No anal fin
Anal fin present
Body flattened, raylike, mouth terminal
Body not raylike,
mouth ventral
Snout elongated, sawlike
Snout short, not sawlike
6 or 7 gill slits, one dorsal fin
5 gill slits,
2 dorsal fins
No fin spines
Dorsal fin spines
Mouth behind
front of eyes
Nictitating eyelids, spiral
or scroll intestinal valve
No nictitating eyelids,
ring intestinal valve
Mouth well in front of eyes
SQUATINIFORMES
Triassic onwards
PRISTIOPHORIFORMES
Jurassic onwards
SQUALIFORMES
Jurassic onwards
HEXANCHIFORMES
Permian onwards
CARCHARHINIFORMES
Jurassic onwards
LAMNIFORMES
Jurassic onwards
ORECTOLOBIFORMES
Jurassic onwards
HETERODONTIFORMES
Triassic onwards
Extant Shark Orders
Recognisable external characteristics