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New technology finds clues in an ongoing Scottish paleontological mystery

Researchers used micro-computer tomographic scans to find in fossils what peels couldn’t – fossil deformation, synapomorphies, and hints at a common ancestor.

(CN) — When approaching the mystery of certain fossils unearthed over a century ago, researchers from the National Museums Scotland first tried the traditional methods. While that captured a general picture of what these fossils were, it failed to yield advanced details. Undeterred, the researchers used new technology to determine the extent of a suspected connection between the reptilian fossils and pterosaurs, the first vertebrates to evolve powered flight.

Collected from the Lossiemouth East Quarry in Lossiemouth near Elgin (Moray, Scotland, UK), Scleromochlus taylori was a reptile no longer than 20 centimeters long with features such as a large head, slender body, and uncertain evolutionary history, according to the study published Wednesday in Nature. Initially, the poorly preserved remains did little to help scientists learn much beyond the idea that it potentially belonged in several different groups.

“The fossils from the Elgin area (collectively known as ‘Elgin reptiles’) are peculiar because in most specimens the fossilized bone is missing (dissolved or washed away by natural processes or sometimes mechanically removed to facilitate study,") wrote the study’s corresponding author Davide Foffa via email.  “However, the bones left spectacular impressions on the hard sandstone (moulds/holes/cavities.) These cavities are effectively negative impressions of the skeletons and have been studied using moulding techniques (filling the cavities with waxes or moulding material and making a ‘peel.’")

Foffa explained that while the peels showed the general shape of the skeletons, micro-computer tomographic scans did more to uncover details that potentially confused the results of previous studies. This included how the rib cage of some specimens flattened, while others contained stacked ribs. However, Foffa went on to note that he considered the team lucky that the specimens were complete for the most part.

Additionally, the study said that this new tool revealed anatomical features that allowed researchers to classify Scleromochlus as a gracile, digitigrade ground-dwelling runner, as well as finding clues that connected the fossils to other species.

According to the study, Scleromochlus shares a minimum of eight unambiguous synapomorphies, or characteristics inherited exclusively from a common ancestor, with Pterosauromorpha. This group includes pterosaurs as well as lagerpetids, a group of small reptiles and Scleromochlus’ closest relatives.

As for what this common ancestor is, the answer is still unknown. Based on its unusual proportions and hindlimb morphology, the researchers suggest that the common ancestor of pterosaurs and lagerpetids was a tiny, probably digitigrade, grown-dwelling runner that was potentially bipedal. Meanwhile, the researchers used the available evidence to suggest that Scleromochlus have a closer relation to lagerpetids than pterosaurs, and that it lacked adaptations to fly or live in trees.

“The lack of flight-related adaptations in Scleromochlus and lagerpetids suggest that the evolution of the distinctive pterosaurian body plan remains to be found in the approximately 18 million years ago gap between the first pterosaurs and the origin of pterosauromorphs,” the study said.

Foffa credited the enthusiasm of the team and the detailed reconstruction of the scans with finding as much information as they did, and he hopes to find more paleontological evidence to solve this mystery.

“We still need more fossils to fit in the gaps between pterosaurs and their closest relatives to better understand how their body-plan came together,” Foffa wrote. “The specimens of Scleromochlus have been known for over 100 years, yet only recently we became equipped with the right tools to fully understand them, and to provide new data for controversies that have seen scientists discussing for decades.”

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