Round to oval, scalelike siliceous microstructures from cherts in Cambrian limestones of the western Yukon Territory suggest affinity with chrysophycean algae. At least six morphotypes present include porous forms with single branching processes and nonporous oval, ringlike forms. Partially dissolved specimens may indicate a contribution to contemporaneous or early diagenetic chert formation.

Cambrian Orsten-type fossils have yielded specimens with a uniquely detailed morphology from the early stages of animal evolution. A newly discovered crustacean larva illustrates how morphology and lifestyle over half a billion years ago closely resembled those of extant relatives.

We report new discoveries of embryos and egg capsules from the Lower Cambrian of Siberia, Middle Cambrian of Australia and Lower Ordovician of North America. Together with existing records, embryos have now been recorded from four of the seven continents. However, the new discoveries highlight secular and systematic biases in the fossil record of embryonic stages. The temporal window within whi...

N o paleontological subject comes close to stimulating the public's interest like dinosaurs, but the origin of animals is probably a solid second. As is well known, representatives of nearly all of the animal phyla (e.g., arthropods, molluscs, echino-derms) appear at roughly the same moment in geologic time, the beginning of the Cambrian period, about 550 million years ago. Their sudden appeara...

Development of the animal body plan is controlled by large gene regulatory networks (GRNs), and hence evolution of body plans must depend upon change in the architecture of developmental GRNs. However, these networks are composed of diverse components that evolve at different rates and in different ways. Because of the hierarchical organization of developmental GRNs, some kinds of change affect...

Cambrian lobopodians are important for understanding the evolution of arthropods, but despite their soft-bodied preservation, the organization of the cephalic region remains obscure. Here we describe new material of the early Cambrian lobopodian Onychodictyon ferox from southern China, which reveals hitherto unknown head structures. These include a proboscis with a terminal mouth, an anterior a...

The morphological disparity of lophotrochozoan phyla makes it difficult to predict the morphology of the last common ancestor. Only fossils of stem groups can help discover the morphological transitions that occurred along the roots of these phyla. Here, we describe a tubular fossil Yuganotheca elegans gen. et sp. nov. from the Cambrian (Stage 3) Chengjiang Lagerstätte (Yunnan, China) that exhi...

The decline in origination rate of new metazoan body plans following the Cambrian radiation has been suggested to reflect developmental canalization in derived taxa, limiting their ability to evolve forms with radically different morphotypes. Segmentation is a fundamental aspect of arthropod body plan, and here we show that a derived trilobite that secondarily converged on a morphotype characte...

—Burgess Shale-type fossil assemblages provide a unique record of animal life in the immediate aftermath of the so-called “Cambrian explosion.” While most soft-bodied faunas in the rock record were conserved by mineral replication of soft tissues, Burgess Shale-type preservation involved the conservation of whole assemblages of soft-bodied animals as primary carbonaceous remains, often preserve...

New geochronological and geochemical data document a new widely distributed succession of igneous sedimentary rocks within the Sibumasu that extend from SW Yunnan through SE Asia as far Sumatra. Our revealed presence an Ordovician-Silurian (mainly ?490–430 Ma) zone. The early Paleozoic granites in zone display similar elemental Sr–Nd–Pb–Hf isotopic compositions. They were derived common mixed s...