Lobsters are a ubiquitous and economically important group of decapod crustaceans that include the infraorders Polychelida, Glypheidea, Astacidea and Achelata. They include familiar forms such as the spiny, slipper, clawed lobsters and crayfish and unfamiliar forms such as the deep-sea and "living fossil" species. The high degree of morphological diversity among these infraorders has led to a dynamic classification and conflicting hypotheses of evolutionary relationships. In this study, we estimated phylogenetic relationships among the major groups of all lobster families and 94% of the genera using six genes (mitochondrial and nuclear) and 195 morphological characters across 173 species of lobsters for the most comprehensive sampling to date. Lobsters were recovered as a non-monophyletic assemblage in the combined (molecular + morphology) analysis. All families were monophyletic, with the exception of Cambaridae, and 7 of 79 genera were recovered as poly- or paraphyletic. A rich fossil history coupled with dense taxon coverage allowed us to estimate and compare divergence times and origins of major lineages using two drastically different approaches. Age priors were constructed and/or included based on fossil age information or fossil discovery, age, and extant species count data. Results from the two approaches were largely congruent across deep to shallow taxonomic divergences across major lineages. The origin of the first lobster-like decapod (Polychelida) was estimated in the Devonian (∼409-372 Ma) with all infraorders present in the Carboniferous (∼353-318 Ma). Fossil calibration subsampling studies examined the influence of sampling density (number of fossils) and placement (deep, middle, and shallow) on divergence time estimates. Results from our study suggest including at least 1 fossil per 10 operational taxonomic units (OTUs) in divergence dating analyses. [Dating; decapods; divergence; lobsters; molecular; morphology; phylogenetics.].

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The genus Portunus encompasses a comparatively large number of species distributed worldwide in temperate to tropical waters. Although much has been reported about the biology of selected species, taxonomic identification of several species is problematic on the basis of strictly adult morphology. Relationships among species of the genus are also poorly understood, and systematic review of the group is long overdue. Prior to the present study, there had been no comprehensive attempt to resolve taxonomic questions or determine evolutionary relationships within this genus on the basis of molecular genetics. Phylogenetic relationships among 14 putative species of Portunus from the Gulf of Mexico and other waters of the western Atlantic were examined using 16S sequences of the rRNA gene. The resultant molecularly based phylogeny disagrees in several respects with current morphologically based classification of Portunus from this geographical region. Of the 14 species generally recognized, only 12 appear to be valid. We recommend that P. vossi be hereafter regarded as a junior synonym of P. spinimanus and that P. bahamensis be regarded as a junior synonym of P. depressifrons . Our analysis suggests that western Atlantic members of the genus can be subdivided into at least three well-defined clades. Pending further molecular analyses with a large subset of species, it appears that the genus is not monophyletic and that it warrants further taxonomic revision.

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