One of biggest turtles of all time, a monster that weighed more than a ton, swam in the rivers of the Amazon about 10 million years ago. Newly discovered fossils of the animal indicate that its carapace could reach 2.4 m in length, surpassing any other tortoise, past or present.
According to the authors of a new study, Stupendemys geographicus had a wide geographic distribution, in a large arc that extended from the state of Acre to northern Venezuela, passing through Peru and Colombia. The team led by Edwin Cadena, from Universidad del Rosario, Bogotá, has just published data on the species' superhull and other recently excavated fossils in the specialized journal Science Advances. He also participates in the study Orangel Aguilera-Socorro, from UFF (Universidade Federal Fluminense), in Niterói (RJ).
Animals of the genus Stupendemys have been known since the 1970s, having acquired fame for their portentous size (or stupendous, as the scientific name says). But there was a mess about the diversity of species associated with it in South America during the geological era of the Miocene, when the animals lived. In part, this is due to the fact that some of the species have been described on the basis of carapaces, others from skulls and others by analysis of the post-cranial skeleton (roughly, from the neck down).
In the new study, paleontologists compared in detail the new fossils they excavated with materials deposited in museums and came to the conclusion that there was a single giant species of the group in the region, S. geographicus itself.
Small differences between individuals can be attributed to sexual dimorphism, that is, variations in the characteristic aspect between males and females. The boys 'carapace was apparently adorned by two small horns on either side of the neck, which may have served for combat between male rivals, whereas the females' did not have these horns.
“Everything that leaves the Miocene of the Amazon is monstrously giant”, recalls paleontologist Tito Aureliano, from Unicamp. In addition to the turtle – or tortoise, the term most popularly used for forms of fresh water -, the region, at this geological time, also housed the superjacaré Purusaurus (over 12 m) and an extinct relative of capybaras that could reach 700 kg .
It is not difficult to understand why. The configuration of South American rivers was quite different in the Miocene, leading to more direct connections between the waters of present-day Brazil and those of the countries to the north and west, and the formation of a superpantanal, the so-called Pebas system, which ran from the Amazon and from Peru to Venezuela.
It was a resource-rich and highly connected habitat, which would allow the animals to increase in size, thanks to abundant food, and easy transit throughout the region. In fact, it is known that S. geographicus interacted in a not very friendly way with other giants of its time, because alligator teeth marks were found on some of its shells.
The authors of the new study, based on the analysis of the species' mandible, propose that the super-tortoise had a varied diet. He would be able to grind hard shells of mollusks – an abundant food source in the primeval wetland – and to eat fish and other vertebrates. On the other hand, his closest relative alive today, the tortoise known as the loggerhead (Peltocephalus dumerilianus), usually also feeds on fruits of Amazonian palms. Therefore, paleontologists speculate that, with its mouthpiece, it would be able to swallow even the largest fruits of these palms.
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