Evolution has led to the emergence of both herbivorous and carnivorous animals, but what factors were involved? What kinds of food did extinct vertebrates consume? Moreover, how can we uncover the dietary habits of these ancient creatures? For living animals, it’s straightforward to observe their current eating habits. For species that no longer exist, however, scientists depend on the morphological and chemical data that fossils can provide. Recently, a research team has created a reference framework comprising isotope data that helps identify the diets of existing reptiles, thereby creating a valuable resource for studying the diets of fossil reptiles.
The process of evolution has led to the formation of both herbivores and carnivores, but what mechanisms were at play? What kind of diets did extinct vertebrates follow? And how can we gain an understanding of these ancient diets? Observing the feeding patterns of current animals is relatively easy. Yet, for extinct species, researchers must rely on morphological and chemical evidence gleaned from fossils. A team spearheaded by Professor Thomas Tütken from Johannes Gutenberg University Mainz (JGU) has developed a reference framework of isotope compositions that reveal the dietary habits of existing reptiles, which will prove useful in reconstructing the diets of ancient reptiles. “This reptile reference framework is a useful tool for us to reconstruct the diets of extinct animals such as dinosaurs,” Tütken explained. “Comparable data like this has not been previously available.” Their findings were published in the journal Proceedings of the Royal Society B.
Diverse Diets Among Reptiles
Modern reptiles exhibit a wide array of dietary habits, from herbivorous to carnivorous feeding. Some species focus on specific food groups: for instance, the Galapagos marine iguana feeds on algae, chameleons eat only insects, Gila monsters have a taste for eggs, while apex predators like the saltwater crocodile and the Komodo dragon consume almost exclusively meat. “This wide-ranging diversity complicates our efforts to reconstruct the diets of extinct reptiles,” Tütken noted, highlighting the challenges faced by paleontologists in studying these ancient diets.
The earliest relatives of today’s reptiles appeared over 300 million years ago. The first known reptile, Hylonomus, resembled a lizard and thrived around 315 million years ago in present-day Canada. These primitive reptiles displayed common skull, jaw, and tooth structures that suggest an inclination towards insectivorous diets. However, it remains uncertain when reptiles transitioned from predominantly insect-eating lifestyles to those that included meat and plants.
Establishing a Geochemical Reference Framework Using 28 Reptile Species
The reference framework established in Mainz is instrumental for understanding the diets of both living and ancient vertebrates. Tütken’s team gathered data from 28 contemporary reptile species by examining the calcium and strontium isotopes found in their bones and teeth. These isotopes reveal systematic variations depending on dietary choices. “We chose reptiles known for their herbivorous or carnivorous behaviors, and included some with highly specialized diets to broaden our comparison,” Tütken elaborated. Studied species included alligators, monitor lizards, iguanas, and chameleons. The researchers focused particularly on the calcium-44 and calcium-42 isotopes, discovering that as one moves up the food chain, the concentrations of these isotopes decrease. “Insectivorous reptiles exhibit the highest values, making them distinctly different from those with other feeding habits,” says Dr. Michael Weber, lead author of the study. The research found a consistent reduction in isotope ratios in herbivores and more so in carnivores, successfully identifying unique dietary patterns in marine iguanas and reptiles that feed on eggs.
The stable isotope ratios of strontium-88 to strontium-86 were also analyzed within the same species, offering additional nutritional insights. “By developing an extensive reference system of stable strontium isotopes for dietary analysis, we found that results align closely with those from calcium isotopes regarding various dietary types,” explained Dr. Katrin Weber, a co-author and former researcher in Tütken’s team. “However, strontium is less prevalent in teeth and bones and more susceptible to alteration during fossilization, making calcium a more dependable option for extinct species.” The analysis revealed that the calcium isotope ratio in reptiles exceeds that found in mammals, even when their diets are similar. Researchers factor in various physiological reasons for this difference, indicating that mammalian data cannot be directly applied to assess the diets of prehistoric reptiles like dinosaurs.
Tooth Wear Patterns Provide Additional Dietary Insights
In conjunction with chemical analysis, the research team also examined the mechanical wear patterns on teeth caused by diet as an additional approach for dietary reconstruction. By observing tiny scratches on tooth surfaces, scientists can assess whether an animal consumed primarily hard or soft foods, further enriching the understanding of extinct species’ diets. This data was compiled from observations of modern reptiles in partnership with Dr. Daniela Winkler at Kiel University, integrating it with the new isotopic data. The intersection of these two data sources allows researchers to differentiate between faunivores that would have consumed abrasive materials like shells or bones and those that primarily ate softer foods.
“For accurate interpretation of chemical and mechanical dietary patterns derived from fossils, we first needed to establish the relevant data for modern counterparts with known diets. This has provided us with a comparative reference framework that enhances our ability to assess diets and accurately reconstruct the feeding habits of ancient species,” concluded Professor Thomas Tütken, who received an ERC Consolidator Grant in 2016 to support his work on the dietary habits of the first land vertebrates, which helped facilitate the current research project.
