The AMNH's Trilobite Website has a page on trilobite injuries. Over the many years that trilobites existed and considering the many, many fossil specimens that have been (and will be) found, there had to be some with signs of predation. And, of those, there had to be some that got away from the predator. There were many threats to our little friends, Anomalocars, Euryperids, fish and even other trilobites are just a few.
Judging by the variety of lethal-looking bite marks and healed injuries that frequently adorn their fossilized exoskeletons, it seems safe to say that life as a trilobite presented some daunting challenges. Such stark evidence offers emphatic proof that the primal seas in which these Paleozoic arthropods flourished for 270 million years rarely provided a hospitable environment. Indeed, those ancient oceans were filled with an ever changing, and ever more dangerous array of predators, all seemingly intent on turning the local trilobite population into little more than an afternoon snack.
From the moment they emerged on the world stage some 521 million years ago, trilobites were in constant peril from a lethal cast of predators, ranging from the legendary Cambrian-age Anomalocaris, to giant Silurian eurypterids, to armored Devonian fish. Current theory even speculates that some trilobites, such as the large Cambrian genus Olenoides (which often exceeded 12 cm in length), may have taken an occasional cannibalistic turn upon some of their smaller trilobite brethren. Fossilized trilobite carapaces sporting either healed or potentially fatal bite marks are pervasive in certain locales, such as the famed Middle Cambrian Elrathia kingi beds of Utah.
By the dawning of the Ordovician, 485 million years ago, a majority of trilobite species had developed the ability to enroll, which provided them with at least a degree of protection from the hostile world which surrounded them. Other trilobites had evolved to grow rows of menacing spines that covered their carapaces and afforded additional defense from predators. Still others apparently were able to generate increasingly thick calcite shells with each successive molt, providing these trilobites with a greatly enhanced ability to survive and pass along their genetic advantages.
Bathyuriscus fimbriatus Robison,1964
Late Middle Cambrian
Marjum Formation, House Range
Millard County, Utah, U.S.A.
2 cm
Note: Defect left pygidium consistent with bite injury. The smooth edges of the defect suggest repair on a subsequent molt.
Elliptocephala sp.
Lower Cambrian
Rosella Formation, Atan Group
British Columbia, Canada
14 cm
Note: Large defect on left side consistent with possible bite mark
Glossopleura gigantea Resser, 1939
Middle Cambrian
Spence Shale
Utah, U.S.A.
13 cm
Note: Defects on right posterior pleural tips and pygidium consistent with bite injury. The rounded edges of the shortened pleural tips suggest subsequent healing.
