Few creatures were built to soar like pterosaurs. Tens of millions of years before the earliest birds, these Mesozoic reptiles had pioneered flight with sail-shaped wings and lightweight bones.
The origins of these reptiles have remained murky because of a lack of fossils from the earliest flyers. “The oldest pterosaur we have already had wings and were capable flyers,” said Davide Foffa, a paleontologist at Virginia Tech, which makes it difficult to chart their aerial evolution.
For decades, paleontologists have postulated that the earliest pterosaurs dwelled in trees and experimented with gliding before flying. But Foffa and his colleagues may have discovered a more ground-bound origin for these ancient aviators. In a study published recently in the journal Nature, the researchers reanalysed a cache of fossils and concluded that the earliest pterosaur relatives were off to a running start long before they took off.
The team examined sandstone blocks excavated around the turn of the 20th century from a quarry in Scotland. These hunks of rock entomb the remnants of armour-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 on a hand.
Its fossils are difficult to study because the bones disappeared long ago.
Foffa and his colleagues placed blocks containing Scleromochlus specimens under a micro CT scanner to digitally reconstruct the skeleton in 3D.
The researchers identified several traits Scleromochlus shared with lagerpetids, small reptiles that scurried around Pangea during the Triassic Period. That includes a 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, lagerpetids appear to have been bipedal creatures reminiscent of pint-size dinosaurs. Their anatomy, however, reveals a much closer affinity to pterosaurs.
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 and would have been awkward in trees, says paleontologist Kevin Padian: “They’re long-legged and short-armed. That’s not how an arboreal animal like a squirrel is built.”
Instead, Scleromochlus was most likely more comfortable pursuing insects on the ground. This left its forearms free, potentially setting the stage for such animals to eventually flap. — NYT
