Sporadoceratid ammonoids from the Shotori Range (east-central Iran) – a case of putative gigantism caused by hydraulic sorting?

Authors

  • Dieter Korn Museum für Naturkunde Berlin, Invalidenstraße 43, 10115 Berlin
  • Abbas Ghaderi Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad
  • Léa Devaere Museum für Naturkunde Berlin, Invalidenstraße 43, 10115 Berlin
  • Vachik Hairapetian Department of Geology, Khorasgan (Esfahan) Branch, Islamic Azad University, P.O. Box 81595-158, Esfahan
  • Mohammad Khanehbad Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad
  • Zdzisław Bełka Adam Mickiewicz University, Isotope Laboratory, Krygowskiego 10, PL 61-680 Poznań

Keywords:

Late Devonian, Famennian, Iran, Ammonoids, Body size, Conodonts

Abstract

The Shotori Range of east-central Iran (east of Tabas) has yielded Famennian ammonoid assemblages dominated by the family Sporadoceratidae. Four genera Maeneceras Hyatt, 1884, Iranoceras Walliser, 1966, Sporadoceras Hyatt, 1884 and Erfoudites Korn, 1999 are represented. The conodont assemblage of one sample containing Iranoceras revealed an Upper marginifera Zone age. The ammonoid assemblages are characterised by comparatively large specimens; they reach conch diameters of 300 mm (including the body chamber) and the mean size is larger than 100 mm. The preservation of the material from the Shotori Range and size comparison with sporadoceratid assemblages from the Anti-Atlas of Morocco and the Rhenish Mountains of Germany suggest that hydraulic sorting has resulted in a bias towards large conchs, explaining the size distribution, rather than latitudinal differences. The new species Maeneceras tabasense is described; the genus Iranoceras is revised with a new description of the two species Iranoceras pachydiscus (Walliser, 1966) and Iranoceras pingue (Walliser, 1966).

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Published

2019-04-12

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Articles