PHYLOGENETIC ANALYSIS OF THE SCAPHITIDAE (AMMONOIDEA) USING PARSIMONY AND BAYESIAN TIP-DATING APPROACHES

The Scaphitidae are a long-lived family of heteromorph ammonites extending from the late Albian to the late Maastrichtian (and possibly into the early Paleocene). They comprise at least 20 genera and more than 250 species according to some counts. We present a cladistic analysis of Scaphitidae using a novel character matrix sampling approximately 300 morphological characters that includes species from all genera within the family. Phylogenetic analyses were conducted using both maximum parsimony and Bayesian tip-dating (BTD) methods. BTD methods are probabilistic approaches to inferring phylogenies that integrate morphologic and stratigraphic data via mathematical models of trait evolution, species diversification, and fossil sampling. Where applicable, we incorporate temporal data by placing uniform distributions on species occurrences corresponding to their earliest known biozone intervals. To our knowledge, the combination of our large phylogenetic character matrix (~300 characters) and high-resolution temporal data (resolved to biozones) is unprecedented for a fossil marine invertebrate dataset, making it an ideal empirical case study for documenting macroevolutionary patterns in a phylogenetic context. Characters informative for higher level phylogeny include the presence/absence and shape of the umbilicolateral, lateral, ventrolateral, and ventral tubercles; the presence/absence of apertural lappets on microconchs (males); the presence of a bulge on the umbilical shoulder of the shaft of macroconchs (females); the degree of branching and intercalation of ribs; bifid or trifid first lateral lobes; the relative size of the spire, shaft, and hook; the degree of recurvature of the hook; and the projection of the ribs on the venter of the spire, shaft, and hook (backward, straight across, or forward). Our results provide insight into the monophyly of major scaphitid groups, evolutionary relationships among species, and recognition of synapomorphies. In addition, this study provides a framework for future studies investigating patterns of morphologic evolution and species diversification within Scaphitidae.