As a group, sharks belong to the superorder called Selachimorpha. Sharks are in the Chondrichthyes class (along with Chimaeras) under the subclass Elasmobranchii. This subclass is also where rays and skates fall and some sharks are thought to be very closely related to certain ray species (even more so than to other sharks, in fact). Selachimorpha is split into two superorders: Galeomorphii and Squalea.
1. Group Of Galea Sharks
Four orders of sharks are part of the Galea group.
- Heterodontiformes: e.g. Bullhead or Horn Sharks ( although some scientists believe these to belong to the Squalea group)
- Orectolobiformes: e.g. Zebra, Nurse, Wobbegongs and Whale sharks
- Lamniformes: e.g. Basking, Megamouth, Goblin, Thresher, Mako (Longfin and Shortfin) and the Great White sharks
- Carcharhiniformes: e.g. Blue, Tiger, Bull, Caribbean, Whitetip Reef, Oceanic Whitetip, Grey Reef, and Blacktip Reef sharks
Note: Orectolobiformes and Carcharhinoids form a clade;that is, they are believed to come from one common ancestor. This is a fairly recent discovery and has proven most exciting amongst researchers.
2. Group Of Squalea Sharks
The Squalea group is divided into Hexanchoidei and Squalomorpha.
Hexanchoidei comprise:
- Hexanchiformes: e.g. Cow Shark
- Chlamydoselachiformes: e.g. the Frilled Shark
The Squalomorpha consist of:
- Squaliformes: e.g. Bramble, Dogfish, Roughsharks and Prickly sharks (part of Hypnosqualea)
- Squatiniformes: Angel Sharks (part of Hypnosqualea)
- Pristiophoriformes Sawsharks: (part of Pristorajea)
- Batoidea :e.g. stingrays, skates and electric rays (part of Pristorajea)
There are a total of eight official orders (when considering Hypnosqualea and Pristorajea as two groups) in which all known shark species are adequately represented. Their known evolutionary order follows:
- Hexanchiformes
- Squaliformes
- Pristiophoriformes
- Squatiniformes
- Heterodontiformes
- Orectolobiformes
- Carcharhiniformes
- Lamniformes