A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes: Squaliformes) based on dental characters

Abstract

Squaliformes comprise the major proportion of modern deep‐water sharks, yet their fossil history and phylogenetic relationships are still poorly understood. New analyses have been undertaken, however, and new living and fossil species have been discovered during the past 10 years. A cladistic analysis involving 29 dental characters has been made and most living and fossil genera are included. On the basis of their dental morphology, the monophyly of the Squaliformes can be supported if the fossil genus Protospinax is excluded. The traditional phylogenetic positions of most living genera, Protosqualus, Cretascymnus and Eoetmopterus, are confirmed despite the fact that the Oxynotidae, Etmopterinae, Palaeomicroides, Proetmopterus and Microetmopterus have some atypical phylogenetic relationships within the Squaliformes. The addition of the palaeontological data in a phylogenetic tree including fossil and living Squaliformes demonstrates some gaps in the fossil record. Nevertheless, and as a consequence of that stratigraphy‐phylogeny inference, two particular events can be pinpointed in the history of the Squaliformes: the first one occurs after the major Cenomanian‐Turonian anoxic event and the second one after the Cretaceous/Tertiary crisis. The first radiation involves the majority of the living Squaliformes (Somniosinae, Centrophorinae, most of the Etmopterinae, Oxynotinae) in deep‐sea waters, the second, the more epipelagic sharks (most of the Dalatiidae), suggesting a secondary adaptation to more shallow environments.

The lantern shark's light switch: turning shallow water crypsis into midwater camouflage

“…We therefore suggest that this species turned the initial shallow water crypsis mechanism into a midwater bioluminescent camouflage, more efficient in the darkness of the deep-sea. This functional transition might have occurred during colonization of the deep-sea by lantern sharks during the late Cretaceous (Adnet & Capetta 2001 …”

Dental abnormalities of the southern thorny skate Amblyraja doellojuradoi (Chondrichthyes, Rajidae)

“…Teeth morphology is an important tool widely used in taxonomic, biological and fossil teeth studies of cartilaginous fishes (Herman et al 1994, 1995, 1996, Kemp 1999, Adnet & Cappetta 2001, Sáez & Lamilla 2003. According to the consumed prey, chondrichthyan's teeth may take different forms which are attributed to different functions (Motta 2004).…”

Squaliform shark teeth of the genus <i>Centroselachus</i> from the Miocene of Japan

“…Remarks. -Dental terminology is summarized by Kuga and Goto 1980, Cappetta 1987, Herman et al 1989, Yabe and Goto 1999, and Adnet and Cappetta 2001 , whose terminology is widely accepted, is shown in Fig. 4.…”

“…According to Herman et al 1989: 119-121 Kuga and Goto, 1980, Cappetta, 1987, Herman et al, 1989, Yabe and Goto, 1999, modified from Adnet and Cappetta, 2001 . Measurements.…”