Abstract
BackgroundThe fossil record reveals surprising crocodile diversity in the Neogene of Africa, but relationships with their living relatives and the biogeographic origins of the modern African crocodylian fauna are poorly understood. A Plio-Pleistocene crocodile from Olduvai Gorge, Tanzania, represents a new extinct species and shows that high crocodylian diversity in Africa persisted after the Miocene. It had prominent triangular “horns” over the ears and a relatively deep snout, these resemble those of the recently extinct Malagasy crocodile Voay robustus, but the new species lacks features found among osteolaemines and shares derived similarities with living species of Crocodylus.Methodology/Principal FindingsThe holotype consists of a partial skull and skeleton and was collected on the surface between two tuffs dated to approximately 1.84 million years (Ma), in the same interval near the type localities for the hominids Homo habilis and Australopithecus boisei. It was compared with previously-collected material from Olduvai Gorge referable to the same species. Phylogenetic analysis places the new form within or adjacent to crown Crocodylus.Conclusions/SignificanceThe new crocodile species was the largest predator encountered by our ancestors at Olduvai Gorge, as indicated by hominid specimens preserving crocodile bite marks from these sites. The new species also reinforces the emerging view of high crocodylian diversity throughout the Neogene, and it represents one of the few extinct species referable to crown genus Crocodylus.
Highlights
It was thought that the ancestors of modern African crocodiles would be found among Oligocene through Pliocene fossils found in Africa [1,2,3,4]
Fossil and molecular data suggest a Neogene divergence among living species of Crocodylus, and they usually support a close relationship between the C. niloticus and a clade of Neotropical species [21,22,23,24,25], but relationships among other species of Crocodylus are largely unresolved, as is the placement of the African sharp-nosed crocodile (Mecistops cataphractus), which may be related to either Crocodylus or Osteolaemus [23,25,26,27,28,29]
The choana is partially preserved on a KNM specimen from Frida Leakey Korongo North I (FLKNI), and the pterygoid surface was slightly elevated around the aperture, there was no choanal ‘‘neck.’’ Posteriorly, each pterygoid bears a small triangular process adjacent to the basioccipital, anterior to the lateral Eustachian foramen (Fig. 5C)
Summary
It was thought that the ancestors of modern African crocodiles would be found among Oligocene through Pliocene fossils found in Africa [1,2,3,4]. The anterior ramus is flat and passes laterally over the maxilla It forms the ventral margin of the orbit and bears one or two large foramina between the medial surface and postorbital bar. The ascending ramus is not completely preserved, but based on sutural surfaces on the quadrate and jugal, it formed most of the posterior margin of the infratemporal fenestra, extending from just dorsal to the posteroventral corner to nearly to its dorsal apex; but whether it contacted the squamosal is unknown. The choana is partially preserved on a KNM specimen from FLKNI, and the pterygoid surface was slightly elevated around the aperture, there was no choanal ‘‘neck.’’ Posteriorly, each pterygoid bears a small triangular process adjacent to the basioccipital, anterior to the lateral Eustachian foramen (Fig. 5C). Most osteoderms (presumably from the dorsal shield) are square in dorsal view and, in most cases, bear a robust dorsal keel (Fig. 3B); at least one (Fig. 7B) is oval in dorsal view, suggesting it is from the nuchal shield
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