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Swimming reptiles make their mark in the Early Triassic; delayed ecologic recovery increased the preservation potential of vertebrate swim tracks

Tracy J. Thomson and Mary L. Droser
Swimming reptiles make their mark in the Early Triassic; delayed ecologic recovery increased the preservation potential of vertebrate swim tracks
Geology (Boulder) (February 2015) 43 (3): 215-218

Abstract

Fossil tetrapod swim tracks have been reported from deposits throughout the world, ranging in age from the Carboniferous (Mississippian) to the Neogene (Pleistocene). A normalized analysis of these occurrences demonstrates that lower Triassic strata contain an anomalously high number of occurrences. Lower Triassic swim tracks also tend to be better preserved, showing exceptionally detailed features such as scale striae and crescent-shaped claw margins. Preservation of these features required a firm and semicohesive substrate in order to maintain track detail before and after burial. Swim-track localities from the lower Triassic Moenkopi Formation in Utah (USA) are characterized by sedimentary and trace fossil features that demonstrate the widespread development and persistence of firmground substrates in a large delta plain complex. Within this delta, complex low-diversity invertebrate trace fossil assemblages consist of locally high densities of diminutive, millimeter-scale traces characteristic of stressed brackish-water faunas. We suggest that the depauperate infauna characteristic of such environments was repressed due to delayed biotic recovery following the end-Permian mass extinction, resulting in extremely low intensities of bioturbation. Lack of biogenic mixing promoted semiconsolidation of dewatered mud substrates and the widespread production and persistence of firmgrounds capable of recording and maintaining swim tracks. Thus a combination of factors, unique to the Early Triassic, increased the preservation potential of detailed swim tracks: (1) depositional environments that promoted the production of firmground substrates, (2) delayed ecologic recovery resulting in the lack of well-bioturbated sediment, and (3) the swimming behavior of various Early Triassic tetrapods.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 43
Serial Issue: 3
Title: Swimming reptiles make their mark in the Early Triassic; delayed ecologic recovery increased the preservation potential of vertebrate swim tracks
Affiliation: University of California-Riverside, Department of Earth Sciences, Riverside, CA, United States
Pages: 215-218
Published: 20150205
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 30
Accession Number: 2015-017352
Categories: StratigraphyVertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2015076
Illustration Description: illus. incl. sketch map
N37°00'00" - N42°00'00", W114°04'60" - W109°04'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201509
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