Shell structure and its bearing on the phylogeny of Late Ordovician-Early Silurian strophomenoid brachiopods from Anticosti Island, Quebec

摘要

Four shell types are recognized from strophomenide brachiopods from Anticosti Island based on their fibrous or laminar character and on the type of taleolac. The shell types consistently co-vary with the types of cardinal process and style of socket plates. Treating shell structure as a conservative, non-reversing character implies that there are four groups of strophomenide brachiopod. The laminar-shell strophomenoids probably originated two separate times; one origination giving rise to two groups within the Strophomenida and one origination producing the Orthotetida. This matches the Treatise classification with only minor variation. The fourth group, that with fibrous shell and trilobed cardinal process and which includes the Plectambonitoidea, does not clearly fit into the Strophomenata and may be more closely related to the Clitambonitoidea. A limited cladistic analysis supports the idea that shell structure should be an important factor in establishing evolutionary kinship and points to ways of optimizing the Treatise classification.