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GEOREF RECORD

The Ordovician zone index conodont Amorphognathus ordovicicus Branson & Mehl, 1933 from its type locality and the evolution of the genus Amorphognathus Branson & Mehl, 1933

Abstract

The 2003 rediscovery of the long "lost" Ozora, Missouri classical conodont locality of Branson & Mehl (1933b), from which the world's first Late Ordovician conodont fauna was described, has made it possible to obtain topotype specimens of the several important conodont species introduced by Branson and Mehl from this site. A taxonomic reassessment of the Ozora conodont fauna indicates that it includes at least 14 multi-element species, eight of which were previously known from this locality. Several specimens of the taxonomically diagnostic M element of the biostratigraphical key species Amorphognathus ordovicicus were recovered. This element was previously not known from the type locality of the species at Ozora. A general review of the evolution of the genus Amorphognathus shows that some elements, particularly the M and Pa elements, exhibit relatively rapid gradual morphological changes that are helpful for distinguishing a series of biostratigraphically useful species through the Upper Ordovician (Sandbian-Hirnantian) interval. No ancestor of Amorphognathus has yet been identified but currently available data suggest that the genus appeared in the latest Darriwilian or earliest Sandbian and went extinct in the late Hirnantian. None of the Early Silurian platform genera appears to be closely related to Amorphognathus.


ISSN: 0262-821X
EISSN: 2041-4978
Serial Title: Journal of Micropalaeontology
Serial Volume: 29, Part 1
Title: The Ordovician zone index conodont Amorphognathus ordovicicus Branson & Mehl, 1933 from its type locality and the evolution of the genus Amorphognathus Branson & Mehl, 1933
Affiliation: Ohio State University, School of Earth Sciences, Columbus, OH, United States
Pages: 73-80
Published: 201005
Text Language: English
Publisher: British Micropalaeontological Society, London, United Kingdom
References: 45
Accession Number: 2010-070225
Categories: StratigraphyVertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, strat. cols., sketch map
N37°40'00" - N38°04'60", W90°27'00" - W89°55'00"
Secondary Affiliation: James Madison University, USA, United States
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 201038
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