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A symmoriiform from the Late Devonian of Morocco demonstrates a derived jaw function in ancient chondrichthyans


Frey, Linda; Coates, Michael I; Tietjen, Kristen; Rücklin, Martin; Klug, Christian (2020). A symmoriiform from the Late Devonian of Morocco demonstrates a derived jaw function in ancient chondrichthyans. Communications Biology, 3:681.

Abstract

The Palaeozoic record of chondrichthyans (sharks, rays, chimaeras, extinct relatives) and thus our knowledge of their anatomy and functional morphology is poor because of their predominantly cartilaginous skeletons. Here, we report a previously undescribed symmoriiform shark, <jats:italic>Ferromirum oukherbouchi</jats:italic>, from the Late Devonian of the Anti-Atlas. Computed tomography scanning reveals the undeformed shape of the jaws and hyoid arch, which are of a kind often used to represent primitive conditions for jawed vertebrates. Of critical importance, these closely fitting cartilages preclude the repeatedly hypothesized presence of a complete gill between mandibular and hyoid arches. We show that the jaw articulation is specialized and drives mandibular rotation outward when the mouth opens, and inward upon closure. The resultant eversion and inversion of the lower dentition presents a greater number of teeth to prey through the bite-cycle. This suggests an increased functional and ecomorphological disparity among chondrichthyans preceding and surviving the end-Devonian extinctions.

Abstract

The Palaeozoic record of chondrichthyans (sharks, rays, chimaeras, extinct relatives) and thus our knowledge of their anatomy and functional morphology is poor because of their predominantly cartilaginous skeletons. Here, we report a previously undescribed symmoriiform shark, <jats:italic>Ferromirum oukherbouchi</jats:italic>, from the Late Devonian of the Anti-Atlas. Computed tomography scanning reveals the undeformed shape of the jaws and hyoid arch, which are of a kind often used to represent primitive conditions for jawed vertebrates. Of critical importance, these closely fitting cartilages preclude the repeatedly hypothesized presence of a complete gill between mandibular and hyoid arches. We show that the jaw articulation is specialized and drives mandibular rotation outward when the mouth opens, and inward upon closure. The resultant eversion and inversion of the lower dentition presents a greater number of teeth to prey through the bite-cycle. This suggests an increased functional and ecomorphological disparity among chondrichthyans preceding and surviving the end-Devonian extinctions.

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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
Language:English
Date:1 December 2020
Deposited On:18 Nov 2020 14:49
Last Modified:20 Dec 2020 08:52
Publisher:Nature Publishing Group
ISSN:2399-3642
OA Status:Gold
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1038/s42003-020-01394-2
Project Information:
  • : FunderSNSF
  • : Grant ID200020_184894
  • : Project TitleTaxonomic, morphological and functional diversity of Placodermi and Chondrichthyes from the Late Devonian of Morocco
  • : FunderSNSF
  • : Grant ID200020_184894
  • : Project TitleTaxonomic, morphological and functional diversity of Placodermi and Chondrichthyes from the Late Devonian of Morocco

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