Coryphodon (from Greek κορῦφὴ, "point", and ὀδοὺς, "tooth", meaning peaked tooth, referring to "the development of the angles of the ridges into points [on the molars].") is an extinct genus of mammal. It was widespread in North America between . It is regarded as the ancestor of the genus Hypercoryphodon of Mid 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. 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.
Estimates of Coryphodon's body mass have varied considerably. Based on a regression analysis of ungulates, Uhen & Gingerich 1995 estimated the mean body mass for the type species C. eocaenus to 340 kg (750 lb), 600 kg (1,300 lb) for C. radians, and possibly as much as 700 kg (1,500 lb) for C. proterus and C. lobatus. Uhen and Gingerich also 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.
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 who 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.
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. At about 1 metre (3.3 ft) at shoulder height and 2.25 metres (7.4 ft) in body length, Coryphodon was the biggest known mammal of its time. It 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.
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. Chemical studies of fossil bone show that in the summer, Coryphodon ate flowers, leaves, and swamp plants. In the winter dark, they survived on pine needles, dead leaves, and fungi. This flexible diet allowed the species to spread widely across the Eocene world.
Coryphodon had very strong neck muscles and short tusks that were probably used to uproot swamp plants. As in most pantodonts, the tusks were larger in males. The creature was very slow, with long upper limbs and short lower limbs, which were needed to support its weight. Coryphodon had one of the smallest brain/body ratios of any mammal, living or extinct, possessing a brain weighing just 90 grams (3.2 oz) and a body weight of around 500 kilograms (1,100 lb).
Notes[edit source | edit]
- Coryphodon in the Paleobiology Database. Retrieved July 2013.
- Uhen & Gingerich 1995, p. 259 citing Owen 1845, p. 608
- Uhen & Gingerich 1995, p. 266
- Uhen & Gingerich 1995, pp. 259–60
- Uhen & Gingerich 1995, Body Mass, pp. 263–5
- Uhen & Gingerich 1995, Dental variation, p. 263
- Uhen & Gingerich 1995, Discussion, p. 286
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 235. ISBN 1-84028-152-9.
References[edit source | edit]
- Owen, Richard (1845). Odontography; a treatise on the comparative anatomy of the teeth. London: Hippolyte Bailliere. OCLC 727240564. Retrieved July 2013.
- Uhen, Mark D.; Gingerich, Philip D. (1995). "Evolution of Coryphodon (Mammalia, Pantodonta) in the Late Paleocene and Early Eocene of Northwestern Wyoming". Contributions from the Museum of Paleontology, University of Michigan 29 (10): 259–89. OCLC 742731820. Retrieved July 2013.