A PHYLOGENETIC RECONSTRUCTION OF THE TRILOBITE FAMILY DALMANITIDAE

RANDOLFE, ENRIQUE A.; BIGNON, ARNAUD; RUSTÁN, JUAN JOSÉ

Congreso; CAPA 2021; 2021

Asociación Paleontológica Argentina

Dalmanitidae Vogdes, 1890, is a classical trilobite family of the suborder Phacopina Struve, 1959, whose cosmopolitan records embrace the Middle Ordovician (470 Ma) to the Middle Devonian (380 Ma). Despite numerous contributions, its diagnosis and intrafamiliar systematics required a review based on a thorough phylogenetic analysis. Some systematic issues to be solved included the interpretation of basal taxa and the definition of Ordovician subfamilies of disputed validity. In addition, the most accepted post-Ordovician subfamilies, Dalmanitinae and Synphoriinae Delo, 1935, clearly do not encompass all the Silurian?Devonian taxa. Indeed, recent reviews highlighted several South American taxa exhibiting diagnostic characters of both of them. Here we report the preliminary results of a phylogenetic hypothesis of the family Dalmanitidae, performed by cladistic methods using parsimony. Using the TNT software, we analyzed 77 genera from 104 characters obtaining 128 best trees with 904 steps. The strict consensus (CI= 0.15; RI= 0.53) shows a clade including virtually all the Silurian?Devonian taxa. The Ordovician taxa are located in successive external groups defining not substantial clades. The basal position of some taxa, close to the outgroups, moved us to revise the diagnosis of the family. The new diagnosis emphasizes characters not taken into account before, including the frontal lobe of the glabella extended laterally, the course of the facial suture far away from the preglabellar furrow, and the nearly subtriangular pygidium. Based on this new definition, a number of taxa previously considered dalmanitids are excluded from the family, such as the genera Dreyfussina Hupé in Choubert et al., 1956, Morgatia Hammann, 1972, and Ormathops Delo, 1935. Dalmanitinae and Synphoriinae are not supported by this new proposal. Moreover, based on new diagnostic characters, some genera previously considered synphoriinids define a clade almost endemic of the Eastern American Realm. The remaining Silurian?Devonian genera are included in a sister group with a Devonian diversification into two large subclades with a high biogeographic signal: one Malvinokaffric (from Southwestern Gondwana) and another from the Old World Realm (mainly including Eurasia).