Phylogeny and Disparity of Ammonoid Family Acanthoceratidae Over Ocean Anoxic Event 2

Authors

Lindsey Howard, University of Nebraska-LincolnFollow

First Advisor

Peter J. Wagner

Committee Members

Margaret Mary Yacobucci, Scott L. Gardner, David Harwood

Date of this Version

7-2024

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Geosciences

Under the supervision of Professor Peter J. Wagner

Lincoln, Nebraska, July 2024

Comments

Copyright 2024, Lindsey Howard. Used by permission

Abstract

The widespread use of genera as proxies for species in paleobiological studies might affect the results of these studies. Although most attention has been given to taxonomic diversity studies, this could also be true of disparity and phylogenetic studies. In particular, the assumption that particular character states truly diagnose all members of a genus might distort results. This study examines the disparity of Acanthoceratid ammonoids at both the generic and species level. 149 species from 42 genera were examined with 52 characters measured. Following the measurements, an inverse modeling simulation was run 100 times to generate a simulated phylogeny with the same compatibility as the measured data.

Inter- and intrageneric variation showed very little difference from each other. Through each partition and character type, variation within genera was almost as high as variation between genera. However, when compared to expected disparity, measured variation was consistently lower. This could indicate environmental restrictions limiting change or character suites changing together, combined with a restriction on the total morphological variation.

The Acanthoceratidea are a prominent group of Late Cretaceous ammonoids known from throughout the world and best known for their use in biostratigraphic and biogeographic studies. Two prior phylogenetic analyses were conducted at the genus-level. Analyses were conducted in two phases. The first used a Bayesian reversible jump Markov Chain Monte Carlo (rjMCMC). rjMCMC analyses contrasts different parameters for particular models for the best model to be chosen over the course of multiple iterations. After the best model was chosen, a second MCMC was run using just the best models. This allowed for a more fully realized examination of the hypothesis space and a more likely phylogenetic tree. The tree was also optimized for water depth to examine interactions of phylogenetic relationships and environment. The phylogenetic tree showed a high level of polyphyly. When examining water depth, there is a high level of conservation in environment. This may indicate characters used for phylogenetic analyses are impacted by environment.

Advisor: Peter J. Wagner