Barinasuchus
Barinasuchus is an extinct genus of sebecid mesoeucrocodylian. It lived in Argentina, Peru, and Venezuela between the middle Eocene and the Late Miocene, ~42–11.6 Ma. Described in 2007, based on a severely damaged specimen from which only a snout tip was recovered, Barinasuchus is known from a single species, B. arveloi, named after Alberto Arvelo Torrealba, a local educator and poet.
The type specimen of Barinasuchus, discovered by road workers in Venezuela in 1973, originally consisted of a substantial portion of the skeleton, though much of it was accidentally destroyed when they attempted to excavate it, leaving only a partial snout and mandible. The specimen comes from the Miocene-age Parángula Formation, and was described in 2007 by Alfredo Paolillo and Omar J. Linares. A second specimen of Barinasuchus was recovered from the Miocene Ipururo Formation of Peru, and was described in 1977 by Éric Buffetaut and Robert Hoffstetter, though was originally assigned to Sebecus huilensis. Another was recovered from the Eocene-age Divisadero Largo Formation of Argentina in 1984 by Zulma Brandoni de Gasparini.
Barinasuchus body length has been estimated, based on comparisons with other crocodyliforms, at between, though smaller estimates of were suggested more recently. Its body mass was initially estimated at, which would make it considerably larger than any terrestrial predatory mammal alive today. However, a smaller estimate of has since been put forward. Barinasuchus was heterodont, meaning that it possessed two types of teeth. Those of the premaxilla and the front of the maxilla were longer and more conical than those further back, which were shorter and thinner. Its mandible was very robust in comparison to other sebecids, and was widest at the point of the fourth mandibular tooth. That tooth was very large, and slotted into a prominent notch between the premaxilla and maxilla when the jaws were closed.
Barinasuchus primarily inhabited lacustrine environments. During the Miocene, it inhabited the Pebas Mega-Wetland, or Pebas System, a expanse of lakes and marshes formed by the growth of the Andes. It, alongside its contemporary relative Langstonia, were part of an endemic northern South American predatory guild which consisted primarily of reptiles and birds. Both were among the last and largest of the sebecids, and significantly outlasted other giant taxa, such as the European Dentaneosuchus, possibly due to their isolation. The extinction of Barinasuchus and other parts of this reptile-heavy guild may have been the result of the loss of the Pebas Mega-Wetland, or the diversification of mammalian predators and the phorusrhacid birds, although this has been questioned by some studies.
Discovery and naming
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. While attempting to remove the specimen from the strata by themselves, the workers accidentally caused extensive damage to it. Only a few fragments remained at the site when it was inspected by archaeologists. What remained of the specimen, the anterior half of a skull and mandible, had been removed prior to their arrival, but had fortunately been relocated to an institution, the in Barinas, by an unknown party.Three years later, in 1977, Éric Buffetaut and Robert Hoffstetter published on a sebecid specimen recovered from the Ipururo Formation of eastern Peru, 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. As far back as 1986, Arthur B. Busbey III expressed uncertainty over whether the specimen could truly be classified as Sebecus, noting that its teeth were less strongly compressed laterally, it had a wider skull, and it was far larger than any described sebecosuchian at the time.
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. In the same paper, Paolillo and Linares assigned two other specimens to the genus. The first was Sebecus cf. huilensis; S. huilensis proper was assigned by them to a genus of its own, Langstonia. The second was a fragmentary specimen, collected by Dr. Edgardo Rolleri and assigned to Sebecosuchia indet. by Zulma Brandoni de Gasparini in 1984. Whereas the other two specimens were Miocene, this one comes from middle Eocene-age strata of Argentina's Divisadero Largo Formation. As with the holotype and the Sebecus cf. huilensis specimen, it is known from the tip of a snout, specifically the premaxilla and the dentary. 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, a group of terrestrial notosuchians which survived into the Cenozoic. This lineage appears to have initially taken over apex predator niches occupied by theropod dinosaurs prior to the extinction event at the Cretaceous–Palaeogene boundary. Several other large sebecid genera are known, such as Dentaneosuchus and Langstonia. Due to the near-total destruction of the holotype, the postcranial skeleton of Barinasuchus are unknown, and much of the skull is also absent.Body size and mass estimates
The fragmentary nature of BarinasuchusSkull and dentition
The holotype skull, as preserved and measured from the anterior tip of the rostrum to the posterior end of the damaged surangular, measures in length, and in height. Based on these dimensions, Barinasuchus likely had a total skull length of about. Its rostrum was tall and laterally compressed, a condition which, in crocodyliforms, is referred to as being oreinirostral. This condition is similar to that of most other sebecids, including such as Langstonia and Sebecus. The nasals are curved, forming a narrow dome shape. Like Ogresuchus and Sebecus, the perinarial fossa 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 which opened at the roof of a deep cavity in the anterior portion of the pterygoid.Barinasuchus mandible was very robust, and its describers noted that the condition seen in this genus was the precise opposite of that seen in Sebecus icaeorhinus. While they believed its mandible could be differentiated from that of other sebecids by the presence of a series of deep pits in the vicinity of the mandibular symphysis, such structures are observed in several other sebecids and non-sebecid sebecosuchians, including baurusuchids and peirosaurids. The mandible of Barinasuchus was almost round at the front, though changed shape posteriorly. The alveolar process, the part of the mandible which bore teeth, was widest and highest at the base of the fourth mandibular tooth. The dorsal surface of the mandibular symphysis bore a shallow, subcylindrical canal. The splenial bones contributed to the symphysis ventrally.
Whereas many sebecids had fairly small teeth and a high tooth count, Barinasuchus and Dentaneosuchus had a condition more similar to baurusuchids, in which the teeth are reduced in number and hypertrophied. 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, and was curved. Due to how the holotype of Barinasuchus is preserved, the lower dentition, beyond the fourth mandibular tooth, is not known.