Thesis
Middle and Upper Ordovician encrinurid trilobites from the Maquoketa Formation (Katian) of Iowa and the Table Cove Formation (Darriwilian) of Newfoundland
University of Iowa
Master of Science (MS), University of Iowa
Spring 2026
Abstract
In northeastern Iowa, outcrops of the Elgin Member of the Maquoketa Formation (upper Katian) yield a rich trilobite fauna. Most taxa were described over a century ago, and most remain inadequately studied. One family, Encrinuridae Angelin, 1854 (Order Phacopida; Suborder Cheirurina), is represented by the cybeline Cybeloides iowensis Slocom, 1913, and the encrinurine Encrinuroides pernodosus (Slocom, 1913). Cybeloides iowensis is the type species of the diverse and widely distributed genus Cybeloides Slocom, 1913, and Encrinuroides pernodosus has rarely been mentioned in the literature. For both species, poor quality, early twentieth century photographs remain the only published images. These species are revised based on new images of the type specimens, along with a suite of newly collected specimens with detailed locality information. These new data document numerous apparent autapomorphies of Cybeloides iowensis, and clarify the position of Encrinuroides pernodosus within the paraphyletic Encrinuroides (s.l.) group, with morphological affinities to Encrinuroides gibber (Dean, 1979), Encrinuroides gelaisi (Lespérance and Desbiens, 1995), and Physemataspis Evitt and Tripp, 1977. Additionally, five cybeline taxa are described based on silicified material from the Table Cove Formation (mid-Darriwilian) of western Newfoundland, Canada. Atractopyge mikaelaae n. sp. and Atractopyge michaeli n. sp. are interpreted as the oldest Laurentian species of Atractopyge Hawle and Corda, 1847. Aperipyge n. gen. (type species A. heatherae n. sp.) is proposed as a new monotypic cybeline genus with close affinities to early (Dapingian– Darriwilian) Chinese species of Sinocybele Sheng, 1974. Cybelurus? hannahae n. sp., is tentatively referred to Cybelurus based on pygidial morphology, and fragmentary material of Cybelurus mirus (Billings, 1865) shows several features not discussed or misinterpreted by earlier authors, including glabellar furrow morphology. All Newfoundland taxa show that the variably developed postaxial region of cybelines is likely homologous with pygidial pleurae.
Details
- Title: Subtitle
- Middle and Upper Ordovician encrinurid trilobites from the Maquoketa Formation (Katian) of Iowa and the Table Cove Formation (Darriwilian) of Newfoundland
- Creators
- Ethan Bley
- Contributors
- Jonathan M Adrain (Advisor)Christopher A Brochu (Committee Member)Stephen R Westrop (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Geoscience
- Date degree season
- Spring 2026
- Publisher
- University of Iowa
- Number of pages
- x, 173 pages
- Copyright
- Copyright 2026 Ethan Bley
- Language
- English
- Date submitted
- 04/27/2026
- Description illustrations
- illustrations, maps
- Description bibliographic
- Includes bibliographical references (page 161-173).
- Public Abstract (ETD)
Trilobites are a diverse group of extinct marine arthropods that had a global distribution throughout the Paleozoic Era (541–252 million years ago). One trilobite family, Encrinuridae Angelin, 1854, is known from the Ordovician through the earliest Devonian (485–410 million years ago). This thesis examines seven species of encrinurid trilobites belonging to the subfamilies Encrinurinae Angelin, 1854, and Cybelinae Holliday, 1942. Two species, Cybeloides iowensis Slocom, 1913, and Encrinuroides pernodosus (Slocom, 1913), are revised based on the type material and new specimens from the Upper Ordovician (Katian) Maquoketa Formation of northeastern Iowa. These revisions are accompanied by a review of the history of study of other trilobites from the Maquoketa Formation and a discussion of encrinurid morphology.
Also included are images and discussion of new material of Cybelurus mirus (Billings, 1865) and the proposal and description of four new species attributable to Atractopyge Hawle and Corda, 1847, Cybelurus Levickij, 1962, and a new cybeline genus. These specimens are from the Middle Ordovician (Darriwilian) Table Cove Formation of the east coast of the Great Northern Peninsula of Newfoundland and are secondarily replaced with silica. Secondary silicification preserves exceptional, three-dimensional detail, which allows for observation of uncommonly preserved features. These specimens challenge traditional views regarding cybeline tail structure.
- Academic Unit
- School of Earth, Environment, and Sustainability
- Record Identifier
- 9985177074102771
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