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Rukwasuchus

Rukwasuchus is an extinct genus of notosuchian crocodyliforms known from the Late Cretaceous Galula Formation of southwestern Tanzania. Only a limited number of fossils are known, including parts of the skull and a few isolated teeth, however the preservation of the holotype meant that the endocast could be described in detail. Phylogenetic analysis generally recover Rukwasuchus as being a member of the clade Peirosauria, either within Peirosauridae as originally proposed or more recently as a basal member of the family Itasuchidae, the members of which are sometimes also placed within Peirosauridae as the subfamily Pepesuchinae. Rukwasuchus inhabitet what is now Tanzania during the Cenomanian to Campanian, at which point the region was covered by an extensive braided river system. While several purportedly closely related forms have been interpreted as semi-aquatic, some features of the brain of Rukwasuchus may indicate more terrestrial habits. The genus is monotypic, it contains only a single species, Rukwasuchus yajabalijekundu.

History and naming
Rukwasuchus is known from its holotype, RRBP 08630, a well-preserved rear part of the skull including the cranial table, braincase, and interorbital region lacking the rostrum, the front portion of the palate, both lacrimals, jugals, and quadratojugals, as well as the mandible. RRBP 08630 was collected during 2008 at Namba 2 locality (also known as RRBP 2007-02), together with the titanosaurian Rukwatitan bisepultus which is exclusive to this locality. Material referred to Rukwasuchus includes four isolated teeth, which came from the neighboring localities RRBP 2007-01 yielding the 3 teeth RRBP 07351, 07369, 09362, and RRBP 2009-01 yielding the tooth RRBP 09367. All specimens came from approximately 25 km south of Lake Rukwa in the Galula Study Area, Rukwa Rift Basin of southwestern Tanzania, belonging to the Namba Member of the Galula Formation, which though initially interpreted as being late Aptian to early Cenomanian The generic name refers to Lake Rukwa and the Rukwa Rift Basin, located in southwestern Tanzania, where the holotype of Rukwasuchus and other vertebrates were collected by the Rukwa Rift Basin Project, and suchus, Latinized from the Greek souchos, an Egyptian crocodile god. The specific name yajabalijekundu is derived from the Swahili language meaning "of/from the red outcrop", in reference to the Red Sandstone Group deposits exposed at the basin. ==Description==
Description
Rukwasuchus is only known from comparably limited material consisting of the skull table, orbital region and braincase but lacking most of the rostrum, dermatocranial material and preserving no postcrania. The skull of Rukwasuchus has been described as taller and narrower than that of Stolokrosuchus, an animal from the Cretaceous of Niger with an extremely elongated snout, and has further been noted as most closely resembling that of Hamadasuchus. and the wider posterior section located on the skull table. There the frontal forms part of the supratemporal fossae, raised suture laterally. The squamosal then form the posterior corner of the skull table, the dorsal surface divided into an anterior, posterior and medial process. The anterior process is the part of the squamosal that comes into contact with the postorbital along the dorsally medially, then anterolateral suture, however in truth the squamosal extends much further, underlying the postorbital and even reaching as far as the postorbital bar. Finally, the medial process is the smallest of the three and comes into contact with the parietal. The squamosal also forms a portion of the posterior wall of the supratemporal fossa. The parietal forms the posterior and central parts of the skull table, with the anterior and posterior ends wider than the narrow section sandwiched between the fenestrae. The supraoccipital is exclusively visible in posterior view as it is fully overlain by the parietal on the skull table, which furthermore forms a ventral deflection that gives this bone a pronounced U-shape. that are interprited as the exits for a number of nerves and the internal carotid artery. The basioccipital lies just below the otoccipitals as a subtriangular plate that when complete would form part of the occipital condyle and contributes to the basal tubera, both of which the otoccipitals also contribute to. The surface of the basioccipital is generally smooth but divided by a vertical crest and the outer edges form rugose tubera that overhang the parabasisphenoid ventrally and ventrolaterally. Aside from these tubera however the basioccipital underlies the parabasiphenoid, which sandwiches both the larger opening of the median Eustachian formane and the smaller slit-like lateral Eustachian foramina between the two bones. which ends in a moderately broad olfactory bulb. However the olfactory bulb differs in being very well developed and also more downturned compared to other crocodyliforms. while other crocodylomorphs the olfactory bulbs tend to be undivided. Another distinct feature of the endocast of Rukwasuchus noted in the 2014 description is a prominent indentation just behind the cerebrum The CT scans also shows the main dorsal part of the large The endocast of Rukwasuchus also bears a pair of protrusions referred to as the pericerebral spines, which are accompanied by lateral ridges and otherwise only known in Zulmasuchus and Campinasuchus among notosuchians. The underside of the endocast features a prominent hypophyseal fossa and a pair of cavernous dural venous sinuses, the latter of which are located behind the hemispheres of the cerebrum, the postpituitary notch and the well developed ventral longitudinal dural venous sinus on the hindbrain. The longitudinal sinus on top of the endocast is connected to the ventral cavernous sinus via the sphenoparietal dural venous sinus, which passes transversely just behind the cerebrum. Some regions, though not fully preserved, can be inferred in their location. For instance the prominent flocculus was likely located just before where the opistotics projects into the skull cavity, pinching the endocast, as is the common placement. Passing through the anterior edge of the flocculus was most likely the transverse dural venous sinus. The pituitary gland is described as rather small and the pituitary fossa, like in the not especially closely related baurusuchids, is directed almost ventrally. Size Nicholl and colleagues describe Rukwasuchus as being a medium-to large-bodied animal. ==Phylogeny==
Phylogeny
The phylogenetic analysis initiallyconducted by Sertich and O'Connor suggested that Rukwasuchus was closely related to either the more robust Hamadasuchus or the longirostrine Stolokrosuchus, with all three taxa recovered in a trichotemy. This groupings next closest relative in the analysis was found to be the problematic genus Trematochampsa, which essentially resulted in a clade of derived African peirosaurids in a clade otherwise known from South America. These results placing Rukwasuchus among oreinorostrine peirosaurids are contrasted with analysis that incorporate a greater number of longirostrine forms, which in said analysis generally form a monophyletic group either referred to as Itasuchidae or Pepesuchinae. The successive studies describing the itasuchids Epoidesuchus, Sissokosuchus and Ibirasuchus all recovered Rukwasuchus as an early member of this group, building on each others results and only significantly differing in nomenclature choices and the inclusion of new taxa. Featured below are the results of Ruiz et al. 2024 as well as Wilberg et al. 2025, the former using the name Pepesuchinae whereas the latter places these animals in the family Itasuchidae. In the former scenario, these animals are regarded as a subfamily of Peirosauridae and sister group to Peirosaurinae while in the latter case the grouping is elevated to family leven and considered to be the sister group to Peirosauridae. In both instances Rukwasuchus diverged after the Argentinian Kinesuchus and Stolokrosuchus from Niger, but before the majority of South American forms. ==Paleobiology==
Paleobiology
Barrios and colleagues have argued that the enlarged olfactory bulbs, which are associated with a keener sense of smell on land, support the idea that Rukwasuchus was a terrestrial animal, as was the ancestral condition. The team has however also highlighted that the length of the rostrum, which is unknown in Rukwasuchus, could favor somatosensation over the animal's sense of smell. The enlarged cerebellar flocculus maybe be associated with the animal performing more complex movements of the head and living a more active lifesetyle. Multiple other fossil animals have been named based on remains from these sediments, including the notosuchian Pakasuchus,, titanosaurs such as Rukwatitan These animals inhabited what has been interpreted as a long-lived, torrential braided river system with thin, discontinuous floodplains. Roberts and colleagues calculate that the channels of the Namba Member ranged between in depth and may have been several hundred meters wide, with the entire system's width possibly approaching kilometers. Paleocurrent analysis suggests that att the time of Rukwasuchus this river system would have flown into a north-western direction. While the underlying Mtuka Member appears to represent a seasonally dry, sub-arid environment, the Namba Member was deposited after a subtle shift in climate that changed environmental conditions to be wetter and sub-humid with paleosol matching an open forest environment. The conditions that the holotype of Shingopana was preserved under suggest that despite the wetter conditions the river system nonetheless experienced cycles or seasons of changing conditions, leading to river channels becoming abandoned and being filled in. == References ==
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