Tissue diversity and evolutionary trends of the dermal skeleton of Silurian thelodonts
2013 (English)In: Historical Biology, ISSN 0891-2963, Vol. 25, no 2, 143-154 p.Article in journal (Refereed) Published
Previously described scale morphotypes of Silurian thelodonts, constrained by their representation as isolated dermaldenticles are reassessed to provide a more robust character basis for their inclusion in future phylogenetic studies. Asrelatively common microfossils, thelodonts are important biostratigraphical markers, but their interrelationships withgeologically younger species known by complete skeletons are still unresolved. We examined scales of 21 knownmorphotypes from north-eastern Europe, Siberia and central Asia and described their distinct tissue arrangementsconsidering (1) thickness and direction of dentine tubules, (2) presence or absence of a pulp canal, (3) number and positionof pulp canals, (4) the presence or absence of a distinct outer crown layer and (5) the extent of Sharpey’s fibres penetratingthe scale base. We correlated the traditional thelodont scale type morphologies with these distinct scale histologies, as foundin Silurian thelodonts. In addition, a new histological type for thelodont scales, the Talimaalepis type, is described torepresent a new taxon, from the Early-Mid Silurian. Our study suggests that, through time, there is a general trend ofincreasing complexity in thelodont dermal tissue structures. Three types of dentine and internal scale organisations weredistinguished in Silurian species studied, namely (1) irregular, thin tubular dentine; (2) irregular, thick tubular dentine, withtwo subtypes as a function of pulp canal development and (3) regular, tubular dentine (orthodentine).
Place, publisher, year, edition, pages
2013. Vol. 25, no 2, 143-154 p.
Natural Sciences Evolutionary Biology Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:uu:diva-209296DOI: 10.1080/08912963.2013.766184OAI: oai:DiVA.org:uu-209296DiVA: diva2:656654