Echinoderm phylogeny: how congruent are morphological and molecular estimates?

A Total-Evidence Dated Phylogeny of Echinoidea Combining Phylogenomic and Paleontological Data

Phylogenomic and paleontological data constitute complementary resources for unraveling the phylogenetic relationships and divergence times of lineages, yet few studies have attempted to fully integrate them. Several unique properties of echinoids (sea urchins) make them especially useful for such synthesizing approaches, including a remarkable fossil record that can be incorporated into explicit phylogenetic hypotheses. We revisit the phylogeny of crown group Echinoidea using a total-evidence dating approach that combines the largest phylogenomic data set for the clade, a large-scale morphological matrix with a dense fossil sampling, and a novel compendium of tip and node age constraints. To this end, we develop a novel method for subsampling phylogenomic data sets that selects loci with high phylogenetic signal, low systematic biases, and enhanced clock-like behavior. Our results demonstrate that combining different data sources increases topological accuracy and helps resolve conflicts between molecular and morphological data. Notably, we present a new hypothesis for the origin of sand dollars, and restructure the relationships between stem and crown echinoids in a way that implies a long stretch of undiscovered evolutionary history of the crown group in the late Paleozoic. Our efforts help bridge the gap between phylogenomics and phylogenetic paleontology, providing a model example of the benefits of combining the two. [Echinoidea; fossils; paleontology; phylogenomics; time calibration; total evidence.].

Not all written in stone: interdisciplinary syntheses in echinoderm paleontology

The fossil record of the Echinodermata is relatively complete, and is represented by specimens retaining an abundance of features comparable to that found in extant forms. This yields a half-billion-year record of evolutionary novelties unmatched in any other major group, making the Echinodermata a primary target for studies of biological change. Not all of this change can be understood by studying the rocks alone, leading to synthetic research programs. Study of literature from the past 20 years indicates that over 1400 papers on echinoderm paleontology appeared in that time, and that overall productivity has remained almost constant. Analysis of papers appearing since 1990 shows that research is driven by new finds including, but not restricted to, possible Precambrian echinoderms, bizarre new edrioasteroids, early crinoids, exquisitely preserved homalozoans, echinoids at the K-T boundary, and Antarctic echinoids, stelleroids, and crinoids. New interpretations of echinoderm body wall homologies, broad-scale syntheses of embryological information, the study of developmental trajectories through molecular markers, and the large-scale ecological and phenotypic shifts being explored through morphometry and analyses of large data sets are integrated with study of the fossils themselves. Therefore, recent advances reveal a remarkable and continuing synergistic expansion in our understanding of echinoderm evolutionary history.