How many orders of living sharks are commonly recognized? Eight is the commonly cited answer.
Those orders group the great variety of modern sharks by evolutionary relationships and anatomy. They include familiar lineages such as ground sharks in Carcharhiniformes, dogfish sharks in Squaliformes, mackerel sharks in Lamniformes, carpet sharks in Orectolobiformes, and bullhead sharks in Heterodontiformes. The remaining commonly listed orders include frilled and cow sharks, angel sharks, and sawsharks.
The number can vary between references because shark classification changes as researchers compare fossils, anatomy, and genetic evidence. Some authorities recognize additional orders, especially when groups such as the bramble sharks are separated from other squalomorphs. That is why a source may mention nine or more orders, while a general reference still presents eight as the standard count for living sharks.
This count applies to sharks, not to all elasmobranchs. Rays, skates, and sawfishes belong to Batoidea, a separate major lineage within the cartilaginous fishes. Chimaeras are farther removed still, in Holocephali.