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Two sides of the same fossil: The story of a small arboreal reptile from the Jurassic period

Paleontologists have identified a new ancient reptile from the Solnhofen limestone slabs, thanks to a chance discovery. A Ph.D. student recently found the counterpart of the original fossil at the Natural History Museum in London. The research team their findings in the Zoological Journal of the Linnean Society.

The lizard-like fossil has actually been known since the 1930s: a Solnhofen limestone slab from the Senckenberg Natural History Museum in Frankfurt shows the body impression of a small, long-limbed reptile, 145 million years old. The animal resembles modern lizards, but is closely related to the tuatara of New Zealand and was previously thought to be a representative of the species Homoeosaurus maximiliani.

A chance discovery has now provided new insights: Victor Beccari, a doctoral student at the Bavarian State Collection of Paleontology and Geology and LMU Munich, came across a skeleton at the Natural History Museum in London that was very similar to the Frankfurt specimen described above. In fact, it was the counterslab of the Senckenberg fossil, containing most of the bones of this ancient reptile.

The new specimen provides key information for understanding the biology of ancient reptiles and represents a new species, Sphenodraco scandentis. Beccari has now published the results of the study together with an international team of experts, including SNSB paleontologist Prof. Oliver Rauhut, an expert on the Solnhofen reptiles.

The limestone slabs from the valley of the Altmühl between Solnhofen and Kelheim in central Bavaria are world-famous for their many excellently preserved fossils, including the famous "urvogel" Archaeopteryx.

This is also due to the very special way in which they are preserved: the fossils from this site are embedded flat in layers of limestone. When fossil collectors split the limestone slab, they usually find part of the skeleton in one slab and the body impression in the counterslab. These are usually kept together.

"Apparently, the two parts of this fossil were sold separately almost a century ago to the museums in Frankfurt and London, where they can still be visited today. However, the connection between the two plates was lost. Until now, scientists were only aware of the Frankfurt half," says Beccari, lead author of the study.

Today, only one living species of the lizard-like Rhynchocephalia is known: the tuatara from New Zealand. During the Triassic and Jurassic periods, rhynchocephalians were widespread and lived alongside dinosaurs on almost all continents.

"The Solnhofen Archipelago is known for its species-rich Rhynchocephalia fauna. We know of hundreds of well-preserved, almost complete skeletons of these lizard-like reptiles from there. Every new fossil provides us with more insights into their evolution and way of life, including Sphenodraco scandentis," says Beccari.

The now complete fossil from Frankfurt and London shows characteristics that differ from previously found Rhynchocephalia: For example, Sphenodraco has very long limb bones in relation to its small body size. A comparison with modern lizards with a similar body structure suggests that the animal was probably a good climber and lived in trees, perhaps being the first truly arboreal species from the rhynchocephalian group, according to the researchers.