Systematics and biostratigraphy of Lower Cambrian trilobites of western Laurentia
Date
2018-07-20
Authors
Bohach, Lisa Lynn
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Medial Lower Cambrian strata from continental shelf deposits of western Laurentia yield
abundant, low diversity trilobite faunas. New faunas from the Cranbrook and Eager formations
(southeastern British Columbia) and the upper Campito, Poleta, Harkless and Saline Valley
formations (southwestern Great Basin, California and Nevada) have yielded: 33 species of
Olenellina (20 new); 2 new species of Edelsteinaspidae (Redlichiina); 13 species of
Corynexochida (5 new); 4 species of Ptychopariina (1 new); 1 new species of Eodiscina; 1
species of Oryctocephalidae; 1 new species of Protypidae; and 1 possible species of
Cheiruroideidae. One new genus, Wannerellus, is established and tentatively assigned to the
Wanneriidae.
Systematic studies emphasize the importance of early ontogenetic features and ventral
morphology in determining supraspecific relationships. Major changes are made to the
suprageneric classification of the Olenelloidea: the Wanneriidae is recognized as a family
separate from the Olenellidae; the Laudoniinae and Gabriellinae are abandoned and their type
genera assigned to the Wanneriidae; the Mesonacinae is characterized as a peramorphic
subfamily of the Olenellidae; and the Bristoliinae is synonymized with the Biceratopsinae
(Olenellidae). The Corynexochidae is also changed in membership to include the Dorypyginae
(=Ogygopsidae). Heterochrony is a major pattern of evolutionary change in Lower Cambrian
trilobites.
Biostratigraphic division of the medial lower Cambrian comprises 10 new subzones of 4 zones
and is the first species-based trilobite zonation for Laurentia. It replaces previous genus-based
zonations that are imprecise and questionable in recognition. In ascending order, the zonation
includes: the Nevadia weeksi and Nevadia palmeri subzones of the Nevadia Zone; the Nevadella
parvoconica and Nevadella eiicharis subzones of the Nevadella Zone; the Elliptocephala stewarti,
Gabriellus poletensis and Wannerellus alcatrazensis subzones of the Elliptocephala Zone; and the
Wanneria logani, Wanneria dunnae and Proliostracus buelnaensis subzones of the Olenellus transitans
Zone. These zones and subzones can be correlated with other successions in western and eastern
Laurentia.
Biofacies differentiation of restricted shelf deposits is poorly developed in the Nevadella though
Elliptocephala Zones. For this interval, the Nevadella and Wanneriid biofacies are successive
biofacies of restricted shelf deposits and the Labradoria and Ekwipagetia biofacies are successive
biofacies of open shelf deposits. Biofacies differentiation is well developed in the Olenellus
transitans Zone, with an Olenellus Biofacies in elastics; a Wanneriid Biofacies in silty and oolitic
carbonates; a Bonnia Biofacies in pure carbonates; and an Ogygopsis Biofacies in open shelf
deposits.
Description
Keywords
Paleontology, British Columbia, Cambrian, Trilobites