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REEF-DWELLING GYPIDULOID BRACHIOPODS IN THE LOWER SILURIAN ATTAWAPISKAT FORMATION, HUDSON BAY REGION.
- Source :
-
Journal of Paleontology . Jan2005, Vol. 79 Issue 1, p48-62. 15p. 7 Black and White Photographs, 5 Graphs, 1 Map. - Publication Year :
- 2005
-
Abstract
- Gypidula was a common pentameride brachiopod in the Silurian and Devonian periods and its oldest-known form, Gypidula akimiskiformis new species, occurs as a common component of a distinct Gypidula Association of the rich and diverse reef-dwelling brachiopod fauna in the Lower Silurian (upper Telychian) Attawapiskat Formation of the Hudson Bay Basin. This pioneer species has a high degree of morphological plasticity, with several infraspecific variations significant for the study of gypiduloid taxonomy and early evolution: 1) the sparsely costate shells may have strong to faint medial ribs, with some shells being quasi-smooth and 2) the inner hinge plates are commonly basomedially inclined toward the dorsal valve floor (not united to form a cruralium), but may also be subparallel or slightly basolaterally divergent toward the valve floor (similar to those in Clorinda). This implies that the basomedially inclined inner hinge plates were not a stable character at the initial stage of evolution of Gypidula during the late Telychian. Another gypiduloid from the Attawapiskat Formation, Erilevigatella euthylomata new genus and species, is characterized by a shell lacking fold or sulcus but having Clorinda-type, basolaterally divergent inner hinge plates and double-flanged crura. Compared to Levigatella, which has been regarded as an intermediate between Clorinda and Gypidula because of its Gypidula-type dorsal sulcus and Clorinda-type inner hinge plates, the rectimarginate shells of Erilevigatella make the distinction between Clorinda and Gypidula even more blurred at the early stage of their evolution. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00223360
- Volume :
- 79
- Issue :
- 1
- Database :
- Academic Search Index
- Journal :
- Journal of Paleontology
- Publication Type :
- Academic Journal
- Accession number :
- 15728016
- Full Text :
- https://doi.org/10.1666/0022-3360(2005)079<0048:RGBITL>2.0.CO;2