Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil turtles, placodonts and invertebrates, as well as "bone-crushing" mammalian carnivores such as hyenas. Durophagy requires special adaptions, such as blunt, strong teeth and a heavy jaw. Bite force is necessary to overcome the physical constraints of consuming more durable prey and gain a competitive advantage over other organisms by gaining access to more diverse or exclusive food resources earlier in life. Those with greater bite forces require less time to consume certain prey items as a greater bite force can increase the net rate of energy intake when foraging and enhance fitness in durophagous species.
In the order Carnivora there are two dietary categories of durophagy; bonecrackers and bamboo eaters. Bonecrackers are exemplified by hyenas and borophagines, while bamboo eaters are primarily the giant panda and the red panda. Both have developed similar cranial morphology. However, the mandible morphology reveals more about their dietary resources. Both have a raised and dome-like anterior cranium, enlarged areas for the attachment of masticatory muscles, enlarged premolars, and reinforced tooth enamel. Bamboo eaters tend to have larger mandibles, while bonecrackers have more sophisticated premolars.
Fish
Many fish exhibit durophagous behaviour including the triggerfish, some teleosts and some cichlids.
Triggerfish (Balistidae) Triggerfish have jaws that contain a row of four teeth on either side, the upper jaw containing an additional set of six plate-like pharyngeal teeth. Triggerfish do not have jaw protrusion and there are enlarged jaw adductor muscles for extra power to crush the protective shells and spines of their prey.
Teleosts (Teleostei) Teleosts crush hard prey and do so with the use of their pharyngeal jaws, with the aid of their protrusible mouth for enabling the grabbing of prey to draw it into their mouth. The pharyngeal jaws found in more derived teleosts are more powerful, with left and right ceratobranchials fusing to become one lower jaw and the pharyngeal branchial fusing to create a large upper jaw that articulates with the neurocranium. They have also developed a muscle, the hypertrophied pharyngeal, to crush prey with help from the molariform pharyngeal teeth. This allows for the consumption of hard-shelled prey.
Cichlids (Cichlidae) Mollusk shells can be crushed to expose soft parts of the prey to digestive juices or the soft parts can be removed from the shell. Species that crush shells are defined by their large and greatly thickened pharyngeal bones. These bones have flat-crowned teeth and along with their dorsal fellows drawn by powerful muscles, create a crushing mill. The jaws are less derived as they are for just for picking up relatively large objects.
The second method cichlids use is to crush mollusk shells between powerful jaws armed with suitable teeth. Cichlids possess short, broad jaws armed with an outer row of relatively few, strong and conical teeth and several inner rows of finer, also conical teeth. Along with these features are the presence of foreshortening of the skull and development of particularly powerful mandibular adductor muscles. To feed with this type of structure the fish can protrude its mouth ventrally to permit muscles to be seized by the jaws and the mouth then is retracted rapidly so the hard-toothed jaws crush the mollusk shell with the resulting force. A series of biting movements completes the process and the shell fragments are spat out and the soft body is swallowed.
Chondrichthyans
Within the chondrichthyans, horn sharks (Heterodontidae), some rays (Myliobatidae) and chimeras (Holocephali) exhibit durophagous behaviour. They have adaptations to allow for this including stout flattened teeth, hypertrophied jaw adductor muscles and robust jaws to feed on hard prey such as crustaceans and molluscs. Sharks that crush prey have teeth with small, low rounded cusps that are numerous per row, or are molariform. The molariform teeth are smoothly rounded, lack cusps, and there are numerous teeth per row.
Horn sharks (Heterodontiformes) Horn sharks have molariform teeth. The anterior teeth are pointed and are used for grasping while the posterior teeth are molariform and are used for crushing. Horn sharks feed primarily on limpets, bivalve molluscs and blue crabs.