Eremosuchus is an extinct genus of sebecosuchian notosuchian from the Early Eocene El Kohol Formation of Algeria. It was first described on the basis of isolated cranial and postcranial material in 1989, although much of the original collection has since been lost. Like other sebecids it had serrated, blade-like teeth, a condition referred to as ziphodonty. Phylogenetic analysis conducted using Eremosuchus material yield inconclusive results, but overall support a close relationship with the terrestrial members of Sebecidae best known from the Cenozoic of South America, although also well established in Paleogene Europe. It is possible that the lineage leading to Eremosuchus split off as sebecids dispersed between South America and Europe or that its ancestors arrived in North Africa from Europe after crossing the Tethys sea. It is currently the only named sebecid from Africa.
History and naming The first fossil remains of Eremosuchus were discovered by the combined efforts of the Université d'Oran, Sorbonne Universités and Université de Montpellier in 1982 at the El Kohol site in northern Algeria, specifically in the strata of the El Kohol Formation. The 1982 expedition to El Kohol yielded a variety of fossil remains including an isolated dentary bone as well as further mandible remains, some vertebrae, a fibula and even several teeth and osteoderms. After having initially been reported on that same year by Eric Buffetaut, the material was given a more thorough description in 1989, with the dentary (UO-KB-301) serving as the holotype of the new genus Eremosuchus. Much of the other material found at El Kohol was referred to Eremosuchus in the same study, barring the osteoderms, which were not explicitly assigned to the genus.
In 2025 Cecily S. C. Nicholl and colleagues published an in-depth redescription of Eremosuchus based on both the material initially assigned to the genus by Buffetaut as well as previously undescribed fossils from the type locality, including the lower jaw of a juvenile individual. However, by this point most of the original remains had been lost, sans the holotype itself and a single vertebral centrum, with the missing remains only redescribed based on prior writings and illustrations. Ultimately Nicholl and colleagues suggest that only the holotype dentary and the juvenile remains they described can be confidently assigned to Eremosuchus, with the referral of the other material remaining tentative.
Description
The dentary of Eremosuchus is a slender bone significantly narrower than it is high and measures a total of in the presumably adult holotype specimen. Based on the preserved right dentary the two halves of the lower jaw would have diverged at an angle of about 10 - 15°, though this angle appears to have been greater in younger individuals. The mandibular symphysis was likely narrow and U-shaped based on the curvature of the outer surface of the anterior dentary bone. The symphysis was clearly elongated and extended to at least the fifth dentary tooth in the holotype, though the splenial's contribution to this part of the lower jaw is unclear, obscuring the exact length to width ratio. Ventrally the dentary on dentary suture extends a little further, being estimated to terminate at a level between the sixth and seventh alveoli in the holotype. In the smaller referred specimen the suture is slightly longer, reaching the sixth to seventh tooth dorsally and the seventh ventrally. The height of the dentary initially increases from the tip of the lower jaw to the enlarged fourth dentary tooth, where the bone reaches its maximum height of at least . Behind the fourth dentary tooth the dentary's dorsal surface is slightly concave, but remains constant in its height rather than growing taller or shallower. This form closely resembles other sebecids and baurusuchids and distinguishes Eremosuchus from peirosaurians, in which the dorsal margin of the dentary forms two distinct waves.
The mandibular ramus is mostly straight, but does curve somewhat medially towards the back of the dentary. It is furthermore almost vertical across the top 2/3rds of its height following the sixth dentary tooth. However, towards the ventral surface the ramus forms a prominent expansion that essentially forms a broad ridge that runs along the length of the posterior dentary. Similar but far less pronounced ridges are seen in a handful of other sebecids including Sebecus itself and a more dorsally positioned structure can be seen in Dentaneosuchus. The vertical dentary wall just above the ridge likely served to receive the teeth of the rostrum when the jaws were closed. In addition to this Eremosuchus preserves a notch adjacent to the seventh dentary tooth likely serving as a reception pit for one of the teeth in the upper jaw as is the case in most other sebecids.
The surface of the dentary is marked by varying types of ornamentation. The middle and posterior portions are covered by shallow, short and narrow grooves that run length-wise across the bone while the front of the dentary instead bears pits up to wide. Smaller and less developed pits are also seen immediately beneath the toothrow throughout the lower jaw.
Additional material tentatively assigned to Eremosuchus also preserves the more posterior parts of the mandible, specifically the back of the surangular, angular and the entire articular bone. The surangular is described as being expanded towards the top, thinning towards its ventral contact with the angular. It participates both in the glenoid facet and in the retroarticular process where it makes up about two thirds of the structures width. This extensive contribution to the glenoid facet is also seen in sebecids and peirosaurians while baurusuchids only have limited surangular participation in the glenoid facet. The surangulars participation in the retroarticular process is dorsally heavily excavated, medially steeply inclined and laterally forms a shelf. The surangulars portion of the retroarticular process is divided from the articular's participation by a ridge that runs more or less anteroposteriorly to the length of the mandible with only slight outward deflection towards the back, which makes it most similar to the likes of Sebecus and Lorosuchus and sets it apart from the strongly deflecting ridge seen in various baurusuchids. Looking at the retroarticular process from the side shows that the ridge is concave and asymmetrical, with its front end higher up than the back end. The lateral flange is described as so strongly inclined that it essentially faces completely towards the side of the jaw, with only the lowermost portion breaking away from this by forming a small protruding shelf. Towards the posterior end of the process the flange is furthermore described as upturned, while the adjacent medial flange deflects posteromedially, putting them essentially perpendicular to each other. The medial flange bears a small bulge possibly associated with the foramen aerum. The retroarticular process is separated from the glenoid facet, which would articulate with the quadrate condyle, by a protruding ridge that stretches mediolaterally across this portion of the lower jaw. The glenoid facet is wider-than-long with the width being approximately the same as the length of the lateral facet of the retroarticular process. While this is similar to what is seen in most sebecids and peirosaurians, it's noticeably different from baurusuchids where the lateral flange is shorter than the glenoid facet is wide.
Dentition
The dentary of Eremosuchus preserves a total of 12 alveoli, which likely represent the entirety of the mandibular tooth row. This number is probably comparable to Bergisuchus and lower than that of some other sebecids, but nonetheless higher than what is seen in most other notosuchians. The toothrow stretches far back along the dentary as in various other sebecids, helping to set it apart from baurusuchids in which the toothrow often occupies only half the length or even less of the entire dentary bone's length. The individual alveoli are not positioned in a straight line but instead distinctly sigmoidal in their placement, with those in the front of the lower jaw following an outward curve while the toothrow is concave behind the fourth dentary tooth. The anterior teeth are further set apart from those further back in the jaw by their orientation, being procumbent thanks to the more anterior orientation of the alveoli. Each alveolus is separated from its neighbors by a thin septum. This does not apply to the presumed juvenile referred specimen, in which there is no septa to separate the sixth and seventh alveoli, which are instead placed in a single continuous groove. While such septa characterize a number of other sebecosuchians including Dentaneosuchus and Doratodon they are not a universal feature as some taxa like Sebecus and Baurusuchus have more broadly separated teeth with accordingly broader septa. The seventh alveolus in the referred specimen is then immediately followed by a diastema that is not present in the holotype.
Eremosuchus can be recognized by the first and fourth dentary alveoli being very similar in size, with the fourth still the largest in the lower jaw but only by a slight margin. Based on the better preserved teeth of the referred specimen, the anterior-most tooth was recurved with a much more circular in crosssection and a pointed apex. The fourth tooth was comparably more compressed but nonetheless retained a classic caniniform morphology and possessed thinning distal and medial edges. The alveoli following the fourth caniniform tooth on the other hand are fairly uniform in size, their diameter only ranging between . The posterior alveoli are not only smaller but also much more labiolingually compressed, meaning the corresponding teeth were narrower than those in the front of the jaw. Preserved teeth of Eremosuchus confirm this assumption, with the tenth tooth of the holotype dentary being noticeably compressed. The sixth tooth is lanceolate in shape with its apex mildly rounded while even more posterior teeth are similar but more triangular with straighter edges. The cutting edges or carinae of these teeth bear symmetrical denticles, giving the teeth a pronounced serration that together with the labiolingual compression qualifies them as ziphodont.
The enamel of the teeth found still in situ in the jaw bones is described as smooth towards the base of the crown but more wrinkled towards the apex with no signs of a wear facet or apicobasal ridges. However, Nicholl and colleagues also describe a number of isolated teeth from the same locality as the holotype that resemble the teeth of Eremosuchus in every facet other than the fact that they preserve apicobasal ridges running along the crown of the tooth, being especially prominent around the apex and weaker towards the base. Some teeth furthermore transition from apicobasal ridges towards a globular texture. However Nicholl and colleagues highlight that the specific ornamentation of the tooth enamel can vary among species and even individuals, with Eremosuchus possibly being an example of this.
Limbs