Razanandrongobe (meaning "ancestor [of the] large lizard" in Malagasy) is a genus of carnivorous ziphosuchian crocodyliform from the Middle Jurassic of Madagascar. It contains the type and only species Razanandrongobe sakalavae, named in 2004 by Simone Maganuco and colleagues based on isolated bones found in 2003. The remains, which included a fragment of maxilla and teeth, originated from the Bathonian-aged Sakaraha Formation of Mahajanga, Madagascar. While they clearly belonged to a member of the Archosauria, Maganuco and colleagues refrained from assigning the genus to a specific group because the fragmentary remains resembled lineages among both the theropod dinosaurs and crocodylomorphs.
Further remains (including a premaxilla and lower jawbone) had been discovered as early as 1972, but were not described until 2017 by Cristiano Dal Sasso and colleagues. These remains allowed them to confidently assign Razanandrongobe as the oldest-known member of the Notosuchia, a group of crocodylomorphs, which partially filled a gap of 74 million years in the group's evolutionary history. Razanandrongobe shows a number of adaptations to a diet containing bones and tendons, including teeth with large serrations and bony structures reinforcing its palate and teeth. Measuring long, it was the largest member of the Notosuchia and may have occupied a predatory ecological niche similar to theropods.
Discovery and naming Initial discovery
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.
Simone Maganuco, Cristiano Dal Sasso, and Pasini described these specimens in 2006 as representing a new genus and species, Razanandrongobe sakalavae, with MSNM V5770 as the holotype. The genus name is a composite of the Malagasy words "razana-" (ancestor), "androngo-" (lizard), and "-be" (large), collectively meaning "ancestor of the large lizard". The species name is Latin for "of Sakalava", referring to the ethnic group which inhabits the region.
Additional specimens
Between 1972 and 1974, the assistant director of technical services of the Sugar Company of Mahavavy had previously collected a dentary (lower jawbone) and a premaxilla from the area where the holotype of Razanandrongobe was discovered. Under the authorization of the Mines and Energy Directorate of Madagascar, these specimens were exported and stored in the collection of D. Descouens. After they were prepared, these fossils were discovered to pertain to Razanandrongobe; based on the fact that they fit together perfectly, they were further inferred to belong to the same individual. In April 2012, these specimens were acquired by Museum of Natural History of Toulouse (MHNT), where they are respectively catalogued as MHNT.PAL.2012.6.1 and MHNT.PAL.2012.6.2.
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
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.
Among crocodylomorphs, Maganuco and colleagues demonstrated that Razanandrongobe had characteristics intermediate between the basal evolutionary grade "Sphenosuchia" (which is not a proper clade) and the derived Mesoeucrocodylia: the maxilla would have bordered both the internal choanae (nostril openings, like "sphenosuchians") and the suborbital fenestrae (like mesoeucrocodylians); the antorbital fenestrae would have had a narrower front margin and were retracted further back on the skull than "sphenosuchians"; and the paradental shelf was more developed than "sphenosuchians". Its vertical tooth sockets resembled "sphenosuchians", baurusuchians, sebecosuchians, and peirosaurids, while the positioning of the palatal depressions and the globe-shaped teeth particularly resembled peirosaurids (though these teeth bear "necks" in peirosaurids). However, the height of the paradental shelf, the large tooth serrations, the width of the teeth from the side of the jaw, and the relatively flat interdental plates were found to be unusual for crocodylomorphs.