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Nature and significance of intraspecific variation in the Early Cambrian oryctocephalid trilobite Oryctocephalites palmeri Sundberg and McCollum, 1997

Mark Webster and Frederick A. Sundberg
Nature and significance of intraspecific variation in the Early Cambrian oryctocephalid trilobite Oryctocephalites palmeri Sundberg and McCollum, 1997
Journal of Paleontology (January 2020) 94 (1): 70-98

Abstract

Oryctocephalid trilobites are seldom abundant and often tectonically deformed, creating problems for robust species delimitation and compromising their utility in biostratigraphic and evolutionary studies. By studying more than 140 specimens recovered from the upper portion of the Combined Metals Member (Pioche Formation, Nevada; Cambrian Stage 4, Series 2), we exploit a rare opportunity to explore how morphological variation among oryctocephalid specimens is partitioned into intraspecific variation versus interspecific disparity. Qualitative and quantitative analyses reveal that two species are represented: Oryctocephalites palmeri Sundberg and McCollum, 1997 and Oryctocephalites sp. A, the latter known from a single cranidium stratigraphically below all occurrences of the former. In contrast to the conclusions of a previous study, there is no evidence of cranidial dimorphism in O. palmeri. However, that species exhibits considerable variation in cranidial shape and pygidial spine arrangement and number. Cranidial shape variation within O. palmeri is approximately one-half of the among-species disparity within the genus. Comparison of cranidial shape between noncompacted and compacted samples reveals that compaction causes significant change in mean shape and an increase in shape variation; such changes are interpretable in terms of observed fracture patterns. Nontaphonomic variation is partitioned into ontogenetic and nonallometric components. Those components share similar structure with each other and with interspecific disparity, suggesting that ontogenetic shape change might be an important source of variation available for selection. This highlights the importance of ontogenetic and taphonomic sources of variation with respect to species delimitation, morphospace occupation, and investigation of evolutionary patterns and processes.


ISSN: 0022-3360
EISSN: 1937-2337
Coden: JPALAZ
Serial Title: Journal of Paleontology
Serial Volume: 94
Serial Issue: 1
Title: Nature and significance of intraspecific variation in the Early Cambrian oryctocephalid trilobite Oryctocephalites palmeri Sundberg and McCollum, 1997
Affiliation: University of Chicago, Department of the Geophysical Sciences, Chicago, IL, United States
Pages: 70-98
Published: 202001
Text Language: English
Publisher: Paleontological Society, Lawrence, KS, United States
References: 102
Accession Number: 2020-006896
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF Grant EAR-1410503
Illustration Description: illus. incl. strat. cols., 2 plates, 1 table, sketch map
N37°00'00" - N38°00'00", W115°30'00" - W114°30'00"
Secondary Affiliation: Museum of Northern Arizona, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, The Paleontological Society. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202006
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