Why aren't lemon sharks mammals?

There are a number of live bearing fish and sharks, but in every case what is going on there is the fish or shark lays eggs, which are then fertilized, and then the eggs are carried somewhere on or inside the fish (or shark) until they hatch. read more

In fact, live offspring are neither restricted to mammals, nor are all mammals livebearers. A characteristic shared by all members of a group because of their common descent is called a synapomorphy. Live young is not a synapomorphy of mammalia. Mammaries are. Lots of fish, reptiles, and mammals give birth to live young. read more

The lemon shark (Negaprion brevirostris) is a stocky and powerful shark. A member of the family Carcharhinidae, lemon sharks can grow to 3.4 metres (11 ft) in length. They are often found in shallow subtropical waters and are known to inhabit and return to specific nursery sites for breeding. read more