We live on an absolutely amazing planet, in the best sense of the word. We are still a long way from mapping all the millions of species that share the Earth with us right now, but two things in this regard are already quite clear.
The first is that the web of interrelationships among this multitude of living creatures is far more complex than anything we can conceive of. The second is that this infinitely intricate fabric exists in four dimensions: not just the three of space, but also of time.
Indeed, every time we go back a few tens of thousands of years, a substantial proportion of the actors enter or leave the stage, but the scene remains just as variegated. And this has been repeated for at least several hundred million years: a living planet, always different, but, perhaps for that very reason, carpeted with a web of interrelationships that we can detect and understand.
It may sound crazy, but the fact is that the above reflections — not very original, I agree, but sincere — came to my mind because of a single fossilized bone. This is a vertebra in the middle of a dinosaur’s tail. For the time being, it is the only trace of the animal to be found, still insufficient for it to be given one of those beautiful scientific names that mix Latin and Greek. Even so, the solitary vertebra helps paint a clearer and more complex picture of the interweaving of relationships between the animals that ruled the Earth some 70 million years ago.
Details about the discovery are coming out in the Journal of South American Earth Sciences. Rafael Delcourt and Max Cardoso Langer, paleontologists from USP in Ribeirão Preto and authors of the study on the fossil, report that it was found, along with similar remains of turtles and extinct relatives of crocodiles, in the São Paulo municipality of Osvaldo Cruz (northwest of the state). .
The characteristics of the vertebra make it clear that it is an already adult animal and that it belonged to the group of abelisaurids, which were among the main predatory dinosaurs in South America at the end of the Cretaceous period (the last of the Age of Dinosaurs). If you are one of those people who always felt a little sorry for the short arms of the tyrannosaurus rexplease save most of your pity for the abelisaurids: one of the group’s most distinguishing features is its tiny front legs — “almost vestigial,” write the paleontologist duo.
Microarms didn’t stop abelisaurids from becoming formidable predators, of course. “We had an extremely different fauna from this group here in Brazil”, says Delcourt. “The largest of the abelisaurs, called Pycnonemosaurus, which was 9 meters long, lived here.” Other more modest but still formidable species have also been described in Brazilian territory.
But the vertebra from the interior of São Paulo shows that there were also relatively dwarf abelisaurs at the end of the Brazilian Cretaceous: calculations that use the size of these bones to estimate the total body size indicate that the animal reached about 3.5 meters in length, not unlike a today’s good sized alligator.
It’s fascinating to think about what that means. Cretaceous ecosystems were not cartoon simplifications, with a single giant carnivore terrorizing helpless prey, but a three-dimensional world, with species of different sizes occupying different spaces. If Pycnonemosaurus were jaguars, the mysterious vertebra abelisaur and its relatives might have been ocelots. More mysteries like these are waiting for us.
