Itasuchus is an extinct genus of itasuchid notosuchian from the Late Cretaceous of Brazil. Fossils of the type species I. jesuinoi, first described in 1955 by Llewellyn Ivor Price, have been found from the Serra da Galga Formation, though later finds also support its presence in the sediments of the Presidente Prudente Formation. It possessed a somewhat elongated and flattened snout with interlocking teeth similar to what is seen in modern crocodilians, a thick osteoderm armor potentially covered by a thick layer of leathery skin and has been estimated to have reached a total body length of .
Itasuchus is the namesake of the family Itasuchidae, established in 2004 to accommodate both it and Malawisuchus after Itasuchus has varyingly been regarded a goniopholidid and trematochampsid throughout the 1900s. Itasuchidae did not see widespread use at first until the clade was redefined by Pinheiro and colleagues in 2018 to include other similarly platyrostral peirosaurians like Roxochampsa and Pepesuchus, though that same year the same forms had also been used to establish the clade Pepesuchinae. It is now frequently thought that regardless of the nomenclature, Itasuchus and its relatives were close kin to the Peirosauridae within the clade Notosuchia.
Itasuchus inhabitet the meandering river systems of the Presidente Prudente and Serra da Galga Formation during the late Campanian and early Maastrichtian, an environment shared with the closely related Roxochampsa, non-itasuchid notosuchians, turtles, various fish, abelisaurid theropods and titanosaur sauropods. Like other itasuchids Itasuchus too is thought to have been a semi-aquatic animal, a hypothesis supported in part due to the overall similarities to modern crocodiles. This is supported by the laterally flattened tail and keeled osteoderms, which may have been a factor in making the animal more hydrodynamic. The overall snout proportions have been described as an intermediate between longirostrine and brevirostrine forms and have been specifically likened to modern nile crocodiles.
History and naming Itasuchus was named by Brazilian paleontologist Llewellyn Ivor Price in 1955 based on fossil material recovered near Peirópolis in sediments of the Late Cretaceous (Early Maastrichtian) Bauru Group, specifically the Serra da Galga Member of the Marília Formation, which in some works has been elevated to full formation status. The original material, designated the specimen number DGM 434-R, consisted of a fairly complete lower jaw, parts of the left skull from the posterior maxilla to the quadrate, four vertebrae each of the neck, torso and tail, 20 osteoderms and other well preserved postcrania including some complete limb bones. The description of the genus, which was published in the same study as that of Peirosaurus, was chiefly based on the cranial remains, which were deemed sufficient for establishing a new genus by Price. Though mentioned, and despite having been regarded as one of the best known mesoeucrocodylian skeletons from its locality, the postcrania were neither described in detail nor figured, with Price promising that the material would be dealt with "in due course".
The late 80s saw the discovery and eventual description of a complete, well-preserved semi-aquatic crocodyliform from Brazil's Araripe Basin that closely resembled Itasuchus. This form, named Caririsuchus by Brazilian paleontologist Alexander Kellner, was eventually removed from Brazil and was next mentioned as having been shipped to Europe, where it was briefly examined by Eric Buffetaut. While maintaining the status of Caririsuchus as a distinct species, Buffetaut noted several similarities to Itasuchus, ultimately regarding Caririsuchus camposi a species of Itasuchus, creating the combination Itasuchus camposi. The fossil material once again vanished after this, presumably having been sold to a private collector. Despite Buffetaut's proposal, subsequent papers generally kept Itasuchus and Caririsuchus as distinct genera.
In 2004 Carvalho and colleagues established the family Itasuchidae to include both Itasuchus and Malawisuchus, but this grouping was not widely recovered in subsequent studies and generally fell out of use until 2018 when it was redefined to include several platyrostral forms similar to Itasuchus. Since the paper recovered all members of the newly revised Itasuchidae in a polytomy, Pinheiro and colleagues mentioned that it would be possible to sink all four taxa into the genus Itasuchus, but ultimately retained all four forms as distinct genera.
By 2018 a second specimen, MUGEO 218-V, had also been referred to the genus Itasuchus, although only at a genus level. The specimen, represented by a mandible fragment with teeth, is notably less complete than the holotype material and comes from the Late Campanian to Early Maastrichtian Presidente Prudente Formation. A more substantial piece of a rostrum, specimen UFRJ DG 687- R, was eventually also tentatively referred to Itasuchus jesuinoi as well. This specimen, like MUGEO 218-V, came from the Presidente Prudente Formation.
The name Itasuchus derives from the Tupi word "ita" for "stone" and "suchus", the Greek word for "crocodile". The species name derives from Jesuino Felicissimo Junior, who is credited for having reported the first fossils from the site that yielded the remains of Itasuchus.
Description The cranium of Itasuchus is known from two different specimens, the holotype and a tentatively referred rostrum from a different formation. The holotype preserves mostly the posterolateral parts of a skull, two parts of the maxilla, the jugal, quadratojugal (including the postorbital bar) and the quadrate bone. The tentatively referred rostrum meanwhile preserves both halves of the anterior snout from the external nares backward, but lacks the very tip of the snout. Even prior to the discovery of this specimen, the shape of the lower jaw suggested that the skull of Itasuchus was long, narrow and flat. Price estimated that the skull of Itasuchus was approximately long, with a mandibular length of up to .
Even with the additional rostral elements, some of the anatomy of Itasuchus remains unclear. The nares open anterodorsally, meaning forward and upward, and were located close to the snout tip. The edges of the nares were not inflated and instead were level with the rest of the surface of the snout. Due to the damage to the specimen it is unclear whether or not there was a prominent process that extended into the opening or even separated them via a septum, though there is evidence for at least a small extension of the premaxillae. The nares are entirely surrounded by the premaxillae, completely preventing any contact with the paired and spear-shaped nasal bones, though the nasals do divide the posterior elements of the premaxillae via their pointed tips. The premaxillae construct abruptly behind the fourth teeth to create a prominent notch for the large fourth dentary tooth. However rather than marking the point of separation between premaxilla and maxilla, the premaxilla extends further backwards even behind the notch. There the premaxilla contacts the maxilla along a V-shaped suture. The maxilla then form most of the rostrum, running along the nasals. Unlike the lower jaw, the bottom margin of the maxilla is almost straight and lacks the distinct sinusoidal contour created by the festooning of the toothrow.
The jugal is elongated with a straight lower edge and an expanded anterior process that is over twice as tall as the posterior part of the bone. The quadratojugal is described as small and does not participate in the articulation for the lower jaw. Instead the quadrate, which flares outward like in modern crocodiles, is entirely responsible for the articulation with the mandible. The infratemporal fenestra is described as large and longer than tall.
The mandible is mostly known from the dentaries, which in the holotype lack teeth in the very front. Price described this part of the lower jaw as "slightly scarred" and considered the possibility that the terminal dentaries were naturally toothless, but conceded that more material was required to be certain. Later studies like that of Pinheiro and colleagues eventually came to disregard this idea, suggesting that at least two pairs of teeth were present in the damaged region. The mandibular symphysis, where the two halves of the lower jaw meet, is described as long, narrow and flat with clear evidence that it was not just formed by the dentaries but also incorporated the splenials. The symphysis has also been described as spatulate, with specific comparison being drawn to Kinesuchus. The dentaries remain connected until the sixth dentary tooth, though Filippi and colleagues later identify the 7th as the end point for the dentary symphysis, while the splenial's contribution to the symphysis stretches until at least the 10th, though the matter is unclear as the splenials themselves aren't actually preserved. Behind the mandibular symphysis the two halves diverge outwards and also grow taller. Overall the lower jaw displays noticeable festooning both dorsoventrally and mediolaterally, meaning that both in top down and sideview the lower jaw has a clear sinusoidal contour, in both instances coinciding with the tooth size. Specifically, the lower jaw is dorsally convex and rather wide around the fourth dentary tooth (the second of the ones preserved in the holotype). The enlarged fourth dentary tooth, which is common among crocodyliforms, is preceded by the rather flat terminal part of the mandible and immediately followed by a concave and narrower section around the position of the 5th and 6th teeth. The dentary rises again and reaches its tallest point at the level of the 11th and 12 teeth, at which point the height of the bone remains consistent. Looking at the lower jaw from the side also shows that the dentary is split towards the back to form the upper and lower margins of the mandibular fenestra. The retroarticular process, formed by the articular bone, is long and curves upwards like in modern crocodiles, but Price has noted that the inner lobe of the articular is comparably more developed in Itasuchus.
Little is known about the incisive foramen other than that it had straight edges and may have been contacted by the anterior of the maxillae, meaning that unlike the nares the incisive foramen was not entirely enclosed by the palatal shelves of the premaxillae. Pinheiro and colleagues note that the contact between the palatal shelves of the premaxillae and maxillae are marked by several striations at approximately the level of the third premaxillary tooth and a few nutrient foramina. The maxillary shelves are further noted to be flat (lacking a parasagittal torus) and form a wide secondary palate with several irregularly placed nutrient foramina close to the tooth sockets.
Dentition