TRILOBITES AS PREDATORS: MELDING THE MORPHOLOGICAL AND ICHNOLOGICAL DATA

The interpretation that some trilobites were predators comes from two separate lines of evidence: (1) morphological; specifically, inferences of the functional morphology of the hypostome and proximal limb structure, and (2) ichnological; specifically, the co-occurrence of “worm” burrows with the trace fossil Rusophycus. Trilobites with attached, conterminant hypostomes have been interpreted to have had a predatory habit and to have been associated with distinctive Rusophycus traces that preserve casts of the ventral anatomy of the trilobite. Trilobites with detached, natant hypostomes have been interpreted to have had a detritivorous habit, and whose associated “bean-shaped” Rusophycus may or may not bear scratch marks but show no other trace of ventral anatomy. A review of the literature on Rusophycus associated with “worm” burrows, and a survey of the hypostome morphology of the probable trilobite trace- makers indicates that the proposed relationship between hypostome morphology and Rusophycus morphology is not as straightforward as originally proposed. The lack of a clear correlation may indicate intraspecific variability in trilobite feeding habits, and that some trilobites, although primarily detritivorous, were also opportunistic or facultative predators or scavengers.