PHYLOGENETIC ANALYSIS OF ARGENTINIAN OLENIDAE (TRILOBITA, PTYCHOPARIIDA) FROM THE FURONGIAN AND ORDOVICIAN

MONTI, DANIELA S.; CONFALONIERI, VIVIANA A.

Mendoza, Argentina

Congreso; 4th International Paleontological Congress. The history of life: A view of the Southern Hemisphere.; 2014

To evaluate the relationships between the Argentinian members of Olenidae Burmeister, a cladistic analysis was performed. A total of 20 species were included (eleven Triarthrinae, two Hypermecaspidinae, one Plicatolininae, four Oleninae and two Pelturinae). Seventy five characters were codified (55 of the cephalon, eight of the torax, eight of the pigydium and four of the entire exoesqueleton), of which 23 are quantitative (20 ratios and three meristic) and were all codified either as discrete (additives and non-additives) or as median. This latter statistic descriptor was elected because it has the advantage that is little affected by few high values in the frequencies analyzed. When continuous characters are treated as such, the standardization versus the use of the raw data were explored. The data matrices were analyzed with TNT version 1.1 applying maximum parsimony and implied weights as optimality criteria. Analyses with implied weighting were conducted by means of values for the concavity constant k= 5?16. Since several authors considered Olenus Dalman as the ancestral genus of Olenidae, the most parsimonious tree was rooted with Olenus gibbosus (Wahlenberg). With respect to the continuous characters codification, similar results were obtained when treated as discrete additives or as medians. When cuantitative characteres are codified as medians, application of implied weights criteria is more efficient than standardization of raw data for solving scaling problems. Regarding to the relationships of species, these are partially consistent with previous proposals based on direct morphological comparison and stratigraphy. Parabolinella Børgger is a monophyletic group and Plicatolina scalpta Harrington and Leanza is its sister group. Triarthrus jachalensis (Harrington and Leanza) is included in the genus Bienvillia Clark. The Thiarthrinae are paraphyletic, because it do not include P. scalpta. Both Oleninae and Pelturinae would not be monophyletic groups. While the genus Angelina Salter is a well supported monophyletic group, Parabolina (Neoparabolina) argentina (Barrande) is more closely related to Jujuyaspis keideli Kobayashi than Angelina genus. On the other hand, Leptoplastides marianus (Hoek) is recovered as the sister group of Triarthinae. The two species of Hypermecaspis Harrington and Leanza form a monophyletic group but, unlike previous proposals, preliminary results show no relationship between this genus and the subfamily Thriarthtinae.