One Planet News: Jaw dropping - the evolution of jaw shapes in lizards and snakes
New research highlights complex factors in lizards and snakes evolutionary process
By Annette J Beveridge
A new study shines a spotlight on the complex factors affecting the evolution of lizards and snakes jaw shapes.
Lizards and snakes form the most diverse group of land vertebrates with almost 12,000 species and since their origins has diversified into a myriad of sizes and body plans.
These changes can be seen in the disparity of cranial and postcranial (bones behind or below the skull) morphologies.
Various groups have independently acquired semiaquatic habits while a few snake lineages have adapted to aquatic environments. Diet is also another aspect of ecology.
The skull
The skull is an interesting system to research.
It helps to decipher the ecological drivers of morphological (relating to the scientific study of the structure and form of animals and plants) evolution. This is because it is involved in multiple functions like feeding, locomotion and defence.
The team from the University of Bristol found that snakes are morphological outliers. They have highly flexible skulls and mechanics enable them to swallow prey many times larger.
There is a rich variety of skull configurations shaped by the loss and gain of skull bones as well as the acquisition of different kinds and degrees of cranial kinesis, (significant movement of skull bones relative to each other in addition to movement at the joint between the upper and lower jaws).
Dr Antonio Ballell Mayoral, at Bristol’s School of Earth Sciences, said: “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.”
This work highlights the critical role of morphological innovation in promoting the diversification of highly biodiverse groups like lepidosaurs (subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia).
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.”
Habitat
Terrestrially, snakes and lizards inhabit diverse microhabitats on the ground, or in trees, on rocks or in crevices, while several lineages of lizards and snakes have independently evolved fossorial lifestyles (burrowing or digging), - body elongation or limb reduction.
Looking ahead, the team plans to delve deeper into the evolution of the lepidosaur head.
