Dyrosaurid (Crocodyliformes: Mesoeucrocodylia) Fossils from the Upper Cretaceous and Paleogene of Mali: Implications for Phylogeny and Survivorship across the K/T Boundary

Abstract

We describe new dyrosaurid fossils from three localities in Mali, representing strata of Maastrichtian, Paleocene, and Eocene ages. The fossils significantly extend the temporal and geographic ranges of several known dyrosaurid taxa. Rhabdognathus keiniensis and Chenanisuchus lateroculi are identified for the first time from Maastrichtian sediments. Additional material is referred to Phosphatosaurus gavialoides and, tentatively, the genus Sokotosuchus. These discoveries represent the first occurrence of Chenanisuchus and possibly of Sokotosuchus from Mali. Previously unknown morphological character states are incorporated into existing data matrices, reducing the amount of missing data. Phylogenetic analyses largely corroborate prior hypotheses of dyrosaurid relationships, but indicate a need for new characters to resolve the relationships of certain genera and species. The occurrence of both basal (e.g., Chenanisuchus lateroculi) and highly nested (e.g., Rhabdognathus keiniensis) members of Dyrosauridae on both sides of the K/T boundary indicates that dyrosaurid diversification was well underway by the latest Cretaceous, and that most, if not all dyrosaurid species survived the extinction event. The geology of the Mali's Tilemsi Valley is clarified; some rocks previously assigned to the Iullemmeden Basin actually represent extensions of other basins: the Taoudeni Basin and Gao Trench.

Multispecies Shark Feeding in the Trans-Saharan Seaway: Evidence From Late Cretaceous Dyrosaurid (Crocodyliformes) Fossils From Northeastern Mali

“…In particular, the presence of a prominent ventral keel (hypapophyis) on the vertebra supports affinities with Hyposaurinae. Additionally, more complete dyrosaurid material is already known from Mali-8, including specimens of Rhabdognathus keiniensis and Chenanisuchus lateroculi (McCartney and Hill 2007;Hill et al 2008). The new specimens are most similar in size to the R. keiniensis fossils, and may pertain to this species.…”

“…Its lithology and geography, as well as its relationship to other sections in the Gao Trench and the Taoudeni and Iullemeden basins, were figured in a composite section published by Tapanila et al (2004; see also Hill et al 2008). The lithology of the composite section overall consists of interbedded paper shale, phosphate, and marly limestone (Tapanila et al 2004Hill et al 2008) that conformably overlie deltaic sandstone beds at the base of the section. The exposure ranges from 80-200 m thick across the composite section as a whole, and is 35 m thick at Mali-8.…”

“…The fossiliferous bed at Mali-8 occurs at the 26 m level approximately, and is a phosphatic conglomerate that consists of lithoclasts, coprolitic clasts, and fragmented polished bone. This succession of rocks has produced a diverse range of taxa , including early Eocene fossil mammals (O'Leary et al 2006), Eocene ichnofossils recording boring bivalve activity (Tapanila et al 2004, Late Cretaceous myliobatid chondrichthyans (Claeson et al 2010), and Late Cretaceous-Paleogene dyrosaurid crocodyliforms (Hill et al 2008). …”

“…The specimens are from Upper Cretaceous rocks of northeastern Mali, an area from which the fossil record is only beginning to be extensively documented (Tapanila et al 2004O'Leary et al 2006;Hill et al 2008). These fossils provide important information about the faunal composition and paleoecology of the Trans-Saharan Seaway at the end of the Cretaceous Period.…”

A middle Eocene mesoeucrocodylian (Crocodyliformes) from the Kaninah Formation, Republic of Yemen

“…These include dyrosaurids, goniopholidids, and trematochampsids (e.g., Markwick, 1998;Hill et al, 2008). The discovery of an atoposaurid crocodyliform in the middle Eocene would further corroborate the hypothesis that crocodyliform lineages did not universally experience a diversity crises caused by the event (Markwick, 1998;Fara, 2000).…”