QUANTIFYING THE FIDELITY OF THE MACRO-INVERTEBRATE FOSSIL RECORD ACROSS MULTIPLE HIGHER TAXA IN NEARSHORE MARINE ASSEMBLAGES

Studies assessing the mismatch between living communities, and concurrently accumulating death assemblages across multiple phyla are critical for studying large-scale patterns in the fossil record, where multiple groups are analyzed jointly to assess macro-evolutionary models. As past research has primarily focused on single higher taxa with hard parts (e.g., mollusks), and few studies have included multiple phyla, we currently lack analyses intended to simultaneously evaluate all phyla. Thus, we know little about multi-taxon fidelity patterns or variation in fidelity across classes and phyla.

To evaluate higher-taxon fidelity and taphonomic biases within and across higher taxa, dredging of sympatric live and death assemblages was conducted in coastal North Carolina (USA). 53 localities representing a wide range of depths and habitats were sampled, and targeted 7 higher taxa with variable skeletal types in both live and dead material. Species richness and relative abundance for live and sympatric death assemblages were examined within and across higher taxa, and relative fossilization potential was estimated for each major taxonomic group.

Samples included 12,981 live and 58,548 dead individuals, 247 species, and 7 phyla (arthropods, annelids, brachiopods, cnidarians, echinoids, mollusks, and sponges). Although preservation potential was elevated for more heavily biomineralized taxa with fewer skeletal components (e.g., mollusks) and depressed for phyla with multiple skeletal elements and limited or no biomineralization (e.g., echinoderms, arthropods, and annelids), the fidelity of the relative abundance of phyla was high (Spearman’s r=0.82, p=0.03).

These results suggest that multi-taxic faunal fidelity is high at class or phylum level but declines when examined at species level within individual phyla and classes. Not surprisingly, within-taxon fidelity appears to be much higher for mollusks comparing with other taxa, which generally display very low compositional fidelity. Whereas a single case study cannot provide reliable generalizations, these results serve as a starting point toward developing numerically-grounded strategies for considering taphonomic overprints in multi-taxic analyses.