Adamantinasuchus is an extinct genus of notosuchian crocodylomorph from and named after the Late Cretaceous Adamantina Formation of Brazil. It is known from only one fossil, holotype UFRJ-DG 107-R, collected by William Nava (hence the specific name navae). The fossil consists of a partial skull, fragmentary limb bones and a few broken vertebrae, and was found 25 km SW of the town of Marilia, near a reservoir dam. Adamantinasuchus was approximately 60 cm long from nose to tail, and would have only weighed a few kilograms.
Features
Skull
Adamantinasuchus's skull is quite well preserved; most of the right anterior part is present, along with some of the right posterior part, but the cranium is crushed and the left side of the skull is altogether missing. The right lower jaw is also preserved, along with many of the teeth. The skull is small, only 60 mm long and around 30 mm high, but the elliptical orbits are very large, almost as long as the rostrum, which might suggest the animal was nocturnal.
Premaxilla and maxilla
The premaxilla is covered in grooves and ridges, making it the most ornamented bone from the entire fossil. At the anterior end the premaxillae come together in a short triangular projection pointing ventrally and in another pointing dorsally. These would have been connected by a cartilaginous septum separating the two external nares, although this has not been preserved. The premaxilla bears two incisiform teeth and one caniniform tooth; this has led some to place it in the sphagesaurid group of crocodyliforms, since these also had differentiated teeth, although as the cladogram below suggests this is disputed. The maxillary dentition appears to bear out this theory as it bears seven molariform teeth of varying sizes. The maxilla itself is mostly triangular, with a long anteroposterior base at the ventral side of which is a thin crest that covers the border of the dental alveoli. Towards the posterior end the maxilla is elongated, and it forms a long suture with the jugal beneath the large orbits. There are two large foramina at the posterior end of the maxilla, and three small foramina at the anterior end, close to the premaxillary-maxillary border where another foramen is located.
Nasal, prefrontal, frontal and lacrimal
The nasal bone is very incompletely preserved; what there is curves around ventrally, and is slightly sculptured towards the anterior end. The nasal projects back far enough to contact the frontal bone with a thin, short blade. The prefrontal is triangular, and both left and right prefrontals are preserved, although the left prefrontal is only fragmentary. The prefrontal and frontal bones form a sinuous suture, although not a fully interdigitating one. The prefrontal's outer surface is very smooth, possibly due to contact with a palpebral bone (not preserved). The lacrimal bone is very small and has no distinguishing features, but contacts all of the nasal, prefrontal and frontal bones. The frontal is weakly convex in the middle and the anterior, but the posterior area of it is very flattened. Although the parietal bone is not preserved, the interdigitating suture between parietal and frontal is still present, as is the crest across the bone here in the medial part.
Postorbital, jugal and quadratojugal
The postorbital is fragmentary; from what is there, it is evident that it was squarish and posterolateral to the frontal bone rather than curving downwards. The jugal is thin, with a triangular transversal section and three branches. Its outer surface is smooth and there is a large foramen in the anterior section of the bone, close to the very thin crest in the medial portion that comes to a slender edge. The jugal is arched medially, curving out laterally away from the orbit, and is widest just behind the long suture with the maxilla, tapering to a bladelike portion at the posterior end. The postorbital bar is almost vertical, with an oval cross-section. The quadratojugal is just behind the laterotemporal fenestra, and is slender and branched.