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  Estonian Journal of Earth Sciences

ISSN 1736-7557 (electronic)  ISSN 1736-4728 (print)
An international scientific journal

Formerly: Proceedings of the Estonian Academy of Sciences, Geology
Published since 1952

Estonian Journal of Earth Sciences

ISSN 1736-7557 (electronic)  ISSN 1736-4728 (print)
An international scientific journal

Formerly: Proceedings of the Estonian Academy of Sciences, Geology
Published since 1952

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A unique Late Silurian Thelodus squamation from Saaremaa (Estonia) and its ontogenetic development; pp. 137–146

(Full article in PDF format) doi: 10.3176/earth.2011.3.02


Authors

Tiiu Märss

Abstract

A partly preserved squamation of Thelodus laevis (Pander) from the Himmiste outcrop (Saaremaa Island, Estonia) is described. Most of the trunk with a pectoral fin fragment and three fragments of posterior fins are present, while part of the head and the caudal fin are absent. Ontogenetic development of the scale cover of T. laevis is explained by comparing it with the squamation of Lanarkia horrida Traquair, Loganellia scotica (Traquair) and a modern fish. It is supposed that newly forming trunk scales of early juvenile Thelodus were smooth and rhomboidal. When the individual grew, ridged scales were added between smooth ones in irregular rows in the posterior part of the trunk. Adult individuals were covered with species-specific scales with particular morphology and sculpture of the crown. Co-occurrence of smooth and ridged scales on the trunk in the specimen studied corresponds to a young stage of ontogeny.

Keywords

Thelodus, Thelodonti, squamation, ontogeny, Late Silurian, Estonia.

References

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