A groundbreaking University of Bristol study has shed light on how lizards and snakes -the most diverse group of land vertebrates with nearly 12,000 species – have evolved remarkably varied jaw shapes, driving their extraordinary ecological success.

This research, led by a team of evolutionary biologists and published in the Proceedings of the Royal Society B today, offers a new understanding of the intricate factors influencing the evolution of lower jaw morphology in these animals, known collectively as lepidosaurs.

The researchers 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).

In terms of jaw shape, the team found that snakes are morphological outliers, exhibiting unique jaw morphologies, likely due to their highly flexible skulls and extreme mechanics that enable them to swallow prey many times larger than their heads.

“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,” explained Dr Antonio Ballell Mayoral based in Bristol’s School of Earth Sciences.

“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.”

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This work underscores the critical role of morphological innovation in promoting the diversification of highly biodiverse groups like lepidosaurs. The lower jaw – a vital component of the vertebrate feeding apparatus – has been a key element in their ecological experimentation and adaptation.

Looking ahead, the team plans to delve deeper into the evolution of the lepidosaur head.

Dr Ballell Mayoral added: “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.”

IMAGE CREDIT: Donald Tong.