Environmental controls on the distribution of neoselachian sharks and rays within the British Bathonian (Middle Jurassic)

Abstract

Extensive sampling from a range of facies within the Bathonian (Middle Jurassic) of southern England has allowed the palaeoenvironmental distribution of a number of taxa of neoselachian sharks and rays to be assessed. Faunas were collected from a number of recurrent facies, with different assemblages being characteristic of particular palaeoenvironments. Palaeoenvironmental specificity occurred at both ordinal and specific level. Samples from offshore facies contain high diversity faunas containing members of all neoselachian groups known to have been present in the Middle Jurassic. Shallower water assemblages contain lower diversity faunas lacking Synechodontiformes and Hexanchiformes. Samples from lagoonal facies contain low diversity faunas typically comprising different species from open marine settings. The presence of different taxa within different palaeoenvironments suggests that by the Bathonian neoselachians had differentiated into a wide range of niches and ecologically more diverse than has previously been recognised. Implications for early neoselachian palaeoecology, salinity tolerance and diversification are discussed.