Prehistoric Lizard Claimed as Missing Link

When amateur fossil finder Van Turner discovered a small vertebra at a construction site near Dallas 16 years ago, he knew the creature was unlike anything in the fossil record.

Scientists now know the significance of Turner's fossil as the origin of an extinct line of lizards with an evolutionary twist: a land-dwelling species that became fully aquatic.

Turner took the remains to paleontologists at the Dallas Museum of Natural History, but it took several years before scientists dubbed the find Dallasaurus turneri.

Word of Dallasaurus is now reaching the scientific community with a special issue of the Netherlands Journal of Geosciences, featuring an article by Southern Methodist University paleontologist Michael Polcyn and Gordon Bell Jr. of Guadalupe National Park in Texas.

They describe Dallasaurus, a three-foot long lizard who lived 92 million years ago in the shallow seas and shores of what was then a stretch of Texas mostly under water, and also used the fossil to better understand the mosasaur family tree.

Polcyn and Bell painstakingly pieced together an understanding of the anatomy and natural history of Dallasaurus from the bones Turner discovered and from some matching skeletal remains at the Texas Memorial Museum at the University of Texas in Austin.

Dallasaurus represents a missing link in the evolution of a group of creatures called mosasaurs, prehistoric animals that started out on land, but evolved in the seas and dominated the oceans at the same time dinosaurs ruled the land.

One aspect of Polcyn and Bell's research is the revelation that Dallasaurus retained complete limbs, hands and feet suitable for walking on land, whereas later mosasaurs evolved their limbs into flippers.

"This is pretty close to the beginning of the mosasaur family tree," says Dallas Museum of Natural History Earth Sciences Curator and SMU Adjunct Professor of Paleontology Anthony R. Fiorillo, Ph.D. "It is the most complete mosasaur retaining all of its limbs found in North America."

Mosasaurs lived and became extinct alongside dinosaurs, but few paleontologists specialize in them. Later mosasaurs grew as large as their dinosaur brethren, reaching up to 45 feet in length. Until the discovery of Dallasaurus, however, only five primitive forms with land-capable limbs were known, all of them found in the Middle East and the eastern Adriatic.