Publications by authors named "R Gaines"
Article Synopsis
- Modern poriferans are divided into four classes based on spicule structure, but classifying fossil specimens is complicated due to their varied forms and structures.
- Fossils from early periods, notably those from the Cambrian and Ordovician, show features—like hexactine spicules—that don't fit neatly into current classifications of modern sponges.
- A newly identified poriferan from the Drumian Marjum Formation in Utah displays unique anatomical features, suggesting that the body plan of hexactinellids may have originated much earlier than previously thought, shedding light on the evolution of early glass sponges.
The Emu Bay Shale (EBS) of South Australia is anomalous among Cambrian Lagerstätten because it captures anatomical information that is rare in Burgess Shale-type fossils, and because of its inferred nearshore setting, the nature of which has remained controversial. Intensive study, combining outcrop and borehole data with a compilation of >25,000 fossil specimens, reveals that the EBS biota inhabited a fan delta complex within a tectonically active basin. Preservation of soft-bodied organisms in this setting is unexpected and further underscores differences between the EBS and other Cambrian Lagerstätten.
View Article and Find Full Text PDFPyritization of soft tissues of invertebrates is rare in the fossil record. In New York State, it occurs in black shales of the Lorraine Group (Late Ordovician), the best-known example of which is Beecher's Trilobite Bed. Exceptional preservation at the quarry where this bed is exposed allowed detailed examination of trilobite and ostracod soft-tissue anatomy.
View Article and Find Full Text PDFKnowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system.
View Article and Find Full Text PDFArticle Synopsis
- The evolution of Earth's oxygen cycles has been shaped by the production and consumption of molecular oxygen, particularly during the Neoproterozoic-Paleozoic transition, which saw a significant rise in oxygen levels due to increased burial of organic carbon.
- New research based on lithium isotopic data from marine mudstones indicates a sharp rise in continental clay formation after 525 million years ago, likely due to global climate changes and crust composition shifts.
- A biogeochemical model suggests that enhanced continental weathering and increased clay delivery to oceans may have improved the burial of organic carbon, contributing to higher oxygen levels in the early Paleozoic oceans.