Didymoconus, Mesonyx, Triisodon and Wyolestes

Didymoconus colgatei (Matthew WD and Granger W 1924. Gingerich 1981, Eocene 52mya) is a former enigma taxon here nesting with mesonychids. This species has a longe rostrum. Note the four relatively huge molars.

Didymoconus berkeyi (Matthew WD and Granger W 1924. Gingerich 1981, Wang X et al 2001; IVPP V11983, Eocene 52mya) is a former enigma taxon here nesting basal to desmostylians. The zygomatic arches are wider posteriorly and the orbits are dorsally open in this phylogenetically miniaturized taxon.

Mesonyx obtusidens (Cope 1872, Eocene, 51 mya, 1.5m long, YPM VP 013066) Widely considered a carnivore, Mesonyx had the same large canine fangs also found in Hippopotamus, which is also an herbivore. Mesonychids have been linked to whales, but toothed whales like Maiacetus are descendants of tenrecs.Baleen whales are descendants of Mesonyx. hippos and desmostylian in that order.

Here the extant bush dog, Speothos, is compared to extinct Mesonyx. This is when smaller carnivores evolved to become large, hippo-like herbivores.

Triisodon quivirensis (Cope 1881; Early Paleocene) is a basal mesonychid known from most of a 3D skull. Note the tiny orbit and large canine alveolus. The premaxillary teeth have three cusps.

Carroll RL 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Co. New York.

Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465.

Cope ED 1881. On Some Mammalia of the Lowest Eocene Beds of New Mexico. Proceedings of the American Philosophical Society. 19 (109): 484–495.

Gingerich PD 1981. Radiation of Early Cenozoic Didymoconidae (Condylarthra, Mesonychia) in Asia, with a New Genus from the Early Eocene of Western North America. Journal of Mammalogy 62(3):526-538.

Hatcher JB 1901. Report of the Princeton University Expeditions to Patagonia 1869-1899. Mammalia of the Santa Cruz Beds. IV. Astrapotheria. Scott WB ed. Vol. 6,

Matthew WD and Granger W 1924. New Carnivora from the Tertiary of Mongolia. American Museum Novitates (104).

Wang X et al 2001. Didymoconus (Mammalia: Didymoconidae) from Lanzhou Basin, China and its stratigraphic and ecological significance. Journal of Vertebrate Paleontology. 21 (3): 555–564.

wiki/Mesonyx
wiki/Triisodon
wiki/Didymoconus