New Study Sheds More Light on Evolution of Lepidosaurs | Sci.News

New research led by University of Bristol scientists sheds light on how lepidosaurs — the most diverse clade of tetrapods, including lizards and snakes — have evolved remarkably varied jaw shapes, driving their extraordinary ecological success.

Lepidosauria is the clade comprising lizards, snakes and the tuatara, and with over 11, 000 species, represents the most speciose group of tetrapods today.

Since their origin at more than 240 million years ago, lepidosaurs have diversified into a myriad of sizes and body plans.

Among living species, the range in body size spans three orders of magnitude, as exemplified by the approximately 1.7-cm-long Sphaerodactylus geckos and the approximately 10-m-long green anaconda.

Extremes in large body size become even more dramatic when extinct mosasaurs are considered (up to 17 m in length).

Disparity in body form is reflected in the different degrees of body elongation, and reduction or modification of limb elements seen in multiple lineages, with snake-like body plans evolving at least 25 independent times.

Similarly, lepidosaurs show a rich variety in skull configurations shaped by the loss and gain of skull bones during their evolutionary history, and the acquisition of different kinds and degrees of cranial kinesis.

As a result of this diversification of forms, lepidosaurs have conquered diverse ecological niches across most of the globe.

In the new study, University of Bristol researcher Antonio Ballell Mayoral and his colleagues discovered that jaw shape evolution in lepidosaurs is influenced by a complex interplay of factors beyond ecology, including phylogeny (evolutionary relatedness) and allometry (scaling of shape with size).

In terms of jaw shape, they 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 specialized 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,” Dr. Ballell Mayoral said.

“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.”

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.

“Lower jaws are important, but they work together with the jaw closing muscles to support essential functions like feeding and defense,” Dr. Ballell Mayoral said.

“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.”

The team’s work was published today in the Proceedings of the Royal Society B.

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Antonio Ballell et al. 2024. Ecological drivers of jaw morphological evolution in lepidosaurs. Proc. R. Soc. B 291 (2036): 20242052; doi: 10.1098/rspb.2024.2052