Comments on hexanchiform phylogeny (Pisces, Neoselachii)

The Hexanchiformes (Cow Sharks) are regarded as a monophyletic taxon. Cladistic analysis shows that among the various neoselachian taxa proposed so far as the sister group of the Hexanchiformes a sister group relationship between the Hexanchiformes and a (still unnamed) taxon comprising the Squaliformes and Pristiophoriformes appears as the most probable hypothesis. In addition, MAISEY and WOLFRAM'S (1984) concept of hexanchiform interrelationships is critically reviewed. An alternative cladogram of hexanchiform interrelationships is developed which includes Recent as well as fossil hexanchiform taxa. In this cladogram the living genera Hexancbus and Notorynchus are sister groups and both taxa together form the sister group of the Recent Heptranchias. The fossil taxa +Notidanoides, +“Hexanchus” gracilis, +Notidanodon and +Weltonia are arranged in the stem lineage of recent Hexanchiformes.