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The oldest ammonoids of Morocco (Tafilalt, lower Emsian)


Becker, Ralph Thomas; Klug, Christian; Söte, Till; Hartenfels, Sven; Aboussalam, Zhor Sarah; El Hassani, Ahmed (2019). The oldest ammonoids of Morocco (Tafilalt, lower Emsian). Swiss Journal of Palaeontology, 138(1):9-25.

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.

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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Scopus Subject Areas:Physical Sciences > Paleontology
Uncontrolled Keywords:Palaeontology, Ammonoids, Emsian, Taxonomy, Stratigraphy, Morocco
Language:English
Date:1 March 2019
Deposited On:13 Jan 2020 09:45
Last Modified:29 Jul 2020 12:22
Publisher:Springer
ISSN:1664-2376
OA Status:Closed
Publisher DOI:https://doi.org/10.1007/s13358-019-00189-1
Official URL:https://link.springer.com/article/10.1007/s13358-019-00189-1
Project Information:
  • : FunderSNSF
  • : Grant ID200020_132870
  • : Project TitleVariability, Macroecology, Morphogenesis and Evolution of early Ammonoidea

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