Article contents
North American Devonian Carydiidae (Bivalvia): systematics, phylogeny, and implications in early diversification of the class
Published online by Cambridge University Press: 19 May 2016
Abstract
Although past authors have regarded the Carydiidae as a European family, six species of Carydium are reported here from the Devonian of eastern North America. Two of these belong to a single morphocline common in the Hamilton shales; another (Carydium clarkei) is new. Due to lack of well preserved hinges most of these species were earlier placed in Nucula because serrations or striations on dental elements were mistaken for a taxodont dentition.
New data require modification of carydiid phylogenies of earlier authors. 1) Two independent pre-Devonian derivations from Lyrodesma are inferred. 2) Noradonta shergoldi, a carydiid-like lyrodesmatid from the Ordovician of Australia, is recognized as an important phyletic link between the Carydiidae and the Lyrodesmatidae. 3) The previous view of three distinct lineages within Carydium is not supported. Anamorphic data suggest as few as two main lineages and show two of the hinge types to be homeomorphic grades appearing separately or within one or the other of the main lineages.
Though too young to be directly involved in the early diversification of the Bivalvia, the actinodont, subheterodont, and pseudotaxodont hinge morphologies of Carydium supply models for the origin of heterodont and taxodont hinges. Anamorphic and other evidence suggests that both are iterative types, and fundamental differences between them may be few. Hence, their preeminence as diagnostic criteria among higher taxa is diminished.
- Type
- Research Article
- Information
- Copyright
- Copyright © The Paleontological Society
References
- 2
- Cited by