Crocodile or salamander? The role of the giant amphibians in the Triassic ecosystems

A new study published in Scientific Reports journal analyze the biomechanics of the skull in Temnospondyls – a group of extinct amphibians of huge sizes- to elucidate the role of these animals in the ecosystems about 250 million years ago. The results show an ecological position different from the extant salamanders but also different from crocodiles – being those resembling in size and appearance. 

Comparison between the models of bilateral bite in different animals. From left to right, the extant giant salamander of California, two extinct temnospondyls and an alligator. In red, the areas that present more stress during the biting (Josep Fortuny / ICP)

The study closes a historical debate about the role that played the temnospondyls in the Triassic ecosystems. This group of amphibians dominates the freshwater aquatic environments (rivers, lakes, swamps…) and some members of this group tended to gigantism, reaching 5-6 meters long. Although the relationship of temnospondyls with salamanders and newts, the scientists debated –though to the external appearance and its huge sizes more similar to crocodiles – if the biology of these animals was similar to the living giant salamanders (as from China or California), or was more similar to crocodiles, although there were still 25 million years for the appearance of crocodiles.

“Nor as crocodiles, neither as salamanders”, explains Josep Fortuny, head of the Virtual Paleontology research group of the ICP that heads the study. “The biomechanical analysis of the temnospondyl skulls and its comparison with crocodiles and salamanders shows that these extant amphibians occupied a peculiar ecological position, very different to the position that occupies the extant animals”, explains Fortuny. In some issues – as the skull shape- these extinct amphibians resembles the crocodiles, but its amphibian nature determined its flat morphology of the skull and difficult the apparition of a secondary palate, a character present in crocodiles that also allows them to breathe with the mouth full of water. The two temnospondyl species analyzed are Edingerella madagascariensis and Stanocephalosaurus birdi.

Previous studies analyzed the ecological diversity of temnospondyls: while some species used suction to feed as many extant salamanders, other species hunted its preys by active direct biting, as used nowadays by the crocodiles. Precisely, the descent of temnospondyls during the Early Jurassic coincides with the appearance of the first crocodile members. “The cause of the descent of these giant amphibians is still an open question, but, with the current information, it cannot be discarded that the appearance of the first crocodiles members could be correlated with its descent.”, explains Fortuny

The results from this study have been obtained thanks to computational biomechanics, a powerful research tool to study and understand different ecological issues from living and extinct animals. It consists in 3D simulations of a biological structure to understand its function based on its morphology. Thanks to these models, it can be simulated the bite of an animal and analyze the force generated by the jaws, just to cite one example. From the obtained results is it possible to make an approach on its diet, hunt mode, etc. Also, the computational biomechanics is a powerful tool to deep in the biology of species scarcely known or endangered, as the case of the giant Chinese Salamander.

Video animation that shows the stress areas present during a bilateral bite in the different species analyzed.  

The journal Scientific Reports where the study has been published is member of the Nature publishing group. The research has been performed in collaboration with researchers from Institut Català de Paleontologia Miquel Crusafont (ICP) (Barcelona, Catalonia), the Muséum National d’Histoire Naturelle of Paris, the Centrum fur Naturkunde (University of Hamburg), de Geological Department of the Universitat Autònoma de Barcelona and the Universitat Politècnica de Catalunya.

Seize the crisis

The disappearance at the end Permian up to 90% of the species meant a great opportunity for different groups during the Triassic to evolve, as the case of the turtles, and to reach until nowadays. This great mass extinction occurred about 250 million years ago – less known than the biotic crisis that caused the disappearance of the dinosaurs, but more sever – also was a great opportunity for the temnospondyls to re-radiate and dominate most of the freshwater ecosystems. Other groups, as the dinosaurs, first appeared also during the Triassic (Late Triassic, about 200 million years ago) and dominated the terrestrial ecosystems until the end of the Cretaceous.

+ info: Fortuny, J. et al. Comparative 3D analyses and palaeoecology of giant early amphibians (Temnospondyli: Stereospondyli). Sci. Rep. 6, 30387; doi: 10.1038/srep30387 (2016).

Text: Pere Figuerola – ICP

Picture in the front: Reconstruction of Calmasuchus acri, a capitosaur temnospondyl that lived in Catalonia, Spain (Mauricio Antón / ICP)


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