Uruguayan paleontologists recently excavated fossils of mesosaurs much larger than those known so far. These ancient aquatic reptiles, which lived around 270 million years ago, were known for their small size and aquatic lifestyle. However, the new specimens, found in the Mangrullo Formation, reveal the existence of giant mesosaurs, challenging previous knowledge about these creatures. This discovery challenges our understanding of their evolution and their environment.
An intriguing discovery
THE mesosaurs were aquatic reptiles that evolved during the Permian, a period marked by significant geological and climatic upheavals. These creatures represent one of the first examples of reptiles having readapted their lifestyle to an aquatic environment, after evolving from terrestrial ancestors. Their distinct morphology, characterized by an elongated body and a skull with an extended snout, made them perfectly adapted to aquatic life. They mainly fed on small fish and other aquatic organisms.
That being said, fossils found, particularly in South Africa and South America, have long described mesosaurs of modest size, generally measuring between 70 and 90 cm longhence the interest of this new discovery. The study of fossils recently found in the Mangrullo formation, in Uruguay, reveals specimens much larger than those previously known. These giant mesosaurs could reach up to 2.5 meters long. The fossils also include skulls measuring between 15 and 20 cm, suggesting that these creatures could have weighed several hundred kilograms as an adult.
How can we explain this particular gigantism?
The researchers have some leads. Recall that, according to Bergmann's rule, animals living in colder environments tend to have larger body sizes. This allows them to retain heat more efficiently. However, this hypothesis does not seem to fully apply to mesosaurs. At the time when these reptiles lived, Uruguay was in fact part of the supercontinent Gondwanaan environment marked by high temperatures.
The researchers then suggest that this gigantism could be linked to specific geological events. Indeed, massive volcanic eruptions modified the aquatic and terrestrial environments of the time. These events likely disrupted ecosystems, creating conditions conducive to animal growth. THE abundant food resources available after these eruptions would also have favored the growth of giant mesosaurs. In addition, these creatures could have developed more significantly to exploit a larger space, particularly due to the predator reduction in the region.
Why it matters
In any case, this gigantism did not allow mesosaurs to survive. Their extinction around 270 million years ago appears to be linked to severe environmental changes. Major volcanic events, combined with increasing drought, have altered living conditions in regions of Gondwana, reducing favorable habitats for these reptiles. So although mesosaurs evolved into giant forms, these changes were fatal to their species.
Despite everything, the discovery of these large specimens provides a more complex and nuanced vision of the evolution of these aquatic reptiles. Their gigantism and the conditions that favored their growth allow us to know more about the interactions between species and their environment, as well as the evolutionary mechanisms that shaped these fascinating creatures. Overall, this study contributes to enriching our understanding of paleontology and opens the way to new research on the impact of geological and climatic changes on prehistoric fauna.
The results of the study are published in the journal Fossil Studies.
