Molecular and morphological evidence has shown that the African slender-snouted, or sharp-nosed, crocodile Mecistops cataphractus (Cuvier, 1824) is comprised of two superficially cryptic species: one endemic to West Africa and the other endemic to Central Africa. Our ability to characterize the two species is compromised by the complicated taxonomic history of the lineage and overlapping ranges of variation in distinguishing morphological features. The name M. cataphractus was evidently originally based on West African material, but the holotype is now lost. Although types exist for other names based on the West African form, the name M. cataphractus is sufficiently entrenched in the literature, and other names sufficiently obscure, to justify retypification. Here, we designate a neotype for M. cataphractus and restrict it to West Africa. We resurrect M. leptorhynchus as a valid species from Central Africa and identify exemplary referred specimens that, collectively, overcome the obscurity and diagnostic limits of the extant holotype. We additionally indicate suitable neotype material in the event the holotype is lost, destroyed, or otherwise needing replacement, and we rectify the previously erroneous type locality designation. We provide a revised diagnosis for crown Mecistops, and revise and update previous descriptions of the two living species, including providing both more complete descriptions and discussion of diagnostic characters. Finally, we provide considerable discussion of the current state of knowledge of these species’ ecology, natural history, and distribution.

Brochuchus is a small crocodylid originally based on specimens from the early Miocene of Rusinga Island, Lake Victoria, Kenya. Here, we report occurrences of Brochuchus from several early and middle Miocene sites. Some are from the Lake Victoria region, and others are in the Lake Turkana Basin. Specimens from the middle Miocene Maboko locality form the basis of a new species, Brochuchus parvidens, which has comparatively smaller maxillary alveoli. Because of the smaller alveoli, the teeth appear to be more widely spaced in the new species. We also provide a revised diagnosis for Brochuchus and its type species, B. pigotti. A phylogenetic analysis supports a close relationship between Brochuchus and tube-snouted Euthecodon, but although relationships among crocodylids appear poorly resolved in the set of optimal trees, this is because Brochuchus and Euthecodon, along with early Miocene “Crocodylus” gariepensis from the early Miocene of Namibia, jointly adopt two distinct positions—either closely related to the living sharp-nosed crocodile (Mecistops) or to a group including the living dwarf crocodiles (Osteolaemus). Character support for a close relationship with Mecistops is problematic, and we suspect a closer relationship to Osteolaemus will be recovered with improved sampling, but the results here are ambiguous. In either case, Brochuchus is more closely related to living groups not currently found in East Africa. This material helps constrain the timing of crocodylian faunal turnover in the East African Rift Valley System, with endemic lineages largely being replaced by Crocodylus in the middle or late Miocene possibly in response to regional xerification and the replacement of continuous rainforest cover with open grasslands and savannas. UUID: http://zoobank.org/e6f0b219-5f3e-44e5-bdb9-60a4fae8d126

Thanks to my advisor, C.A. Brochu, for his guidance and expertise in all things crocodylian, and committee members A.F. Budd and L.D. Densmore III. This project was funded by the Department of Geoscience at the University of Iowa and the International Union for the Conservation of Nature Crocodile Specialist Group. Specimen access was kindly provided by J.S. Steyer at the Museum national d'Histoire naturelle, G. Lenglet at the Royal Belgian Institute for Natural Sciences, G. Cael at the Royal Museum for Central Africa, G. Köhler at the Senckenberg Museum, M. Rödel at the Museum für Naturkunde, and C. Mehling and D. Kizirian at the American Museum of Natural History. J.M. Patterson was instrumental and invaluable in his help with specimen photography, geographic information systems, and constructive feedback. E.W. Wilberg and the UI Paleo Group provided consistently helpful comments. Finally, thanks to Mom, Dad, Michelle, Tipper, Bumbledog, and Fen for their constant support even though I wouldn't go to law school.

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