PRELIMINARY PHYLOGENETIC ANALYSIS OF THE OXYSTOMATA SENSU LATO (CRUSTACEA: DECAPODA: BRACHYURA): NEW HYPOTHESES ABOUT BRACHYURAN EVOLUTION

The status of the Oxystomata, a group of brachyuran decapods (crabs), has been debated for over a century. In most recent decapod classifications, it has been eliminated as an obsolete term. However, a recent phylogenetic analysis of adult foregut characters of selected Brachyura suggests that the Oxystomata may be a viable taxon (Brösing, 2002). We tested this hypothesis using 31 extinct and extant brachyuran taxa and 31 adult morphological characters that are usually observable in well-preserved fossil specimens. Members of extinct families, the Dakoticancridae, Necrocarcinidae, Orithopsidae, and Torynommidae, and the enigmatic genus Camarocarcinus were included in the study. These extinct taxa have not before been placed with other decapod families in a phylogenetic analysis. Most of these extinct taxa historically have been allied with the Oxystomata. The data matrix was analyzed using NONA version 2.0 and WinClada ver. 1.00.08. The result was one most parsimonious tree, and although bootstrap values were modest for many branches, Bremer support was moderate to high for many branches.

Results of the analysis confirm that the Oxystomata is generally valid and embraces the traditionally included Calappidae, Leucosiidae, and Dorippidae as well as the Hepatidae, Parthenopidae sensu lato, and the extinct Necrocarcinidae, Orithopsidae, and Torynommidae. Most Raninidae, traditionally included as oxystomes, were excluded from the group. The extinct Notopocorystes, historically placed within the Raninidae, may not belong to the family; according to our analysis, it is more closely allied with the Calappoidea and Leucosoidea.

The extinct Dakoticancridae and Camarocarcinus were allied with the podotrematous, or primitive, crabs in our analysis. This is the first step toward resolving their phylogenetic placement within the Brachyura.

Most importantly, use of adult dorsal carapace and macroscopic sternal and abdominal characters, often eschewed by neontologists, produces the same general familial arrangement as use of molecular data or pleopod and pereiopod characters commonly used for brachyuran classification and phylogenetics in the neontological literature. In nearly every case, even with incomplete data, fossil and extant congeners were sister taxa in the analysis.