BACULITID PHYLOGENETIC RECONSTRUCTION FROM A BAYESIAN PERSPECTIVE

Baculitidae, a family of heteromorph ammonoid cephalopods, are well known for their use in biostratigraphy, especially in the Late Cretaceous North American Western Interior Seaway (WIS). However, the understanding of evolutionary relationships between species of baculitids not only in the WIS but also in other North American localities has been limited thus far. A Bayesian phylogenetic analysis was performed on North American baculitids using the fossilized birth-death model, a relatively new method for reconstructing morphology-based phylogenies from a Bayesian approach. A total of 23 baculitid ornamentation, shell shape, and suture characters were coded in a character matrix for 43 operational taxonomic units. Estimated ranges for first appearances were drawn from occurrences in the Paleobiology Database. The evolutionary relationships of Late Cretaceous baculitid species from the North American Eastern Pacific Coast, Western Interior Seaway, Gulf Coastal Plain, and Atlantic Coastal Plain were modeled to produce a time calibrated Maximum Compatibility Tree. Speciation, extinction, sampling, diversification, and turnover rates were also obtained over 10 intervals through the Cretaceous. Sciponoceras, one of the earliest baculitid genera, forms the basal stem of the family. One of the most well supported clades in this phylogenetic tree suggests that the turnover event at the Cenomanian-Turonian boundary, associated with Ocean Anoxic Event 2, gave rise to the clade that contains most of North America’s Baculites species. The tree also suggests that several Baculites species anagenetically evolved into Trachybaculites and Eubaculites species, indicating the need for taxonomic revisions within this important ammonoid family.