Tooth Replacement Pattern in Primitive Mammal

Feb. 13, 2002

SMU RESEARCHERS DISCOVER TOOTH REPLACEMENT PATTERN IN PRIMITIVE MAMMAL

DALLAS (SMU) -- Researchers from Southern Methodist University have published an account of how the tooth replacement system in modern mammals may have come about.

In an article to be published in the Feb. 22 issue of Proceedings of the Royal Society of London, SMU researchers describe how they found both a baby tooth and a replacement tooth in the jaw of a 110-million-year-old fossil mammal known as Slaughteria eruptens.

Slaughteria was a shrew-like mammal no larger than a small mouse. It is significant because it lived about the time when placental mammals and marsupials diverged from a common ancestor. Slaughteria, or an animal like it, could have given rise to both marsupials and placentals.

Bob Slaughter, former director of the Shuler Museum of Paleontology at SMU, discovered the Slaughteria jaw on a farm in Wise County, Texas, in 1967.

Early examinations of the Slaughteria jaw did not reveal any replacement teeth. Using the high-resolution X-ray Computed Tomography Facility at The University of Texas at Austin, the SMU researchers found a previously unrecognized replacement tooth hidden in the middle of the lower jaw under a tooth once thought to be a permanent molar.

"It is rare to find any teeth on a jaw of fossils like this, and replacement teeth are even rarer," said Dale Winkler, the current director of the Shuler Museum of Paleontology. Winkler co-authored the paper along with Louis Jacobs, president of the Institute for the Study of Earth and Man at SMU, and Yoshitsugu Kobayashi of the Fukui Prefectural Dinosaur Museum in Japan. Kobayashi began the study while he was a graduate student at SMU.

Winkler said that to date, it has been unclear how the remarkably different systems of tooth replacement used by modern mammals (marsupials and placentals) came about. Marsupials replace only one milk tooth, whereas placentals replace more than one.

Slaughteria's primitive pattern of tooth replacement offers the first glimpse of the system that may have been shared by the common ancestor of most modern mammals.

Winkler said that discovery of the replacement tooth in Slaughteria may prompt researchers to re-evaluate fossils of other mammals that have been found in the same Lower Cretaceous deposits in north central Texas.

Note to editors: photos of the Slaughteria jaw may be found online at http://www.newsmedia.smu.edu/releases/01223.html

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