Guitarfishes in Rocks of All Ages

The Batoidea (rays, skates and guitarfishes) comprise over half of living chondrichthyans, and presently inhabit virtually all marine, and some freshwater, environments. An extremely morphologically and ecologically disparate clade, all of its major lineages are known, or predicted, to have appeared prior to the end of the Cretaceous and as early as the Jurassic. Little study has been carried out on the affinities of Jurassic batoids, despite their key role in understanding batoid evolution. Although fossil chondrichthyans are known largely from isolated teeth, several species of batoids are known from the Late Jurassic on the basis of well preserved skeletons within lägerstatten. These Jurassic forms are morphologically conservative and all fit within the “guitarfish” or “rhinobatid” body plan. Modern “guitarfish” are now recognized as a polyphyletic group sharing a primitive body shape, but it is unclear whether the Jurassic taxa belong within one or more of the extant clades, would form a basal sister clade to crown Batoidea, or represent a paraphyletic group of stem batoids. The discovery of two incomplete but exceptionally well preserved batoid specimens from the Kimmeridge Clay Formation (Kimmeridgian to Lower Tithonian) of Kimmeridge, southern England represent the first examples of batoid skeletons from Britain, and also the first from offshore mudstone facies. These specimens represent a previously unknown taxon and have allowed the phylogenetic position of Late Jurassic batoids to be investigated along side the extant members of Batoidea. Preliminary phylogenetic analyses indicate Jurassic batoids are not the same as modern ‘rhinobatoids’ while Cretaceous batoid skeletons do resemble modern ‘rhinobatoids.’ However, neither the Jurassic nor Cretaceous batoids lend support to a monophyletic Rhinobatidae.