The Shock of Unexpected Conservatism

a Counter-signal to Pachycormid Divergence?

Abstract

Pachycormid taxonomy has accepted the twin lineage pattern of toothed and toothless tribes, leading respectively to the Late Cretaceous Protosphyraena and Bonnerichthys, for over ten years. Recent work on pectoral fin morphotypes has revealed a diversity of forms, reflecting specialization in swimming styles. Examination of pectoral girdle components led to an unexpectedly similar set of characteristics between these two genera, supposedly separated by a gap of over 100 million years since their common ancestor. This raises the question of whether these two taxa are as distantly related as current pachycormid phylogenetic hypotheses suggest.