Thesis
A description and phylogenetic relationships of a new species of crocodyliform from the Early Cretaceous Cloverly Formation of Montana
University of Iowa
Master of Science (MS), University of Iowa
Summer 2023
DOI: 10.25820/etd.007069
Abstract
Eusuchian crocodyliforms are traditionally diagnosed by procoelous vertebrae and an internal choana fully enclosed within the pterygoids, but recent phylogenetic analyses have recovered taxa lacking some of these diagnostic features, particularly the pterygoid-bound choana, within Eusuchia. To help resolve this inconsistency, we report a new crocodyliform from the Early Cretaceous Cloverly Formation of Montana. It is represented by a nearly complete diminutive skull and other referable fragmentary material. This skull bears a striking similarity to both Theriosuchus pusillus and Wannchampsus kirpachi, and is approximately 62 millimeters long, with a secondary choana bound anteriorly by the palatines and laterally and posteriorly by the pterygoid, as well as a compound palpebral comprised of a large anterior and a small posterior element. The skull is from an adult individual, which would have likely been around 1 meter long. Additional cranial material was found associated with procoelous vertebrae.
A maximum parsimony analysis recovers this crocodyliform as closely related to W. kirpachi basal within Paralligatoridae. This new taxon can be diagnosed by the following autapomorphies: anteriorly diverging nasals, and transversely expanded prefrontal pillars. This form emphasizes the disassociation of procoelous vertebrae and pterygoidal choanae at the root of Eusuchia. Moreover, it reinforces the concept that early eusuchians were small and outwardly resembled modern smooth-fronted caimans (Paleosuchus) and dwarf crocodiles (Osteolaemus), suggesting that the semiaquatic ambush predators that dominate modern crocodylian diversity arose from small, less-aquatic ancestors.
Details
- Title: Subtitle
- A description and phylogenetic relationships of a new species of crocodyliform from the Early Cretaceous Cloverly Formation of Montana
- Creators
- Daniel Leaphart
- Contributors
- Christopher Brochu (Advisor)Bradley Cramer (Committee Member)Stephanie Pierce (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Summer 2023
- DOI
- 10.25820/etd.007069
- Publisher
- University of Iowa
- Number of pages
- vii, 47 pages
- Copyright
- Copyright 2023 Daniel Leaphart
- Language
- English
- Date submitted
- 07/24/2023
- Description illustrations
- Illustrations, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 45-47).
- Public Abstract (ETD)
I am studying a small crocodilian relative, probably only about one meter long, from the Cloverly Formation of Montana dating to around 110 million years old (Early Cretaceous). This skull is notable as it reflects a unique combination of ancestral and derived characteristics, indicating that it was a close relative of modern crocodiles and alligators, though its exact relationship with modern crocodilians has been disputed. Because of these traits, it has been included in numerous studies on the relationships of crocodilian relatives. However, in these studies, it has been lumped in with another specimen thought to be the same species, and this relationship is no longer generally accepted.
The goal of this research is to describe and name this specimen. A description of this species will help clarify the traits that would be present in the common ancestor of modern crocodilians, as well as to determine the placement of this species relative to other crocodilian relatives. Additionally, the size and unique characteristics challenge the popular notion of crocodiles and alligators as “living fossils” that have remained unchanged for millions of years. The bulk of this research is focused on a nearly complete skull on loan from Harvard’s Museum of Comparative Zoology (MCZ), as well as fragmentary material from the Cloverly Formation, housed at both MCZ and the Sam Noble Oklahoma Museum of Natural History (OMNH).
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984454642602771
Metrics
1 File views/ downloads
25 Record Views