Population analysis and orientation studies of graptoloids from the Middle Ordovician Utica Shale, Quebec

Rigby, Susan (1993) Population analysis and orientation studies of graptoloids from the Middle Ordovician Utica Shale, Quebec. Palaeontology, 36 (2). pp. 267-282. ISSN 0031-0239

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Item Type:Article
Item Status:Live Archive

Abstract

Three large populations of graptoloids from the Utica Shale contain Orthograptus quadrimucronatus micracanthus and Amplexograptus praetypicalis. Detailed orientation studies show that the two species reached the bedding plane at different times and were probably present in the water mass as monospecific shoals. Some size ranges of each population are orientated, suggesting that current sorting occurred. Few siculae are present, either because of current winnowing or because of geographical separation of growth stages in life. Length-frequency graphs of complete specimens suggest that both species grew throughout life. Length-frequency graphs of complete specimens suggest that both species grew throughout life. Survivorship analysis indicates that some populations died from constant environmental stress while others lived long enough for increasing length (or age) to become a hanidcap. The origin of synrhabdosomes is considered to be taphonomic. -Author

Keywords:graptolite, Ordovician, orientation study, population analysis, Utica Shale, Canada, Quebec
Subjects:C Biological Sciences > C180 Ecology
C Biological Sciences > C182 Evolution
Divisions:Professional services > Vice Chancellors Office
ID Code:20130
Deposited On:27 Jan 2016 13:16

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