MOOI, R.; BRYAN, R.*; CERVANTES, S.*; California Academy of Sciences, San Francisco; University of Florida; Dominican University, San Francisco: Eccentric phylogeny: biodiversity and evolution of fossil and extant sand dollars from the northern Pacific

The rich diversity of clypeasteroids (sand dollars and keyhole urchins) of the northern Pacific Ocean encompasses many common yet poorly known taxa. Among the more than 130 nominal species and approximately 20 genera, there are 3-holed forms of uncertain affinity, large “dinner plates” from Alaska, highly miniaturized species placed in the wrong suborder, and several clades in which the usually central apical system has been displaced posteriorly to create “eccentric” sand dollars. Our phylogeny strongly supports the hypothesis that this eccentricity evolved no fewer than 3 times. A survey of all taxa within the global distribution of Clypeasteroida indicates that eccentricity is found only in clades occurring along northeastern Pacific coasts from Alaska to Mexico. Is this by chance, or is there some underlying characteristic of this region that might lead to multiple occurrences of eccentricity? If so, what is the adaptive significance of eccentricity? A detailed case study of a major clade of sand dollars in the genus Echinarachnius indicates that long-cherished taxonomies of even these most familiar and perhaps important groups need drastic revision, and that at least some of the genera are not monophyletic. Echinarachnius was once thought to be the sister group of another diverse clade of Miocene forms often used in biostratigraphy, Astropdapsis, but it is clear from our results that Astrodapsis evolved within Echinarachnius, and that the latter consists of several clades that are successive outgroups to the former. We discuss the implications of these findings in the context of major evolutionary events in the history of these sand dollars from the Eocene to the present.