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New Research Reveals an Ancient Reptile Had Bizarre Forelimb Evolution
drepanosaur

New fossils from 212 million-year-old rocks in New Mexico indicate that the small reptile Drepanosaurus used its massive claw and powerful and unusual limp arm to rip away tree bark to expose insects within it.   Credit: Victor Leshyk

STONY BROOK, N.Y., September 30, 2016 – Fossil remains from an ancient reptile known as Drepanosaurus reveals unusual skeletal adaptations in the forelimb that scientists have never before recorded in land animals. A Stony Brook University-led national team of paleontologists published their findings in Current Biology . Their findings suggest that more than 200 million years ago reptiles had already evolved specialized modern ecological roles with their strange forelimb adaptation.

The research stems from a decade-long project collecting Late Triassic fossils, including those of Drepanosaurus, from the Hayden Quarry in Ghost Ranch, northern New Mexico. Drepanosaurs are an extinct group of reptiles that although lizard-like are not lizards nor are they dinosaurs. Most were small (only 1 to 2 feet in length) and known to have lived exclusively during the Late Triassic (235 to 201 million years ago). Prior to the team’s discoveries at Ghost Ranch, Drepanosaurus was known from decades-old, badly crushed skeletons from Italy.

In nearly all four-limbed vertebrates, including in diverse species such as dolphins, bats, or birds, the forelimb consists of two elongate and parallel bones—the radius and ulna. These bones contact a set of wrist bones that form the bridge between the forearm and the hand. However, the researchers found that in Drepanosaurus the radius and ulna are no longer parallel, and the ulna is flat and retracted toward the elbow. Additionally two of the wrist bones have effectively moved into the forearm.

“Many of the Drepanosaur fossils we collected are preserved in three dimensions but are very fragile”, said co-author Alan H Turner, PhD, Associate Professor in the Department of Anatomical Sciences at Stony Brook University School of Medicine. “Because of this we were able to leverage high resolution imaging, such as microCT, to reveal aspects of the forelimb and claw morphology previously unattainable from the Italian fossils. This proved critical in unraveling the strange anatomy of these animals.”

Drepanosaurus really stretches the bounds of what we thought were the evolutionary constraints on limb evolution,” added Dr. Adam Pritchard, lead author and a postdoctoral fellow at Yale University. “Ecologically, the animal seems to be a sort of chameleon-anteater hybrid, which is really bizarre for the Triassic Period. It possesses a totally unique forelimb among vertebrate animals.

“When you combine this with a claw nearly as large as the arm, you get an arm well adapted for powerful hook-and-pull digging. Think of anteaters digging into insect mounds.”

In addition to the forelimb specialization, Drepanosaurus had grasping feet and a claw-like structure at the end of the tail that might have assisted a life spent in the trees.

The research was funded by the National Science Foundation, the Stony Brook Research Foundation, University of California Museum of Paleontology, University of Utah, Field Museum Women’s Board, and the National Geographic Society Committee for Research & Exploration.

Co-authors of the paper are Randall Irmis of the University of Utah, Sterling Nesbitt of Virginia Polytechnic Institute and State University, and Nathan Smith of the Dinosaur Institute at the Natural History Museum of Los Angeles County.

 

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Part of the State University of New York system, Stony Brook University encompasses 200 buildings on 1,450 acres. Since welcoming its first incoming class in 1957, the University has grown tremendously, now with more than 25,000 students and 2,500 faculty. Its membership in the prestigious Association of American Universities (AAU) places Stony Brook among the top 62 research institutions in North America. U.S. News & World Report ranks Stony Brook among the top 100 universities in the nation and top 40 public universities, and Kiplinger names it one of the 35 best values in public colleges. One of four University Center campuses in the SUNY system, Stony Brook co-manages Brookhaven National Laboratory, putting it in an elite group of universities that run federal research and development laboratories. A global ranking by U.S. News & World Report places Stony Brook in the top 1 percent of institutions worldwide.  It is one of only 10 universities nationwide recognized by the National Science Foundation for combining research with undergraduate education. As the largest single-site employer on Long Island, Stony Brook is a driving force of the regional economy, with an annual economic impact of $4.65 billion, generating nearly 60,000 jobs, and accounts for nearly 4 percent of all economic activity in Nassau and Suffolk counties, and roughly 7.5 percent of total jobs in Suffolk County.