TESTING HYPOTHESES OF SURVIVORSHIP WHEN PSEUDOEXTINCTION GETS IN THE WAY: TEREBRATULIDE GENERA AT THE PERMO-TRIASSIC BOUNDARY

Of all the various types of extinction selectivity recognized and studied in the fossil record, phylogenetic selectivity is perhaps the least investigated and the least understood of all. 100% generic extinction of terebratulide brachiopods (and near 100% extinction of rhynchonellides) at the end–Permian requires some estimate of phylogenetic relationship in order to link Paleozoic and Mesozoic lineages; selectivity due to ecological or biogeographical factors cannot be interpreted in the absence of such a framework when 100% taxonomic extinction is recorded. In order to evaluate hypotheses of phylogenetic selectivity at the end-Permian, we analyzed 44 morphological characters as they vary among 36 Late Permian to Middle Triassic terebratulide genera to establish hypotheses of lineage continuity across this major extinction boundary. How did extinction map out phylogenetically among these taxa? Where did originations occur phylogenetically? We then used these results as a framework for testing several additional hypotheses concerning terebratulide survivorship, and determining what pattern of selectivity, if any, emerged within clades: 1) smaller-bodied terebratulides survive or originate preferentially relative to larger, 2) more spherical lineages survive or originate preferentially relative to less spherical, 3) lineages with larger geographical ranges survive preferentially relative to those with smaller ranges, and 4) non-tropical lineages survive or originate preferentially relative to tropical lineages. For example, were small-large sister-group pairs relatively common, or was body size more commonly a feature of a larger clade? Were large taxa selected against, or not? If so, did small taxa that originated following the end-Permian episode typically have large-bodied sister groups, or small-bodied sister groups? Placing the origination of particular morphological, as well as ecological and biogeographical, features in a phylogenetic context, makes it possible to evaluate them evolutionarily. We conclude by comparing these results from the end-Permian with earlier results examining morphological and phylogenetic selectivity among terebratulide brachiopods at the end-Devonian.