Phylogeny of the Phreatoicidea

Protamphisopus wianamattensis (Chilton, 1918) from the Middle Triassic (Anisian) Ashfield Shale in the Sydney Basin, Australia, is the earliest-known freshwater representative of the basal isopod suborder Phreatoicidea. In contrast, the late Paleozoic Palaeophreatoicidae species, which are morphologically distinct from extant families, are found in marine or estuarine facies. Comparison of Protamphisopus wianamattensis with living Phreatoicidea permits the external morphology of the fossils to be reconstructed and the species to be coded for cladistic analysis using a revised and expanded character set developed for living phreatoicideans. In resulting parsimonious trees as well as immediately suboptimal trees, Protamphisopus is nested within clades related to the family Amphisopodidae. Therefore, a minimum age of Middle Triassic can be assigned to the basal branches within the phreatoicid crown group.

FIGURE 14 (right, from Wilson and Edgecombe, 2003 ) — Cladogram of the Phreatoicidea. Strict consensus of 28 trees, length=911 (CI excluding uninformative characters=0.39, RI=0.66, RC=0.21), Bremer support values higher than 1 shown above branches; Bremer support higher than 1 for analysis without Protamphisopus shown beneath branches for clades in or adjacent to Amphisopodidae sensu lato. All taxa except for Protamphisopus are extant; monophyletic family-level clades indicated by line types, as shown in legend. Wilson and Keable (2002b) provide additional details on specimens used in the analysis. The QLD sp.1 & 2 are the two species of Ponderella.