Mid-Cretaceous fish assemblages in north-eastern Mexico: A case-study for the actinopterygian diversification and global palaeobiogeography

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During our previous research work on Cretaceous vertebrates from NE Mexico (DFG FR 1314/4-1, 6-1, 7-1, 9-1, STI 128/9-1, 9-2, VW I/78866) we discovered several localities yielding numerous well-preserved fishes. One of these is the early Turonian fish assemblage at Vallecillo, Nuevo Leon, which yields complete but crushed specimens of various sharks and actinopterygian taxa. Preliminary accounts have already been published about the Vallecillo fish assemblage, but a synoptic global study of this assemblage is still pending. Recently, new attention has been paid to the Upper Turonian -Coniacian laminated marly limestones exposed north of Muzquiz in the northeastern state of Coahuila. In this area, small commercial quarries yield fossils, which are exceptionally well preserved. At present, localities and assemblages are unknown to the scientific community. Our initial survey at Muzquiz resulted in several species of fishes (selacheans, holosteans and teleosts) in which even delicate muscle fibres and gill filaments, as well as fossilised stomach contents are preserved, sometimes in three dimensions. Both localities, and especially Muzquiz, bear great potential to carry out thorough anatomical description of the taxa and to draw up the temporal turnover within the succession offish assemblages against coeval changes of the palaeoenvironment. The principal objectives of the present project are: 1) Understanding the palaebiogeographical links of the mid-Cretaceous Mexican fish assemblages with the adjacent realms (Central Tethys, South Atlantic, Western Interior Sea and Pacific). 2) Testing the scenario of a mid-Cretaceous actinopterygian worldwide radiation based on existing hypotheses about causality offish diversification.