Pterosaur Fossil Found Near Dallas Shows That Flying Reptiles Spread From Europe

The fossil of a pterosaur discovered just outside Dallas, Texas, may change what we know about the evolution and spread of some of the West’s giant flying reptiles, scientists say.

The specimen was found near the reservoir of Lewisville Lake just north of the city, in a bed of 95-million-year old shale laden with fossils of ammonites, crustaceans, and other animals.

An amateur fossil hunter found the bones and took them to Southern Methodist University, where paleontologist Dr. Timothy Myers quickly realized that “he had found something amazing.”

Not only was the bone part of a pterosaur’s skull — a rarity by any measure in North America — they also turned out to closely resemble those another species of ancient reptile originally discovered more than 150 years ago, in England.

Myers discovered that the specimen was a new, but closely related species, to the English pterosaur — providing evidence that some of ancient America’s flying reptiles originated from species in Europe.

“This find is exciting for a number of reasons,” Myers said, “and foremost among these is the additional evidence it provides for close biogeographic ties between the pterosaurs of modern-day Texas and England in the middle Cretaceous, between 105 to 90 million years ago.”

Cimoliopterus dunni Texas pterosaur fossil
The pterosaur rostrum found in Texas, with a a lithograph illustrating the fossil of the animal’s likely European cousin, Cimoliopterus cuvieri. (Photo by Hillsman Jackson, courtesy SMU)

The specimen consists largely of the animal’s upper jaw, including the length of its rostrum or snout, and the distinctive bony crest on top.

When Myers began studying the specimen, one feature quickly grabbed his attention, he said: its teeth.

Most pterosaurs found in North America are toothless, Myers explained.

Only two other toothed species have been found on the continent from the Cretaceous period — both in Texas.

But both of those animals are obviously different from the Dallas specimen, Myers said.

One toothed Texas pterosaur, known as Coloborhynchus, sported a thicker crest than the Dallas specimen, and had more robust jaws and two big buck teeth projecting from the end of the upper jaw. Plus, it lived 11 million years earlier.

The only other toothed pterosaur found in North America, known as Aetodactylus, was smaller, more slender, and had no crest.

“Without these three specimens from Texas, the fossil record of pterosaurs in the Cretaceous of North America looks very different,” Myers said.

“It would comprise only remains of toothless pterosaurs.”

But even though all of these fossils were found in the Lone Star state, the Dallas specimen most closely resembles one that, until now, had only been found in England — the genus known as Cimoliopterus. [See a curious discovery with roots in Texas: “Origin of ‘Spanish Armor,’ Said to Have Been Found in Texas Desert, Stumps Scientists“]

In the newly found fossil, Myers said, “the snout end is more sloped, and the first two teeth would have assumed a more downward angle” than in its English counterpart.

But otherwise, the two species share many similarities, especially in their jaws and dentition.

In honor of the fossil prospector who made the find, named Brent Dunn, Myers dubbed the new species Cimoliopterus dunni.

But the question remains how Cimoliopterus could have established a presence in both England and Texas — even 95 million years ago, when Europe and North America were already separated by a slowly growing Atlantic Ocean.

“The transatlantic distribution of Cimoliopterus suggests one of two biogeographic scenarios,” Myers explained.

Cimoliopterus cuvieri pterosaur picture
An artist’s rendering depicts Cimoliopterus cuvieri (right), the European species thought to have been related to the newly found species in Texas. (By Dmitry Bogdanov)

“Either an earlier Cimoliopterus population distributed across North America and Europe, [and then] became divided by the opening of the North Atlantic, and diverged evolutionarily to form two separate species, or some individuals dispersed from one side of the Atlantic to the other, colonizing a new region and eventually evolving into a new species.”

Based on the pterosaur fossils found throughout the Western hemisphere, he said, the more likely explanation is the second of these: Some Cimoliopterus migrants from Europe must have found their way across the ocean and established a colony in the New World. [Read about another recent pterosaur find: “Rare Pterosaur Tracks Discovered in Alaska’s Denali National Park“]

“We don’t have enough data at present to determine which scenario is correct,” Myers said, “but given the high dispersal potential of pterosaurs and published biogeographic analyses of other pterosaur species, I tend to favor the latter hypothesis.”

The theory is reasonable, he added, considering that the same is thought to have happened with one of Texas’s other two toothed pterosaurs — Coloborhynchus — because it, too, is found in Texas and England.

Even if the new specimen doesn’t quite solve the mystery, the Dallas fossil does add another crucial piece to the puzzle of pterosaurs’ spread, Myers said. [By the way, pterosaurs never coexisted with humans: “Prehistoric Utah Rock Art Does Not Depict a Pterosaur, Study Confirms“]

Cimoliopterus dunni provides further evidence of biogeographic linkage between pterosaur populations [in North America] and in Western Europe during the mid-Cretaceous,” he said.

“The discovery of Coloborhynchus provided the first evidence of this linkage, and Cimoliopterus dunni reinforces this relationship.”

Myers reports his findings in the Journal of Vertebrate Paleontology.


ResearchBlogging.org

Myers, T. (2015). First North American occurrence of the toothed pteranodontoid pterosaur

Journal of Vertebrate Paleontology, 35 (6) DOI: 10.1080/02724634.2015.1014904


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