Recurrent Groups of Bonded Species in Mixed Death Assemblages
James W. Valentine, Bob Mallory · The Journal of Geology · 1965
Marine fossil assemblages in the Californian Pleistocene frequently contain mixtures of species that have lived in separate biotopes. From 225 assemblages, selected molluscan species that are bonded by significant numbers of mutual occurrences, as defined by $$x^{2}$$, are formed into recurrent groups. The environmental significance of the groups is evaluated by using recorded living occurrences of the species, in the light of group properties that are owing to bonding and grouping techniques. Significance of groups may vary according to their size and the frequency of occurrence of their members. Large groups composed of species that occur at intermediate frequencies tend to represent distinctive biotopes; groups of species of high frequency of occurrence probably do not represent a single biotope; and small groups of rare species may have any of several origins. Pleistocene groups composed of shallow-water species correspond well to previously described fossil "Communities." Pleistocene groups of deeper-water species do not agree well with previously described "communities," partly owing to an inappropriate choice of biotope parameters for community delimitation.