LLANDOVERY (EARLY SILURIAN) ORTHIDE BRACHIOPOD ASSOCIATIONS FROM ANTICOSTI ISLAND, EASTERN CANADA

Large collections of brachiopods on Anticosti Island have been made by Copper and his colleagues since 1966. Several groups of the collections have been studied and published monographically, with the latest on Orthida by Li and Copper (2006).  The numerous brachiopods are deemed to be analyzed quantitatively to delineate paleocommunities and to reveal information on faunal survival and recovery from the Late Ordovician mass extinction. The present study on associations of Orthida was based on 9044 Orthide brachiopod specimens, comprising 23 species attributed to 18 genera of Llandovery, extracted from 239 collections. Cluster analysis was employed to quantitatively delineate associations.  Jaccard coefficient was used to calculate the similarity index of the binary data of presence and absence. Ward's method of clustering was applied to produce both clusters of taxa and collections. The results enable the recognition of five associations of the taxa (A, B, C₁, C₂, D), and five groups of the collections (Table 1).  The orthide associations seem to be controlled by stratigraphic position, which in term is related to water depth (Table 1).   Table 1.  Orthide associations and their composition and stratigraphic occurrence

 

<>Association	<>Nominal Taxa	<>Associated Taxa	<>Occurrence
A: Levenea rica - Jupiterella eumorpha	Levenea (75%) Jupiterella (10%)	Glyptorthis marilara (<1%), Dicoelosia dauphinensis (12%), Dalejina hybrida (2%), and Pionodema hypermeca (<1%)	Mainly Lower Jupiter Fm.
B: Flabellitesia adaia - Dalejina junonis – Levenea media	Flabellitesia (56%) Dalejina (25%) Levenea (17%)	Visbyella concavoconvexa (2%)	Mainly Upper Jupiter Fm.
C1: Isorthis (Ovalella) natiscotekia	Isorthis (90%)	Platystrophia regularis aporegularis (2%)and Diceromyonia ciona (8%)	Becscie Fm.
C2: Mendacella bleikeriensis	Mendacella (92%)	Platystrophia hongueda (1%)and Heterorthina cybele (7%)	Gun River Fm.
D: Mendacella udauberis -  Levenea mera	Mendacella (84%) Levenea (16%)		Merrimack Fm.