Giant Turtle with a Rounded Shell – Reptiles Ruled When Dinosaurs Died Out
Palaeontologists and field workers have been marvelling at the latest discovery of huge reptile fossils from Columbia’s Cerrejon coal mine. After the dinosaurs died out, there were many gaps in ecosystems, these were rapidly filled by animals that had survived the Cretaceous mass extinction event that saw the demise of the Dinosauria. In the geological time period that followed the Cretaceous, known as the Palaeogene, global temperatures soared and planet Earth became a paradise for those reptile genera that survived.
The research team have uncovered the carapace of another enormous freshwater turtle from the coal mine. This sixty million year old fossil was found in a section of the open cast mine known as La Puente pit. Scientists have already built up a picture of the reptile dominated swampland and rain-forest that made up this part of South America, just a few million years after the dinosaurs became extinct. Giant crocodiles took over the predatory role of dinosaurs such as the abelisaurids and huge turtles swam in the lakes and rivers of the area. The apex predator of the region, the stuff of nightmares was a huge constrictor snake, possibly the largest snake that has ever lived. This animal has been named Titanoboa and the fossils found of this animal indicate a snake with a length in excess of fifteen metres, twice the size of any species of snake alive today.
To read an article about the discovery of Titanoboa: Titanoboa – Huge Snake of the Palaeogene.
This new giant, freshwater turtle has been formally described and named Puentemys mushaisaensis. It measured over 1.5 metres in length and it was named after the part of the coal mine where the carapace (top part of the turtle’s shell was found). The palaeontologists have classified P. mushaisaensis as a turtle belonging to the Bothremydid family of the Chelonia (turtles and tortoises). Although many types of turtle have been discovered at the Cerrejon mine, this is the first Bothremydid turtle to be found in Palaeogene deposits in South America.
The palaeontologists responsible for the scientific description of this table-sized turtle have suggested that its nearest relative known in the fossil record is a genus of turtles whose fossils have been found in Upper Cretaceous strata in Europe. This has perplexed palaeontologists as during the Late Cretaceous the Atlantic Ocean was already vast and it is difficult to imagine how even a large turtle could have made its way from Europe to South America. A number of theories have been put forward to explain this distribution. Perhaps turtles of this type lived in estuaries and spread across the planet by moving along coastlines to exploit new habitats. Or perhaps individuals were washed out to sea and survived the long crossing between Europe and the east coast of South America. Alternatively, turtles may have reached South America by “island hopping”, slowly making their way across the Atlantic over millions of years by colonising islands of the coast of Africa and then it was from these that some individuals got washed westwards to the Americas.
Puentemys mushaisaensis had a very rounded shell, described by field workers when they first excavated the fossils as being “rounded like a car tyre”. Round shelled turtles had existed during the reign of the dinosaurs. Columbian scientists have proposed that a very round shell would have had two advantages. Firstly, with huge crocodiles and the enormous Titanoboa about, the round shell would have offered considerable protection. Crocodiles would have found it difficult to get a purchase on the carapace with their teeth. The constrictor snake Titanoboa would have had difficulty swallowing a turtle with such a rounded shell. So the strange shape to the carapace could have evolved as an adaptation to the large predators that P. mushaisaensis shared its habitat with. Secondly, the shell being so round would have enabled a large surface area to be presented to the sun, permitting a cold-blooded turtle to be warmed quickly by the sun’s rays. Being sluggish when surrounded by such formidable predators would not have been a good idea.
Scientists from the various museums and institutes who have been working in the area are confident that the coal mine will yield more spectacular reptile fossils from a time in the Earth’s history immediately after the dinosaur extinction.
To read an earlier article about Cerrejon turtle fossil discoveries: Giant Freshwater Turtle from a Columbian Coal Mine.