A new spinosaurid dinosaur species from the Early Cretaceous of Cinctorres (Spain)
By: Andrés Santos-Cubedo, Carlos de Santisteban, Begoña Poza & Sergi Meseguer
Summarized by: Michael Holowiak. Michael lives in Putnam Valley, New York, and is a student at Binghamton University who is currently pursuing a B.S. in biology. He works in a psychiatric hospital in White Plains, New York. One of Michael’s favorite activities is to go country line dancing every week.
What data were used? Researchers used a newly found dinosaur bones that were found in Cinctorres, Spain from the Early Cretaceous period (145 million to 100.5 million years ago).. Researchers also modified a dataset from a previous research study (Sereno et al. (2022)) that originally contained 120 cranial (skull) and post cranial (vertebral) features (e.g. orientation, grooves, outlines and shape of bones) of different spinosaurid species and compared their evolutionary relationships. Spinosaurids are large bipedal dinosaurs (heavier than Tyrannosaurus rex) with large arms and long narrow skulls that resemble crocodiles. They are all carnivores, with many features adapted to feed on fish. Researchers in this study added in the missing vertebral characters of Baryonyx walkeri (a spinosaurid species in the Baryonychinae subfamily) and compared 25 cranial and post cranial characters of the new fossil to the dataset. The characters were identified from the preserved bones (vertebrae/upper jaw bone) (Figure-1).
What was the hypothesis being tested? This study focused on the identification of a new spinosaurid species based on character comparison of the new fossils (vertebrae and upper jaw bone) to known information of others in the clade, specifically those in the Baryonchinae subfamily, which scientists hypothesized the new species may belong to.
Methods: The fossils of the new spinosaurid were recovered by a separate team within the Arcillas de Morella Formation, which contains rocks deposited during the Lower Cretaceous Period and exposed near Cinctorres, Spain. Scientists created a modified dataset to add in missing information of other species in the Baryonychinae subfamily (like Baryonyx walkeri) to compare the new fossils to. Phylogenetic (evolutionary) analyses were conducted wherein cranial and post cranial characters from specimens in the dataset were matched with 25 characters of the new fossil to identify synapomorphies (shared traits, e.g. synapomorphies of mammals are mammary glands and hair/fur) and autapomorphies (unique traits no other species has) within the tree. Scientists identified the most parsimonious tree amongst all of the trees inferred; the most parsimonious tree would be the one with the simplest explanation of evolutionary relationships (i.e. the least amount of convergent evolution, where features evolve independently in many groups).
Results: The new fossil was determined to be a new species and they named it Protathlitis cinctorrensis. Phylogenetic analyses resulted in over 9.3 million potential trees regarding the relation of the clade, and researchers narrowed these down to find the most parsimonious one. From that tree, researchers identified the new fossil’s most closely related relatives within the spinosaurids (these were spinosaurids Baryonyx, Ceratosuchops,and Suchominus). Protathlitis cinctorrensis was identified to be a part of the Baryonychinae clade (subfamily of spinosaurids) due to the unique feature of its upper jaw bone; a depression in the antorbital fossa (i.e. the area towards the back of the upper jawbone behind the opening in the skull and in front of the eye socket). However, it was differentiated from other species within Baryonychinae by its combination of unique characters in its caudal vertebrae (the vertebrae of the tail).
Why is this study important? This study is important because the discovery of a new species (especially in a group where mostly full skeletons are rarely found) can provide insight into the origins and evolutionary history of the clade. New discoveries can fill in gaps and extend the known phylogenetic tree allowing for a broader understanding of what the time period looked like. The discovery of the new species confirms that spinosaurids had appeared during the Early Cretaceous in Laurasia (the ancient continent consisting of parts of North America, Europe, and Asia).
Broader Implications beyond this study: Finding more fossils of new species in areas that have been researched before enforces the idea that scientists really haven’t scratched the surface of what is out there and that the fossil record is very incomplete. There have been two species of spinosaurid taxa that have been found within the Arcillas de Morella Formation, but there are likely more to be discovered with time that will continually fill in gaps of knowledge of Earth’s past, especially in parts of the world that have been searched less for fossils.
Citation: Santos-Cubedo, A., de Santisteban, C., Poza, B., & Meseguer, S. (2023). A new spinosaurid dinosaur species from the Early Cretaceous of Cinctorres (Spain). Scientific Reports, 13(1), 6471. https://doi.org/10.1038/s41598-023-33418-2