230-million-year-old fossil reveals the origin of pterosaurs

At the beginning of the last century, scientists discoveredfossils of an unknown creature, which led them into confusion. The study showed that the animal died about 231 million years ago in sand dunes in what is now Scotland. None of his bones have survived, but there are clear outlines, “engraved” in sandstone. To better understand what kind of creature it was, the plates were even filled with wax and plastic. The results showed that the animal was a 20 cm reptile that had long hind limbs, a short neck, a thin body and a huge head. The fossil was named scleromochlus taylori, but scientists could not decide on its species. As a result, scleromochlus has been constantly tossing around the reptile family tree since its discovery. Many generations of scientists tried to find out what kind of creature it was and what kind of life it led. And now, after many years, thanks to modern technology, we finally managed to answer these questions.

Scientists have found out what were the early ancestors of pterosaurs

Ancient reptiles lagerpetidae

To find out who Scleromochlus was after all,scientists took high-resolution x-rays of the fossils. Then the authors of the work converted a large number of 2D images into a 3D model. Thanks to this, it was possible to reveal many anatomical features of the creature, which were not previously known.

The study showed that scleromochlusbelongs to a group of lagerpetids that lived between 240 and 201 million years ago, as the researchers reported in the journal Nature. Lagerpetids are a very poorly understood group, since until recently, all discovered fossils included only hind limbs and fragments of the skull.

Scientists were able to create a three-dimensional model of scleromochlus

In 2020, an extensive study found thatLagerpetids share many anatomical features with pterosaurs. Thus, the study helped scientists close a gap in the fossil record that obscured the evolutionary origin of pterosaurs.

“Because the fossils of scleromochlusrepresent almost a complete skeleton, they give us for the first time a much more complete picture of the anatomy of lagerpetids,” says Martin Escurra, a paleontologist at the Bernardino Rivadavia Museum of Natural Sciences in Argentina, one of the authors of the study.

What were the ancestors of pterosaurs

About 252 million years ago, at the end of the Permianperiod, the Earth experienced the most massive extinction known. It was associated with a catastrophic climate warming caused by the release of a huge amount of greenhouse gases from volcanoes in the territory of modern Siberia. As a result of this event, more than 95 percent of the species became extinct.

But in the subsequent early Triassic period, liferecovered and quickly became diversified. At that moment, it can be said that the basis for the emergence of groups of modern terrestrial vertebrates arose. Scleromochlus also belongs to the new species that arose on Earth at that time.

3D skull model of Scleromochlus

As shown by the three-dimensional model, the ribs of the creature onwere actually longer than originally thought. In addition, scientists managed to reconstruct the front and back legs, which no one had ever seen before. This was very important, since it was the ends of the femur of Scleromochlus that confirmed that this creature was a lagerpetid.

The study showed that Scleromochlus isa very early ancestor of the therosaurs. Obviously, he belongs to one of the oldest branches of the Lagerpetid family tree. It didn't have any of the obvious climbing adaptations that pterosaur gliding ancestors should have.

In addition, there are no bones in the creature's pelvis.fortifications, which can be seen in the skeletons of jumping creatures such as jerboas. Instead, Scleromochlus was likely able to run on its hind legs and move to all fours.

There is a gap of 30 million years in the evolutionary record of pterosaurs

How did pterosaurs originate?

Pterosaurs are poorly understood compared to othersdinosaurs. Well-preserved fossils are a rarity, as discussed in our article on stolen fossils from the pterosaur Tupandactylus navigans.

The absence of fossils is partly due to the fact thatthat the bones of pterosaurs were hollow and brittle. In addition, in the early Triassic, when the first pterosaurs appeared, there were rarely suitable conditions for the formation of fossils on the ancient Earth. I must say that petrification is generally a complex process that occurs only under certain conditions.

As a result, in the history of the origin of pterosaursthere was a gap of 30 million years. The oldest known pterosaurs, around 220 million years ago, were fully formed flying creatures. Therefore, it was impossible to understand what animals existed before their appearance.

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Scleromochlus does not completely eliminate thisa gap, as it lacks the elongated ring fingers that were developed in pterosaurs and a number of other anatomical features that appeared later. Nevertheless, the creature closed the gap in knowledge by about 18 million years, and made it clear what the earliest ancestors of pterosaurs were. Scientists hope that in the near future they will be able to obtain more information about the origin of pterosaurs.