Coryphodon

Coryphodon (from Greek κορῦφὴ, 'point', and ὀδοὺς, 'tooth', meaning peaked tooth, referring to 'the development of the angles of the ridges into points .') is an extinct genus of mammal. 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. At about 1 metre (3.3 ft) at shoulder height and 2.5 metres (8.2 ft) 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 90 grams (3.2 oz) and a body weight of around 500 kilograms (1,100 lb). 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. 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. 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.