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Proc Biol Sci. 2019 Oct 9;286(1912):20191336. doi: 10.1098/rspb.2019.1336. Epub 2019 Oct 2.

The early elasmobranch Phoebodus: phylogenetic relationships, ecomorphology and a new time-scale for shark evolution.

Author information

1
Paläontologisches Institut und Museum, University of Zurich, Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland.
2
Department of Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th Street, Chicago, IL 60637, USA.
3
Faculty of Geology, University of Warsaw, al. Żwirki i Wigury 93, 02-089 Warszawa, Poland.
4
Department of Geology, Khorasgan Branch, Islamic Azad University, PO Box 81595-158, Esfahan, Iran.
5
Naturalis Biodiversity Center, Postbus 9517, 2300 RA Leiden, The Netherlands.
6
Gloor Instruments AG, Schaffhauserstrasse 121, 8302 Kloten, Switzerland.

Abstract

Anatomical knowledge of early chondrichthyans and estimates of their phylogeny are improving, but many taxa are still known only from microremains. The nearly cosmopolitan and regionally abundant Devonian genus Phoebodus has long been known solely from isolated teeth and fin spines. Here, we report the first skeletal remains of Phoebodus from the Famennian (Late Devonian) of the Maïder region of Morocco, revealing an anguilliform body, specialized braincase, hyoid arch, elongate jaws and rostrum, complementing its characteristic dentition and ctenacanth fin spines preceding both dorsal fins. Several of these features corroborate a likely close relationship with the Carboniferous species Thrinacodus gracia, and phylogenetic analysis places both taxa securely as members of the elasmobranch stem lineage. Identified as such, phoebodont teeth provide a plausible marker for range extension of the elasmobranchs into the Middle Devonian, thus providing a new minimum date for the origin of the chondrichthyan crown-group. Among pre-Carboniferous jawed vertebrates, the anguilliform body shape of Phoebodus is unprecedented, and its specialized anatomy is, in several respects, most easily compared with the modern frilled shark Chlamydoselachus. These results add greatly to the morphological, and by implication ecological, disparity of the earliest elasmobranchs.

KEYWORDS:

Devonian; Morocco; chondrichthyes; gnathostomes; neurocranium

PMID:
31575362
PMCID:
PMC6790773
[Available on 2020-10-09]
DOI:
10.1098/rspb.2019.1336

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