Razanandrongobe

Snout bones

Reconstruction of the snout, viewed from the front; bony nostrils marked as ano

Razanandrongobe has a highly specialized skull, with a robust and rounded (U-shaped) snout that is taller than it is wide (oreinirostral), like Dakosaurus. At the front of the snout, the openings of the bony nostrils - the apertura nasi ossea - face forward, and are fused at the midline. Smooth fossae known as the perinarial fossae extend down from the nostrils to the level of the teeth. The remainder of the premaxilla has a roughened surface, covered in crests, ridges, and pits. On the palate, two sub-circular depressions are visible at the front of the snout, where the first pair of teeth from the lower jaw would have been located when the mouth was closed. The palatal portion of the maxilla does not close off the bottom edge of the premaxillae, leaving a large opening - an incisive foramen - which is about half as long as the premaxilla is wide. On the inside of the tooth row, there is a paradental shelf covered in ridges and furrows.^[2]

The maxilla is similarly tall and robust to the premaxilla, and the paradental shelf continues onto it. The surface of the palate is placed unusually high above the tooth row, at about halfway up the depth of the tooth sockets. Below the eye sockets, the maxillary palate is thickest. At this position, it meets the portion of the palate formed by the palatine bones, and borders the openings known as the suborbital fenestrae. In this way, the palate of Razanandrongobe is similar to the Ziphosuchia, including Araripesuchus. On the interior of the maxilla, there is a smooth groove, which may correspond to a pneumatic opening in the skull that is also seen in Alligator.^[2]

Lower jaw

Like the snout, the lower jaw is also tall and robust. Uniquely, the tip of the lower jaw that is devoid of teeth, for a section of the dentary bone corresponding to the diameter of more than one tooth. The front of the jaw would have been fused; on the inside of the bone, there is a scar running along the rear 20% of the fused portion, representing the attachment of the splenial bone. Like the premaxilla, the outer surface of the dentary is textured, bearing a dense network of zigzagging canals for blood vessels (i.e., vascular canals). On the interior surface, immediately adjacent to the tooth row, there is a row of pits, which become enclosed in a groove towards the back of the jaw. The top margin of the bone is convex at the front, then transitions into a concave region.^[2]

Teeth

Razanandrongobe had five teeth in each premaxilla, at least ten in each maxilla, and eight in each half of the dentary. Most of the tooth sockets are sub-circular, although the inner half of the sockets in the maxilla and the front of the dentary are rectangular. All of them are wider than they are long, and are nearly vertical. Larger sockets are separated by narrower distances than smaller teeth, and the separating surfaces are ornamented like the paradental shelves. The teeth themselves are unusual; they bear large serrations on both the front and rear edges, which are proportionally even larger than those of dinosaurs such as Tyrannosaurus. They are also thick, non-constricted, and slightly recurved (pachydont), and are sub-oval to U-shaped (or salinon-shaped) in cross section. The smallest teeth are globe-shaped. None of the teeth are particularly hypertrophied like the canine teeth of mammals (i.e., caniniform), but the first three dentary teeth are larger than the rest.^[2]