The mid-Cambrian (Series 3, Drumian–Guzhangian; Marjuman) trilobite Holmdalia Robison, 1988, in western Newfoundland and its biostratigraphic significance

Abstract

Holmdalia Robison, 1988 (Family Marjumiidae), was proposed as a monotypic taxon that occurred in mid-Cambrian outer shelf settings in New York and Greenland, with a subsequent report from northwestern Canada. New collections from the Shallow Bay Formation of western Newfoundland record a succession of at least seven species that spans most of the Drumian and all of the Guzhangian stages, and demonstrate that the genus has considerable, previously unrecognized biostratigraphic potential. Older, Drumian species, including the type species, H. punctata (Rasetti, 1967), have longer palpebral lobes and, hence, larger eyes than a group of younger, Guzhangian species. Restudy of the type material shows that previous records of H. punctata outside the type area in New York are misidentifications, but the species does occur in Newfoundland. New Drumian species are H. palpebra and H. tenaga; an additional Drumian species is placed in open nomenclature. New Guzhangian species are Holmdalia glabra, H. lata, and H. tubercula.