Crocodile or Salamander? The Role of Giant Amphibians in the Ecosystems of the Triassic Period

28/07/2016

The research was led by Josep Fortuny, researcher at the Catalan Institute of Palaeontology (ICP), and included the participation of UAB researchers from the Department of Geology.

The study analyses the biomechanics of the temnospondyls' cranium using computational biomechanics techniques and ends the historical debate on the role these amphibians played in the ecosystems of the Triassic Period. This group dominated fresh water areas (rivers, lakes, marshes, etc.) and some specimens became very large, up to 5 and 6 metres in length. Although they are similar to salamanders and newts, scientists have long debated - due to their external appearance and large dimensions, closer to a crocodile - whether these animals could be biologically closer to current giant salamanders (such as the ones in China and California) or if they had a lifestyle similar to today's crocodiles, even if another 25 million years would have to pass before they appeared on Earth.
 
“Neither crocodile nor salamander”, explains Josep Fortuny, head of the virtual ICP palaeontology research group and leader of the study. “When we biomechanically analyse the cranium of temnospondyls and compare it to that of crocodiles and salamanders, we can see that the extinct amphibians occupied a very different position in the ecosystem to what these animals occupy now”, Fortuny states. Some aspects such as the form of their cranium are similar to that of a crocodile; however, their amphibian nature determined the flat shape of their head and made it difficult to develop a secondary palate, a trait which is present in crocodiles and which allows breathing even when their mouth is filled with water. The two temnospondyl species analysed were Edingerella madagascariensis and Stanocephalosaurus birdi.
 
Previous studies have analysed the ecological diversity of temnospondyls: while some species suctioned their food as current salamanders do, other species were active hunters, similar to how crocodiles act today. Precisely the extinction of temnospondyls at the beginning of the Jurassic period coincides with the appearance of the first crocodilian forms. “The cause of the decline of these giant amphibians continues to be an open question. However, given current data, it wouldn't be foolish to think that the appearance of the first crocodiles had something to do with their disappearance”, Fortuny states.
 
The data from this study was obtained through computational biomechanics, a very powerful research tool used to study ecological aspects of living and extinct animals. It consists in simulating the functioning of specific biological structures based on their morphology. For example, the bite of an animal can be simulated and then the strength of the jaws while biting analysed. Based on the results obtained, researchers can make estimates on their diet, hunting habits, etc. Computational biomechanics has also demonstrated to be valuable for more in-depth research into the biology of rare or endangered species, such as the Chinese giant salamander.
 
The study was published in the journal Scientific Reports, which is part of the Nature publishing group. Collaborating in the study were also researchers of the French National Museum of Natural History in Paris, the Center of Natural History, Universität Hamburg; and the Universitat Politècnica de Catalunya.

Making Use of the Crisis

The disappearance of up to 90% of species represented an opportunity for several other groups during the Triassic period, including turtles, which continue to exist today. This extinction event which took place 250 million years ago, less known than the one which extinguished all dinosaurs, but much more severe, also represented an opportunity for temnospondyls to diversify and dominate the majority of fresh water territories. Other groups, such as the dinosaurs, appeared at the end of the Triassic period (some 200 million years ago) and dominated all ecosystems until the end of the Cretaceous period.
 
There are several sites in Catalonia containing the remains of temnospondyls such as Sarroca de Bellera (Pallars Jussà) and La Móra in the Montseny mountain region, where the species Calmasuchus acri is well represented and known as “the Capitosaurus of the Montseny”.
 
Original article: Fortuny, J. et al. "Comparative 3D Analyses and Palaeoecology of Giant Early Amphibians (Temnospondyli: Stereospondyli)". Sci. Rep. 6, 30387; DOI: 10.1038/srep30387 (2016).