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

Discussion.-Our analysis suggests that palinuran lobsters are a paraphyletic group. Representatives of the family Palinuridae form a clade based on the absence of chelae on all pereiopods (character 13[2]) and an uncalcified posterior portion of the telson (character 18[3]). The family Scyllaridae is usually considered to be closely related to the Palinuridae, with both families classified in the superfamily Palinuroidea. Our analysis groups Scyllarus with the Polychelidae based on the presence of two apomorphies: a first pereiopod that is larger than the second through fifth pereiopods (character 15[1]) and the presence of a dorsal ridge on the abdomen (character 16[1]). This is an interesting result that warrants further investigation in the future.

Scholtz and Richter (1995) coined the term Fractosternalia for four of their monophyletic groups (Astacida, Thalassinida, Anomala and Brachyura) based on the separation of the eighth thoracic sternite from the rest of the sternum. This feature is present in crayfish, thalassinids, and anomalans but is presumably lost in brachyurans. The fractosternate condition is difficult to assess for fossil lobsters, especially glypheids and erymids, which are preserved rarely in ventral view. We were able to code this feature only for modern taxa. Presence of the fractosternum arises at node 55 in our analysis and defines a clade that includes nephropoids, erymoids and glypheoids as well as groups included by Scholtz and Richter (1995). The topology requires reversals in the brachyura and the Nephropoidea. A free eighth thoracic sternite was recognized in Neoglyphea inopinata by Schram (2001) but the fractosternate condition is unknown for all other taxa above node 42. The results of our analysis predict the presence of a fractosternum in erymoids, but no direct fossil evidence confirms this. Because this character represents missing data for fossil taxa, we ran an identical analysis with the fractosternum excluded in order to determine the extent of the influence of this character on our result. Nodes 56, 55 and 54 collapsed as a result of the exclusion of the fractosternum, but the monophyly and ingroup relationships of the Astacidea were not affected.

A large clade composed of taxa from the infraorders Anomura, Thalassinidea, and Brachyura is defined at node 54. This group corresponds to the monophyletic Thalassinida-Anomala-Brachyura group in cladograms produced by Scholtz and Richter (1995) and Schram (2001). The purpose of including representatives of these taxa in our analysis is to allow an assessment of the monophyletic status of the Astacidea. Further investigation into the ingroup relationships of this clade will not be attempted here.

Our cladistic analysis agrees with the molecular analysis of Crandall and others (2001) by defining a monophyletic Astacidea, here diagnosed by the presence of a diaresis on the exopod of the uropod (character 19[1]) and a subcylindrical carapace cross section (character 1[2]). A diaresis is also present on the exopod in the Laomediidae and in some taxa in the Axiidae. The universal presence of this character in every taxon within the Astacidea and complete absence of a diaresis in all other taxa except for two highly derived families leads us to believe that it was derived independently in these groups and is a synapomorphy of the Astacidea. All three families of the superfamily Glypheoidea are firmly placed within the infraorder Astacidea, confirming the suggestion of Forest and de Saint Laurent (1989) and Martin and Davis (2001). It is our opinion that the taxa retained within the superfamily Glypheoidea may be incorporated into the infraorder Astacidea by emending the definition of the infraorder to include sub- to pseudochelate forms. This solution formalizes the suggestion made by Forest and de Saint Laurent that the Glypheoidea are more closely related to astacideans than to palinurans. Note, however, that contrary to Forest and de Saint Laurent (1989), we include the Mecochiridae within the superfamily.