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The oldest ammonoids of Morocco (Tafilalt, lower Emsian)

  • Ralph Thomas BeckerEmail author
  • Christian Klug
  • Till Söte
  • Sven Hartenfels
  • Zhor Sarah Aboussalam
  • Ahmed El Hassani
Regular Research Article

Abstract

During a fieldtrip of the 10th International Cephalopod Symposium to the Tafilalt (SE Morocco), a fauna with the so far oldest ammonoid of the region was discovered at the top of the basal Emsian Deiroceras Limestone of Jebel Mech Irdane. The new material confirms the record of a single, poorly preserved specimen of the same age from Ras El Kebbar in the northwestern Tafilalt. All specimens are assigned within the Chebbitinae n. subfam. (Mimosphinctidae) to Praechebbites debaetsi n. gen. n. sp., which differs from the slightly younger Chebbites reisdorfi mostly in the lack of a dorsal lobe and dorsal imprint zone. In the conodont succession, the new species and genus falls in the top of the Eolinguipolygnathus excacatus M114 Zone, which has been proposed to define in future the base of the Emsian. Since the new taxon is morphologically already advanced, it is likely that even older ammonoids with loosely coiled conchs will be discovered in the future. A block from a Lower Carboniferous olistostrome of the adjacent Tinerhir region contained the gyroconic Ivoites n. sp. only. The global comparison of oldest ammonoid faunas shows the rarity of assemblages assigned to Lower Devonian (LD) III-B, often dated by conodonts and dacryoconarids. These faunas display a high level of endemism, which suggests that ammonoid origin and early evolution took place in regional populations with a restricted dispersal of genera and species.

Keywords

Ammonoids Emsian Taxonomy Stratigraphy Morocco 

Notes

Acknowledgements

We like to thank our friend, Prof. Dr. Lahssen Baidder (Casablanca), who co-organized and jointly led the spring 2018 field trip of the 10th International Cephalopod Symposium. CK acknowledges the support of the Swiss National Science Foundation (Project Number 200020_132870). We also thank K. De Baets (Erlangen) and an anonymous second reviewer for their useful comments.

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Authors and Affiliations

  1. 1.Institut für Geologie und PaläontologieWestfälische Wilhelms-UniversitätMünsterGermany
  2. 2.Palaeontological Institute and MuseumUniversity of ZurichZurichSwitzerland
  3. 3.Institut für Geologie und MineralogieUniversität zu KölnCologneGermany
  4. 4.Institute ScientifiqueUniversity Mohammed VRabatMorocco

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