Geology Today最新文献

The mid-Cretaceous Kem Kem beds of Morocco contains an overabundance of giant theropod dinosaurs, including Spinosaurus and Carcharodontosaurus—both longer than Tyrannosaurus. Compared to modern and other Mesozoic continental ecosystems, in which herbivores represent most of the vertebrate biomass, predators are overrepresented in the mid-Cretaceous of North Africa. The reason is thought to be niche partitioning, with Spinosaurus being semi or perhaps even fully aquatic with other large theropods having a more traditional lifestyle. These conclusions are based on evidence from stable isotopes, skeletal anatomy and biomechanical studies which we will discuss in this article.

Traces and trace fossils are the spoor of organisms, such as tracks, trails, burrows, borings and coprolites. They provide a unique suite of data for geology, including stratigraphy, sedimentology and palaeontology.

Borings are traces that can be transported easily within clasts and shells. One of the commonest recent borings around the British Isles is the club-shaped Gastrochaenolites Leymerie. In the Mesozoic and younger, Gastrochaenolites was commonly a boring of bivalves, sometimes preserved in situ, but it extends back to the Ordovician with no evidence of the producer.

Small round holes in shells—the trace fossil Oichnus Bromley—range throughout the Phanerozoic and were doubtless the spoor of diverse invertebrates. Their function may have been predatory, parasitic or a domicile, but how do we tell which from the fossil evidence?

Foraminifera comprise a group of heterotrophic zooplankton, which inhabit all depths within the world's oceans from the sunlit surface ocean to the depths of the abyssal plains. Many species build a shell of calcium carbonate (predominantly calcite), which records vital geochemical information from the oceans as it grows. Studies based on microscopic foraminifera are often at the forefront of pioneering research by palaeoclimatologists into Cretaceous–Cenozoic climates. In this feature, I summarize how foraminifera are obtained from the deep ocean and describe how rapidly evolving planktic foraminifera species can be used to date marine sediments. I then explain how benthic foraminifera can be used to reconstruct high-resolution long-term climate records, focusing on the use of stable oxygen isotopes to elucidate deep ocean temperatures from the greenhouse climate of the late Paleocene–early Eocene.

Gastropods expanded into niches vacated by both terrestrial and marine organisms following the end-Cretaceous mass extinction, to become one of the dominant mollusc groups of the Cenozoic. The Selsey Formation of Eocene age was deposited within a shallow marine embayment across the Hampshire Basin (southern England) and contains a particularly diverse gastropod assemblage, forming the surface geology across the northern part of the New Forest National Park. Here, I use closely related gastropod species alive in the seas today to offer insights into the lifestyles and habitats of extinct Eocene species. By integrating this with other geological evidence, including gastropod preservation and other associated fossils, I paint a picture of the climate and environment on the New Forest seafloor during the Eocene epoch.

The affinities of the Tully monster (Tullimonstrum gregarium), from the late Carboniferous Mazon Creek Lagerstätte (~309 Ma) of Illinois, have been debated since its discovery. Tullimonstrum is up to ~35 cm long with a long proboscis ending in pincers and an elongate tapering body with caudal dorsal and ventral fins. This iconic evolutionary enigma or ‘weird wonder’ has been suggested to relate to arthropods, various ‘worms’, tunicates, conodonts, lancelets, vetulicolians and even vertebrates, but it may be a mollusc (Caenogastropoda) such as a pterotracheid (heteropod) pelagic gastropod, similar to Pterotrachea coronata (the ‘sea elephant’).