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Anisian (Middle Triassic) ammonoids from British Columbia (Canada): biochronological and palaeobiogeographical implications


Ji, Cheng; Bucher, Hugo (2018). Anisian (Middle Triassic) ammonoids from British Columbia (Canada): biochronological and palaeobiogeographical implications. Papers in Palaeontology, 4(4):623-642.

Abstract

New Anisian (Middle Triassic) ammonoids are reported from British Columbia (BC), Canada. Eight species are reported, including one new genus and two new species: Eofrechites roopnarini gen. et sp. nov. and Parafrechites cordeyi sp. nov. New ammonoid subzones are recognized, leading to improved correlation between BC and Nevada: the Hollandites minor Zone is correlated with the interval intercalated between the Unionvillites hadleyi Subzone and the Pseudodanubites nicholsi Subzone; an Eogymnotoceras thompsoni – Anagymnotoceras spivaki Zone is recognized in BC and correlated with the interval intercalated between the Augustaceras escheri and Anagymnotoceras spivaki subzones; Gymnotoceras weitschati is found in BC for the first time and co‐occurs with Eogymnotoceras deleeni, suggesting either a rough correlation with the sum of G. weitschati, G. mimetus and G. rotelliformis zones of Nevada or a strong diachronism of G. weitschati and G. rotelliformis along the Palaeopacific margin of North America. The rare occurrences of low‐palaeolatitude restricted species in the mid‐palaeolatitude record indicate that exchanges were more frequent than previously documented during the Anisian. Despite a preservation bias in north‐eastern BC due to the lower carbonate content, it clearly emerges that the enhanced sampling effort leads to maximal association zones with duration of the same order of magnitude as those of Nevada, indicating that evolutionary turnover rates of ammonoids did not decrease toward higher latitude. Therefore, the common view that geographically differentiated evolutionary rates originates from the latitudinal gradient of taxonomic richness does not hold for Anisian ammonoid faunas along the Palaeopacific margin of North America.

Abstract

New Anisian (Middle Triassic) ammonoids are reported from British Columbia (BC), Canada. Eight species are reported, including one new genus and two new species: Eofrechites roopnarini gen. et sp. nov. and Parafrechites cordeyi sp. nov. New ammonoid subzones are recognized, leading to improved correlation between BC and Nevada: the Hollandites minor Zone is correlated with the interval intercalated between the Unionvillites hadleyi Subzone and the Pseudodanubites nicholsi Subzone; an Eogymnotoceras thompsoni – Anagymnotoceras spivaki Zone is recognized in BC and correlated with the interval intercalated between the Augustaceras escheri and Anagymnotoceras spivaki subzones; Gymnotoceras weitschati is found in BC for the first time and co‐occurs with Eogymnotoceras deleeni, suggesting either a rough correlation with the sum of G. weitschati, G. mimetus and G. rotelliformis zones of Nevada or a strong diachronism of G. weitschati and G. rotelliformis along the Palaeopacific margin of North America. The rare occurrences of low‐palaeolatitude restricted species in the mid‐palaeolatitude record indicate that exchanges were more frequent than previously documented during the Anisian. Despite a preservation bias in north‐eastern BC due to the lower carbonate content, it clearly emerges that the enhanced sampling effort leads to maximal association zones with duration of the same order of magnitude as those of Nevada, indicating that evolutionary turnover rates of ammonoids did not decrease toward higher latitude. Therefore, the common view that geographically differentiated evolutionary rates originates from the latitudinal gradient of taxonomic richness does not hold for Anisian ammonoid faunas along the Palaeopacific margin of North America.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Language:English
Date:1 November 2018
Deposited On:31 Oct 2018 11:41
Last Modified:24 Sep 2019 23:50
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:2056-2802
OA Status:Closed
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1002/spp2.1222
Project Information:
  • : FunderSNSF
  • : Grant ID200020_160055
  • : Project TitleMid-Early Triassic Extreme Climatic Oscillation (METECO): biotic-abiotic global couplings
  • : FunderFP7
  • : Grant ID230667
  • : Project TitleUNIQUE-CHECK - Development of a unique means of detecting and proving illegal administration of recombinant somatotropin in dairy cows

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