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Phenacodontidae
Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the wastebasket taxon Condylarthra, that may represent early perissodactyls.〔. Retrieved April 2013.〕 They lived between the Paleocene and Eocene epochs (about 60-50 million years ago) and their fossil remains have been found in North America and Europe.
==Description==
These animals had a variety of body sizes, and could be as small as domestic cats (''Tetraclaenodon'' and ''Ectocion'') and as large as sheep (''Phenacodus''). The skeleton of phenacodontids show several primitive characteristics (the long and heavy tail for example) but also a number of advanced, Perissodactyla-like adaptations: the long legs, for example, had five fingers, but the first finger showed a clear reduction, and in some forms (like ''Phenacodus'') the fifth finger was reduced as well. The skull of phenacodontids is long and narrow, and equipped with a small braincase. Some species had tapir-like adaptations suggestive of the presence of a short proboscis or a strong prehensile lip.
The teeth of phenacodontids, particularly in the latter forms, were quite specialized: the molars and premolars were equipped with low cusps that sometimes joined in ridges, similar to the condition found in some perissodactyls. Some forms, like ''Meniscotherium'', had enlarged ridges. This adaptation is unusual for mammals as old as phenacodontids.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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