Tech UPTechnologyThe last giant dinosaurs before extinction

The last giant dinosaurs before extinction

The discovery of a giant dinosaur in the Pyrenees recently made the news, a new species called Abditosaurus kuehnei from the remains excavated at the Orcau-1 site , in Pallars Jussà, 70.5 million years old . A partially articulated skeleton and the most complete of this group of herbivorous dinosaurs discovered so far in Europe. And as if this were not enough, its dimensions – almost 18 meters long and an estimated weight of 14 tons – make it the largest species of dinosaur of this age in the Ibero-Armorian domain, the ancient region that currently groups Iberia and the south of France.

But in order to understand this finding, beyond the new species, we have to talk about sauropod dinosaurs .

Dinosaurs are traditionally divided into two main groups according to the orientation of the pubis, one of the hip bones. In saurischians , the pubis faces forwards, as in lizards. In ornithischians , however, it is oriented backwards, in a manner similar to that of birds. This differentiation could be simple, but the truth is that it is usually very confusing, since we now know that the birds belong to the saurischians. And obviously birds don’t have hips like a lizard… Originally, this classification was proposed solely because of the external resemblance of the pelvis to lizards or birds, without taking into account any direct relationship.

Within the saurischians there are two large groups, the theropods (predators, carnivores, with sharp teeth and claws, which include forms as famous as Tyrannosaurus , Velociraptor , Deinonychus or Spinosaurus ) and the sauropodomorphs (sauropods with long necks and close relatives, such as Diplodocus , Brachiosaurus , Camarasaurus , or Brontosaurus ).

Sauropodomorphs are a group of saurischian dinosaurs that appear in the fossil record in the Late Triassic . The first forms to appear are what have traditionally been called prosauropods , lasting into the Jurassic. The other large group of sauropodomorphs is Sauropoda , the sauropods, of which there is also a record from the Upper Triassic to the end of the Cretaceous . And as we have mentioned before, broadly speaking, anatomically they stand out for their long necks and tails.

Within Sauropoda there are several groups depending on their greater or lesser relationship. Thus, there are more primitive, and more derived or specialized, as is the case of the diplodocoidea (group to which Diplodocus or Apatosaurus belong) or the titanosauriformes (group to which the famous Brachiosaurus and the protagonists of this article, the Titanosaurs , belong). .

The titanosaurs were a predominantly Cretaceous group, and in fact were the last remaining sauropods before the extinction at the end of the Cretaceous. But beware, that they were the last does not mean that there were few left: in recent years dozens of species of titanosaurs from the Late Cretaceous have been described.

They were characterized by having small and elongated heads at the end of their long necks, by having bone plates on their backs (they did not armor them, but they did have osteoderms along their backs) and by having the bones of their spinal column. very hollow , filled by air sacs in connection with their lungs.

These hollow bones also appear in other sauropod dinosaurs and are one of the reasons they were able to grow so large, one of the engines of their gigantism . And among them, this characteristic, that of hollow bones, or “pneumaticity” as we call it in biology, reached its maximum expression precisely in titanosaurs. Not surprisingly, the largest dinosaurs described so far, Argentinosaurus and Patagotitan , were titanosaurs that inhabited South America in the Cretaceous and are estimated to be more than 30 meters long .

But what happened in Europe ? What is today this continent was an archipelago of islands during the Cretaceous. And on the islands, space and resources are more limited than on the mainland. This is why many large animals, by speciating on islands, become smaller in size . And that is what the majority of Cretaceous dinosaurs (and especially from the Upper Cretaceous) show in European sites. The titanosaurs described so far in these places were smaller (compared to the sauropods of other times and places, for which measuring 20 meters in length was “normal”). And that is where this recently discovered Abditosaurus stands out: it is estimated to be about 18 meters long, a not insignificant size for a sauropod. And this raises questions about its paleoecosystem : did it live on a larger island, with more resources? Or at that precise geological moment did not have so much competition? We will see what the next discoveries hold for us.

 

References :

Vila, B. et al. 2022. A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe. Nature Ecology & Evolution. DOI: 10.1038/s41559-021-01651-5

Bonaparte, J.; Coria, R. 1993. A new gigantic titanosaur sauropod from the Río Limay Formation (Albian-Cenomanian) of Neuquén Province, Argentina. Ameghiniana 30 (3): 271-282.

Díez Díaz, V. et al. 2016. A new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Lo Hueco (Cuenca, Spain). Cretaceous Research, 68: 49-60.

Gascó-Lluna, F. 2015. Functional anatomy of Turiasaurus riodevensis (Dinosauria, Sauropoda) . Doctoral Thesis, Autonomous University of Madrid.

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