Experts agree Arlington dinosaur is new species

From The Shorthorn: Experts agree Arlington dinosaur is new species
Several experts agreed with Derek Main that there is enough evidence to justify the discovery of a new species of dinosaur found at the Arlington Archosaur Site.

“Arlington definitely has its own dinosaur,” Main, a doctoral candidate, said.

Last week at the Royal Tyrrell Museum’s 2011 Hadrosaur Symposium, Main presented evidence that a new species of hadrosaur was found eight years ago by two students and two local residents. Researchers are hoping the species will help bridge an evolutionary transition between two animals: iguanodonts and hadrosaurs.

The Arlington hadrosaur will be named in honor of the discoverers, but the official name cannot be revealed until after Main’s paper is reviewed and published in 2012, he said.

Chris Noto, University of Wisconsin-Parkside biology professor, has worked at the Arlington site and studied the hadrosaur bones to understand how the anatomy compares to other related dinosaurs, such as Protohadros. When the remains were first discovered in Arlington, it was first thought they belonged to a Protohadros.

Protohadros is recognizable primarily by the skull, said Andrew McDonald, University of Pennsylvania doctoral candidate.

Volunteers at the Arlington Archosaur Site recovered most of the Arlington hadrosaur’s skeleton, except for the skull.

Main said the only parts of the skull recovered from the site were a piece of the dentary, or jawbone where teeth attach, and a few teeth.

McDonald said to know if the Arlington remains are from a new species, the skull needs to be found for better comparison to that of a Protohadros.

Main said the Arlington hadrosaur’s dentary and teeth provide enough diagnostic information to distinguish the Arlington’s hadrosaur from Protohadros.

“A complete skull is always better,” Main said. “But we have enough fossils that we can say something, and we’re still digging.”

Regardless of whether it’s a new species, the Arlington hadrosaur is a very important specimen, McDonald said.

Main said for years scientists have known that hadrosaurs evolved from iguanodonts.

The entire skeleton has a mix of characteristics from iguanodonts and hadrosaurs, said Noto.

“The evolutionary transition between iguanodonts and hadrosaurs is still not well understood, and we’re hoping this new specimen helps resolve some of those issues,” said Noto.

A good record of primitive iguanodonts exists in rocks from the early Cretaceous period, approximately 100 to 146 million years ago, said McDonald. Iguanodonts disappeared during the late Cretaceous, approximately 90 to 100 million years ago, and early hadrosaurs took over in the late Cretaceous, 70 to 100 million years ago.

This is a period that transitioned from widespread, successful iguanodonts, to widespread, successful hadrosaurs, McDonald said.

Dinosaur fossils from this transition in North America are rare, he said. At the time, an inland sea, the Western Interior Seaway, stretched from the Gulf of Mexico through Canada. This time seems to be, in North America, when more primitive iguanodonts gave rise to early hadrosaurs, but exactly when and how this transition occurred is still not well understood, McDonald said.

He said some of the most important parts for comparing iguanodonts and hadrosaurs are the skull, hipbones and shoulder bones.

The Arlington hadrosaur’s shoulder is robust, an iguanodont character, and the hipbones show a mix of iguanodont and hadrosaur characters, said Noto.

The dentary fragment and teeth are completely hadrosaurid . The spine is mostly hardosaurid, with a few iguanodont characters, said Main.