PHYLOGENETIC ANALYSIS OF AMMONOID FAMILY ACANTHOCERATIDAE IN A BAYESIAN FRAMEWORK

Ammonoid family Acanthoceratidae was a diverse clade that evolved in the Albian and proliferated during the Cenomanian and Turonian across the world, but mainly in the Western Interior Seaway, Europe, and Northern Africa. This group’s phylogenetic relationships have been examined in the past using parsimony analyses, but never in a Bayesian framework. Along with this, previous studies have been completed at taxonomic levels higher than the species level. In this study, I ran a species-level Bayesian phylogenetic analysis on 149 members of the Acanthoceratidae family. I conducted analyses using Reversible Jump Markov Chain Monte Carlo (rjMCMC) analysis that jumps between “simpler” and “more complex” models, with different models considered for clocks (strict and relaxed), character partitions (all characters; general shell vs. suture; shell shape vs. shell sculpture vs. Suture) and diversification partitions (constant rates vs. several models adding rate shifts around major events such as the OAE2). For clocks, partitions and diversification, the rjMCMC analyses supported the most complex models. The maximum credibility tree contained a large amount of polyphyly within the subfamilies and genera, with many members multiple genera spread across the tree. I then used BioGeoBEARS to optimize the tree to examine the morphology in a different light – if environment, such as ocean depth of locality, impacts the morphology of the ammonoids. The optimized tree showed a branch early in the phylogenetic history between species that can live in shallow or deep water and those that can only live in deep water. This indicates that morphology of ammonoid family Acanthoceratidae is impacted not only by phylogeny, but also by environment.