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MORPHOLOGY AND SYSTEMATICS OF THE BRYOZOAN GENUS METRARABDOTOS
Author(s) -
Schopf Thomas J. M.
Publication year - 1970
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/j.1558-5646.1970.tb01781.x
Subject(s) - systematics , citation , genus , morphology (biology) , anthropology , biology , library science , zoology , taxonomy (biology) , sociology , computer science
The cheilostome bryozoan genus Metrarabdotos is represented in modern marine epifaunas by two partially sympatric species, distributed in the tropical Panamic, Caribbean, and West African biogeographic provinces. The morphology and taxonomy of these species provide a basis for interpreting the systematics of their fossil congeners, which include at least eleven species having allopatric distributions in areas bordering the Atlantic, the Gulf of Mexico, the Caribbean, and the Mediterranean in deposits as old as late Eocene. Detailed collections from the American Tertiary, less detailed Recent and Eurafrican Tertiary material, and museum specimens have been studied to clarify external and internal morphologic features and their taxonomic distribution through the genus. Extensive overlap in single morphologic characters among species has necessitated use of biometric techniques, including variation, correlation, and principal components analyses, to evaluate quantitative characters and numerical and clustering procedures to compare samples. The five resulting phenetic groups, based on twenty-three characters expressed in weighted codes, were projected into a time-stratigraphic framework. Inferred phylogenetic relationships within and among groups provided a basis for taxonomic interpretation. The morphologic overlap among groups resulted from convergent and parallel trends in size, position, orientation, and differentiation of avicularia and in denticulation of the secondary orifice in the American and Eurafrican stocks which probably were isolated through most of their history. The complex of fossil and Recent material studied includes four polytypic species, divided into twelve subspecies, and seven monotypic species here assigned to the following subgenera: M. (Metrarabdotos) Canu, upper Miocene-Pleistocene (type species : Eschara monilifera Milne Edwards) ; M. {Porometra) , n. subgen., middle Miocene-Pliocene (type species: Trigonopora helvetica Roger and Buge) ; M. (Rhabdotonietra), n. subgen., upper Eocene-lower Miocene (type species: Escharella micropora Gabb and Horn); M. (Biavicularium) , n. subgen., lower Miocene-Recent (type species: Smittia tenuis Busk) ; M. (Uniavicularium) , n. subgen., upper Miocene-Recent (type species: Metrarabdotos unguiculatum Canu and