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

Abstract

Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.

The origin and early radiation of dinosaurs

“…Theropods were more taxonomically diverse in the Early Jurassic and evolved into a range of major clades and body plans during this time. How this diversification may relate to the Triassic-Jurassic extinction is unclear, but it is possible that theropods expanded in diversity, morphological disparity, and possibly ecological roles after the extinction of many carnivorous crurotarsan lineages (phytosaurs, ornithosuchids, rauisuchians) at or near the Triassic-Jurassic boundary (Olsen et al, 2002;Benton, 2004Benton, , 2005Brusatte et al, 2008b). In any case, the overall picture of theropod rarity and morphological conservatism during the Late Triassic, and expansion in diversity and disparity in the Early Jurassic, argues against the hypothesis that theropods radiated rapidly soon after they originated (e.g., Hunt, 1991;Heckert and Lucas, 1995;Hunt et al, 1995;Carpenter, 1997).…”

“…Overlying Early Jurassic strata preserve a diverse assemblage of ornithischians, sauropodomorphs, and theropods in the Glen Canyon Group (e.g., Tykoski, 2005). The dinosaur record of eastern North America is primarily documented by footprints, with extensive late Carnian, Norian, and Rhaetian dinosauromorph assemblages from the Newark Supergroup (Olsen and Huber, 1998;Olsen et al, 2002), but it also includes Early Jurassic body fossils of the sauropodomorph Anchisaurus (e.g., Yates, 2004) and theropods (Talbot, 1911;Colbert and Baird, 1958). Norian and Rhaetian terrestrial strata from the Germanic Basin in Europe are dominated by basal sauropodomorphs (e.g., Yates, 2003b), but theropods are also present (Schoch and Wild, 1999).…”

“…The Chinle Formation of the Colorado Plateau in western North America is traditionally considered late CarnianNorian in age (e.g., Litwin et al, 1991;Lucas, 1998), but new U-Pb radioisotopic age constraints indicate that even the oldest fossiliferous strata are Norian in age (Riggs et al, 2003;Irmis and Mundil, 2008;Mundil et al, 2008). Footprint assemblages from the Newark Supergroup of eastern North America (e.g., Olsen et al, 2002) are tied to a high-resolution magnetostratigraphic record that is calibrated using palynomorph biostratigraphy (Kent and Olsen, 1999). Most other classic early dinosaur assemblages from the Late Triassic are dated primarily using biostratigraphic methods (conchostrachans, palynomorphs, vertebrates).…”

A triász és a jura időszak határán lezajlott globális krízis és annak nyomai magyarországi rétegsorokban

“…A szárazföldi gerincesek jelentős faunaváltására utaló jelek is megfigyelhetőek a jó rétegtani felbontású észak-amerikai rétegsorokban (OLSEN et al 2002). Globális elemzések alapján feltételezhető, hogy a triász-jura határ forduló pont volt az őshüllők fejlődéstörténetében.…”

“…A kréta végi kihalást égitest-becsapódással magyarázó Alvarez-hipotézis sikerén felbuzdulva a triász végi kihaláshoz is keresték és megtalálni vélték az impaktra utaló bizonyítékokat (OLSEN et al 2002). Az irídiumano -mália nagysága azonban nem meggyőző, a Newark-medencén kívül megbízhatóan reprodukálni pedig nem sikerült, mindössze egy szintén szerény dúsulást jelentettek Japán egy mélytengeri rétegsorából (HORI et al 2007).…”