HIDDEN TRIASSIC ECHINOID DIVERSITY; EXPLORING LINEAGES WITH NO FOSSIL RECORD

Echinoid diversity experienced a severe bottleneck at the end of the Paleozoic and into the Triassic, with direct fossil evidence of only one lineage, the Miocidaridae, crossing the boundary. However, previous phylogenetic analysis supports the hypothesis that at least two echinoid lineages survived into the Mesozoic, the cidaroids and euechinoids. All modern echinoids belong to these two sub-classes, and the first appearance of cidaroids in the fossil record, with the occurrence of Eotiaris keyserlingi in the Capitanian (Permian, 265 Ma), implies the existence of the euechinoid sister group as well. However, fossil euechinoids are unknown before the Carnian (Triassic, 237 Ma), signifying a 30 Ma fossil gap. The scarcity of echinoid fossil diversity in the Permian and Triassic can be attributed to a number of things, including the poor preservation potential of non-sutured tests, geographic range restrictions, or dependence on Lagerstätte-quality preservation for taxonomic identification of specimens. Despite the scarcity of whole test specimens from this time, multiple Triassic deposits preserve disarticulated echinoid material, sometimes occurring in concentrated beds, suggesting that echinoid were not rare in shallow marine settings. Here we present an occurrence database of all known Triassic echinoids reported from the literature, including disarticulated remains, as well as a preliminary phylogenetic analysis of Permian and Triassic echinoid species. The phylogenetic analysis suggests that at least one additional lineage of Triassic echinoids can be linked to a Permian ancestor and had therefore crossed the boundary as well. Additionally, a recent discovery of a presumed Proterocidarid from the Muschelkalk of France suggests another lineage that crossed the boundary for which no fossil evidence exists for a period of 30 Ma. In light these findings and the limited echinoid fossil record of this time, it is highly likely that currently unknown and unrepresented lineages crossed into the post-Paleozoic, and the echinoid bottleneck of diversity is a rock record artifact.