Extinct genus of reptiles
Dentaneosuchus is a genus of large bodied sebecid crocodylomorph from the Middle Eocene of Issel and Réalmont (France). Originally described as "Atacisaurus crassiproratus", the discovery of additional remains led to it being placed in a separate genus in 2023. It was tentatively recovered as the basalmost member of the family Sebecidae. Because of this "Dentaneosuchus" could play an important part in deciphering the origins and dispersal of European sebecids, as their presence on the continent, far away from their primary range in South America, is still not entirely resolved. It reached a similar size to the enormous "Barinasuchus", making it not only one of the biggest sebecids but also the biggest terrestrial carnivore of Cenozoic Europe. "Dentaneosuchus" would have been an apex predator of its environment, capable of taking large prey such as "Lophiodon". However, for as of yet unknown reasons crocodylomorphs would lose their spot as top predator in this part of the world by the end of the Eocene, with "Dentaneosuchus" representing one of the last members of its group in Europe.
History and naming.
The first fossil of "Dentaneosuchus", a mandibular symphysis catalogued as specimen MHNT.PAL.2006.0.53., was discovered in the Sables du Castrais Formation near Issel in southern France and assigned to the genus "Atacisaurus" by Gaston Astre in 1931, creating the name "Atacisaurus crassiproratus". When describing "Iberosuchus" in 1975, Miguel Telles Antunes considered the possibility that the Issel remains may have belonged to the same animal, tentatively referring the symphysis to his new genus, and Ortega "et al." (1996) agreed with this placement.
In 2018 Godinot and colleagues went as far as to fully place the specimen in "Iberosuchus" while retaining the species name, creating the new combination "Iberosuchus crassiproratus". However, the referral of various European sebecid specimens to "Iberosuchus" was at times done under less than ideal conditions, as much of the material didn't overlap and the assignment was in large parts based on very few characters not exclusive to the genus. Excavations in France meanwhile continued to yield sebecid material, including specimens discovered in 1997 near Réalmont. It is possible that this specimen was a once nearly complete skull, however, it was damaged during the dig, with much associated material being gathered from the surrounding debris. Despite this a lot of material could be gathered regardless, which remain in the collection of the Muséum de Toulouse until the fossils were studied by Martin and colleagues.
Martin "et al." compared the Réalmont material with both "Iberosuchus" and the Issel symphysis, determining that there were no differences between the mandibular remains from the two localities yet clear deviations from "Iberosuchus macrodon". As the Issel material had been validly described and diagnosed in 1931, the species name could be retained, however the matter of the genus name was more complicated. When naming "Atacisaurus", Astre declared "A. glarea" the type species, but in the following years the holotype had been lost and available figures failed to show any diagnostic traits. Material previously assigned to "Atacisaurus glarea" meanwhile was initially considered to serve as a lectotype, but lacked shared features with the lost material and was instead found to have belonged to a gavialoid then named "Kentisuchus astrei". This rendered "Atacisaurus" a nomen dubium, leading Martin and colleagues to coin a new genus name for "A. crassiproratus", "Dentaneosuchus".
The name "Dentaneosuchus" derives from the Latin "dentaneo", which roughly translates to "showing teeth" or "frightfull" in allusion to its hypothesized role as apex predator, and the Greek "souchos" meaning crocodile, derived from the name of the Egyption deity Sobek.
Description.
Skull.
The skull of "Dentaneosuchus" was altirostral, meaning that unlike in modern crocodilians, it was higher than it was wide. This is clearly shown by the preserved premaxilla. The nares are preserved in the form of two narial openings separated by processes of the premaxilla and nasal bone that meet in the middle. They, like the skull, are higher than wide and face forward. The premaxilla contains five teeth on either side, with the bone bulging around the roots of tooth. The first premaxillary tooth, located close to the midline, is the smallest and the teeth get progressively larger until reaching their maximum size at the fourth tooth, which is twice the size of the second. The fifth is smaller again, about as large as the third tooth. The premaxillary teeth are followed by a pronounced notch, which likely received an enlarged dentary tooth. Very little of the maxilla is preserved, but it still reveals important information on the skull of "Dentaneosuchus". The maxilla appears to be fused to the nasal bone, obscuring the suture between the two. Furthermore, the way the two elements connect shows that the rostrum of "Dentaneosuchus" would have been trapezoid in cross section, meaning it was broader around the toothrow and narrowed towards the top. More is known of the nasal, which is preserved in two large chunks. The first is connected to the maxillary fragment, while the more posterior piece is still connected to the skull table. The nasal duct was separated by a septum and the surface of the nasal bone shows no suture, indicating that rather than being paired, the nasal bones were fused into a single elongated element. The nasal was long, stretching from the front of the rostrum where it contacts the premaxilla and likely contributed to the bony wall separating the nares to the frontal bone. As the bone tapers towards the front of the skull, it takes on a wand-like appearance. The prefrontals are plate-like bones situated atop the head and overhanging the eye sockets. The lacrimal bones are only poorly preserved, but face more to the sides than the prefrontals. The various bones of the skull table (frontal, parietal, supraoccipital and exoccipital) are all fused into a single mass. In "Dentaneosuchus" the space between the orbits and the supratemporal fenestrae is preserved. Only a small piece of the quadratojugal is preserved.
The mandibular symphysis is formed by the fusion of both dentaries and a part of the splenial, encompassing the first seven teeth of the lower jaw and being overall spoon-shaped. A total of at least 19 teeth is thought to have been present in the mandible of "Dentaneosuchus". The teeth of the lower jaw initially form a semicircle at the tip of the lower jaw extending from the first dentary tooth to the fourth, after which there is a slightly larger space before the fifth tooth. However this small break is not to be confused with a true gap in the dentition (diastema) as seen in some other crocodylomorphs. From the fifth onward, the teeth are organized in a single, straight row of closely spaced alveoli. The overall shape of the toothrow creates two distinct waves, with the top of the first wave being crowned by the fifth dentary tooth. The largest tooth of the lower jaw is however the fourth, as typically the case, and the teeth behind it gradually decrease in size. It is uncertain how that continues onto the second wave, as it is too poorly preserved to determine. Both the angular and surangular bone contribute to the mandibular fenestra and form the back of the lower jaw. The fenestra itself is noted for its strange, boomerang-like shape.
Although the teeth of "Dentaneosuchus" are generally robust thanks to the nearly circular tooth roots, they are still truly ziphodont, with slight compression and carinae covered in fine serrations.
Postcrania.
Although the skull material makes up the majority of known "Dentaneosuchus" remains, a variety of postcranial fossils have also been collected. This includes a nearly complete humerus, which is a robust bone with a well-defined deltopectoral crest. The ischium is incomplete, with one articular process missing and the other being highly eroded. However, the preserved elements show that the anatomy is unique and the anterior articular process in particular is covered in a complex system of muscle insertions and tendon passages. This region is notably better developed in "Dentaneosuchus" compared to what is seen in modern crocodiles, but Martin and colleagues hesitate to draw any specific conclusions in regards to the musculature from this. Only a single vertebra is known and primarily composed of the centrum, with much of the neural spine missing. The vertebra is amphicoelous and equally wide, long and high.
Four osteoderms have been discovered, but as no sebecid preserves articulated armor it is not certain where on the body they would have been located. Martin and colleagues describe two types of osteoderms, both of which are tipped with a pronounced central crest and show highly indented outlines. The larger type is sub-trapezoid, while the smaller osteoderm variety is ovoid and longer than wide. Both bear some resemblance to those of "Baurusuchus", but are sufficiently distinct. Prior studies on the osteoderms of various Notosuchians have indicated that these bones were much more deeply nested in the skin than they are in modern crocodiles and possibly covered in a thick, leathery layer similar to what is observed in softshell turtles.
Size.
As the skulls of most sebecid genera do not exceed in total length ("Langstonia" barely surpasses this size at ), it can be said that "Dentaneosuchus" is among the largest known sebecids. The lower jaw of this genus measures up to (not accounting for the retroarticular process), which puts it in a similar size range as the giant "Barinasuchus" from the Miocene of South America. In fact, with a preserved mandibular length of and an estimated total mandibular length of close to , "Barinasuchus" may be only slightly larger than "Dentaneosuchus". "Dentaneosuchus" could have even exceeded "Barinasuchus" in skull length considering that the type specimen from Issel is slightly larger than the more complete material from Réalmont.
This does however leave the issue of determining body size from skull length. This is rendered especially difficult by the lack of fully preserved postcranial skeletons for members of this group, which means that body size is generally estimated based on the proportions of other terrestrial Notosuchians, leading to vastly different results. Using the proportions of the incomplete peirosaurid "Uberabasuchus" for example would give "Dentaneosuchus" a body five to six times longer than its skull. Using the baurusuchid "Stratiotosuchus", Molnar and de Vasconcellos calculated that the body length of "Barinasuchus" could range anywhere from to a gigantic . Martin and colleagues suggest a much more conservative body length with a proportionally bigger head, estimating the total body length of the two at between . Regardless of the specifics, this renders "Dentaneosuchus" the largest terrestrial predator of Cenozoic Europe.
Phylogeny.
Phylogenetic analysis conducted on the material of "Dentaneosuchus" places it in the family Sebecidae, which was recovered as closely related to the South American Baurusuchidae with which it forms Sebecosuchia. Several features of "Dentaneosuchus" allow it to be easily distinguished from other groups of ziphodont Notosuchians. The fused nasals and splenials, shape of the supratemporal fenestrae and presence of a large notch between the premaxilla and maxilla are among several cranial features that clearly set it apart from members of the Peirosauridae. From baurusuchids it differs mostly in the anatomy of the lower jaw, including the longer toothrow and position of the dentary-surangular suture relative to the mandibular fenestra. Many of the traits do however line up with sebecids, explaining its placement. Within Sebecidae, "Dentaneosuchus" was recovered as having affinities with the German "Bergisuchus". While Martin and colleagues raise the possibility that some of the difference between the two could change with age, they conclude that it would be premature to make any conclusive statements on what this may imply. Furthermore, the authors also point out that there are still many unknowns regarding the anatomy of "Dentaneosuchus" that would greatly impact its phylogenetic placement and how future discoveries could change its position drastically.
Age.
The precise age of "Dentaneosuchus" and European sebecids in general is subject to change as the various Paleogene localities of Europe are studied more closely and more information important for the stratigraphy is found. "Iberosuchus" stems from strata previously thought to have been deposited prior to the Bartonian, with a mammalian tooth from the locality suggesting an age between the middle Lutetian and Bartonian, while the layers directly overlying the "Iberosuchus" horizon have been dated to the Bartonian itself based on the presence of "Anchilophus". The pre-Bartonian age was later corroborated by Badiola &amp; Cuesta (2008), who place it firmly within the MP13-14 biozones (Lutetian), a similar