252 million years ago, during the Permian mass extinction, which marked the beginning of the Triassic period, volcanic eruptions and dramatic climate change killed most of the animals on the ground and nearly all of the oceans, setting the stage for the subsequent emergence of dinosaurs on Earth and an explosion of new marine life.
One type of marine reptile, the ichthyosaur, would eventually go on to rule the seas, becoming a terrifying, yet graceful predator, much like dolphins (only they were reptiles).
What do we know about ichthyosaurs? They could be about twenty feet long, and swim at about 25 miles per hour, dominating the planet’s oceans for about 50 million years. They were reptiles and probably archosaurs, that is, they are more closely related to crocodiles, dinosaurs and birds than to lizards and snakes.
Now a lab has uncovered more details about the tools of some ichthyosaurs to adapt to Triassic marine ecosystems. When scanning the fossil of a Cartorhynchus lenticarpus (of the ichthyosaur family), the scientists discovered round-shaped teeth, like pebbles or boulders, (in the study they are described as pebble-shaped ) hidden in its short snout. The Cartorhynchus used these strange teeth to crush the shells of snails and clams, the researchers estimate.
As we have noted, the article focuses on a specimen of Cartorhynchus lenticarpus , one of the oldest and smallest ichthyosaurs ever discovered. Other species of ichthyosaurs were like dolphins, with long snouts filled with sharp teeth and sleek, streamlined bodies to cut through the water. But while those ichthyosaurs looked like killer dolphins, Cartorhynchus was more like a tadpole. Its name means ‘short snout’.
Ichthyosaurs evolved into creatures that lived in the open ocean, but smaller species like Cartorhynchus probably lived closer to shore and collected invertebrates to eat from the sea floor.
This new study builds on the description of Cartorhynchus issued by several of the same scientists in 2014, including the corresponding author of the new paper, Ryosuke Motani of the University of Californi: “When we first described Cartorhynchus , we thought it had no teeth. and that it fed by suction. But later, the researchers realized that it had some teeth in its jaws. In this study, we used CT scans of the fossil to see the teeth that were hidden in its skull, and we found that they had this unusual shape of boulders “.
Teeth like boulders, perfect for gnawing on shells
Rounded teeth appear to have arisen in several other species of ichthyosaurs, suggesting that the trait evolved independently more than once , rather than all round-toothed ichthyosaurs evolved from a common round-toothed ancestor. On the other hand, many other early ichthyosaurs had pointed cone-shaped teeth.
These different forms of teeth that arise in different families give us an idea of the world in which ichthyosaurs evolved. According to Rieppel: “There were no marine reptiles before the Triassic. That’s what makes these early ichthyosaurs so interesting. After the mass extinction, marine biology was almost empty and ready to be recolonized, “he explains, in a press release announcing the study.
The teeth of animals can tell us a lot about their lifestyle: what they ate and how, but also what ecosystems they inhabited, how was their relationship with their peers, who were their potential predators … Ichthyosaurs with different types of teeth is indicative of how they took over the oceans, playing different ecological roles.
It is also likely that the repeated evolution of rounded crushing teeth in ichthyosaurs such as Cartorhynchus and others was driven by the evolution of the hard shell of their prey. This means that, over time, those best adapted to gnaw on these types of shells prospered over those who were not so adapted.
Referencias:
‘Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition’. Jian-dong Huang. (2020) Scienfict Reports.
