ASSESSING MONOPHYLY OF THE SPATANGOID ECHINOID GENUS MECASTER WITH IMPLICATIONS ON DIVERSITY AND EXTINCTION PATTERNS IN THE LATE CRETACEOUS

In order to better understand diversity and extinction patterns of the spatangoid echinoid clade Mecaster, and to place the clade into a robust paleobiogeographic context, its relationships with major groups need to be better resolved and species level synonymies worked out. Furthermore, data recently collected from Latin America needs to be placed into the larger phylogenetic picture. The genus Mecaster has been both included in and excluded from the spatangoid echinoid family Hemiasteridae – one of three families in crown Spatangoida. The most recent phylogenetic analyses support exclusion and indicate a sister taxon relationship, though this assessment is based on only a few species. A potential relationship of some Mecaster species with Schizasterdae (another family in crown Spatangoida) has also been proposed, making it a grade of organization rather than a clade. Here we test the monophyly of Mecaster by performing a detailed phylogenetic analysis of crown Spatangoida including species from Mecaster, Hemiasteridae, Schizasteridae, and Micrasteridae with species from Toxaster and Heteraster as outgroups. Prior attempts to characterize groupings within Mecaster based on test plate features and arrangements focused on the North African species or smaller subsets of wider spread species. Of the more than 80 named species assigned to Mecaster, some 50 have been assessed so far in this study and include material from Africa, Asia, Europe, North America, and South America. Within the high number of Mecaster species there are numerous synonymies required. Morphometric data is used to create further discrete characters which better describe variation in test shape. This study provides enhanced understanding of echinoid diversification and extinction patterns in the Late Cretaceous up to and through the End Cretaceous Mass Extinction.