A partial braincase and other skeletal remains of Oligocene angel sharks (Chondrichthyes, Squatiniformes) from northwest Belgium, with comments on squatinoid taxonomy
A detailed redescription of a chondrocranium from the basal Boom Clay Formation (Rupelian, Upper Oligocene) at the SVK clay pit, Sint-Niklaas (province of Oost-Vlaanderen, Belgium), previously assigned to the sawshark Pristiophorus rupeliensis, is presented. The chondrocranium is re-identified as that of an angel shark (Squatinidae), based on comparative anatomy of extant Squatina, inclusive of CT scans of Squatina africana, S. australis, S. dumeril, S. guggenheim and S. squatina, with different geographic distributions and representing all four angel shark clades as defined in a previous molecular study. Differential characters for chondrocrania listed in earlier accounts to discriminate angel shark species from the southwest Atlantic proved to be even more revealing when comparing angel sharks from different regions/clades. Despite this wide interspecific variation, the fossil chondrocranium compares well with modern Squatina, but differs in having a UUU-shaped ventral margin of the occipital region and rounded margins of the upper postorbital processes. The distal expansion of the upper postorbital processes present in modern species has not yet been observed in extinct squatinoids and might constitute a derived character for modern representatives only. Angel shark teeth and vertebrae are well known from the same basal deposit at the SVK clay pit, but Cenozoic squatinid taxonomy remains problematic. It is here discussed in detail for the Oligocene taxa S. angeloides, S. rupeliensis and S. beyrichi. For the time being, all SVK material is left in open nomenclature and referred to as Squatina sp.
|Keywords||chondrocranium, CT scanning, neurocranium, Pristiophorus, Squatina, vertebrae|
|Journal||Contributions to Zoology|
|Rights||Released under the CC-BY 4.0 ("Attribution") License|
Mollen, F.H, van Bakel , B.W.M, & Jagt, J.W.M. (2016). A partial braincase and other skeletal remains of Oligocene angel sharks (Chondrichthyes, Squatiniformes) from northwest Belgium, with comments on squatinoid taxonomy. Contributions to Zoology, 85(2), 147–171.