A NEW FAMILY OF TRIASSIC LOBSTERS (DECAPODA: ASTACIDEA) FROM BRITISH COLUMBIA AND ITS PHYLOGENETIC CONTEXT

Journal of Paleontology, Jan 2004 by Amati, Lisa, Feldmann, Rodney M, Zonneveld, John-Paul

Another important recent work (Martin and Davis, 2001) presents a classification of the Decapoda that might be viewed as a compromise position, also based on neontological criteria that can not be applied to fossil taxa. Many of the reassignments in the Martin and Davis classification bear a resemblance to those of Scholtz and Richter (1995) and Schram (2001), but traditional names of the taxa have been conserved. Martin and Davis recognize the conventional classification of the Astacidea, with the addition of the Enoplometopoidea and Glypheoidea, and consider the group to be monophyletic. Including the glypheids in the infraorder Astacidea introduces a problem of nomenclature. The Astacidea have traditionally been grouped into families, while the Palinura are arranged in superfamilies. In order to maintain a uniform level of hierarchical classification, we follow the precedent of Martin and Davis (2001) in using the superfamily level of classification for clades within the Astacidea (Nephropoidea, Glypheoidea, Erymoidea). Martin and Davis (2001) further suggest that it is misleading to treat the two groups of crayfish, Astacoidea and Parastacoidea, as superfamilies. We agree and retain the traditional rank of family for the Astacidae and Parastacidae and name the monophyletic superfamily Astacoidea.

A molecular analysis of decapod relationships using nuclear and mitochondrial DNA also supports the monophyly of the Astacidea (Crandall et al., 2000). This analysis produced a monophyletic clade including the Astacoidea, Parastacoidea and Nephropoidea.

The present study seeks to answer questions of taxonomic affinity of fossil decapods and, therefore, cannot employ the same characters used in the studies mentioned above. Instead, the phylogeny generated herein is based solely on morphological characters that are preserved in the fossil record. Prior research suggests that including fossil taxa in morphology-based phylogenetic analyses provides insight into phylogenetic relationships not possible when limiting analyses to modern taxa (e.g., Gautier et al., 1988; Donoghue et al., 1989; O'Leary and Geisler, 1999). Incorporation of fossil taxa into the analysis thus provides an important basis for comparison with the works of Scholtz and Richter (1995), Schram (2001), and Martin and Davis (2001).

Chimaerastacus pacifluvialis is most appropriately classified within the infraorder Astacidea Latreille, 1802, as emended herein. However, it shares distinctive characters with certain members of the superfamily Glypheoidea, including three longitudinal ridges on the cephalic region and the placement of the cervical, post-cervical and branchiocardiac grooves. The Glypheoidea has been traditionally placed within the infraorder Palinura, although Forest and de Saint Laurent (1989) suggested that it be removed. The glypheids possess only two characteristics that might argue against their inclusion within the infraorder Astacidea: presence of subchelae and, by current definition, the fusion of the epistome with the frontal margin of the carapace. An examination of numerous, well-preserved fossil glypheid specimens from the collection at Kent State University indicates that, although the epistome has a long edge of contact with the frontal margin of the carapace, it is not physically fused with the carapace (Feldmann and de Saint Laurent, 2002) as in brachyurans and many palinurans. This observation is confirmed by studies of the relatively recently discovered extant member of this group, Neoglyphea inopinata (Forest and de Saint Laurent, 1981, 1989).