Razanandrongobe

Initial discovery , Madagascar|upright=1.25 All known remains of Razanandrongobe originate from strata belonging to the Sakaraha Formation in the badlands (locally called tanety) surrounding the town of Ambondromamy, Madagascar. In October 2001, Giovanni Pasini first verified the presence of fossil-bearing strata in this region. During an associated field survey of the locality, local collectors discovered two tooth-bearing skull fragments on the surface of the ground, which belonged to two different kinds of reptiles. These fragments were later acquired by Gilles Emringer and Francois Escuillié from Gannat, France, who intended to make them available for research. Based on the potential for further research, four temporary permits were obtained in the area for exploration from the Mining Cadastral Office of Madagascar. In April 2003, a joint team from the Milan Natural History Museum (MSNM) and Civic Museum of Fossils of Besano launched a privately funded expedition to the region. Pasini collected a number of teeth during this expedition. In June 2003, he gained access to one of the two skull fragments, a maxilla, and recognized that the teeth were identical. The MSNM acquired this specimen; it is now catalogued as MSNM V5770, while the teeth are catalogued as MSNM V5771-5777. The MHNT also acquired six skull fragments from Descouens, which are catalogued as MHNT.PAL.2012.6.3–8. The source locality of these specimens is unknown. Among these fragments, the larger ones are spongy with pieces of the surrounding rock (matrix) attached; the smaller ones are denser, whitish, and polished, suggesting prolonged exposure to air and sunlight. The MSNM acquired a further specimen, a tooth crown catalogued as MSNM V7144. This specimen had been collected by the Italian agronomist G. Cortenova, who gave the specimen to the amateur entomologist G. Colombo before his death. Colombo donated the specimen to the MSNM. All of these additional specimens were described in 2017 by Dal Sasso, Pasini, Maganuco, and Guillaume Fleury. ==Description==

, Barinasuchus, Sarcosuchus, the saltwater crocodile Crocodylus porosus, and Purussaurus'' Based on available remains, Razanandrongobe is the largest known Jurassic non-marine member of the Mesoeucrocodylia, and the largest member of the Notosuchia overall. In life, the length of its skull likely surpassed that of Barinasuchus, which has been estimated at long. Dal Sasso and colleagues inferred a body shape similar to the Baurusuchidae, producing an overall length of , a height at the hip of , and a weight of . Snout Razanandrongobe had a highly specialized skull, with a robust and rounded (U-shaped) snout that was taller than it was wide (oreinirostral), like Dakosaurus. At the front of the snout, the openings of the bony nostrils, the apertura nasi ossea, faced forward, and were fused at the midline. Smooth depressions known as the perinarial fossae extended down from the nostrils to the level of the teeth. The remainder of the premaxilla had a roughened surface, covered in crests, ridges, and pits. On the palate, two sub-circular depressions were situated near 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 did not close off the bottom edge of the premaxillae, leaving a large opening —- the incisive foramen —- which was about half as long as the premaxilla was wide. Like its premaxilla, the maxilla of Razanandrongobe was tall and robust. The surface of the palate, which was thickest below the eye sockets, was placed unusually high above the tooth row, at about halfway up the depth of the tooth sockets. At this position, it met the portion of the palate formed by the palatine bones, and bordered the openings known as the suborbital fenestrae. In this way, the palate of Razanandrongobe resembled those of the Ziphosuchia, including Araripesuchus. On the interior of the maxilla, there was a smooth groove, which may have corresponded to a pneumatic opening in the skull that is also seen in the modern Alligator. The inside of the tooth row on the premaxilla and maxilla bore a paradental shelf covered in ridges and furrows. Lower jaw The lower jaw of Razanandrongobe was also tall and robust. Uniquely, the tip of the lower jaw was devoid of teeth, for a section of the dentary 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 was a scar running along the rear 20% of the fused portion, representing the attachment of the splenial bone. The tip of the lower jaw would have been strengthened by being upturned at an angle of about 50°. Like the premaxilla, the outer surface of the dentary was 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 was a row of pits, which were enclosed by a groove towards the back of the jaw. The top margin of the bone was convex at the front, followed by a concave region behind it. 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 were sub-circular, although the inner half of the sockets in the maxilla and the front of the dentary were rectangular. All of them were wider than they were long, and were nearly vertical. Larger sockets were separated by narrower distances than smaller teeth, with the separating surfaces being 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 were also thick, non-constricted, and slightly recurved (pachydont). Several types of teeth are present, making Razanandrongobe heterodont: the teeth at the front of the jaw were U-shaped (or salinon-shaped) in cross-section, while those on the sides were incisiform (incisor-like) and sub-oval in cross-section, with the smallest teeth at the rear being globe-shaped. The smallest teeth were globe-shaped. None of the teeth were particularly hypertrophied like the canine teeth of mammals (i.e., caniniform), but the first three dentary teeth were larger than the rest. ==Classification==

Archosaurian affinities In 2006, Maganuco and colleagues identified Razanandrongobe as a member of the Archosauriformes by its serrated teeth and the thecodont condition of its teeth (i.e. their deep implantation in tooth sockets). Both characteristics are widespread among archosauriforms, and Maganuco and colleagues suggested that the former is a synapomorphy (shared specialization) of the group. They also noted that Razanandrongobe possessed unfused interdental plates covering the inner (lingual) surface of its teeth; they are absent in the non-archosauriform archosauromorphs, present but unfused in several lineages among the Archosauriformes, and fused in some theropod dinosaurs. Maganuco and colleagues suggested that unfused interdental plates are either a synapomorphy of Archosauriformes, or a plesiomorphic (ancestrally present) characteristic of crocodyliforms, theropods, and poposaurids. Considering these characteristics, Maganuco and colleagues placed Razanandrongobe in the Archosauria, but not as part of any basal (early-diverging) lineages due to its heterodont teeth and tall maxilla. While it resembles the Prestosuchidae in the depth and shape of its maxilla, heterodont teeth, paradental shelves, and large size, Maganuco and colleagues considered these traits to have been convergently acquired. Within the Archosauria, they identified two possible positions for Razanandrongobe: Crocodylomorpha and Theropoda, the only lineages of large predatory archosaurs to have survived past the Triassic. However, the original material of Razanandrongobe, consisting of a maxilla and teeth, was too fragmentary to be included in a phylogenetic analysis of archosauriforms, since it lacks nearly all characteristics used in such analyses. found that Razanandrongobe was a member of the Ziphosuchia, closely related to Sebecosuchia. The former relation was supported by the lack of constricted tooth crowns and the contact between the dentary and splenial, while the latter was supported by the deep dentary, the similarly sized and symmetrical serrations, the concavity of the dentary, and a dip in the dentary below the level of the tooth sockets at the middle of the tooth row. Their resulting phylogenetic tree (the majority-rule consensus tree) is partially reproduced below. Evolutionary context Little is known about the origins and early evolution of notosuchians, but the fact that they are the brother group of the Neosuchia (which contains all living crocodilians) in the Mesoeucrocodylia implies that they must have first appeared during the Jurassic. Prior to the recognition of Razanandrongobe as a notosuchian, the oldest-known notosuchians were the Aptian-aged (Cretaceous) Anatosuchus, Candidodon, Malawisuchus, and Uruguaysuchus, leaving a ghost lineage of 74 million years between the group's presumed origin and its oldest members. The phylogenetic position of Razanandrongobe in the Notosuchia makes it the oldest-known representative of the group. Razanandrongobe predates all of these notosuchians by 42 million years, partially filling the ghost lineage. Its retention of plesiomorphic characteristics is consistent with its status as an early notosuchian; however, for this reason, Dal Sasso and colleagues noted that its close relation to Sebecosuchia — a much younger lineage, being known from the Santonian forward — must be treated as provisional. Dal Sasso and colleagues supported the notion that notosuchians primarily lived on the continent of Gondwana through their evolutionary history (although the remaining ghost lineage prior to Razanandrongobe precludes inferences about their origins). ==Palaeobiology==

In 2006, Maganuco and colleagues analyzed wear patterns on the surface of Razanandrongobes teeth. For the teeth at the sides of the jaw, most of the wear is present on the outer (lingual) surface of the teeth, on which a U-shaped chip is present on the top third of the crown. There is also a thinner chip on the front (mesial) edge of the tooth, flattening some of the serrations. By contrast, for the teeth at the front of the jaw, the wear is more present on the inner (labial) surface. They inferred that these wear surfaces more strongly resemble those resulting from tooth-food contact than from tooth-tooth contact, with the enamel having flaked off as the animal bit into bones or other hard objects, of Razanandrongobe feeding on bones|left Skull anatomy also supports a diet for Razanandrongobe that included hard tissues like bones and tendons. Like tyrannosaurids, the serrations on the teeth of Razanandrongobe were adapted to biting into bone in terms of their size, shape, and also the presence of a rounded depression at the base between neighbouring serrations. In tyrannosaurids, the latter was inferred to have distributed force over the serrations and prevented cracks from spreading, or possibly to have gripped meat fibres. The incisiform teeth of Razanandrongobe also resembles the bone-scraping teeth on the premaxillae of tyrannosaurids, and the teeth at the sides of the jaw were similarly reinforced through thickening (though to an even greater extent). The rest of the skull would have been strengthened by the expansion of the paradental shelves to form a "secondary palate", which would have greatly increased resistance to vertical bending and torsion, while the fused interdental plates would have protected the teeth from transverse forces. In 2017, Dal Sasso and colleagues suggested that these feeding adaptations — along with a large skull and body size — made Razanandrongobe a highly specialized terrestrial predator. They inferred that it could have competed with and occupied the ecological niches of theropods in the local ecosystem. ==Palaeoecology==

''; the body is speculatively restored|upright=1.25 The strata from which Razanandrongobe fossils were recovered has been referred to as the "Facies Continental" or "Bathonien Facies Mixte Dinosauriens" (Bathonian mixed dinosaurian facies) of the Sakaraha Formation (or the Isalo IIIb Formation) in the Isalo Group. This geological formation consists of cross-bedded layers of sandstone and siltstone with "calcareous paves" and multi-coloured claystone banks. The sandstone surrounding the holotype of Razanandrongobe is fine-grained ( in diameter) and is mainly composed of quartz, with rarer grains of ilmenite, garnet, and zircon. The depositional environment has been inferred to be fluvial (river-based) or lacustrine (lake-based). Teeth of pterosaurs were also found at the locality. Animals from other localities include the sauropods Lapparentosaurus and "Bothriospondylus" madagascariensis, and another sauropod based on teeth; theropods of the groups Abelisauridae, basal Ceratosauria, Coelurosauria, and possibly Tetanurae, along with tracks of the ichnogenus Kayentapus; thalattosuchian crocodyliforms; a mammal belonging to the Tribosphenida; plesiosaurs; and possibly ichthyosaurs. Silicified wood is also present in the strata. ==References==