A Triassic sponge from Vancouver island: possible holdover from the Cambrian

Abstract

Tiny cap-shaped fossils recovered from silicified residues in Upper Triassic rocks of Vancouver Island (Wrangellia) are identified as a calcareous sponge Nucha? vancouverensis sp. nov. The genus Nucha Pickett and Jell was first reported from Middle Cambrian rocks of Australia. The Triassic example constitutes the first occurrence outside the Cambrian system and the continent of Australia. The absence of representatives in rocks between Triassic and Cambrian age suggests that it is a long-range refugium taxon. The occurrence of such a wide-ranging holdover organism reinforces the role of refugia in preferential survivorship over long periods of geologic time. Other holdover taxa are known from volcanic displaced terranes of western American Cordillera, and their study may help clarify neglected aspects of survival and evolution.