Barinasuchus

In 1973, road workers near Qedabra Socó, a tributary of the Rio Masparro river in Venezuela, near the eastern foothills of the Andes, discovered what was apparently a near-complete skeleton of a large sebecid while constructing an access road to the town of El Toro. The specimen, later catalogued as MAAT-0260, was found in strata belonging to the upper Parángula Formation, dated to the lower middle Miocene, possibly the Friasian South American Land Mammal Age. dated to the middle Miocene. The specimen was referred to as Sebecus cf. huilensis, though no specimen number was provided, and it has since fallen into the hands of a private collector. In 2007, as part of a paper describing multiple genera of South American sebecids, Alfredo Paolillo and Omar J. Linares described MAAT-0260, and assigned it to a taxon of its own, Barinasuchus arveloi. Buffetaut and Hoffstetter's specimen was assigned to the same taxon. The binomial name refers to Barinas, the Venezuelan state from which the holotype is known, and to Alberto Arvelo Torrealba, a local educator and poet, the namesake of the museum where it is housed. Whereas the other two specimens were Miocene, this one comes from middle Eocene-age strata of Argentina's Divisadero Largo Formation. It is notably smaller than the two Miocene specimens, and has four premaxillary teeth, as opposed to the three observed in those. M.L.P. 73-III-15-1 had, in a dissertation, previously been tentatively assigned to Bretesuchus. == Description ==

Barinasuchus was one of the largest known sebecids, In 2016, Ralph E. Molnar and Felipe Mequita de Vasconcellos used several anatomical proxies in an attempt to determine its size. Firstly, they used another sebecosuchian, the baurusuchid genus Stratiotosuchus, as a frame of reference, due to its completeness. In doing so, they arrived at a length estimate of . Using modern crocodilians, specifically the American and saltwater crocodiles, as reference points, they attained a larger estimate of about . Based on the variability of head-length-to-total-length ratios in modern taxa, they suggested that Barinasuchus may have attained a maximum body length of . For body mass, they provided an estimate of . Even taking a margin of error of 50% into account, this would make Barinasuchus heavier than any (extant) terrestrial predatory mammal, and is roughly equal in mass to a black rhinoceros. However, considerably smaller sizes, both in terms of body length and body mass, were proposed by subsequent papers. The 2023 paper describing Dentaneosuchus, for example, suggested that both it and Barinasuchus were somewhere around in length. Similarly, in the supplementary materials of a paper published in 2025, Gonzalo Gabriel Bravo and colleagues calculated a considerably lighter mean body mass of accounting for a very large margin of error; estimates otherwise ranged from . Skull and dentition The holotype skull, as preserved and measured from the anterior tip of the rostrum to the posterior (rear) end of the damaged surangular, measures in length, and in height. The nasals are curved, forming a narrow dome shape. Like Ogresuchus and Sebecus, the perinarial fossa (a depression on the lower margin of the nasal opening) was slightly larger than in other sebecids. Barinasuchus premaxillae were short and high, and their junction with the maxilla bore a prominent notch, which accommodated the fourth mandibular tooth. The maxillae were fairly short, and were very high posteriorly. The pterygoid cavity was large and concave, and was broader posteriorly. The basisphenoids, two bones that lay between the basioccipital and presphenoid bones, were strongly compressed. While the palatine-pterygoid region is poorly known in most other sebecids, it has been noted that Barinasuchus shares with Bretesuchus and Sebecus a palatine bone morphology wherein they were proportionally short, and choanae (internal nostrils) which opened at the roof of a deep cavity in the anterior (front) portion of the pterygoid. Barinasuchus dentition was heterodont, meaning that multiple tooth morphologies were present. The teeth of the premaxilla and the anterior portion of the maxilla are more conical than those of the posterior portion of the maxilla, which are shorter and more laterally compressed. All of the teeth were laterally compressed, particularly those of the posterior maxilla. The fourth mandibular tooth was the largest (out of both upper and lower jaws), and was curved. Due to how the holotype of Barinasuchus is preserved, the lower dentition, beyond the fourth mandibular tooth, is not known. == Classification ==

In their 2007 paper describing Barinasuchus, Alfredo Paolillo and Omar J. Linares suggested that Barinasuchus may have descended from Sebecus (or from an as-yet unknown close relative of Sebecus), based on dentition, body size, the compression of the nasal and maxillary bones, and the angle of the snout. In another analysis published that year, Barinasuchus was recovered as the most basal sebecid genus. }}In 2023, Jeremy E. Martin and colleagues published their paper describing Dentaneosuchus. In that paper, they recovered Barinasuchus in a more derived position within Sebecidae, as the sister taxon to a clade comprising the so-called Lumbrera form, Ogresuchus, Sebecus, and Zulmasuchus. The below cladogram reflects the 2023 results of Martin and colleagues: == Palaeoecology ==

Although most early Cenozoic ecosystems were dominated by large mammalian carnivores, some ecosystems in the immediate aftermath and for a considerable time following the end-Cretaceous mass extinction (especially in Europe and South America) appear instead to have been dominated by predatory sauropsids. The Eocene of Europe, for example, had early sebecids, the cariamiform bird Eleutherornis (a possible phorusrhacid), and planiocraniid crocodilians such as Boverisuchus, though a large mammalian carnivore, in the form of the hyaenodont Kerberos, was present. In South America, the predator guild for much of the Cenozoic prominently included both mammalian and non-mammalian predators, such as sparassodont metatherians (relatives of modern marsupials), large flightless phorusrhachid "terror birds", sebecids like Barinasuchus, and snakes. Up to around the middle Miocene, when the later specimens of Barinasuchus lived, the northern South American predatory guild was mostly non-mammalian, with many constituent taxa being reptiles and especially archosaurs. Notable, though mostly aquatic examples are the Palaeocene snake Titanoboa, the Miocene turtle Stupendemys, and the Miocene crocodilians Brachygnathosuchus—although that taxon might be Pliocene—Gryposuchus, and Purussaurus. Only three definite sebecosuchians of similar size are known: one, Dentaneosuchus, lived in Europe and became extinct in the Eocene; or Pebas System, an expanse of lakes and poorly oxygenated marshlands with an area of roughly , formed by the uplifting of the northern Andes. The holotype of Barinasuchus was recovered from strata belonging to the upper part of the Parángula Formation, dating to the lower middle Miocene. The area from which it was recovered do not otherwise bear fossils, and the closest fossiliferous Parángula Formation site is on the bank of the Tucupido River, about northeast; Alfredo Paolill and Omar J. Linares instead interpreted them as being part of the Parángula. The strata in question were deposited in a fluvial (river) environment, and preserve the remains of crocodiles, turtles, and a ground sloth, Pseudoprepotherium venezualanum. the IN-DTC site further preserves the toxodont Pericotoxodon cf. platignathus, and three xenarthrans: a mylodontid ground sloth, an indeterminate glyptodont, and the extinct armadillo Neoglyptatelus. The mid-Eocene Divisadero Largo Formation, from which the earliest Barinasuchus specimen is known, was similarly deposited in a shallow lacustrine environment. It preserves the allothere Groeberia, the notoungulates Acamana, Adiantoides, Allalmeia, Brachystephanus, Phoradiadius, Trigonostylops, and Xenostephanus, and another sebecid, Ilchunaia. The dominance of large reptiles in Europe, at least, had subsided by the Bartonian stage of the Eocene. Increased competition, reduction in prey availability, and environmental changes have all been suggested as causes for the eventual extinction of South American sebecids. It is possible that changes in the Pebas Mega-Wetland may have led to terminal ecological disruption; as apex predators are particularly susceptible to major environmental changes, this may have been responsible for their extinction, == Notes ==