is now northern North America, replacing ''Barylambda'', an earlier pantodont. It is regarded as the ancestor of the genus ''Hypercoryphodon'' of Late Eocene Mongolia.

''Coryphodon'' is known from many specimens in North America and considerably fewer in Europe, Mongolia, and China. It is a small to medium-sized coryphodontid who differs from other members of the family in dental characteristics.

Description

At about at shoulder height and in body length, ''Coryphodon'' is one of the largest-known mammals of its time. The creature was very slow, with long upper limbs and short lower limbs, which were needed to support its weight. ''Coryphodon'' does not seem to have been in need of much in the way of defences, however, since most known predators of the time seem to have been much smaller than ''Coryphodon''.

''Coryphodon'' had one of the smallest brain/body ratios of any mammal, living or extinct, possessing a brain weighing just and a body weight of around .

Estimates of ''Coryphodon'''s body mass have varied considerably. Based on a regression analysis of ungulates, estimated the mean body mass for the type species ''C. eocaenus'' to , for ''C. radians'', and possibly as much as for ''C. proterus'' and ''C. lobatus''.

Taxonomy and systematics

Since the first fossil was found in Wyoming, the taxonomy of ''Coryphodon'' and its family have been in disarray – five described genera have been synonymized with ''Coryphodon'' and thirty-five proposed species have been declared invalid.

Species

* ''C. anax'' was named by Cope (1882); it was synonymized with Coryphodon lobatus by Osborn (1898) and Uhen and Gingerich (1995).
* ''C. anthracoideus'' was named by de Blainville (1846).
* ''C. armatus'' was named by Cope (1872).
* ''C. dabuensis'' was named by Zhai (1978).
* ''C. eocaenus'' was named by Owen (1846); it was reassigned to ''Lophiodon eocaenum'' by Blainville (1846); it was revalidated by Cope (1877), Lucas (1984) and Uhen and Gingerich (1995).
* ''C. gosseleti'' (=C. grosseleti lapsus calami) was named by Malaquin (1899).
* ''C. hamatus'' was named by Marsh (1876); it was synonymized with ''Coryphodon anthracoideus'' by Lucas (1984) and Lucas and Schoch (1990); it was synonymized with Coryphodon radians by Uhen and Gingerich (1995).
* ''C. lobatus'' was named by Cope (1877).
* ''C. marginatus'' was named by Cope (1882); it was synonymized with'' Coryphodon eocaenus'' by Lucas (1984) and Uhen and Gingerich (1995).
* ''C. oweni'' was named by Hebert (1856).
* ''C. pisuqti'' was named by Dawson (2012)
* ''C. proterus'' was named by Simons (1960).
* ''C. repandus'' was named by Cope (1882); it was synonymized with'' Coryphodon radians'' by Uhen and Gingerich (1995).
* ''C. radians'' was named by Cope (1872).
* ''C. singularis''? was named by Osborn (1898); it is a nomen dubium due its to pathology.
* ''C. subquadratus''? was named by Cope (1882); it was synonymized with Manteodon.
* ''C. tsaganensis'' was named by Reshetov (1976)
* ''C. ventanus'' was named by Osborn (1898); it was synonymized with ''Coryphodon lobatus'' by Uhen and Gingerich (1995).

Synonyms

* ''Bathmodon radians'' was named by Cope (1872); it was synonymized with Coryphodon anthracoideus by Lucas (1998b); it was reassigned to Coryphodon radians by Cope (1877), Simpson (1948a), Simpson (1951), Simpson (1981) and Uhen and Gingerich (1995).
* ''Bathmodon semicinctus'' was named by Cope (1872); it was reassigned to Loxolophodon semicinctus by Cope (1872); it was revalidated by Cope (1873); it was reassigned to Coryphodon semicinctus by Wheeler (1961); it was synonymized with Coryphodon radians by Gazin (1962); it was considered a nomen dubium by Uhen and Gingerich (1995).
* ''Ectacodon cinctus'' was named by Cope (1882); it was reassigned to Coryphodon cinctus by Osborn (1898); it was synonymized with Coryphodon radians by Uhen and Gingerich (1995).
* ''Letalophodon''?
* ''Loxolophodon''? was named by Cope, (1872)
* ''Manteodon subquadratus'' was named by Cope (1882); it was reassigned to Coryphodon subquadratus by Lucas (1984); it was synonymized with Coryphodon radians by Uhen and Gingerich (1995).
* ''Metalophodon testis'' was named by Cope (1882); it was reassigned to Coryphodon testis by Osborn (1898); it was synonymized with Coryphodon radians by Uhen and Gingerich (1995).

Size evolution

''Coryphodon'' evolved from the Late Paleocene ''C. proterus'', one of the largest species found and the only one known from the Clarkforkian NALMA. The body size then decreased until ''C. eocaenus'' appears at the Clarkforkian-Wasatchian transition (55.4 Ma, near the PETM), from where ''Coryphodon'' evolved into the large species ''C. radians''. ''C. radians'' in its turn evolved into two contemporaneous species that appear in the Early Eocene, the small ''C. armatus'' and the very large ''C. lobatus''. These changes in size are thought to be linked to global climate change, with the size minimum in the ''Coryphodon'' lineage occurring shortly after Paleocene-Eocene boundary.

Paleobiology

Feeding and diet

''Coryphodon'' had a semi-aquatic lifestyle, likely living in swamps and marshes like a hippopotamus, although it was not closely related to modern hippos or any other animal known today. ''Coryphodon'' had very strong neck muscles and short tusks that were probably used to uproot swamp plants. The other teeth in the mouth were suited for processing plants that had been grabbed by browsing.

Fossils found on Ellesmere Island, near Greenland, show that ''Coryphodon'' once lived there in warm swamp forests of huge trees, similar to the modern cypress swamps of the American South. Though the climate of the Eocene was much warmer than today, plants and animals living north of the Arctic Circle still experienced months of complete darkness and 24-hour summer days. Isotopic studies of tooth enamel revealed that during the summer period of extended daylight ''Coryphodon'' would eat soft vegetation such as flowering plants, aquatic plants and leaves. However during the extended periods of darkness when plant photosynthesis was impossible, ''Coryphodon'' would switch to a diet of leaf litter, twigs, evergreen needles and most revealingly fungi, an organism and food source that does not require light to grow. Not only does this study reveal the dietary range of ''Coryphodon'', but it also reveals the behaviour of the northern populations living within the Arctic Circle. In this respect, ''Coryphodon'' did not migrate south or hibernate, it simply switched between two seasonal food sources.

Sexual dimorphism

noticed a sexual dimorphism in ''Coryphodon'': the canines tend to be either very large or very small compared to cheek teeth, and, comparing to modern hippos, there is reason to assume males had larger canines than females.

See also

References

Sources

*
*
*
*
*
*

External links

*
Ferae Past and Present (Phylogenetic tree)
at Okapiland

{{authority control

Paleogene mammals of North America
Pantodonts
Paleocene mammals
Eocene mammals
Eocene mammals of Europe
Eocene genus extinctions
Paleogene United States
Fossils of the United States
Paleontology in the Northwest Territories
Paleogene Canada
Fossils of Canada
Fossils of Great Britain
Fossils of England
Paleogene mammals of Asia
Eocene mammals of Asia
Fossils of Mongolia
Fossils of China
Paleocene first appearances
Fossil taxa described in 1845
Taxa named by Richard Owen
Prehistoric mammal genera