Bullhead shark

Bullhead sharks belong to the genus Heterodontus. They are the only living members of the family Heterodontidae. They are also the only survivors of the order Heterodontiformes. These sharks are relatively small in size. They live in tropical and subtropical waters. Most species are bottom feeders. This means they search for food along the sea floor. They often live in coastal littoral environments. These areas are usually shallower than the deep ocean.

The bodies of bullhead sharks are tapered. Their colors vary between shades of grey, brown, and red. Many species have patterns like spots or stripes. They have blunt heads that are large for their bodies. Their nostrils are large, and they have ridges above their eyes. They possess two dorsal fins on their backs. The first dorsal fin is larger than the second. Both fins have a rigid fin spine at the front. These sharp spines serve as a deterrent to predators. They also have an anal fin and a large tail fin.

Feeding is a complex process for these sharks. They use a method called suction feeding to ingest prey. This involves pulling food into the mouth using suction. Bullhead sharks have differentiated teeth to handle different foods. The teeth at the front are cusped for grasping. The teeth at the back are flattened for crushing. They eat various invertebrates. This includes hard prey like sea urchins and crustaceans. They also eat soft prey like octopuses and fish. Adults use their flat teeth to crush hard shells. Juveniles typically eat softer prey than the adults do.

The history of these sharks spans millions of years. Heterodontiforms appear in the fossil record during the Early Jurassic. The oldest fossils of the modern genus date to the Late Jurassic. Phylogenetic evidence shows a specific evolutionary path. All living species in this genus come from one common ancestor. This ancestor survived the Cretaceous-Paleogene extinction. The modern species only began to diversify around the mid-Eocene. This means the sharks we see today are very ancient.

Reproduction involves very specialized egg cases. These cases are shaped like an auger. An auger is a tool that twists to drill. The cases have spiral flanges, or ridges, along their length. This shape allows the cases to wedge into rocky crevices. Wedging keeps the eggs safe from predators on the sea floor. Some sharks deposit eggs on seaweed or sponges instead. The Mexican hornshark has a different design. It uses a tendril and rigid flanges to anchor its eggs.

Shark hatchlings are quite large when they emerge. They can reach over 14 cm in length. The eggs typically hatch after 7 to 12 months. This timing depends on the specific species. Some species show interesting social behaviors during this time. The female Japanese bullhead shark may deposit eggs in a specific location. These groups of eggs are called a "nest." This happens when multiple females deposit eggs together.

Scientists have described ten living species of bullhead sharks. The Port Jackson shark was described by F. A. A. Meyer in 1793. The Galapagos bullhead shark was named in 1840. The horn shark was described by Girard in 1855. The Mexican hornshark was described in 1972. The Oman bullhead shark was a recent discovery. However, the Painted hornshark was described even more recently in 2023. This shows that scientists are still finding new details about this ancient group.