A fossil specimen found in Scotland more than 100 years ago is helping to unravel the ancestry of the Pterosauria. A new study of tiny and difficult to interpret fossils representing a reptile named Scleromochlus taylori has provided palaeontologists with a fresh perspective on the evolution of the pterosaurs.

The research, published in the academic journal “Nature”, was undertaken by scientists led by Dr Davide Foffa, a Research Associate at National Museums Scotland, and now a Research Fellow at the University of Birmingham. The study, which involved analysis of the fossils using Computed Tomography (CT scans), has enabled the first, accurate skeletal reconstruction of Scleromochlus taylori.

An early ancestor of the Pterosauria
A tiny reptile measuring approximately 20 cm in length, Scleromochlus is now thought to be an early ancestor of the Pterosauria. Picture credit: Gabriel Ugueto.

Anatomical Details Reveal Link with the Pterosauromorpha

The CT scans revealed new anatomical details that conclusively identify the Scleromochlus genus as a close pterosaur relative. Phylogenetic assessment places this small, agile reptile within a group known as Pterosauromorpha. The Pterosauromorpha comprises pterosaurs and their close relatives the lagerpetid reptiles.

Scleromochlus fossil casts (ancestry of the Pterosauria).
Scleromochlus fossil Casts (NHMUK-PV-R3557). Casts created enabled the scientists to reconstruct the skeleton. Picture credit: London Natural History Museum/University of Birmingham.

Identifying the Ancestry of the Pterosauria (Lagerpetonidae)

Geographically widespread in the Late Triassic, the Lagerpetonidae were typically small and fleet-footed reptiles, classified as basal avemetatarsalians, the branch of the Archosauria leading to birds, dinosaurs and the Pterosauria. Previously thought to be close to the evolutionary tree of the Dinosauria, more recent research, including this newly published paper suggests that the lagerpetids were closer to the pterosaurs (members of the Pterosauromorpha).

Most lagerpetids are described as being about the size of cat or small dog, however, Scleromochlus was smaller, with an estimated body length of around 20 cm.

This new study supports the hypothesis that the first flying reptiles (pterosaurs) evolved from small, likely bipedal ancestors. The placement of the lagerpetids within the avemetatarsalians had caused extensive debate. This paper argues that Scleromochlus, represented an evolutionary step in the direction of pterosaurs.

Poorly Preserved Fossils – the Elgin Reptiles

Analysis of the Scleromochlus fossil material using more traditional methods is extremely difficult. The non-destructive CT scans enabled the research team to examine the fossilised bones in exquisite detail and revealed new anatomical details that had not been observed before.

The sandstone block containing the bones come from Morayshire in north-eastern Scotland, near to the town Elgin. Collectively fossils of vertebrates from these deposits are known as the Elgin Reptiles. The fossils are held mostly in the collections of National Museums Scotland, Elgin Museum and the Natural History Museum. The latter holds Scleromochlus, which was originally found at Lossiemouth.

Scleromochlus fossil (ancestry of the Pterosauria).
A Scleromochlus fossil. Picture credit: Professor Paul Barrett London Natural History Museum/University of Birmingham.

Ancestry of the Pterosauria

Commenting on the significance of the research, Dr Foffa stated:

“It’s exciting to be able to resolve a debate that’s been going on for over a century, but it is far more amazing to be able to see and understand an animal which lived 230 million years ago and its relationship with the first animals ever to have flown. This is another discovery which highlights Scotland’s important place in the global fossil record, and also the importance of museum collections that preserve such specimens, allowing us to use new techniques and technologies to continue to learn from them long after their discovery.”

Professor Paul Barrett at the Natural History Museum added:

“The Elgin reptiles aren’t preserved as the pristine, complete skeletons that we often see in museum displays. They’re mainly represented by natural moulds of their bone in sandstone and – until fairly recently – the only way to study them was to use wax or latex to fill these moulds and make casts of the bones that once occupied them. However, the use of CT scanning has revolutionized the study of these difficult specimens and has enabled us to produce far more detailed, accurate and useful reconstructions of these animals from our deep past.

Scleromochlus fossil casts (close view)
A close-up view of a cast of NHMUK-PV-R3557 with clearly defined Scleromochus fossil bones. Picture credit: London Natural History Museum/University of Birmingham.

The First Vertebrates to Evolve Powered Flight

Co-author of the scientific paper, professor Sterling Nesbitt (Virgina Tech) commented:

“Pterosaurs were the first vertebrates to evolve powered flight and for nearly two centuries, we did not know their closest relatives. Now we can start filling in their evolutionary history with the discovery of tiny close relatives that enhance our knowledge about how they lived and where they came from.”

Everything Dinosaur acknowledges the assistance of a media release from the University of Birmingham in the compilation of this article.

The scientific paper: “Scleromochlus and the early evolution of the Pterosauromorpha” by Davide Foffa, Emma M. Dunne, Sterling J. Nesbitt, Richard J. Butler, Nicholas C. Fraser, Stephen L. Brusatte, Alexander Farnsworth, Daniel J. Lunt, Paul J. Valdes, Stig Walsh and Paul M. Barrett published in Nature.”

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