Elegestolepis and its kin, the earliest monodontode chondrichthyans. Issue 1 (2nd January 2017)

• Record Type: Journal Article
• Authors: Andreev, Plamen S.; Coates, Michael I.; Karatajūtė-Talimaa, Valentina; Shelton, Richard M.; Cooper, Paul R.; Sansom, Ivan J.
• Is Part Of: Journal of vertebrate paleontology. Volume 37:Issue 1(2017)
• Publication Date: 2017-01-02
• Subjects: Vertebrates, Fossil -- Periodicals; Paleontology -- Periodicals; Vertébrés fossiles -- Périodiques; Paléontologie -- Périodiques; Paleozoölogie; Gewervelde dieren; 566.05
• DOI: 10.1080/02724634.2017.1245664
• Languages: English
• ISSNs: 0272-4634

Abstract

ABSTRACT: Chondrichthyan-like scales with simple, single-odontode crowns, reminiscent of those of euselachians, have been reported from Silurian strata in a number of previous studies. These specimens comprise the genera Elegestolepis (from Siberia, Mongolia, and Tuva) and Kannathalepis (from the Canadian Arctic) and have been considered to exhibit contrasting patterns of ontogenetic development. A study of elegestolepid microremains from the Chargat Formation of Mongolia (Llandovery–lower Wenlock) and the Baital Formation of Tuva (Wenlock–Ludlow) has been undertaken using scanning electron microscopy and micro-computed tomography to examine scale canal system and hard tissue structure. These investigations revealed scales at different stages of development, whose morphogenesis is characterized by growth (elongation) of the crown odontode and formation of neck canals. This ontogenetic pattern ( Elegestolepis -type morphogenesis) is also recognized in Kannathalepis and the Lower Devonian species Ellesmereia schultzei and forms the basis for the unification of these taxa into a new chondrichthyan order Elegestolepidida, ordo nov. Similarities in crown vascularization (branching pulp, single neck canal) shared by Elegestolepis, Ellesmereia, and Deltalepis, gen. nov. ( D. magna, sp. nov., and D. parva, sp. nov., erected herein for Mongolian specimens), require the erection of the family Elegestolepididae, fam. nov., that is distinguished from the monogeneric Kannathalepididae (non-branching pulp, multiple neck canals). Elegestolepid scales exhibit characteristics (neck canal formation and lack of enamel and basal bone osteons) consistent with those of the chondrichthyan dermal skeleton. This establishes Elegestolepidida as the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the 'placoid' scales of euselachians, are growing structures.http://zoobank.org/urn:lsid:zoobank.org:pub:46F95C47-6926-4F3DB96D-9890527BA8DE Citation for this article: Andreev, P. S., M. I. Coates, V. Karatajūtė-Talimaa, R. M. Shelton, P. R. Cooper, and I. J. Sansom. 2016. Elegestolepis and its kin, the earliest monodontode chondrichthyans. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1245664.