Newly published research led by scientists at the University of Bristol has shed light on the remarkable evolution of the jaws of snakes and lizards.  These animals are part of the order Squamata which in turn, is part of the Superorder Lepidosauria. The Lepidosauria includes the Squamata and also the Rhynchocephalia. The Rhynchocephalia is today, only represented by one living species the Tuatara (Sphenodon punctatus). However, the fossil record demonstrates that the Rhynchocephalia were once extremely widespread and diverse.

The study focused on the evolution of remarkably varied jaw shapes within the Lepidosauria which drove their extraordinary success.  For example, the snakes and lizards represent the most diverse and speciose of all tetrapods.  Around twelve thousand species have been described.

A team of evolutionary biologists led the research, and it provides a new understanding of the intricate factors influencing the evolution of lower jaw morphology in the lepidosaurs.  The paper has been published in the Proceedings of the Royal Society B.

An image of an anole (a species of “false chameleon”) crushing a snail with its jaws. Picture credit: Professor Anthony Herrel (co-author in the study).

Picture credit: Anthony Herrel (co-author of the study)

To read a related blog post about the discovery of a remarkable fossil in Germany that highlights the evolutionary links between the Squamata and the Rhynchocephalia: Tiny Fossil Sheds Light on Reptile Evolution.

The Jaw Shape of Snakes and Lizards

The scientists discovered that jaw shape evolution in lepidosaurs is influenced by a complex interplay of factors beyond ecology, including phylogeny (evolutionary relatedness) and allometry (the scaling of shape with size). The study demonstrated that at least in terms of jaw shape, snakes are outliers. Snakes exhibit a unique jaw morphology.  This is most likely due to their highly flexible skulls and their ability swallow prey many times larger than the width of their head.

Corresponding author for the study, Dr Antonio Ballell Mayoral (School of Earth Sciences at the University of Bristol), commented:

“Interestingly, we found that jaw shape evolves particularly fast in ecologically specialised groups, such as in burrowing and aquatic species, and in herbivorous lizards, suggesting that evolutionary innovation in the lower jaw was key to achieve these unique ecologies. Our study shows how lizards and snakes evolved their disparate jaw shapes which adapted to their wide range of ecologies, diets, and habitats, driving their extraordinary diversity.”

Jaw evolution in snakes and lizards and wider lepidosaurs.

Diagram showing rates of evolution of lower jaw shape across the ‘family tree’ of lepidosaurs. Picture credit: Dr Antonio Ballell Mayoral and colleagues.

Picture credit: Dr Antonio Ballell Mayoral and colleagues

The Lower Jaw is a Key Element in Ecological Adaptation

This research work underlines the critical role of morphological innovation in promoting the diversification of extremely biodiverse groups like the lepidosaurs.  The lower jaw is a vital component of the vertebrate feeding apparatus, the researchers conclude it is a key element in driving ecological experimentation and adaptation.

As for any future research, the scientists would like to examine the morphology of the entire lepidosaur skull.

Dr Ballell Mayoral explained:

“Lower jaws are important, but they work together with the jaw closing muscles to support essential functions like feeding and defence. We are exploring the relationship between skull shape and the arrangement of the jaw closing musculature through evolution, and how it has impacted the diversification of feeding mechanics and habits.”

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

The scientific paper: “Ecological drivers of jaw morphological evolution in lepidosaurs” by Antonio Ballell, Hugo Dutel, Matteo Fabbri, Elizabeth Martin-Silverstone, Aleksandra Kersley, Chrissy L. Hammond, Anthony Herrel and Emily J. Rayfield published in the Proceedings of the Royal Society B.

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