HETERODONTIDAE bullhead SHARKS

The family Heterodontidae or common name Bullhead sharks, (sometimes just referred to as the Horn sharks), belong to the small order of sharks, Heterodontiformes, also called Bullhead sharks. They are relatively modern sharks with 9 (possibly 10) living species placed in a single genus, Heterodontus. All of them are relatively small, with the largest species reaching a maximum length of just 5.5 feet. They are bottom feeders in tropical and subtropical waters.

The Heterodontiforms are an ancient order which appear in the fossil record as far back as the early Mesozoic era, well before any of the other Galeomorphii, a group that includes all modern sharks except the dogfish and its relatives. However, they have never been common, and their origin probably lies even further back.

Bullhead sharks are distinctive. They all have blunt, pig-like snouts. The small mouth is located anterior to the orbits, and labial cartilages are found in the most anterior part of the mouth. Nasal grooves are present, connecting the external nares to the mouth. The nasal capsules are trumpet-shaped and well-separated from orbits. Skin folds are present, but the rostral process of the neurocranium (braincase) is absent, although a precerebral fossa is present. The braincase has a supraorbital crest. The eyes lack a nictitating membrane. A spiracle is present, but small. The dorsal ends of the fourth and fifth branchial arches are attached, but not fused into a “pickaxe” as in lamniform sharks. Heterodontiforms have two dorsal fins, with fin spines, as well as an anal fin. The dorsal and anal fins also contain basal cartilages, not just fin rays. Bullhead Sharks have distinctive small spikes on the front of their dorsal fins. These are rumored to be poisonous, but no further scientific tests have been completed to prove this hypothesis true or false. They have rough skin, and paddle-like paired fins.

Bullhead sharks have different teeth. The front teeth are smaller gripping teeth, and the back blunt teeth for crushing. They mostly feed on benthic invertebrates.

Bullhead sharks are benthic sharks that are slow, sluggish sharks mostly active at night. Some even crawl over rocky and kelp-covered bottoms. Bullhead sharks are oviparous with extremely unique corkscrew shaped egg cases that can be wedged securely between rocks and crevices. The eggs hatch approximately 5 months later. Two species have identifiable nesting sites where they lay their eggs.  One species is migratory, returning to breeding grounds annually as an adult after long migrations.

Most are rare to uncommon. They aren’t of importance to commercial fisheries, but are commonly taken as bycatch. Bullhead sharks are also subject to being caught by sport fisherman and divers because of their resilience to aquarium living.