Meeting Abstract

P2.108  Tuesday, Jan. 5  The origin and phylogeny of major sea urchin clades since the Paleozoic VOLLRATH, K.**; MOOI, R.; San Francisco State Univ., San Francisco; California Academy of Sciences, San Francisco kvollrath@calacademy.org

Echinoids are an ecologically important clade originating in the Ordovician, and serve as models for the evolution of novel morphologies. The origin of the echinoids has been a subject of much debate. This can be attributed in part to the lack of clearly defined homologies within the Echinodermata, and among the Echinoidea specifically. In addition, the current phylogeny of the Paleozoic urchins is incomplete both in terms of hypothesized homologies and taxon sampling. Here we provide insights into the origin of echinoids, and propose a species-level phylogeny encompassing the full diversity of Paleozoic forms. We use the Extraxial-Axial Theory (EAT) to delineate major homologies among the taxa. Even when not relying on the EAT, many of the characters have not been adequately explored for phylogenetic signal. Our approach sheds new light on when major events occurred during cladogenesis, and on phylogenetic placement of key taxa such as Bothriocidaris, Bromidechinus, Aulechinus, Eothuria, and Ectinechinus. The status of evolutionarily informative homologies is assessed in more than 60 genera, covering extinct and extant species of echinoids, holothuroids, and ophiocistioids by using species descriptions in the primary literature, observing fossil collections, and through dissections. A database of morphological, stratigraphic, and geographic data can then be compiled for each species using MacClade. Ensuing phylogenetic analysis will enable a deeper understanding of biodiversity in Paleozoic echinoids, and of the major events in the origins and diversification of this group. It will also help uncover the origins of major morphological characters among and subsequent divergence of Paleozoic echinoids, modern forms, and holothuroids.