Slow-moving, generally solitary predators, horn sharks hunt at night inside small home ranges and retreat to a favored shelter during the day.

Adult sharks prey mainly on hard-shelled molluscs, echinoderms, and crustaceans, which they crush between powerful jaws and molar-like teeth, while also feeding opportunistically on a wide variety of other invertebrates and small bony fishes.

The French biologist Charles Frédéric Girard published the first scientific description of the horn shark under the name Cestracion francisci in 1855, in the Proceedings of the Academy of Natural Sciences of Philadelphia.

The specific epithet francisci is a reference to San Francisco, although the range of the horn shark does not extend that far north.

The horn shark's supraorbital ridges are low and terminate abruptly; the space between them on top of the head is deeply concave.

[2] The dorsal coloration consists of various shades of gray or brown with many small dark spots, though these may be absent in older sharks; the underside is yellowish.

They often take advantage of large feeding pits excavated by the bat ray (Myliobatis californica) for shelter and food.

As they mature, horn sharks shift into shallower water and their preferred habitat becomes structurally complex rocky reefs or algae beds.

[3] The horn shark is a sporadic swimmer that prefers to use its flexible, muscular pectoral fins to push itself along the bottom.

[2] During the day, horn sharks rest motionless, hidden inside caves or crevices, or within thick mats of algae, though they remain relatively alert and will swim away quickly if disturbed.

[5] Horn sharks maintain small home ranges of around 1,000 m2 (11,000 sq ft), which they may remain faithful to for over a decade, returning to the same shelter every day.

[4] The daily activity pattern of the horn shark is under exogenous control, meaning that it is regulated by environmental factors rather than by an internal physiological cycle.

In nature, horn sharks exposed to a bright light at night may stop swimming and sink to the bottom.

[5] The horn shark is preyed upon by larger fishes and the northern elephant seal (Mirounga angustirostris), which consumes adults, juveniles, and egg cases.

In addition, they are captured and eaten by bald eagles (Haliaeetus leucocephalus) at Catalina Island, and large marine snails are able to drill into their egg cases to extract the yolk.

[7][8][9][10] 95% of the adult horn shark's diet consists of hard-shelled mollusks (e.g. bivalves and gastropods), echinoderms (e.g. sea urchins) and crustaceans (e.g. crabs, shrimp, and isopods).

[3] Other prey items of adults include peanut worms, sea stars, cephalopods, and small bony fishes.

In the summer, diurnally active fishes, in particular the blacksmith (Chromis punctipinnis), are especially abundant and are easily captured at night when they lie dormant.

In the winter, the sharks scavenge on market squid (Loligo opalescens), which die by the tens of thousands after their mass spawning event.

To extract buried or affixed prey, the horn shark grips it and adopts a vertical posture with the head and pectoral fins against the substrate and the tail arched above.

Horn sharks grow slowly and at a highly variable rate that does not correspond to their size; this has frustrated attempts to determine their aging process.

[16] Divers sometimes kill them for sport or to make jewelry out of their fin spines, which may be the cause of a decline in the numbers of horn sharks in the most intensely dived areas of southern California.