TAPHONOMIC CONTROLS ON THE PALEOZOIC ECHINOID FOSSIL RECORD

Understanding the varied environmental, biological, and geological processes which control preservation in the fossil record is crucial for assessing their impact on our perception of ancient biodiversity. Despite this, there are few large datasets which have been used to quantify the preservational state of whole clades or animal groups, and the factors underlying the differential preservation of different specimens. Echinoids, or sea urchins, are generally regarded as having a well-sampled fossil record, and display a variety of preservational styles, from articulated specimens with spines, to single disarticulated skeletal elements. Because of this, they are an ideal model system in which to examine the interplay of environment, phylogeny, and geological history on large-scale trends in fossil preservation. We surveyed the Palaeozoic fossil record of echinoids, using specimen-level data from museum collections and the literature in an attempt to understand the drivers of differential fossil preservation. The quality of fossil specimen preservation was scored using a semi-quantitative index based upon completeness and articulation, which could then be compared to the age, taxonomic group, matrix grain size and lithology for each specimen. Our results show distinct taphonomic patterns are present for different taxonomic groups, which may indicate intrinsic, clade-specific controls on the fossil record of sea urchins resulting from differential suturing of skeletal plating in different taxonomic groups. Furthermore, different preservational styles are seen amongst specimens preserved in rocks with different grain sizes. Our results highlight that the factors controlling the animal macrofossil record are varied, and result from an interplay of both intrinsic features resulting from animal morphology, and extrinsic features resulting from the environment.