Files and links (1)
Thesis10.10 MB
Embargoed Access, Embargo ends: 06/29/2028
Thesis
A new crocodylian from the Eocene (Ypresian) of Wyoming (Greater Green River Basin, USA) and the origins of Longirostres
University of Iowa
Master of Science (MS), University of Iowa
Spring 2026
DOI: 10.25820/etd.008351
Abstract
A new species of crocodylian is herein described based on fossils originating from the lowermost Bridger Formation (Bridger A subunit) of southwestern Wyoming. This new taxon adds to the already speciose eusuchian fauna of western North America during the early Eocene and underscores the potential for cryptic diversity among fossils from this region and interval. While exhibiting general morphology similar to other North American Longirostres-line crocodylians (e.g., “Crocodylus” affinis, Brachyuranochampsa, Prodiplocynodon), a number of morphological characters distinguish the new species from these other taxa, including the presence of prominent anteroposteriorly oriented preorbital ridges, posterodorsal premaxillary processes that extend to between the third and fourth maxillary alveoli, the presence of a posterior maxillary process within the lacrimal, and the ectopterygoid maxillary rami being separated from the suborbital fenestrae by the maxillae. Phylogenetic analysis of a new morphological dataset recovers the new Bridger Formation taxon in a derived position relative to other North American Longirostres-line crocodylians and near the divergence of crown-Longirostres. These phylogenetic results also have important implications for early crocodylian evolution and highlight the importance of North American Cretaceous-Paleogene fossils in understanding the origins of Longirostres.
Details
- Title: Subtitle
- A new crocodylian from the Eocene (Ypresian) of Wyoming (Greater Green River Basin, USA) and the origins of Longirostres
- Creators
- Austin Blair Shaffer
- Contributors
- Christopher Brochu (Advisor)Jonathan Adrain (Committee Member)Jeremy Martin (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008351
- Publisher
- University of Iowa
- Number of pages
- xiii, 177 pages
- Copyright
- Copyright 2026 Austin Blair Shaffer
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- illustrations, maps
- Description bibliographic
- Includes bibliographical references (pages 51-79).
- Public Abstract (ETD)
The Eocene rocks of western North America have produced a diverse assortment of fossil crocodylians and their extinct close relatives, with a number of distinct species currently recognized. Examination of fossil material from the Bridger Formation of Wyoming has revealed a new, previously unrecognized species of crocodylian that further expands the biodiversity of this group in western North America approximately 49-million-years-ago. This new species is distinguishable from other similar fossil crocodylians on the basis of various morphological features, including the sutural relationships of the skull bones and the presence of prominent ridges on the snout. Analyses of a new phylogenetic dataset looking at the evolutionary relationships of the new species recover it in a relatively derived position compared to other Eocene North American crocodylians and close to the origins of some major modern crocodylian lineages (e.g., Gavialoidea, Crocodylidae). This new species and the results of the phylogenetic analyses highlight the importance of North American Cretaceous-Paleogene fossils in understanding the early evolution of Crocodylia and suggests the potential for additional undescribed fossil species.
- Academic Unit
- School of Earth, Environment, and Sustainability
- Record Identifier
- 9985176973802771
Metrics
1 Record Views