Are lizards herbivores or carnivores

Signs of wear and tear on the teeth of scaled lizards provide information on their diet

Microscopic images enable differentiation between carnivores and herbivores / Possibly an important step towards the discovery of the first herbivorous land vertebrates

14.06.2019

With the help of high-resolution microscopic images of the enamel surface of scaled lizards, which include iguanas, monitor lizards, lizards and bridge lizards, it is possible to see what the animals fed on. The signs of wear in the tooth enamel show clear differences between carnivores and herbivores, but they also enable finer distinctions, for example between algae, fruit or mollusc eaters. A research team led by scientists from Johannes Gutenberg University Mainz (JGU) has come to these results. According to their information, it has been difficult to make such dietary distinctions - especially in extinct species - solely on the basis of tooth or skeleton finds, because the shape of the teeth in many reptiles hardly differs.

Like the researchers in the journal Proceedings of the Royal Society B. report, they examined the upper jaw teeth of 77 prepared lizards from the wild, which belong to 23 species that still exist and come from natural history museums. Sometimes the scientists placed pieces of jaw with teeth directly under a confocal microscope, sometimes they took silicone impressions of the teeth and then took pictures of the impressions. They then created 3-D surface models of the teeth and evaluated them according to 46 different characteristics, such as the number of furrows in the tooth enamel and their mean depth. As a result, they found out that the animals can be grouped into different nutritional categories based on the signs of wear and tear. For example, the tooth enamel of the carnivore has only a few and shallow furrows, whereas the tooth enamel of the fruit eater is very furrowed. "This method was developed on mammals. We have now applied it to reptiles for the first time and have shown that it also works here," explains the head of the study, Dr. Daniela Winkler from the Institute for Geosciences at JGU. This was not necessarily to be expected: "Reptiles hardly chew. Most of the time they just bite off and swallow directly. Therefore, we could not necessarily assume that we would find meaningful traces."

The researchers now hope to be able to use the method successfully on the teeth of dinosaurs and synapsids, which are very similar to the teeth of scaled lizards, and thus to find the origin of herbivores among terrestrial vertebrates. Synapsids are mammal-like reptiles that lived on earth around 310 million years ago, 70 million years earlier than dinosaurs. Some of them evolved from carnivores to herbivores. "That was a key event in evolution," says Winkler. "Our big goal is to find out when and in which species this happened exactly."

Scientists from JGU, the Max Planck Institute for Evolutionary Anthropology in Leipzig and the Center for Natural History at the University of Hamburg were involved in the study. As part of the research project "Vertebrate Herbivory" by Prof. Dr. Thomas T├╝tken from the Institute for Geosciences at JGU, which is funded by the European Research Council (ERC) with a so-called Consolidator Grant.