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Molecular clocks have the potential to shed light on the timing of early metazoan divergences, but differing algorithms and calibration points yield conspicuously discordant results. We argue here that competing molecular clock hypotheses should be testable in the fossil record, on the principle that fundamentally new grades of animal organization will have(More)
The early history of crustaceans is obscured by strong biases in fossil preservation, but a previously overlooked taphonomic mode yields important complementary insights. Here we describe diverse crustacean appendages of Middle and Late Cambrian age from shallow-marine mudstones of the Deadwood Formation in western Canada. The fossils occur as flattened and(More)
We report high precision Sr isotopic data on carbonates from the Neoproterozoic Shaler Group, Victoria Island, Northwest Territories, Canada. Lithostratigraphic correlations with the relatively well-dated Mackenzie Mountains Supergroup constrain Shaler deposition to approximately 770-880 Ma, a range corroborated by 723 +/- 3 Ma lavas that disconformably(More)
Panarthropods are typified by disparate grades of neurological organization reflecting a complex evolutionary history. The fossil record offers a unique opportunity to reconstruct early character evolution of the nervous system via exceptional preservation in extinct representatives. Here we describe the neurological architecture of the ventral nerve cord(More)
Silicified peritidal carbonate rocks of the 1250- to 750-million-year-old Hunting Formation, Somerset Island, arctic Canada, contain fossils of well-preserved bangiophyte red algae. Morphological details, especially the presence of multiseriate filaments composed of radially arranged wedge-shaped cells derived by longitudinal divisions from disc-shaped(More)
The fossil record plays a key role in reconstructing deep evolutionary relationships through its documentation of the early diverging stem groups leading to extant phyla. In the middle Cambrian Burgess Shale, two famously problematic worms, Odontogriphus and Wiwaxia, have recently been reinterpreted as stem-group molluscs based on their shared expression of(More)
The relationships of the sponge classes are controversial, particularly between the calcareous and siliceous sponges. Specimens of the putative calcarean Eiffelia globosa Walcott from the Burgess Shale show the presence of diagnostic hexactinellid spicules integrated into the skeletal mesh. The arrangement of these spicules in Eiffelia is shown to be(More)
Animals do not just occupy the modern biosphere, they permeate its structure and define how it works. Their unique combination of organ-grade multicellularity, motility and heterotrophic habit makes them powerful geobiological agents, imposing myriad feedbacks on nutrient cycling, productivity and environment. Most significantly, animals have 'engineered'(More)
The organization of the head provides critical data for resolving the phylogenetic relationships and evolutionary history of extinct and extant euarthropods. The early Cambrian-period fuxianhuiids are regarded as basal representatives of stem-group Euarthropoda, and their anterior morphology therefore offers key insights for reconstructing the ancestral(More)