Rimasuchus

Rimasuchus is an extinct genus of crocodile from the Neogene period of Africa and the Middle East. Its name comes from the Latin words rima, meaning "crack" (referencing the East African rift valley where it was discovered) and suchus, which means "crocodile".[1] Rimasuchus is a member of the subfamily Crocodylinae, which includes over 20 species, eight of which are extinct. The type and only species, Rimasuchus lloydi, lived alongside other crocodiles such as the Nile crocodile.[2] It preyed on large mammals, including early humans.

Description
Rimasuchus grew to 7 meters or more in length. Unlike most living crocodiles, it is brevirostrine, or broad-snouted. Rimasuchus has characteristically short and broad premaxillae, as well as a deep mandibular symphysis connecting the two sides of the upper jaw. The premaxillae do not project as far back on the upper surface of the skull as those of other crocodiles and are noticeably wider than they are long on the palate (unlike those of Crocodylus niloticus and Crocodylus cataphractus). The external nares are positioned close to the tip of the snout. Like other crocodiles, Rimasuchus has an occlusal groove, or notch, between the premaxilla and maxilla that receives the fourth mandibular tooth. However, in Rimasuchus the groove is noticeably shorter anteroposteriorly than that of C. niloticus. The preorbital region is flat and there is no nasal promontorium, or raised nasal region, as in C. niloticus.[4]

The teeth of Rimasuchus are robust and blunt, unlike those of other crocodiles. They become more bulbous toward the rear of the jaws. The crowns of the teeth are rarely sharp, although crown sharpness tends to lessen with size in crocodylians. The teeth are uniquely bicarinate, meaning that there are ridges on the front and back.[4]

Remains of Rimasuchus show variations in size and proportions, and it is likely that they represent different ontogenic (growth) stages. There has been very little study so far on ontogenic variation in Rimasuchus and living crocodiles. There are many similarities between specimens of R. lloydi and C. niloticus, and it is likely that some specimens of Rimasuchus actually represent particularly large examples of C. niloticus.

Taxonomy
Rimasuchus lloydi was first described in 1918 and originally placed in the genus Crocodylus under the name C. lloydi. After cladistic analysis suggested that it did not belong in Crocodylus, however, the new genus was erected in 2003.[4][5][6] Among crocodylines, Rimasuchus is most closely related to the living dwarf crocodile Osteolaemus and is placed within the group Osteolaeminae.

Phylogeny
Cladogram after Brochu C. A., Njau J., Blumenschine R. J., Densmore L. D. (2010).