Newly Described Fossils Could Help Understand Why Some Dinos Have Become So Big – ScienceDaily

The way they grew up ancestors small enough to be found in a modern petting zoo has remained a mystery. A new thorough anatomical description of the best-preserved specimens of a sauropod-sized North American parent the size of a car could help paleontologists solve the mystery.

Adam Marsh, a paleontologist from Petrified Forest National Park, led the description of the dinosaur while earning a Masters degree from the University of Texas at the Austin Jackson School of Geosciences. The results were published on October 10 in the journal PLOS ONE. Marsh co-authored the paper with his advisor, Timothy Rowe, a professor at the Jackson School.

The dinosaur – called Sarahsaurus aurifontanalis – lived about 185 million years ago in the early Jurassic. It might contain important clues about the size of the sauropods, as it belongs to the group of dinosaurs that preceded them. Its evolutionary positioning, combined with the exquisite preservation of specimens, provides researchers with a detailed overview of its anatomy and its links to larger cousins.

"Sarahsaurus preserves in its anatomy the anatomical changes that were occurring in the evolutionary lineage of the Late Triassic and the Early Jurassic, "said Marsh, which can help tell us how big it is to get fat.

The description is based on two skeletons discovered in Arizona by Rowe in 1997. The bones belong to the Navajo Nation, the owner of the land where the fossils were discovered, and are preserved by the Jackson Museum of Earth's History. The bones are slightly crushed and, in some cases, still linked together by body parts such as the hand and the tail. The only missing part is the skull.

"The specimens are well preserved in three dimensions and remarkably complete, which is very rare in the fossil record," said collections director Matthew Brown. "These complete specimens help paleontologists better understand the fragmentary and incomplete remains that we usually find."

Marsh describes Sarahsaurus like a dinosaur "lazy on the ground". He stood, walked on his hind legs, and had powerful front legs with a large, curved claw on the first finger of each hand. He had much in common with the earliest ancestors of sauropods – such as walking on two legs – but he was also beginning to show features that would foreshadow the evolution of his massive parents – such as an increase in height and height. a lengthening of the body. the vertebrae of the neck.

"It's starting to gain magnification characteristics compared to the first members of the group," said Marsh.

The size and length of the neck are characteristics that sauropods would take to the extreme when they would evolve. By studying these traits and others in Sarahsaurusand seeing how they compare to those of other dinosaurs, scientists can help reveal how these changes have occurred over the course of the evolutionary history and relationships between different dinosaurs.

For example, the anatomical review clarified the relationship between Sarahsaurus and two other members of the sauropod family that lived in North America in early Jurassic times. The researchers found that the three countries did not have a common ancestor in North America. Rather, they had evolved from dinosaur lines that had arrived independently in North America.

Marsh is currently working on another study that could shed more light on the evolution of sauropods. Led by Sterling Nesbitt, assistant professor at Virginia Tech and associate researcher at the Jackson School's Vertebrate Collections, the project involves tracking anatomical differences in the bones of dinosaur branches to determine the characteristics related to evolution and those related to the age of an animal. Marsh said that both Sarahsaurus The skeletons reviewed for this paper are a great addition to the project.

"We have two individuals coming essentially from the same hole in the ground, with different bumps and grooves on their femur," said Marsh. "This lends itself very well to this complete anatomical description and will be very important for comparing the early dinosaur anatomy."

The research was funded by the Jackson School of Geosciences and the National Science Foundation. the Sarahsaurus specimens were collected with permission from the Navajo Minerals Department.

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