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The Atacama Desert continues to amaze for its paleontological treasures.
Just over a month ago, researchers from the Faculty of Sciences of the University of Chile and the Museum of Natural and Cultural History of the Atacama Desert presented in the Journal of Vertebrate Paleontology the study that allowed the identification of two genera of plesiosaurs that lived in this area about 160 million years ago.
The same team is now surprising with the first pliosaur fossils found in Chile, a species known to be one of the largest marine predators of the Jurassic.
The find, currently consisting of jaw and limb fragments, represents the second oldest record of pliosaurs in the Southern Hemisphere, after an isolated vertebra found in Argentina corresponding to the Calovian period (168 to 166 million years), and the first associated with the Oxfordian period, a period that ranges from 163 million to 157 million years ago.
Rodrigo Otero, paleontologist of the Fossil Registry and Vertebrate Evolution Project of the University of Chile who led this research, explains that the discovery, together with representing the first national registry of pliosaurs, fills a temporal gap between the remains of the Caloviano and two endemic species Also found in Argentina from the Titonian period (152 to 156 million years ago).
The remains were found at two sites located in the Loa River basin, an area that 160 million years ago was almost completely submerged in the Pacific Ocean. The discovery was possible after different campaigns carried out in the sector since 2017.
“Both specimens come from a sector near Cerritos Bayos, about 20 kilometers west of Calama. From the first we got a jaw fragment. From the second specimen, meanwhile, until now we have recovered part of a waist, apparently pectoral, a relatively complete fin (of which we describe for now only the humerus, while the rest await preparation) and the femur, which had already been largely eroded and was recovered by combing recent sediments, ”he said.
“According to what we have seen in the field, it is possible that the tail and part of the pelvis have eroded, but the interesting thing is that there is a complete fin, apparently the neck, and best of all, we have confirmed that it is preserved the skull, “he added.
What were the pliosaurs like?
Pliosaurs were marine reptiles related to plesiosaurs that reigned in the Jurassic seas. Its enormous head, jaws and teeth, as well as the impressive size that some genera could reach (up to 15 meters or more) are part of the anatomical characteristics that distinguish this mega-predator.
Otero explains that this animal “was characterized by having a large skull with an elongated face, with very robust teeth and firmly attached to the jaw. The neck was short and robust, its body was hydrodynamic and its limbs were adapted like fins ”.
Regarding the characteristics of these Chilean specimens, Otero describes that “the complete fossil must measure between 6 to 7 meters, its skull is about 1 meter long, with chili-shaped teeth, which are around 8 to 10 cm. At the moment, we do not know what gender they may be, but we will be able to clarify that when preparing the skull and / or the complete fin ”.
On the other hand, he points out that it was located at the top of the food chain. “The pliosaur was a predator of large organisms, possibly plesiosaurs, ichthyosaurs, and sharks, among others. Making a parallel with the current marine fauna, the plesiosaurs were more similar to the current seals, while the pliosaur was ecologically similar to the current killer whales “, he emphasized.
“It is very likely that among the pliosaurs were the top predators of the Upper Jurassic food chain,” the paleontologist raises about this species, who adds that “pliosaurs existed until the mid-Cretaceous. After its extinction, its ecological niche was occupied by other reptiles, among them, mosasaurs ”.
Jurassic biodiversity
The remains of these marine reptiles were detected near the sites where the fossils were also found that allowed the identification of the plesiosaur genera Muraenosaurus and Vinialesaurus. The finding of the pliosaur, in this sense, adds key information about the extensive marine biodiversity of this area during the Jurassic.
The researcher from the University of Chile points out that there is still a large fossil record of prehistoric fauna to be identified in the Atacama Desert. “In the sector we are studying, we have found new materials from marine vertebrates, including cranial remains of ichthyosaurs, marine crocodiles and plesiosaurs, along with a diversity of fish ranging from very small forms to giant filter forms that are estimated at about 10 meters long ”, it indicates.
Rodrigo Otero also states that this diversity of marine vertebrates found in the area, until now suggests the hypothesis of a marine corridor or “Caribbean Corridor” that connected the marine fauna of the Sea of Tethys (today’s North Atlantic) and that of the ancient ocean. Pacific during the Middle and Upper Jurassic, when part of the Chilean territory was submerged in the sea and South America still integrated Gondwana. “In any case, this route certainly varied during the Jurassic and could reflect exchange pulses at certain times of that period, without necessarily excluding other routes,” the researcher points out.
The extreme excavation conditions and the current pandemic have made it difficult to continue with the extraction of the remains, adds Otero.
“One of the fossils emerges in a very steep sector, where there is a lot of wind and where the radiation is very high. In addition, there are no roads that allow us to get to the side of the fossil, so its extraction has to be “freehand”, transporting huge blocks between several people down the hill. All this makes recovery and study very slow. To this we have to add the pandemic, which eliminated any possibility of working in the field during this 2020, so this specimen will take more time for its complete study “.
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