Trilobites, an extinct group of marine arthropods, thrived for nearly 300 million years, diversifying into over 20,000 species before their disappearance in the Permian Period. Despite extensive fossil records, the precise dietary habits of many trilobite species remain a subject of ongoing scientific investigation.
Unraveling Ancient Diets
Determining the diets of long-extinct organisms like trilobites presents a challenge. Direct evidence, such as fossilized gut contents or coprolites (fossilized faeces), is rare because soft tissues typically do not preserve well. However, a 465-million-year-old Bohemolichas incola trilobite with intact gut contents provided direct insight, revealing fragments of small crustaceans, bivalves, and extinct starfish relatives. This suggests the species was an opportunistic scavenger, consuming small organisms on the seafloor.
Much understanding of trilobite diets comes from indirect evidence, primarily through analysis of their preserved anatomy and trace fossils. Paleontologists examine mouthparts, such as the hypostome, a hard plate beneath the head that covered the mouth. Gnathobases, spiny projections on their walking legs, also provide clues about food processing. Trace fossils, like the burrowing marks known as Rusophycus, can indicate hunting or feeding behaviors when found with other organism burrows. By comparing these structures and behaviors to modern marine arthropods, scientists infer diverse trilobite diets.
Dietary Habits of Trilobites
Trilobites exhibited a range of dietary habits within ancient marine food webs. Many species were likely detritivores or scavengers, feeding on organic matter within seafloor sediment. The Bohemolichas incola specimen supports this generalist scavenging behavior, showing it consumed small, shelled invertebrates.
Some trilobites were likely filter feeders, collecting microscopic organisms like plankton and algae from the water column. This strategy was prevalent among smaller, free-swimming species; larval trilobites were planktic, consuming phytoplankton. Other trilobites, particularly larger species, were opportunistic predators, preying on small, soft-bodied invertebrates like worms. Trace fossils where trilobite resting traces intersect with worm burrows suggest active hunting. Some species may have also engaged in symbiotic relationships with sulfur-eating bacteria, deriving nutrients.
Diverse Feeding Adaptations
The remarkable success and longevity of trilobites were supported by a wide array of morphological adaptations that enabled diverse feeding strategies. The hypostome, a calcified plate on the underside of the head, was positioned near the mouth and varied significantly in form and attachment. Some trilobites possessed a “natant” hypostome, which was flexibly attached, typically associated with more generalized particle feeding. In contrast, a “conterminant” hypostome was rigidly attached, providing a strong anchor for crushing and processing tougher food items, a feature often linked to predatory species. Specialized hypostomes, sometimes with fork-like projections or rasps, further suggest adaptations for dispatching and consuming prey.
The gnathobases, spiny projections located on the inner surfaces of their walking limbs, played a significant role in food manipulation. These structures functioned to tear, slice, and crush food particles against the hypostome as material was passed forward towards the mouth. The coordinated movement of their biramous (two-branched) limbs could also create currents to sweep food particles towards the mouth or stir up sediment for deposit feeding. The varied forms of these feeding structures across different trilobite species reflect their evolutionary ability to exploit a wide range of food sources, contributing to their widespread ecological presence over millions of years.