During the time when large dinosaurs roamed the world, between approximately 230 million and 66 million years ago, titanosaurs were giant herbivores that protected themselves from predators either with bony plates lining their skin or by delivering powerful blows with their tails. A recently described species, Tiamat valdecii, measured around 10 meters in length and lived around 110 million years ago on what was one of the last connection points between Brazil and Africa, which is now the Northeast region of Brazil.
Biomechanical analyses have indicated that features in the vertebrae of its tail enabled a wide range of movement without disarticulation, as suggested by the article published in May in Zoological Journal of the Linnean Society. The inference was made by Brazilian researchers based on eight vertebrae excavated in the vicinity of the city of Quixeré, in the state of Ceará, where paleontologists are dedicated to studying outcrops of the Açu Formation, in what is known as the Potiguar basin, aged between 113 million and 89.8 million years.
“The Açu Formation is very diverse in terms of animals. We are also going to describe five groups of carnivorous dinosaurs, two titanosaurs, one titanosauriform, and some crocodyliformes, besides turtles and fish,” explains paleontologist Paulo Victor Pereira, collections technician in the Macrofossils Laboratory of the Federal University of Rio de Janeiro (UFRJ). None of the fossils of these groups were known in the sediments of the Açu Formation until 2005, when French geologist Pinheiro de Lima Filho, of the Federal University of Rio Grande do Norte (UFRN), discovered the materials and notified paleontologist Lilian Bergqvist, of UFRJ. She took on the coordination of the projects that, since 2014, have brought together researchers from different institutions in Brazil, as well as from the Bernardino Rivadávia Museum of Natural Science, in Argentina, for excavations in the region.
The area where the titanosaur bones were found was discovered by archaeologist Valdeci dos Santos Filho, of the State University of Rio Grande do Norte (UERN), in whose honor the species was named. The genus was named after the goddess of Sumerian and Babylonian mythology, Tiamat, who is represented as a large serpent or a dragon and is considered the mother of dragons and other gods.
The vertebrae closest to the beginning of the tail of T. valdecii were concaved on the anterior part and convex on the posterior end. Anatomists call this configuration “procoelous,” which aids safe rotational movement of the vertebrae due to these bones fitting together in sequence. In the midsection of the tail, the animal presented a solution for the stability of the vertebrae that had not been seen before in other fossils: a concave-convex structure at the ends of the joints that regulates the movement of the vertebrae. This form of articulation would have prevented disarticulations and allowed for greater movement and balance. “This caught our attention in the description of the species. We compared it with materials from both South America and Africa and concluded that these characteristics were not present in other animals,” explains Pereira.
It is the biomechanical studies, which analyze the voluntary movements of living beings based on mechanical laws and norms, that allow paleontologists access to details about organisms from the past beyond the species classifications. “We go beyond examining inanimate material, which is the fossil, to infer what the animal was like in life, its ability to move, and its strength,” says Bergqvist.
With colleagues from the laboratory, biologist Luciano Vidal assembled a 3D model of the vertebrae using a procedure called photogrammetry, which overlays different images of the same object to assemble the digital model. As part of his PhD, underway in Bergqvist’s group, he compared the vertebrae of T. valdecii with those of other closely related organisms to create a model of what the entire spinal column of the species would have looked like. The final stage of the process included calculating the thickness of the cartilage between the vertebrae, based on new comparisons of the related groups, such as crocodiles and birds, to deduce the position of this titanosaur’s limbs while resting, as well as its maximum range of movement.
Without having participated in the study, Argentinian paleontologist Rodolfo Aníbal Coria, of the National University of Rio Negro, recognized for having described at least five species of dinosaurs, says “the research was done based on solid anatomical arguments and certainly enriches our understanding of ancient ecosystems,” via email to Pesquisa FAPESP. “Everyone likes describing new species, but this alone does not explain how these animals lived. Biomechanics helps us understand which evolutionary paths were taken to solve problems common to other groups and species,” explains paleontologist Thiago Marinho, of the Federal University of Triângulo Mineiro (UFTM), an expert in titanosaurs who also did not participate in the work.
It is an exciting discovery because T. valdecii was found in sediments dated to the final ages of the Early Cretaceous, whereas the majority of titanosaurs known today are from the Late Cretaceous, which began at least around 13 million years later. This, along with the characteristics of the body of the new titanosaur, enables the T. valdecii to be classified as a basal species of this group of dinosaurs, just like the titanosaur Andesaurus delgadoi, found in Argentina. The value of this information lies in knowing, for example, that characteristics such as the procoelous vertebrae, which paleontologists supposed had developed over the course of the evolution of the titanosaurs, was actually present since the first species of the group.
“Remains of titanosaurs from older levels of the Cretaceous are particularly scarce, with just a handful of species found in Patagonia. This new species from Brazil is surprising because of the uniqueness of the period that it represents, while also clearly differentiating itself from Patagonian forms,” says Coria. “Over 30 years after the Andesaurus description, Tiamat provides important anatomical information to advance current phylogenetic hypotheses, especially based on the diversification of the titanosaurs,” he adds.
The Açu Formation was one of the last connection points of Brazil with Africa, previously joined together on the Gondwana continent, together with what today are India, Antarctica, and Australia. The other parts of the world were on the other large continent called Laurasia, in the Northern Hemisphere. “Where do you think the titanosaurs emerged from?” questions Marinho. “There is a complete gap of information from the Lower Cretaceous and early Upper Cretaceous that needs to be understood, and this species has the potential to help with this,” he concluded.
Scientific article
PEREIRA, P. V. L. G. C. et al. A new sauropod species from north-western Brazil: Biomechanics and the radiation of Titanosauria (Sauropoda: Somphospondyli). Zoological Journal of the Linnean Society. vol. 20. may 13, 2024.
