Early lizards and snakes were more diverse than thought

New research from the University of Bristol, published in Royal Society Open Science, sheds light on the diets of ancient lizards and snakes that coexisted with dinosaurs around 100 million years ago. Contrary to previous beliefs, these reptiles had a diverse and advanced range of diets, including flesh-eating and plant-based, similar to modern squamates. Squamates, which include lizards and snakes, now comprise around 10,000 species. Earlier, it was thought that their diversity evolved after the dinosaur extinction, but this study reveals that their dietary specialization was already present 100 million years ago.

Fossils of ancient lizards and snakes are scarce from the Mesozoic era, possibly due to their delicate skeletons, making preservation difficult. Alternatively, it might suggest that these reptiles were rare during the first half of their history. The researchers examined 220 Mesozoic squamates, including lizards, snakes, and mosasaurs (extinct large marine reptiles), analyzing their jaws and teeth to classify them based on dietary patterns, similar to modern forms. Some exhibited long peg-like teeth suited for insect-eating, while others had flat teeth adapted for chopping plant food. Predators possessed sharp, pointed teeth, and snakes had hooked teeth to grasp their prey. These findings provide fascinating insights into the ancient diets and evolutionary history of these reptiles.

Jaw shape variety can be visualised in ‘morpho-spaces’ and linked to diets. Credit: Tom Stubbs

In their surprising discovery, the researchers categorized all the fossil forms into eight feeding categories and assessed their diversity over time. To their astonishment, the sparsely documented Cretaceous squamates exhibited examples of all the modern feeding strategies.

Lead author Dr. Jorge Herrera-Flores, now a Research Fellow at the National Autonomous University of Mexico, commented on their findings, stating that while they are uncertain about the exact diversity of squamates in the Cretaceous, they did find evidence that these reptiles had already achieved a full range of modern feeding modes 100 million years ago. Before that, for over 100 million years, squamates appeared to be primarily insect-eaters.

Co-author Dr. Tom Stubbs, Senior Research Associate at the University of Bristol School of Earth Sciences, emphasized the significance of studying teeth and jaws to understand dietary and ecological variety. Fossil teeth and jaws provide valuable insights into the evolution of squamates in the distant past. Despite potential challenges due to incomplete preservation in the fossil record, additional discoveries could further expand the number of feeding modes identified in the Cretaceous, rather than limiting them.

Image of lizard fossil. Credit: Jorge Herrera Flores

The early surge in dietary experimentation among squamates might be linked to diversification in other aspects of the ecosystem. During the Cretaceous period, flowering plants were flourishing and transforming land ecosystems, while squamates were also thriving in the oceans.

According to co-author Professor Michael Benton, a Vertebrate Palaeontology expert, the “Cretaceous Terrestrial Revolution” led to more complex forests. The emergence of flowering plants offered various food sources for insects and other small creatures, allowing them to feed on leaves, pollen, and nectar and seek shelter in the canopy. This likely triggered a burst of diversity among mammals, birds, and squamates, which diversified around the same time, possibly feeding on the insects, spiders, and other bugs, as well as the new plant food.

Although the research doesn’t pinpoint a single reason for the current diversity of squamates, which is nearly comparable to birds, it does reveal that their ancient ancestors had already explored various feeding niches 100 million years ago, even before the extinction of dinosaurs. This provides valuable insights into the early evolution and dietary habits of these remarkable reptiles.

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