Phylogeny of cardiid bivalves(cockles and giant clams): revision of the Cardiinae and the importanceof fossils in explaining disjunct biogeographical distributions

Despite being the type subfamily of the Cardiidae, theCardiinae has received relatively little attention from systematists.Recent investigations of the phylogenetic relationships betweenand within various subtaxa of cockles and giant clams have incorporatedseveral cardiine representatives. These studies have implied thatCardiinae as usually construed is a paraphyletic group. The presentstudy, a cladistic analysis that includes exemplars of the 18 generallyaccepted genera and subgenera of Cardiinae, as well as exemplarsfrom two notable lineages heretofore not assigned to any genus-leveltaxon, also indicate cardiine paraphyly. Cardiinae is restrictedto Cardium, Bucardium, Vepricardium, Dinocardium, Planicardium, Chesacardium, Acanthocardias.s., A. (Rudicardium) and Schedocardia. Theclosest relatives of Cardiinae are the Eocene Sawkinsia anda clade (the ‘CFTL lineage’) containing Plagiocardium, Maoricardium,Clinocardiinae, Fraginae, Lymnocardiinae and Tridacninae (giantclams). The remaining taxa that have usually been placed in Cardiinaeform a monophyletic group that is the sister taxon to Sawkinsia +Cardiinae + CFTL; the new subfamily Orthocardiinae is erectedfor this group. Orthocardiinae contains the taxa Orthocardium, Loxocardium, Europicardium, Hedecardiums.s., H. (Titanocardium), H. (Iheringicardium) subgen.nov., Agnocardia, Afrocardium and Freneixicardia gen.nov.; only Afrocardium (nine species) and Europicardium (onespecies) are extant. Hedecardium s.l. was not restrictedto New Zealand as usually argued but was present in Myanmar andAustralia, as well as being represented in South America by H. (Iheringicardium).Renewed studies of the long-ignored marine invertebrate Cenozoicfaunas of South America may yield additional examples of taxa longthought to be endemic to New Zealand. The only other orthocardiinewith representatives in the Americas is the extinct Agnocardia. Agnocardia’sclosest relative, Afrocardium, long misconstrued as a memberof Fraginae, is known only from Pleistocene and Recent faunas, usuallyfrom the Indian Ocean. This disjunct biogeographical distributionis found to be a function of a century of misidentification of fossiland Recent species, for species attributable to Agnocardia occurin the Palaeogene of Europe and Africa; likewise, species attributableto Afrocardium occur from the Eocene to Pliocene of Europeand Africa. A greater awareness of modern taxonomy of both fossiland Recent forms is necessary to avoid constructing erroneous biogeographicaldistributions and phylogenetic hypotheses. Discrepancies betweenthe results of (1) rigorous character analysis and phylogenetichypotheses and (2) published stratigraphic and palaeobiogeographicaldistributions of fossils, are not necessarily the results of aninadequate fossil record. Instead, stratigraphic and palaeobiogeographicalanomalies may be the result of inadequate attention paid to theactual fossils by taxonomists. © 2002 The LinneanSociety of London. Zoological Journal of the Linnean Society,2002, 136, 321−369