Professor Susan Evans contributes to theory of ancient tree-climbing reptiles

Early British lizard probably preferred tree-climbing to swimming - their new reality may turn out to be arboreality! Hi-tech scans provide evidence of an alternative lifestyle for relatively small reptiles in the dinosaur era

In a recent paper published by the Royal Society, Professor Susan Evans and co-researchers suggest that certain lizard-like reptiles may have climbed on waterside vegetation and dropped into the water if threatened, rather than being truly semi-aquatic, as previously assumed. This suggestion is based on the fact that scans reveal their hand bones to be more suitable for clinging onto trees than for swimming. 

The paper provides a reassessment of the lifestyle of small, Middle Jurassic, lizard-like reptiles known as Marmoretta (Reptilia: Lepidosauromorpha), based on new high-resolution scans of a specimen from fossil deposits on the Isle of Skye.  These relatively small reptiles lived on Earth around the time of the more-famous dinosaurs, but have been much less researched.  As the NHM (whose David Ford is lead author on the publication) states in their report of this work: "Fossils of these species are often tiny and poorly preserved, making it hard to know what their lives were like".

As Susan explains, "Marmoretta were previously interpreted as partially aquatic because their bones were found in a lagoonal environment, in similar numbers to those of aquatic reptiles and amphibians. The bones of terrestrial members of the assemblage are generally rarer.

"However, new micro-computed tomography (µCT) scans reveal the hand of Marmoretta to have long, curved, penultimate phalanges – a feature of modern tree-climbing lizards, such as geckos and iguanians, that climb on vertical surfaces", as shown in the Figures above. [The Figures show a reconstruction of left manus in (F) dorsal and (G) dorsomedial views. Dashed lines indicate missing elements.]  In contrast, if Marmoretta were swimming reptiles, they would be expected to have flattened 'fingers 'or webbing between the digits.

Susan thinks that a possible scenario to explain the relative abundance of Marmoretta bones is that they may have climbed on vegetation close to the water’s edge, and dropped into the water if threatened. South American basilisk lizards have been seen to do this when cornered on branches by predatory monkeys.

 

As well as David Ford from the Earth Sciences Department, Natural History Museum, Susan - who is Head of the UCL Centre for Integrative Anatomy, was collaborating with scientists from the Division of Paleontology, American Museum of Natural History, New York and the Department of Earth Sciences, University of Oxford:

Ford David P., Benson Roger B. J., Griffiths Elizabeth F. and Evans Susan E. 2025. Evidence for clinging arboreality in a Middle Jurassic stem lepidosaur. Proc. R. Soc. B. 292 20250080 http://doi.org/10.1098/rspb.2025.0080

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