Abstract:
The morphology of the skull and postcranial skeleton of the primitive ruminant artiodactyl Archaeomeryx optatus Matthew et Granger, 1925 from the Middle Eocene Shara Murun Formation of the Ula Usu locality in Inner Mongolia of China is described in detail. In addition to the type collection housed at the American Museum of Natural History, extensive fossil material collected by the Joint Soviet-Chinese Paleontological Expedition in 1959 and stored at the Paleontological Institute of the Russian Academy of Sciences is studied. The material of the type collection, including, among other fossils, one complete articulated and two fragmentary skeletons, is supplemented by 14 additional skeletons. The appearance and ecology of Archaeomeryx are specified. It is shown that, in morphology and ecology, this animal was close to primitive eutherians. New morphological evidence of the early evolutionary stages of the suborder Ruminantia and the order Artiodactyla and comparisons with other primitive artiodactyls and ungulates show that the order Artiodactyla undoubtedly appeared much earlier than was registered in the fossil record and that its roots perhaps go back to the Late Cretaceous. This conclusion supports the hypothesis first proposed by W. Kowalevsky in the 19th century. The adaptatiogenesis and the major principles of macroevolutionary processes are traced based on Ruminantia evolution.
