for National Geographic News
A lizard whose fossilized bones were discovered near Dallas, Texas, 16 years ago is a missing link in the evolution of extinct swimming reptiles known as mosasaurs, a new study says.
The ancient lizard, named Dallasaurus turneri, measured three feet (about a meter) long and lived 92 million years ago in shallow seas that covered what is now Texas.
As an early mosasaur, Dallasaurus is unusual, because it had tiny feet and hands suitable for walking on land. Later mosasaurs developed fin-like limbs and came to dominate the seas at the time when dinosaurs ruled the land.
"This study paints a much more complex picture of the evolution of [mosasaurs] than previously thought," said Michael Polcyn, a paleontologist at Southern Methodist University in Dallas.
Polcyn led the research, which is reported this month in the Netherlands Journal of Geosciences.
Van Turner, an amateur fossil hunter, found the Dallasaurus fossils in 1989 while searching through dirt turned up by bulldozers at a construction site near Dallas.
Remains of early mosasaurs have been difficult to find. They are only found in areas once covered by water and are quick to deteriorate.
This is the first well-preserved early mosasaur found in North America. Only five primitive specimens have been found before, all of them in the Middle East and along the Adriatic Sea.
"To have this discovery in our own backyard is a terrific find," said Anthony Fiorillo, curator of the Dallas Museum of Natural History and an SMU paleontology professor.
The discovery included more than 100 identifiable skeletal pieces, composing about 80 percent of the animal.
Polcyn, who heads SMU's visualization laboratory, used computers to simulate what Dallasaurus looked like and how it swam and moved from land to sea.
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