They lurk in the water for prey and then snap suddenly at the right moment – crocodiles are known to be rabid predators and carnivores. But was that true for all representatives of this ancient group of animals? Once there were apparently crocodiles that only peacefully milled leaves and species that were omnivorous, according to an extensive study of fossil teeth. Accordingly, the former relatives of our present-day crocodiles have developed a vegetarian way of life at least three times independently of one another.
All today existing representatives of the group of crocodiles are carnivores that eat fish or anything living that comes within reach of their sharp teeth. There are 25 species, which are assigned to the three families of real crocodiles, alligators and gavials. They all have a similar build and live semi-aquatic. Their predatory diet is reflected not only in their behavior but also in the characteristics of their teeth. They have pointed, conically shaped teeth of different lengths. They serve the purpose of digging deep into the flesh of prey.
Analytical look at fossil teeth
“Carnivores have simple teeth, while herbivores (herbivores) have much more complex teeth,” says Keegan Melstrom of the University of Utah in Salt Lake City. “Omnivores (omnivores), animals that eat both plant and animal material, are somewhere in between,” explains the scientist. According to him, this basic pattern is found in mammals and also in reptiles, including extinct species. Melstrom and his colleague Randall Irmi systematically investigated the question of which tooth shapes existed in the earlier representatives of the crocodile-like group and which conclusions the structures allow for the diet.
As part of their 2019 study, the scientists analyzed 146 teeth from fossil collections from 16 different groups of extinct representatives of the crocodiles. These animals have lived in different parts of the world during the age of the dinosaurs. The scientists then compared the tooth structures of the extinct forms with those of today’s animals to determine what these creatures were most likely to eat.
“Vegi crocodiles” were once widespread
“Our work shows that there was a surprising range of diets among the extinct forms,” says Melstrom. “Some lived like today’s crocodiles – they were carnivores, while others were omnivores. Still others were probably specialized in plants. These vegetarians existed at different times on different continents – some also lived alongside the early mammals. This shows that herbivorous crocodiles were successful in a variety of settings, ”Melstrom concludes.
“It was particularly interesting for us to find out how frequently extinct crocodile forms were herbivores,” says the paleontologist. Their research shows that in the course of the Middle Ages, a vegetarian way of life in the crocodile-like group developed three times and possibly six times independently of each other. The first developed very early in the evolutionary history of these beings: They came into being shortly after the end of the Triassic era.
After that, until the end of the Cretaceous period, there were always vegetarian crocodiles, the researchers report. In the course of the mass extinction, however, they then disappeared and only the carnivorous species have survived to this day.
Source: University of Utah, Current Biology, doi: 10.1016 / j.cub.2019.05.076