If we think of animals that have been with us for a long time and that are capable of having a life expectancy greater than that of human beings, it is easy for the turtle to come to mind. Along with the elephant, it is the quintessential old animal for our imagination. Most of the time, animated films have been in charge of showing us turtles as old people who, slowly but steadily, represent wisdom and patience. But where does this long-lived animal come from?
Turtles arose very early in the history of life. They populate our planet since the Triassic period, which belongs to the Mesozoic era. Specifically, Eunotosaurus is the first species that we know of, and it lived 260 million years ago. It is true that there is debate among researchers on whether or not to take Eunotosaurus as a species in the evolutionary root of turtles. Be that as it may, it seems that there is consensus in dating the first turtles in the Norian , the Triassic period that occurred between 220 and 205 million years ago. But even before that, a key event occurred for the turtles.
conquer the land
In the Carboniferous , which began 322 million years ago, an evolutionary leap was made with the emergence of the amniotes , a group to which turtles, lizards and crocodiles belong, among other species. Amniotes lay eggs that have a membrane, the amnion , that prevents water loss. This structure made it possible to conquer almost all terrestrial environments since, unlike amphibians, amniotes did not have to return to the water to spawn.
Since the existence of the first turtles, the historical evolution of this animal has undergone few variations to the present day. The most drastic change occurred in the formation of its shell , since the first species did not have the characteristic exoskeleton that protects turtles. Archelon and Protostega are the names given to the giant tortoises that lived during the Cretaceous. These species could weigh two tons and their bones were modified until they became a kind of shell, which eventually evolved into the shell that covers turtles today.
and survive
66.5 million years ago, at the end of the Cretaceous, the species called Hutchemys walkerorum coexisted with the dinosaurs. This turtle had a soft shell and surprisingly it was one of the few species to survive the mass extinction that wiped out the dinosaurs . “Until recently, we didn’t understand these softshell turtles very well. However, we are beginning to learn more about this extinct group of turtles and better understand their evolution, including how they coped with mass extinction,” he said. Steven Jasinski, from the Department of Earth and Environmental Sciences in the University of Pennsylvania School of Arts and Sciences and lead author of the study that has been published in the journal Cretaceous Research. With this study, more information was obtained about the cataclysm that wiped out the dinosaurs. And, as if from a cautionary tale, the huge and flashy dinosaurs fell, and the turtle survived.
Belonging to the Miocene we have Stupendemys Geographicus, a species that lived in what is now the desert of Venezuela. Between 5 and 15 million years ago the region was wet and marshy, with rivers and lakes. There a group of paleontologists discovered the remains of a carapace with horns that measured more than three meters . Its enormous size leads us to think of a turtle that could weigh more than a ton. “ Almost one hundred times the size of its closest living relative , the Amazon river turtle Peltocephalus dumerilianus , and twice the size of the largest existing turtle, the leatherback Dermochelys coriacea ,” according to the investigation with Marcelo Sánchez as head of the study, director of the Paleontological Institute and Museum of the University of Zurich. This species coexisted with Purussaurus , one of the largest known alligator species. Bite marks have been found on the remains of these prehistoric turtles, so it is thought that they must have been prey for alligators.
This brief review of the extensive and exciting research on the origin and species of turtles deserves an outstanding conclusion: turtles established their main features in the late Triassic and, compared to dinosaurs, birds and mammals, they had only slight evolutionary changes . This tells us that turtles are effective model species. This is demonstrated by the diversity of groups, their geographical dispersion and the different habitats that they are capable of populating. With slow pace but immeasurable adaptation, turtles have survived 200 million years on a planet that is constantly changing and has seen so many species disappear.
References:
Chain, EA et al. 2020. The anatomy, paleobiology, and evolutionary relationships of the largest extinct side-necked turtle. Science Advances 6, 7. DOI: 10.1126/sciadv.aay4593.Jasinski, SE et al. 2022. A softshell turtle (Testudines: Trionychidae: Plastomeninae) from the uppermost Cretaceous (Maastrichtian) Hell Creek Formation, North Dakota, USA, with implications for the evolutionary relationships of plastomenines and other trionychids. Cretaceous Research 135 : 105172. DOI: 10.1016/j.cretres.2022.105172.Rieppel, O. 1999. Turtle Origins. Science , 283, 5404, 945-946. DOI: 10.1126/science.283.5404.945.Rougier, GW 1998. The evolution of turtles. Research and Science 258, 62-70.
