S. Adnet et H. Cappetta, A palaeontological and phylogenetical analysis of squaliform sharks (Chondrichthyes : Squaliformes) based on dental characters, LETHAIA, 34(3), 2001, pp. 234-248
Squaliformes comprise the major proportion of modern deep-water sharks, yet
their fossil history and phylogenetic relationships are still poorly under
stood. New analyses have been undertaken, however, and new living and fossi
l species have been discovered during the past 10 years. A cladistic analys
is 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 ex
cluded. The traditional phylogenetic positions of most living genera, Proto
squalus, Cretascymnus and Eoetinopterus, are confirmed despite the fact tha
t the Oxynotidae, Etmopterinae, Palaeomicroides, Proetinopterus and Microet
mopterus have some atypical phylogenetic relationships within the Squalifor
mes. The addition of the palaeontological data in a phylogenetic tree inclu
ding fossil and living Squaliformes demonstrates some gaps in the fossil re
cord. Nevertheless, and as a consequence of that stratigraphy-phylogeny inf
erence, two particular events can be pinpointed in the history of the Squal
iformes: the first one occurs after the major Cenomanian-Turonian anoxic ev
ent and the second one after the Cretaceous/Tertiary crisis. The first radi
ation involves the majority of the living Squaliformes (Somniosinae, Centro
phorinae, most of the Etmopterinae, Oxynotinae) in deep-sea waters, the sec
ond, the more epipelagic sharks (most of the Dalatiidae), suggesting a seco
ndary adaptation to more shallow environments.