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No Gap in the Middle Permian Record of Terrestrial Vertebrates

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No Gap in the Middle Permian Record of Terrestrial Vertebrates No gap in the Middle Permian record of terrestrial vertebrates Michael J. Benton* School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK ABSTRACT STRATIGRAPHY OF KUNGURIAN, ROADIAN, AND During the Permian, tetrapods showed a major transition WORDIAN TETRAPOD-BEARING FORMATIONS from basal synapsid-dominated faunas in the fi rst half to therapsid- The crux of Lucas’ case (Lucas, 2004) was that the North American dominated faunas in the second. The transition was signifi cant in redbed successions terminated before the end of the Kungurian (and so marking the beginning of richer and more complex communities, a before the end of the Early Permian), and that the Russian and South Afri- precursor to modern terrestrial ecosystems. This changeover may can tetrapod-bearing successions did not begin until the Wordian (Fig. 1). have been gradual or abrupt, but its study has been complicated by The stratigraphic position of these key units will be reviewed, considering the postulated occurrence of a substantial hiatus in the fossil record, the Russian succession fi rst. termed “Olson’s Gap”, which obscured the nature of the turnover. The meaning of the Russian Middle and Late Permian stratigraphic New evidence from redating of key tetrapod-bearing units of the series, the Ufi mian, Kazanian, and Tatarian, has changed considerably. American southwest and European Russia confi rms that there is no These largely continental, redbed time divisions were used formerly (e.g., gap in the fossil record of Permian tetrapods. Indeed, evidence for Harland et al., 1982) as the standard international divisions of the Upper substantial sampling bias in the Permian tetrapod fossil record as a Permian. With major revision to the Permian time scale (Gradstein et al., whole is queried. 2004), the former Upper Permian was divided into Middle and Upper Perm- ian, and the standard stages in these were established in North America and INTRODUCTION China respectively. Further, the Middle and Upper Permian together now The Permian was a time of rapid change among terrestrial faunas, span some 20 m.y., compared to 10–11 m.y., as assumed before. not least among tetrapods. In the Middle Permian, some 270 m.y. ago, Opinions have been polarized about the meaning of the Russian it has long been recognized that there was a major changeover from fau- series. On the one hand, Gradstein et al. (2004) moved the Ufi mian, Kaza- nas dominated by basal synapsids ( = “pelycosaurs”) to faunas dominated nian, and Tatarian downward to span from late Kungurian to end-Cap- by therapsids. The therapsids are a major synapsid clade that included in itanian, essentially equivalent to the latest Early Permian plus all of the the Middle and Late Permian some major subclades such as Dinocepha- Middle Permian. Menning et al. (2006) allowed the Tatarian to extend up lia, Anomodontia, Gorgonopsia, and Cynodontia. Some of these animals into the Late Permian, being partly equivalent to Wuchiapingian, whereas reached large size, as large as a hippopotamus, and Late Permian eco- most Russian stratigraphers (e.g., Grunt, 2005; Molostovskiy, 2005; Tver- systems were more complex than those of the Early Permian, with addi- dokhlebov et al., 2005; Sennikov and Golubev, 2006) argue that the Tatar- tional trophic levels. From this clade, the Anomodontia and Cynodontia ian spans the Late Permian, and so the succession extends from late Kun- diversifi ed in the Triassic after the end-Permian mass extinction, and basal gurian to Changhsingian. This has been confi rmed by magnetostratigraphy mammals emerged from among the cynodonts in the Late Triassic. There- (Taylor et al., 2009), which identifi ed all magnetic reversals of the Illa- fore, it has long been recognized that transitions in tetrapod ecosystems warra interval (Fig. 1), confi rming the long-established pattern determined through the Permian are crucial for understanding the richness of mod- by Russian magnetostratigraphers (e.g., Molostovskiy, 2005). It is crucial ern terrestrial ecosystems dominated by mammals, direct descendants of now to consider evidence for the ages of the Ufi mian, Kazanian, and Tatar- the Late Permian therapsids (e.g., Olson, 1962, 1966, 1990; Modesto and ian Russian series, and especially to test whether these span the Roadian. Rybczynski, 2000). The Ufi mian is widely accepted (Gradstein et al., 2004; Menning The key to understanding the replacement of basal synapsids by et al., 2006; Lozovsky et al., 2009) as equating with the upper part of the therapsids is a good fossil record, and yet this has been debated, espe- marine Kungurian series (Fig. 1). In a comprehensive review, Lozovsky et cially because the geographic location of the best fossil records switches al. (2009) used biostratigraphic evidence from foraminifera, ammonoids, from North America for the Lower Permian to South Africa and Russia bivalves, brachiopods, ostracodes, conodonts, insects, fi shes, tetrapods, for the Middle and Upper Permian. The question is whether the young- macroplants, and palynomorphs to show that the Ufi mian correlates with est North American tetrapod-bearing continental deposits overlap in the upper part of the Kungurian; whether the Kungurian, or this upper part time the oldest such deposits in South Africa and Russia. Work by Olson of it, should be regarded as entirely Early Permian ( = Cisuralian) or as (1955, 1962, 1990) and Efremov (1956) suggested that the gap had been partly or wholly Middle Permian ( = Guadalupian) is a separate debated bridged, but this view was challenged by Lucas (Lucas and Heckert, issue (Gradstein et al., 2004; Menning et al., 2006; Lozovsky et al., 2009). 2001; Lucas, 2004, 2006) who identifi es a global hiatus in the tetrapod The Kazanian is widely accepted as roughly equivalent to the entire fossil record, termed “Olson’s Gap”, representing most of the Roadian Roadian (Fig. 1): evidence comes from ammonoids and other marine taxa stage, 2.6 m.y. in duration (Gradstein et al., 2004). If “Olson’s Gap” (Leven and Bogoslovskaya, 2006; Leonova, 2007). For example, the Kaza- exists, then paleontologists will be forever unable to document a remark- nian in the Volga-Urals yields an ammonoid assemblage (abundant Sver- able terrestrial faunal replacement. drupites harkeri and S. amundseni, and rarer Biarmiceras and Medlicottia) The reality of “Olson’s Gap” has been challenged (Reisz and Lau- that indicates a Roadian age: Sverdrupites is exclusively Roadian, and spe- rin, 2002; Amson and Laurin, 2011), and Sahney and Benton (2008) cies of Biarmiceras and Medlicottia are known from the upper Kungurian called it instead “Olson’s Extinction”, arguing that the apparently rapid and Roadian (Leonova, 2007; Lozovsky et al., 2009). replacement of Early Permian by Middle Permian tetrapods represents The Tatarian, under either the restricted (Gradstein et al., 2004), inter- a turnover or extinction event. In this paper, I present evidence for the mediate (Menning et al., 2006), or extended (Taylor et al., 2009) interpreta- ages of deposits spanning the Middle Permian, and consider the conse- tions, is the longest of the three former Russian continental series, lasting 8, quences of the revised dating for understanding of ecosystem evolution 14, or 16 m.y. (Fig. 1). As noted, magnetostratigraphy (e.g., Molostovskiy, and the overall quality of the Permian fossil record of tetrapods. 2005; Taylor et al., 2009) strongly suggests that the Tatarian spans from Wordian to Changhsingian, as do studies of inter fi ngering redbed and *E-mail: [email protected]. © 2012 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, April April 2012; 2012 v. 40; no. 4; p. 339–342; doi:10.1130/G32669.1; 2 fi gures; 1 table; Data Repository item 2012094. 339 Inter- Tetrapod Mag. Russian Gorizonts/ Tetrapod Oklahoma/ national Mag. South Urals svitas faunal South Africa Tetrapods stage series stages zones Texas (selected) Ma Epoch stages complexes 252 R P Archosaurus Vyazniki Chang. 3 rossicus Kutulukskaya/ Vyatkian Kulchomovskaya Scutosaurus Dicynodon 255 Sokolki N2P karpinskii Lopingian n Proelginia permiana Cistecephalus Wuchiapingian aya/ Il’inskoye R2P Sokolki 260 Tatarian inel’sk Tropidostoma ovskaya Malok yaz Deltavjatia vjatkensis Kotel’nich Pristerognathus Severodvinia V Illawarra pareiasaur dominated pareiasaur Isheevo/ Capitanian Ulemosaurus and dinocephalian, Gorgonopsian, N1P Tapinocephalus 265 svijagensis Malaya Kinel Amanakskaya Guadalupian Mezen’ Urzhumian Estemmenosuchus Wordian R P Bolshekinelskaya Ocher Eodicynodon 1 uralensis Dog Creek Shale Povolzhian/Belebey Kazanian Blaine Formation Biarmian 270 Roadian Sokian/Osinovskaya Parabradysaurus Golyusherma Chickasha Flowerpot Fm. dominated silantjevi Caseid and Ocher Fm. Duncan Sst. San Angelo Fm. varanopseid Sheshmian Ufimian Clamorosaurus Clear Fork Group Kiama Solikamian nocturnus Inta Irenian Cisuralian Kungurian Cisuralian “Kungurian” Filippovian 275 Wichita Group dominated Saranian Sphenacodontid "Olson’s Gap" Figure 1. Stratigraphic summary of Middle Permian tetrapod-bearing formations. The key units from the late Early to Late Permian in Rus- sia, South Africa, and North America are shown, based on evidence in Reisz and Laurin (2002), Lozovsky et al. (2009), Newell et al. (2010), and other sources. Tetrapods are, from the bottom, Dimetrodon, Varanops, and Titanophoneus. Chang.—Changhsingian; Fm.—Formation; Mag.—Magnetostratigraphy; Sst.—Sandstone. marine units in the northern Kanin
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