Major Chondrichthyan Subgroups

Chondrichthyes is a monophyletic group of fishes that belongs to subphylum Vertebrata. Within the Vertebrata, chondrichthyans are thought to lie between the Placodermi (a group of extinct vertebrates whose body was covered with plates of dermal armour, and who were the first group of fishes with jaws) and the Acanthodii.

From Benton (2005)

Chondrichthyan phylogeny (= the interrelationships of groups within chondrichthyes) is still a matter of much contention among systematic biologists and palaeontologists. Particularly problematic are the interrelationships of early (i.e. "stem") chondrichthyans. The phylogenetic tree below illustrates one evolutionary hypothesis, and includes both extinct and extant members (each of these groups will be discussed in detail on fossil forms and modern forms pages).


Stem Chondrichthyans

This is a group that comprises the earliest known chondrichthyans. They appear in the Silurian, and diversified through the Devonian. They are known only from fossil remains. These remains are often isolated scales and teeth (as complete cartilaginous skeletons are rarely fossilized). Some fully articulated fossil stem chondrichthyans do exist, however. One such specimen is Cladoselache.


Holocephali

The Holocephali is the group that includes the bizarre looking, deep water-dwelling Chimaeras or ratfishes. This group appeared near the Silurian-Devonian boundary, with modern forms appearing in the Jurassic. There is one extant order in the Holocephali (Order Chimaeriformes).


Elasmobranchii

Elasmobranchs, the group that includes modern sharks, skates and rays and their relatives, are divided into two subgroups: 1) the stem elasmobranchs and 2) the Neoselachii.

1. Stem Elasmobranchs

Stem elasmobranches are the extinct relatives of modern sharks, skates and rays. They were shark-like in appearance, and existed from the Devonian to the Triassic.

2. Neoselachii

The neoselachii comprises all living sharks, skates and rays. The first neoselachii appear in the early Mesozoic, and exhibit a number of modern "shark-like" characters. The neoselachii are subdivided as follows:

Galeomorphs

Squalomorphs



Author: Andrew Gillis
Last updated: 15 November 2004
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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2004-5.