Stratigraphic correlations presented here for the ductilely deformed and metamorphosed rocks exposed in the Shadow Mountains indicate that they formed on the North American continental margin and are not exotic or significantly displaced from their site of origin. These strata represent a depositional history that spans Late Proterozoic and Paleozoic passive margin development, late Paleozoic t...

Charles Darwin suspected that the Cambrian “explosion” might be an artifact of fossil preservation. A more recent, initially controversial hypothesis that repeated true polar wander (TPW) triggered the Ediacaran-Cambrian explosion of animal life has been supported by numerous paleomagnetic and geochronologic refinements. These data imply 75° of TPW between 535 and 515 million years ago, coincid...

The ocean-atmosphere system is typically envisioned to have gone through a unidirectional oxygenation with significant oxygen increases in the earliest (ca. 635 Ma), middle (ca. 580 Ma), or late (ca. 560 Ma) Ediacaran Period. However, temporally discontinuous geochemical data and the patchy metazoan fossil record have been inadequate to chart the details of Ediacaran ocean oxygenation, raising ...

Allison, C.W. and Awramik, S.M., 1989. Organic-walled microfossils from earliest Cambrian or latest Proterozoic Tindir Group rocks, northwest Canada. Precambrian Res., 43: 253-294. Uppermost Tindir Group limestones exposed in the headwaters of Tindir Creek, Yukon Territory, Canada, contain a diverse and abundant microbiota of mineralized and organic-walled microfossils. Preserved primarily in c...

A broad variety of body plans and subplans appear during a period of perhaps 8 million years (my) within the Early Cambrian, an unequaled explosion of morphological novelty, the ancestral lineages represented chiefly or entirely by trace fossils. Evidence from the fossil record can be combined with that from molecular phylogenetic trees to suggest that the last common ancestor of (i) protostome...

This paper presents a phylogenetic analysis of the ‘‘Fallotaspidoidea,’’ a determination of the biogeographic origins of the eutrilobites, and an evaluation of the timing of the Cambrian radiation based on biogeographic evidence. Phylogenetic analysis incorporated 29 exoskeletal characters and 16 ingroup taxa. In the single most parsimonious tree the genus Fallotaspidella Repina, 1961, is the s...

The early–middle Cambrian (Fortunian to Age 4) is characterized by a significant increase in metazoan diversification. Furthermore, this interval is marked by a prominent environmental and ecological expansion of arthropodand echinoderm-rich biotas. Recent redox work has suggested that this shift occurred during stable or decreasing marine oxygen levels, suggesting that these paleobiological an...

Clearly, the fossil record from the Cambrian period is an invaluable tool for deciphering animal evolution. Less clear, however, is how to integrate the paleontological information with molecular phylogeny and developmental biology data. Equally challenging is answering why the Cambrian period provided such a rich interval for the redeployment of genes that led to more complex body plans.

Molluscs are a diverse animal phylum with a formidable fossil record. Although there is little doubt about the monophyly of the eight extant classes, relationships between these groups are controversial. We analysed a comprehensive multilocus molecular data set for molluscs, the first to include multiple species from all classes, including five monoplacophorans in both extant families. Our anal...