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The rare fossils of Thrinaxodon liorhinus, a distant extinct relative of living mammals, have played a central role in understanding both early mammalian evolution and the theory of plate tectonics. Thrinaxodon lived during the early Triassic (240-245 million years ago) and was roughly the size of a house cat. Only about two dozen reasonably complete and well-preserved specimens are known, most of which were discovered in South Africa and reside in museums in Cape Town, Bloemfontein, and Johannesburg.
Thrinaxodon is a basal member of Cynodontia, a lineage that includes mammals and their closest extinct relatives. Thrinaxodon preserves a combination of primitive and derived characters, showing an early stage in the evolution of the characteristics that distinguish modern mammals from other living species. Illustrations and a more detailed explanation of the place of Thrinaxodon in early mammalian history are available in an excerpt from Thrinaxodon: Digital Atlas of the Skull.
The discovery of Thrinaxodon in Antarctica during the 1960's by Edwin Colbert was a stunning revelation to the scientific community- how could this terrestrial animal have made it from South Africa to Antarctica without a land connection between the two? Geophysicists have subsequently amassed a tremendous amount of data that indicates that Antarctica and Africa were connected during the Triassic.
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Cranial anatomy of the cynodont reptile Thrinaxodon liorhinus
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Rowe, T., W. Carlson, and W. Bottorff. 1995. Thrinaxodon
: Digital Atlas of the Skull. CD-ROM (Second Edition, for Windows and Macintosh platforms), University of Texas Press
, 547 megabytes.
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on the University of California Museum of Paleontology webpageThrinaxodon
on the Texas Memorial Museum webpage