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Article: Late Tremadoc graptolites from western Newfoundland

Publication: Palaeontology
Volume: 34
Part: 1
Publication Date: March 1991
Page(s): 1 47
Author(s): S. Henry Williams and Robert K. Stevens
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How to Cite

WILLIAMS, S., STEVENS, R. K. 1991. Late Tremadoc graptolites from western Newfoundland. Palaeontology34, 1, 1–47.

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The Cow Head Group of western Newfoundland preserves a sequence of carbonate-rich sediments ranging from middle Cambrian to middle Ordovician. It yields a rich graptolite fauna both with flattened specimens in black shales and cherts, and three-dimensional and flattened material in nodular limestones which may be isolated from the rock by acid extraction. A continuous succession is present across the Tremadoc-Arenig boundary, containing a well represented graptolite assemblage which is here referred to the A. victoriae Zone. Late Tremadoc graptolite faunas have been documented from many localities around the world, but are commonly found in stratigraphically incomplete sequences and have only been known previously from non-isolated material. The Cow Head Group faunas comprise both flattened and isolated material, allowing detailed observation of proximal developments to be compared with overall rhabdosomc forms. Several taxa possess overall forms, proximal structures and thecal styles somewhat similar to dichograptids and sigmagraptines found in the early Arenig, but they all possess a sicular bitheca; some have additional bithccae associated with the autothecae, and dichotomous branching is commonly far more variable. Because of these differences, all taxa described from this interval are considered to belong to the Anisograptidae, necessitating some generic reassignment and the erection of several new taxa. These include Kiacrograptus unduhitus sp. nov. K. magnus sp. nov., Paratemnograptus isolatus sp. nov., Aorograptus gen. nov., Adelograptus altus sp. nov. and A. filiformis sp. nov.
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