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Plesiosaur fossils are the first evidence of Jurassic vertebrates in Texas

By describing the first known Jurassic vertebrate fossils in Texas, a team of researchers led by the University of Texas at Austin has recently filled a major gap in the state’s fossil record. The weathered bone fragments are part of the limbs and bones of a plesiosaur, a marine reptile that inhabited the shallow sea which covered what is now northeastern Mexico and far western Texas about 150 million years ago.

The fossils were discovered in the Malone Mountains of West Texas during two hunting expeditions led by Steven May, an adjunct research professor of Vertebrate Paleontology at UT Austin.

Texas during the Jurassic 

Before this unprecedented discovery, the only Jurassic fossils found in Texas belonged to marine invertebrates, such as snails and ammonites. The new findings provide solid evidence that massive vertebrates have also inhabited this region millions of years ago.

“Folks, there are Jurassic vertebrates out there. We found some of them, but there’s more to be discovered that can tell us the story of what this part of Texas was like during the Jurassic,” May said.

Jurassic fossils require Jurassic-aged rocks to be preserved in. However, due to its geological history, Texas hardly has any outcrops from this historical period, with the 13 square miles of Jurassic-aged rocks from the Malone Mountains representing most of such rocks in the state.

Previous clues

In 2015, May and his team found a clue in a 1938 paper on the geology of the Malone Mountains by Claude Albritton, who later became a professor of Geology at the Southern Methodist University (SMU): the mentioning of large bone fragments observed in that area. 

Indeed, May’s subsequent research expedition to West Texas confirmed the presence of such bones, which although are eroded and broken up, could still shed more light on Texas’ prehistoric ecosystems and possibly lead to further discoveries in the near future.

“Geologists are going to go out there looking for more bones. They’re going to find them, and they’re going to look for the other things that interest them in their own special ways,” said co-author Louis Jacobs, an emeritus professor of Vertebrate Paleontology at SMU.

Additional specimens found

While today the Malone Mountains rise above a dry desert landscape, during the Jurassic, the sediments were likely deposited just below sea level within miles of the shoreline. Besides the plesiosaur fossils, the researchers also discovered several other specimens providing a glimpse of this ancient shallow marine environment, including petrified driftwood filled with burrows from marine worms, the shells of ammonites, snails, and clams, as well as range of plant fossils, such as a pinecone and wood with possible growth rings. 

According to co-author Lisa Boucher, a paleobotanist at UT Austin, since Jurassic plant fossils from lower attitudes close to the Equator are relatively rare, these findings could make the Malone Mountains a major place of interest to paleobotanists and other scientists working on paleoenvironmental reconstruction.

While the reasons for discovering only recently these prehistoric fossils are not completely clear, the findings highlight the crucial value of field work. “It’s frequently part of the scientific process. There’re a few lines buried in an old publication, and you think ‘surely somebody has already looked at that,’ but often they haven’t. You need to delve into it,” Boucher concluded.

The study is published in the journal Royal Mountain Geology.

More about plesiosaurs

Plesiosaurs were a group of marine reptiles that lived during the Mesozoic Era, specifically from the Late Triassic to the end of the Cretaceous Period, approximately 203 to 66 million years ago. They are known for their distinctive body shape, with a small head, long neck, broad body, and four large flippers.

There were many different species of plesiosaurs, some of which were quite large. The smallest species were about the size of a person, while the largest could grow to lengths of over 15 meters.

There are generally two major body types of plesiosaurs. Some, known as the “plesiosauromorph” plesiosaurs, had long necks and small heads, somewhat similar to the popular image of the Loch Ness Monster. They likely used their long necks to catch fish and other small marine animals. Others, known as the “pliosauromorph” plesiosaurs, had shorter necks and larger heads, and were likely active predators of larger prey.

Plesiosaurs are not dinosaurs, but they lived during the same period. Like dinosaurs, they became extinct at the end of the Cretaceous Period, likely due to the same catastrophic event, often attributed to a large asteroid or comet impact.

The study of plesiosaurs contributes to our understanding of the diversity of life in the Earth’s past and how organisms adapt to their environment over time. They are often studied in the field of paleontology, which involves the study of ancient life forms through the examination of fossil remains.

By Andrei Ionescu, Staff Writer

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