Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary

摘要: Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less 10,000 years after the Triassic-Jurassic boundary 30,000 last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated an iridium anomaly (up to 285 parts per trillion, average maximum 141 trillion) fern spore spike, suggesting bolide impact was cause. Eastern American dinosaurian diversity reached stable 100,000 boundary, marking establishment dinosaur-dominated communities prevailed for next 135 million years. One most striking events Mesozoic rise dominance ecosystems. The cause timing their early ascent have been debated (1‐4), difficulties global correlation low sampling density limiting utility compilations obscuring relations possible forcing mechanisms. However, vertebrate assemblages are temporally better constrained elsewhere provide high-resolution biological geochemical data bearing on this issue. region within tropics during contained rift valleys, which were formed incipient fragmentation Pangea. These basins contain kilometer-thick sections continental strata, termed Newark Supergroup, recorded across 15° paleolatitude (5). Milankovitchtype climate cycles permeate lacustrine strata these basins, conjunction paleomagnetic reversal stratigraphy, all