Origin and spread ofPudoproetus, a survivor of the Late Devonian trilobite crisis

Abstract

One of the most severe restrictions in taxonomic diversity of trilobites coincides with the Late Devonian “Hangenberg” Event, which is characterized by a pronounced eustatic low-stand. One of the survivors of this event isPudoproetus, which, being adapted to shallow water conditions, experienced an opportunistic worldwide spread during this time. The oldest representatives of this genus are reported from the pre-Hangenberg Late Famennian of the Urals and Kazakhstan. Other known occurrences of this genus, midcontinent U.S.A., Utah, southern China, and southern France, occur at the Devonian-Carboniferous boundary, shortly after the Hangenberg event, and in the earliest Carboniferous. This pattern of distribution suggests that neither climatic nor geographic migration barriers existed around the Old Red landmass at that time. On the other hand, the Hangenberg crisis severely affected outer shelf benthic habitats, whereas nearshore trilobites were largely unaffected by the event.A proetine origin ofPudoproetus, as originally proposed by Hessler (1963), is emphasized on the basis of paleoecologic, stratigraphic, and morphological arguments. In particular, the presence of ancestral features, such as the possession of 10 thoracic segments and lateral occipital lobes still occurring in earlyPudoproetusspecies, points to a phylogenetic link with proetines rather than with phillipsiids. Within this group two new species are named:P. priscusandP. mediterraneus.