Geological Society, London, Special Publications The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology Spencer G. Lucas Geological Society, London, Special Publications 2010; v. 334; p. 447-500 doi:10.1144/SP334.15 Email alerting click here to receive free email alerts when new articles cite this service article Permission click here to seek permission to re-use all or part of this article request Subscribe click here to subscribe to Geological Society, London, Special Publications or the Lyell Collection Notes Downloaded by on 15 June 2010 © 2010 Geological Society of London The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology SPENCER G. LUCAS New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104-1375 USA (e-mail: [email protected]) Abstract: The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology divides Triassic time into eight land-vertebrate faunachrons (LVFs) with boundaries defined by the first appearance datums (FADs) of tetrapod genera or, in two cases, the FADs of a tetrapod species. Definition and characterization of these LVFs is updated here as follows: the beginning of the Lootsbergian LVF ¼ FAD of Lystrosaurus; the beginning of the Nonesian ¼ FAD Cynognathus; the beginning of the Perovkan LVF ¼ FAD Eocyclotosaurus; the beginning of the Berdyankian LVF ¼ FAD Mastodonsaurus giganteus; the beginning of the Otischalkian LVF ¼ FAD Parasu- chus; the beginning of the Adamanian LVF ¼ FAD Rutiodon; the beginning of the Revueltian LVF ¼ FAD Typothorax coccinarum; and the beginning of the Apachean LVF ¼ FAD Redonda- saurus. The end of the Apachean (¼ beginning of the Wasonian LVF, near the beginning of the Jurassic) is the FAD of the crocodylomorph Protosuchus. The Early Triassic tetrapod LVFs, Loots- bergian and Nonesian, have characteristic tetrapod assemblages in the Karoo basin of South Africa, the Lystrosaurus assemblage zone and the lower two-thirds of the Cynognathus assemblage zone, respectively. The Middle Triassic LVFs, Perovkan and Berdyankian, have characteristic assem- blages from the Russian Ural foreland basin, the tetrapod assemblages of the Donguz and the Bukobay svitas, respectively. The Late Triassic LVFs, Otischalkian, Adamanian, Revueltian and Apachean, have characteristic assemblages in the Chinle basin of the western USA, the tetrapod assemblages of the Colorado City Formation of Texas, Blue Mesa Member of the Petrified Forest Formation in Arizona, and Bull Canyon and Redonda formations in New Mexico. Since the Triassic LVFs were introduced, several subdivisions have been proposed: Lootsbergian can be divided into three sub-LVFs, Nonesian into two, Adamanian into two and Revueltian into three. However, successful inter-regional correlation of most of these sub-LVFs remains to be demonstrated. Occasional records of nonmarine Triassic tetrapods in marine strata, palynostrati- graphy, conchostracan biostratigraphy, magnetostratigraphy and radioisotopic ages provide some basis for correlation of the LVFs to the standard global chronostratigraphic scale. These data indicate that Lootsbergian ¼ uppermost Changshingian, Induan and possibly earliest Olene- kian; Nonesian ¼ much of the Olenekian; Perovkan ¼ most of the Anisian; Berdyankian ¼ latest Anisian? and Ladinian; Otischalkian ¼ early to late Carnian; Adamanian ¼ most of the late Carnian; Revueltian ¼ early–middle Norian; and Apachean ¼ late Norian–Rhaetian. The Trias- sic timescale based on tetrapod biostratigraphy and biochronology remains a robust tool for the correlation of nonmarine Triassic tetrapod assemblages independent of the marine timescale. Triassic tetrapod (amphibian and reptile) fossils In this paper: FAD ¼ first appearance datum; have long been used in biostratigraphy, a tradition HO ¼ highest occurrence; LO ¼ lowest occur- extending back to at least the 1870s. Lucas (1990) rence; LMA ¼ land–mammal ‘age’; LVA ¼ advocated developing a global Triassic timescale land-vertebrate ‘age’; LVF ¼ land–vertebrate fau- based on tetrapod evolution, and subsequently nachron; and SGCS ¼ standard global chronostrati- Lucas (1998a) presented a comprehensive global graphic scale (the marine timescale). Triassic tetrapod biochronology (Fig. 1). This bio- chronological timescale divides the Triassic into eight time intervals (land-vertebrate faunachrons, Previous studies LVFs) based on successive changes in faunal com- position driven by tetrapod evolution. This model Although tetrapods have been used to correlate non- has been tested and refined for more than a marine Triassic strata since the 1800s, before the decade. Here, I present the current status of the 1990s few attempts were made to establish a Triassic tetrapod-based timescale, incorporating global tetrapod biostratigraphy or biochronology new data, analyses and modifications published of the Triassic (Fig. 2). In the late 1800s, some since 1998. workers did use tetrapod fossils to correlate From:LUCAS, S. G. (ed.) The Triassic Timescale. Geological Society, London, Special Publications, 334, 447–500. DOI: 10.1144/SP334.15 0305-8719/10/$15.00 # The Geological Society of London 2010. 448 S. G. LUCAS J Hettangian Wassonian 201 Protosuchus Rhaetian Apachean Redondasaurus 210 Norian Revueltian Typothorax coccinarum 220 Adamanian Late Carnian Rutiodon 230 Otischalkian Parasuchus TRIASSIC Berdyankian Ladinian Mastodonsaurus 240 giganteus Perovkan Anisian Middle Eocyclotosaurus 250 Olenekian Nonesian Cynognathus Early Induan Lootsbergian 252 Lystrosaurus Permian Changxingian Platbergian Fig. 1. The Triassic timescale based on tetrapod biostratigraphy and biochronology. Restoration of Typothorax by Matt Celeskey. nonmarine Triassic strata on a broad scale, for tetrapod biostratigraphy, for the Lower Triassic of example, Cope (1875) who correlated part of the the Karoo basin in South Africa. He identified German Keuper to the Upper Triassic strata of the three successive biostratigraphic intervals, the American Southwest based on shared taxa of fossil Lystrosaurus, Procolophon and Cynognathus reptiles such as the phytosaur ‘Belodon’. ‘beds’. Watson (1914a, b) later termed these Broom (1906, 1907, 1909) introduced the ear- ‘zones’ and, since Kitching (1970), the Lystrosaurus liest, and perhaps the most influential, Triassic and Procolophon zones have been combined into a Ochev & Bonaparte Romer Lucas (1993a) Lucas & Hunt (1993a) Huber et al. (1993b) Lucas Period Cooper (1982) Shishkin (1966) (Argentina) (1975) China (western USA) (eastern North America) (1998a) (1989) Plateosaurus Apachean lvf Apachean lvf zone Cliftonian lvf Coloradian Revueltian lvf Revuletian lvf Neshanician lvf Placerias LATE LATE zone epoch C TRIASSIC TETRAPODS dinosaurian Adamanian lvf Conewagian lvf Adamanian lvf Ischigualastian Stahleckeria Otischalkian lvf Sanfordian lvf Otischalkian lvf zone TRIASSIC Chanarian Dinodontosaurus Berdyankian lvf zone B epoch Tetragonias Ningwuan lvf Economian lvf Perovkan lvf zone kannemeyeroidean Ordosian lvf Puestoviejan Nonesian lvf A Kannemeyeria Fuguan lvf zone epoch suchian protero- EARLY MIDDLE Jimsarian lvf Lootsbergian lvf Fig. 2. Previous tetrapod-based subdivisions of Triassic time. 449 450 S. G. LUCAS single, Lystrosaurus zone (e.g. Rubidge et al. 1995; and made some necessary modifications that are Botha & Smith 2007). Recognition elsewhere of the incorporated and elaborated upon here. Lystrosaurus and/or Cynognathus ‘beds’ or ‘zones’ has long been possible in Antarctica, South America, India, China and/or Russia because Vertebrate biostratigraphy and some Early Triassic tetrapod taxa are virtually cos- biochronology mopolitan, especially the genera Lystrosaurus and Cynognathus (Lucas 1998a). The term LMA has long referred to intervals of geo- Romer (1975; also see Cox 1973) presented the logical (mostly Cenozoic) time characterized by dis- first global Triassic tetrapod biochronology, by tinctive mammalian fossil assemblages. LMAs have identifying three successive Triassic land– been defined to encompass Cenozoic time intervals vertebrate ‘faunas’: A, Early Triassic; B, Middle on most of the world’s continents (Savage & Russell Triassic; and C, Late Triassic (Fig. 2). Cosgriff 1983), and for the Late Cretaceous of western North (1984) divided Romer’s division A into A1 (¼ America (Cifelli et al. 2004). However, more Lystrosaurus biochron) and A2 (¼ Cynognathus broadly-based LVA or LVF have been introduced biochron). Ochev & Shishkin (1989; also see for parts of the Mesozoic record of Asia, South Anderson & Cruickshank 1978) recognized the America and North America (Lucas 1997b, 2008). same intervals as Romer, but chose to name them Thus, LVAs or LVFs have been proposed for the the: A, proterosuchian epoch; B, kannemeyerioi- Triassic and Jurassic of China (Lucas 1993a, 1996); dean epoch; C, and dinosaurian epoch. the Triassic of Argentina (Bonaparte 1966); the Late Cooper (1982) proposed a more detailed global Triassic of western North America (Lucas & Hunt tetrapod biostratigraphy of the Triassic than did 1993a); the Middle Triassic–Early Jurassic of east- Romer and other workers of the 1970s and 1980s ern North America (Huber et al. 1993a; Lucas & (Fig. 2). In this, he recognized a succession of six Huber 2003; Lucas & Tanner 2007a, b); the Late Triassic zones based largely on a perceived strati- Jurassic–Early Cretaceous of western North graphic succession of dicynodonts (Lucas & Wild America (Lucas 1993e); the Late Cretaceous of 1995 later presented