Co-estimation of phylogeny and divergence times of Argonautoidea using relaxed phylogenetics.

This is the first study to investigate molecular phylogenetic relationships among all four genera of the superfamily Argonautoidea, a clade of diverse pelagic cephalopods with extraordinary characters such as ovoviviparity, dwarf males and secondary "shell" development. Phylogenetic relationships and divergence times within the superfamily were co-estimated using relaxed phylogenetic techniques. A sister-taxon relationship was recovered between Argonauta and Ocythoe and between Tremoctopus and Haliphron. The most recent common ancestor of Argonautoidea was estimated to date from the early Tertiary under the scenario that a lack of a "shell" in the ocythoid lineage is a primary characteristic. In contrast, a later Tertiary most recent common ancestor was estimated under the scenario that a "shell" was present in the early ocythoid lineage and was subsequently lost. Copyright 2009 Elsevier Inc. All rights reserved.