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Fossils Reveal Pterosaur Relatives Before They Evolved Wings

By reanalyzing earlier specimens, scientists linked small, leggy creatures that roamed 237 million years ago to the reptiles that flew through the dinosaur era.

But the origins of these reptiles have remained murky because of a lack of fossils from the earliest fliers. “The oldest pterosaur we have already had wings and were capable fliers,” said Davide Foffa, a paleontologist at Virginia Tech, which makes it difficult to chart their aerial evolution.

The team examined several sandstone blocks that were excavated around the turn of the 20th century from a quarry in northern Scotland. Known as the Elgin reptiles after a nearby Scottish town, these dense hunks of rock entomb the remnants of armor-clad ancestral crocodiles, early dinosaurs and lizards from the late Triassic Period, or 237 million years ago. One of the smallest animals found in these rocks is Scleromochlus, a slender reptile that could fit in the palm of a hand.

Since its discovery in the early 1900s, Scleromochlus has perplexed paleontologists. Its fossils are difficult to study because the bones disappeared long ago, leaving behind empty spaces within the sandstone. For decades, researchers have poured latex or wax into these voids to create casts. But these methods often miss intricate traits.

So instead of forging manual molds, Dr. Foffa, then at the National Museum of Scotland, and his colleagues placed several blocks containing Scleromochlus specimens under a micro CT scanner. This allowed them to digitally reconstruct the skeleton of Scleromochlus in three-dimensions.

Scleromochlus may look like a lanky dinosaur crossed with a chameleon. But after further examination, the researchers identified several traits that Scleromochlus shared with lagerpetids, a group of small reptiles that scurried around Pangea during the Triassic Period. That includes an oddly large skull for its size and a hooked femur head that slots into the hip vertically instead of splayed out to the side like a lizard’s leg.

According to Stephen Brusatte, a paleontologist at the University of Edinburgh and one of Dr. Foffa’s co-authors, lagerpetids appear to have been agile, bipedal creatures reminiscent of pint-size dinosaurs. Their anatomy, however, reveals a much closer affinity to pterosaurs. “At a quick glance, they look nothing like a pterosaur,” Dr. Brusatte said. “But a close look at their skeletons and the similarities with pterosaurs became apparent, like invisible ink being held to the light.”

If Scleromochlus is an early relative of pterosaurs, it challenges the assumption that pterosaurs initially jumped or glided. Scleromochlus lacked the sturdy hips of a hopping animal like a frog and would have been an awkward fit in trees, according to Kevin Padian, a paleontologist at the University of California, Berkeley, who has studied pterosaur evolution for decades. “They’re long-legged and short-armed,” said Dr. Padian, who was not involved with the new study. “That’s not how an arboreal animal like a squirrel is built.”

Dr. Foffa stresses that more fossil evidence is required to connect Scleromochlus with the earliest true pterosaurs. “It doesn’t have wings or anything crazy like that,” he said. “The crazy comes later.”

Category: Science

Source: New York Times

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