INTERPRETING EARLY ARTHROPOD PREDATOR-PREY RELATIONSHIPS AND FEEDING FROM BODY FOSSILS, TRACE FOSSILS, AND TAPHONOMIC EXPERIMENTATION

Our understanding of early Paleozoic predator-prey systems, in which arthropods were major players, is still underdeveloped compared to mid-Paleozoic and Mesozoic-Cenozoic systems. Most interpretations of feeding habits and dietary preferences of ancient arthropods derive from inferences based on morphology and phylogenetic relationships. However, less ambiguous interpretations about how and on what these animals fed, and about the predators of these animals, can be developed through study of the digestive tracts, and study of trace fossils, both in sediment and on sclerites.

Inferences about the feeding behavior of early arthropods, especially arachnomorphs and dinocarids, is advancing through: 1, morphologic interpretation, particularly of appendages and mouthparts; 2, study of preserved remains or sediment in gut tracts; 3, study of unfilled or early mineralized gut tracts and associated digestive glands; and 4, actualistic taphonomic experiments. Numerous early arthropods are known to have large, presumably raptorial, appendages but the prey are not always obvious. Gut tracts of various trilobites, some naraoiids, and some other taxa are sediment-free and sclerite-free, often preserved through early mineralization, and sometimes showing fossilized digestive glands. All this suggests fluid-filled guts at burial, and non-durophagous predaceous habits. Collapsed glabellas in trilobites also indicate fluid-filled, rather than sediment-filled digestive tracts at the time of burial. Trace fossils in sediment confirm that some trilobites preyed on infaunal worms. A few arachnomorph taxa have sediment-filled guts tracts, which most likely reflect sediment deposit-feeding habits. Predation scars on trilobites record the activity of various carnivorous arthropods including dinocarids. In rare examples, fragmented trilobite sclerites have been found within the gut tracts of other arthropods including a dinocarid. Fragmented trilobite sclerites, are common in Cambrian coprolites and abundant in some early Paleozoic deposits. Such broken sclerites likely result mostly from predaceous or scavenging activity, as actualistic taphonomic experiments on modern analogs suggest that breakage by means of mechanical transport in water is difficult.