The location of Deltatheridium in Central Asia suggests that modern marsupials, which today are most diverse in South America and Australia, may have arisen from a lineage that actually originated in Asia.
Before the current discovery, scientists debated whether Deltatheridium should be placed in the placental lineage or the marsupial lineage. Study of the new fossils reveals unequivocally that Deltatheridium is an early relative of marsupials, and in fact is one of the earilest marsupial relatives ever discovered.
Some of the features Deltatheridium shares with modern-day marsupials include a large bony process at the back of the jaw for the attachment of chewing muscles and a distinct pattern of openings in the skull to accommodate blood circulation, but it lacked many other features that arose in modern marsupials.
The juvenile specimen found at Ukhaa Tolgod is particularly important because it died when its adult teeth were just beginning to emerge, so the sequence in which the teeth grew can be observed. Analysis of the teeth of the juvenile Deltatheridium provides one of the strongest links between this animal and modern marsupials unlike any other group of mammals, marsupials replace only one tooth after birth, the last premolar. The juvenile specimen shows this same highly distinctive tooth replacement pattern.
Authors on the December 3 Nature paper are: Guillermo W. Rougier, assistant professor at the Department of Anatomical Sciences and Neurobiology at the University of Louisville, who is also a research associate in the Department of Vertebrate Paleontology at the American Museum of Natural History; John R
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Contact: Elizabeth Chapman, Karen de Seve
chapman@amnh.org/ kdeseve@amnh.org
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American Museum of Natural History
2-Dec-1998