Mosasaur Moment

About Dallasaurus

Dallasaurus was a small lizard that took to the oceans 92 million years ago and prowled the shores and marine margin of what is now North Texas. It has been the focus of a study by a researcher at Southern Methodist University and identified as Dallasaurus turneri in the current issue of the Netherlands Journal of Geosciences.

See animation of a
swimming Dallasaurus.

Some 3 feet long with a narrow body, Dallasaurus represents the first well preserved early mosasaur retaining terrestrial limbs that has been found in North America, says SMU researcher Michael J. Polcyn, whose study was based on two partial skeletons. A journal article co-authored with Gorden Bell Jr. of Guadalupe National Park details their findings.

The Dallasaurus fossils, were found by amateur paleontologist Van Turner in a construction site near Cedar Hill, Texas.  Dallas artist Ross McMillan has sculpted a model of the Dallasaurus.

Mosasaurs lived during the last phase of the age of dinosaurs. Later forms have been studied for more than 200 years, and previously classified into multiple distinct lineages but were united by the possession of fin–like limbs and other aquatic adaptations. More primitive forms retaining limbs capable of walking on land have been known for some time, but considered distinct from the later forms possessing fin-like limbs.

However, the new discovery provides evidence that mosasaurs evolved fin-like limbs and other marine adaptations independently in multiple lineages, said Polcyn, director of the Visualization Laboratory and adjunct research associate in SMU's Department of Geological Sciences. Over time, they evolved from small creatures like Dallasaurus, that could live both on land and in water to finned and streamlined ocean-going reptiles some reaching up to 45 feet in length.

The earliest mosasaur comes from the West Bank, north of Jerusalem, and was described by the Polcyn along with SMU paleontologist Louis Jacobs and Eitan Tchernov of the Hebrew University of Jerusalem in 1999. The fossil named Haasiasaurus gittelmani is dated at 98 million years old, and along with other early forms suggests that the group may have evolved in response to significant changes in earth's climate during a time of global warm temperatures and rising sea levels. Mosasaurs died out with the extinction of the dinosaurs about 65 million years ago.

Other fossils from this time period have been the subject of a number of papers by the SMU team, notably a new snake with legs described in a paper published in Science in March 2000 by Jacobs, Polcyn, and several international co-authors.

Jacobs' and Polcyn’s recent research into the early natural history of mosasaurs provides important new findings and is significant because the early evolution of mosasaurs is not well understood and it is believed the fossils and the rocks from which they were recovered can provide insight into how at least one group of organisms responded to dramatic changes in Earth's climate during the last epoch of the age of dinosaurs.

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