Turtle remains from the Wadi Milk Formation (Upper Cretaceous) of Northern Sudan

Abstract

We describe here turtle remains from lag-type concentrations in channels and scours in the Wadi Milk Formation (Upper Cretaceous) of the Wadi Abu Hashim region in northern Sudan. Due to the isolated nature of the finds and the lack of any diagnostic material, such as skulls or more complete shell fragments, low-level taxonomic assignment was not possible. However, the morphology as well as the superficial ornamentation of most plates indicates pelomedusoid (Pleurodira) affinities, which is consistent with the geographically isolated nature of continental Africa during much of the Upper Cretaceous. The fauna contains one or two smaller sized pelomedusoid taxa as well as at least two large forms that are identified as members of Bothremydidae. A few plates may indicate the presence of other turtle lineages. Bothremydidae are known to have inhabited a variety of fluviatile and marine–littoral/near-coastal environments and thus are poor palaeoenvironmental indicators. However, bone compactness of one of the four peripheral morphotypes indicates the presence of a taxon that was more aquatic than typical Bothremydidae. Many plates show bioerosional traces that are interpreted as bore holes of clionid sponges, indicating a connection to a coastal environment exposed to marine influences. A marine or tidal influence is additionally suggested by sedimentological indicators, such as inclined heterolithic stratification, very variable palaeocurrent directions and partly intense bioturbation.