The Teeth Of Earth's First Ichthyosaurs Told Us About Their Diet
Based on the shape of the teeth, paleontologists suggest that they constantly had to chew the hard shells of ancient mollusks.
Scientists have found in China the well-preserved jaws of one of the first ichthyosaurs on Earth. Analysis of these remains showed that marine reptiles fed on hard-shell mollusks. The research results were published in the scientific journal Scientific Reports.
"We still have a very rough idea of how the ichthyosaurs appeared. Most likely, in evolutionary terms, they were closer to dinosaurs, birds, and crocodiles than to lizards, but even this is not a hundred percent fact. After studying the unusual round teeth of these marine reptiles, we have a better understanding of how they appeared on Earth," said Olivier Rippel, one of the authors of the study, curator of the Field Museum of natural history in Chicago.
The world ocean of the time of the dinosaurs was inhabited by a wide variety of marine reptiles, including Delphine-like ichthyosaurs, long-necked plesiosaurs, and pliosaurs and mosasaurs, which were similar to crocodiles. All of them were not related to dinosaurs, many of them are close to modern lizards and other reptiles.
The remains of marine reptiles are rarely preserved, which is why scientists until recently almost nothing was known about their appearance and habits. However, in recent decades, scientists have learned some details about their lives.
In particular, paleontologists have found that ichthyosaurs began to bear young in the womb, rather than lay eggs, even before the transition to life in the sea. Also, scientists found many common features of appearance and anatomy that United them with modern dolphins.
As noted by Rippel and his colleagues, despite this, scientists do not yet know how the ichthyosaurs arose, how they moved to live in the sea, and what the first representatives of these creatures on Earth ate. Paleontologists obtained the first information of this type by studying fragments of the jaws of the primitive ichthyosaur Cartorhynchus lenticarpus, the remains of which Rippel and his team found several years ago in China.
These ancient reptiles are now considered one of the earliest ichthyosaurs on Earth: at least they had the characteristic ichthyosaur body shape and other features of anatomy. Careringi appeared in the Triassic period, approximately 240 million years ago, long before the first "real" dinosaurs. Their remains, as Rippel and his colleagues note, have forced scientists to radically revise the tree of ichthyosaur evolution.
Initially, scientists believed that these ichthyosaurs either did not have teeth in principle, or they did not survive inside the fossil due to unusual conditions of its formation. After re-examining the skull of Cartorhynchus lenticarpus, paleontologists concluded that some of the teeth could still be preserved inside it. So scientists enlightened the fossil with a CT scan.
There were teeth inside the skull. To the great surprise of scientists, a large part of them was more similar to the round molars of modern mammals, rather than the sharp triangular teeth of other ancient ichthyosaurs and other Mesozoic reptiles. This means that the first ichthyosaurs of Earth ate very hard food, presumably bivalves and other invertebrates with a strong shell.
The structure of these teeth and the pattern of scratches on their surface showed that the first ichthyosaurs were quite small. The length of an adult was about 30 cm, which is several times less than the size of marine reptiles of the subsequent Jurassic period.
The rapid growth of their size, as well as the appearance of many other types of teeth, according to Rippel and his colleagues, indicate that ichthyosaurs were among the most successful inhabitants of the seas of the first half of the Mesozoic. Scientists hope that the remains of other ancient reptiles, as well as new fossils of Cartorhynchus lenticarpus, will help them understand how these reptiles gave up eating shells and switched to other types of food.