Tiny tooth brings big hopes

From The Short Horn, the University of Texas at Arlington student newspaper: Tiny tooth brings big hopes
The recent discovery of a tooth from a rodent-like mammal at the Arlington Archosaur Site could shed light on an otherwise unknown ancient species of mammals.

Found two weeks ago, the tooth is the first and only physical evidence of mammals’s ancient presence at the site.

“The tooth itself is very rare,” said Geb Bennett, who helped UTA researchers identify the small tooth. “So far, there have only been four of its kind found in Texas. It’s one of only about a dozen found in all of eastern North America.”

Bennett is a microvertebrate specialist, someone who deals with smaller animals.

The tooth came from a Multituberculate, a rodent-like animal that dates back to the Mesozoic era, and is among the oldest mammals on the planet, said Derek Main, geology lecturer and Arlington Archosaur Site director.

“They went extinct in the Cenozoic when they were out-competed by more modern mammals,” Main said. “The largest was maybe the size of a beaver.”

Mammal fossils are rare finds for a dig from the Mesozoic era because few of them lived during that time period. Those mammals that did exist in the Mesozoic were often dominated by the dinosaurs and became extinct, Main said.

“Multituberculates, you could say, lived in the shadows of the dinosaurs,” he said. “These tiny, ratlike animals that couldn’t compete with the dinosaurs.”

Large mammals didn’t evolve until after the dinosaurs’s extinction, Main said.

“Once the dinosaurs went extinct after the asteroid impact, the world stage was cleared for other life forms to adapt to this basically empty world,” Main said. “Mammals took over at that point.

The Mesozoic is the age of reptiles, and the Cenozoic is the age of mammals for that very reason.”

Main also said searching for mammal fossils is very different from digging for dinosaur bones.

“People, like Geb, who work with mammals, have a different skill set from the dinosaurs,” he said. “They’re hard to find because they’re so small.”

While most paleontologists who work in the Cretaceous are looking for big dinosaurs, fewer scientists work with the remains of ancient mammals, Main said.

“You see the massive dinosaur excavations, but this is a different type of work,” he said.

Main said he had previously suspected such mammals existed at the site.

“[The site] was once a peat bed from the ancient swamps of the Cretaceous,” he said. “There should be all the animals you’d expect from a swamp. Not just the crocodiles and dinosaurs.”

Discovering mammal teeth and bones is much more time consuming than finding the remains of larger animals, such as dinosaurs and crocodiles, Main said.

First, sediment is collected and sorted into buckets according to where they were found in the site. Then, they are carried down a steep hill to a nearby creek.

“We bring them down here [to the creek] and pour water in them and let them soak,” Main said.

Then the sediment is screen washed and broken down into smaller particles of sediment. Screen washing is a very important part of the process, Main said.

“We’ve been doing screen washing for the past two years now, and gradually we’ve been putting more emphasis on it,” he said.

While screen washing isn’t necessary to discover larger fossils and teeth, it’s necessary to find remains of ancient mammals, said Bennett, paleontology curator at the Shenandoah Valley Discovery Museum in Winchester, Va.

“Some of the really rare things you don’t find unless you screen wash the sediment,” Bennett said.

Many volunteers, like Melissa Rozakis, help by screen washing sediment.

Last Friday was Rozakis’s first time to screen wash in the creek.

“Honestly, this is so zenlike for me,” Rozakis said. “I’m a Yankee, so this summer heat in Texas has been pretty rough on me. But this is great because it’s in the shade, I get to play in the water and the mud. This is like going to a spa for me.”

Main said even after the sediment has been screen washed, no one can tell whether a fossil or tooth is present.

“To us, what looks like a fleck could be a tooth,” Main said.

After the sediment has been screen washed, it is taken back up the hill and spread out on a blue tarp to dry in the sun.

“We take this back to UTA and spend hours looking at all these little pieces under a microscope,” Main said. Each specimen that Main and his team screen wash can be a tooth or a vertebra, he said.

“We look at that through microscopes in the lab, which can take hours and months,” Main said. “Gradually, we find little fossils that we don’t see when we’re out there digging by hand. It’s a lot of work for one little tooth.”

Usually, all that’s found of these mammals are teeth because teeth are the hardest, most structurally-preserved part of any animal, Main said.

“If the teeth are tumbled around in a stream or eroded, it holds up much better than regular bone,” Bennett said.

Main said he plans to publish a paper on the mammal tooth.

“We just discovered it not too long ago, so we’ve got to study it and figure out exactly what it is,” he said. “If we’ve got a different tooth from a new animal, that in itself is probably one paper, just one little tooth.”

Although mammal bones can prove difficult to find, Main said the discovery of the tooth gives him a reason to search for more.

“We’ve got one tooth and we’re looking for more,” he said. “I think it’s possible to find some of the bones, but it’s a long shot.”

Main said he’s not sure people will realize the impact of one of his most recent finds.

“I don’t know if people will realize how big of a deal it is,” he said. “It’s a big discovery for a very small fossil.”