TESTS OF TURTLE PHYLOGENY - MOLECULAR, MORPHOLOGICAL, AND PALEONTOLOGICAL APPROACHES

We present phylogenetic analyses of both molecular and morphological d ata for the 23 major lineages of living turtles and seven key fossil t axa. Nearly 1 kilobase of cytochrome b sequence, 325 base pairs of 12S ribosomal DNA, and 115 morphological characters contained similar phy logenetic information, although each provided unique information on di fferent nodes of chelonian history. A character-based combinability te st (implemented in PAUP) and a nonparametric test of taxonomic congru ence indicated no strong evidence for heterogeneity among data sets, a nd we used a combined approach to estimate a final phylogeny of the ma jor lineages of living turtles. This approach resulted in a very well- resolved tree, with only a few of the deep branches within the Cryptod ira left as an unresolved polytomy. The addition of six relatively com plete fossils chosen to help resolve this basal polytomy provided litt le added resolution to the tree and resulted in a sharp decline in boo tstrap proportions for nodes near the fossils. Branch-length analysis and independent dates from the fossil record suggest that these unreso lved nodes may represent a rapid radiation of the major cryptodiran li neages 90-120 million years ago.