See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/232806070 Guodunites, a low-palaeolatitude and trans- Panthalassic Smithian (Early Triassic) ammonoid genus Article in Palaeontology · February 2009 DOI: 10.5167/uzh-17837 CITATIONS READS 16 14 4 authors: Arnaud Brayard Thomas Brühwiler University of Burgundy 38 PUBLICATIONS 985 CITATIONS 91 PUBLICATIONS 1,742 CITATIONS SEE PROFILE SEE PROFILE Hugo FR Bucher Jim Jenks University of Zurich None - Retired 210 PUBLICATIONS 3,821 CITATIONS 34 PUBLICATIONS 400 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: The second stage of recovery from the end-Permian mass extinction: Ecology, diversity partitioning, and rank-abundance distributions in Middle Triassic marine level-bottom communities View project All in-text references underlined in blue are linked to publications on ResearchGate, Available from: Hugo FR Bucher letting you access and read them immediately. Retrieved on: 22 November 2016 [Palaeontology, Vol. 52, Part 2, 2009, pp. 471–481] GUODUNITES, A LOW-PALAEOLATITUDE AND TRANS-PANTHALASSIC SMITHIAN (EARLY TRIASSIC) AMMONOID GENUS by ARNAUD BRAYARD*–, THOMAS BRU¨ HWILER , HUGO BUCHER à and JIM JENKS§ *LMTG, UMR 5563 CNRS – Universite´ Toulouse – IRD, Observatoire Midi-Pyre´ne´es, 14 Avenue Edouard Belin, F-31400 Toulouse, France; e-mail: [email protected] Pala¨ontologisches Institut und Museum, Universita¨tZu¨rich, Karl Schmid-Strasse 4, CH-8006 Zu¨rich, Switzerland; e-mails: [email protected]; [email protected] àDepartment of Earth Sciences, ETH Zu¨rich, Switzerland; e-mail: [email protected] §1134 Johnson Ridge Lane, West Jordan, UT 84084, USA; e-mail: [email protected] –Present address: UMR 5561 CNRS Bioge´osciences, Universite´ de Bourgogne, 6 boulevard Gabriel, F-21000, Dijon, France; e-mail: [email protected] Typescript received 20 February 2008; accepted in revised form 30 June 2008 Abstract: Based on new, bed-rock controlled material from Its palaeobiogeographical distribution further strengthens the Oman and Utah, USA, the Early Triassic genus Guodunites, existence of significant equatorial faunal exchanges between which was recently erected on the basis of scarce specimens both sides of the Panthalassa at that time. It also suggests from northwestern Guangxi, South China, is now shown to that, in addition to the potential stepping stones represented be a representative of Proptychitidae. This solves the ques- by Panthalassic terranes, vigorous equatorial oceanic currents tion of the previously unknown phylogenetic affinity of this must have contributed largely to the dispersal of ammonoids genus. The genus is restricted to the late middle Smithian, during such time intervals. and to date, its biogeographical distribution comprises Oman, South China and Utah, thus indicating an essentially Key words: Ceratitida, oceanic currents, Oman, Proptychi- low palaeolatitudinal distribution during the Early Triassic. tidae, Smithian (Early Triassic), South China, Utah. Few ammonoid genera survived the Permo ⁄ Triassic have contributed to the patterns of Early Triassic ammo- mass extinction (c. 252 Ma). The Early Triassic ammo- noid distribution. noid recovery followed a global increasing trend in diver- Guodunites, a Smithian ammonoid genus, was first sity with at least two major evolutionary radiations described from northwestern Guangxi, South China by Bra- occurring during the Smithian and early Spathian respec- yard and Bucher (2008). However, the rare and poorly pre- tively (Tozer 1981b; Dagys 1988; Brayard et al. 2006). served Chinese material did not permit a systematic Compared with other marine organisms, this diversifica- assignment at the suprageneric level. The recent discovery of tion was extremely rapid (less than c. 1 myr; Ovtcharova Guodunites in Oman and Utah, USA enables us to establish et al. 2006; Galfetti et al. 2007b) and was accompanied by its phylogenetic affinities and to expand its palaeobiogeo- the formation of pronounced latitudinal diversity gradi- graphical distribution, thus reflecting low-latitude trans- ents during both the Smithian and Spathian evolutionary oceanic dispersal between both sides of the Panthalassa. radiations (e.g. Dagys 1988; Brayard et al. 2006, 2007b). The emergence of such latitudinal diversity gradients par- allels the steepening of the Sea surface temperature gradi- BIOGEOGRAPHICAL AND ent (SST; Brayard et al. 2006). Brayard et al. (2006, BIOSTRATIGRAPHICAL OCCURRENCES 2007b, in press) and Jenks (2007) have also suggested that the occurrence of several nearly-identical Early Triassic South China ammonoid taxa on each side of the Panthalassa aptly demonstrates their capacity for very long-distance dis- Guodunites was first described from the Luolou Fm of persal across this 20000 km wide ocean (Text-fig. 1). northwestern Guangxi, South China (Text-fig. 1B) by Along with SST control, oceanic surface circulation Brayard and Bucher (2008). Ammonoids are very abundant and ⁄ or the use of terranes as stepping stones may also in the Smithian part of this formation, which essentially ª The Palaeontological Association doi: 10.1111/j.1475-4983.2009.00855.x 471 472 PALAEONTOLOGY, VOLUME 52 A B C D TEXT-FIG. 1. Location map of the studied material. A, Wadi Musjah, Oman. B, Jinya and Yuping, northwestern Guangxi, South China. C, Confusion Range, Utah, USA. D, Early Triassic palaeogeographical positions of Oman, South China and Utah. represents the basinal deposit portion of the Nanpanjiang Safra, Wadi Musjah and the famous Baid exotic (Tozer and Basin (Lehrmann et al. 2007). The major component of the Calon 1990; Blendinger 1995; Bru¨hwiler et al. 2007). At early Smithian usually consists of a conspicuous, ledge- Wadi Musjah (75 km SSW of Musqat), Guodunites occurs forming, c. 3 m thick, grey, thin-bedded limestone unit in an exotic block consisting of micritic, red, ammonoid- containing the Flemingites rursiradiatus beds of early rich limestone with Owenites, Inyoites, Paranannites, Lance- Smithian age (Brayard and Bucher 2008). In contrast to the olites, Aspenites and Dieneroceras, thus indicating a late carbonate-dominated lower part of the Smithian, the mid- middle Smithian age. Preservation of ammonoids from this dle and late Smithian portions of the Luolou Fm. consist of locality is sometimes excellent and, in rare cases, organic thin-bedded limestone alternating with dark shales (Galfetti remains of so-called ‘false colour patterns’ have been found et al. 2007a, 2008). Within this succession, Brayard and on specimens of Paranannites (e.g. Klug et al. 2007). Bucher (2008) reported the association of Guodunites with Aspenites, Inyoites, Juvenites, Lanceolites, Owenites, Pseudas- pidites, Pseudoceltites? and Pseudoflemingites, thus defining Utah, USA its biostratigraphical position at the end of the middle Smi- thian (Owenites koeneni beds, Inyoites horizon; Text-fig. 2). New material from western Utah comes from the Early Triassic Thaynes Fm in the Confusion Range (Text- fig. 1C). The ammonoid bearing beds pertaining to this Oman article occupy the uppermost portion of the Smithian and mainly consist of a limestone unit, overlying a red- In Oman (Text-fig. 1A), Early Triassic ammonoids occur dish shale interval almost devoid of ammonoid faunas in exotic blocks of typical Hallstatt facies limestone at Jebel (Bacon 1948; Hose and Repenning 1959; Newell 1959). BRAYARD ET AL.: GUODUNITES, A TRANS-PANTHALASSIC SMITHIAN GENUS 473 c e i l s d s Early d a i i Northwesten Guangxi Oman Utah r Anisian M Luolou Fm exotic blocks Confusion Range T Brayard & Bucher 2008 Brühwiler et al. 2007 Thaynes Fm 248.12 ± 0.28 Anasibirites multiformis beds Anasibirites multiformis beds Anasibirites beds Inyoites horizon Inyoites Inyoites beds Owenites koeneni Owenites c Spathian beds Hanielites horizon beds i new s s Ussuria horizon arctoceratid B a i r T y Flemingites rursiradiatus beds Flemingites rursiradiatus beds l r 250.55 ± 0.4 a E Kashmirites kapila Smithian beds 251.22 ± 0.2 Dienerian Griesbachian 252.6 ± 0.2 TEXT-FIG. 2. Subdivisions of the Early Triassic (Tozer 1967, 1994) and ammonoid zonation of the Smithian from northwestern Guangxi, Oman and Utah (Brayard et al. 2007a; Bru¨hwiler et al. 2007; Brayard and Bucher 2008). Radiometric ages after Mundil et al. (2004), Ovtcharova et al. (2006) and Galfetti et al. (2007b). Shaded zones indicate the biostratigraphical occurrence of Guodunites in northwestern Guangxi, Oman and Utah during the Smithian. Ammonoids from beds immediately underlying the Ana- Repository of figured and measured specimens is abbreviated sibirites beds are relatively well-preserved. Many are com- PIMUZ (Pala¨ontologisches Institut und Museum, Universita¨t plete and retain much of the outer shell. Zu¨rich). Guodunites occurs within the Inyoites beds (informal name introduced here) in association with Inyoites, Order AMMONOIDEA Zittel, 1884 Owenites, Aspenites, Lanceolites, Juvenites, Churkites and Suborder CERATITINA Hyatt, 1884 Pseudaspidites. Thus, occurrences of Guodunites are syn- Family PROPTYCHITIDAE Waagen, 1895 chronous on both sides of Panthalassa. Moreover, in South China and Utah, the immediately overlying Anasib- Genus GUODUNITES Brayard and Bucher, 2008 irites fauna of late Smithian age confirms the late middle Smithian biostratigraphical position of Guodunites. Type species. Guodunites monneti Brayard and Bucher, 2008, Guodunites was initially