3D Histological Architecture And Ontogeny In Two Early Osteichthyan Scales: the Origin Of Cosmine And A Reconsideration Of The Phylogenetic Application Of Paleohistology Data
2013 (English)Conference paper, Abstract (Other academic)
The histology of early osteichthyan scales have been extensively studied using thin sections and acid-etched ground surfaces, and it is known that these rhombic scales are composed of multiple odontodes (tooth-like denticles) in the crown and bony tissues in the base. However, the 2D nature of the ground sections does not allow us to know the 3D morphology and distribution of the odontodes, which contain the ontogenetic history of the scales. To compensate the traditional study based on ground sections, we used Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRµCT) to examine body scales of two early osteichthyans Andreolepis and Psarolepis, both of which are important taxa to understand the origin of osteichthyan crown group.
The reconstructed 3D models of the histological architecture provide novel data of the ontogenetic history of the scales. The crown of Andreolepis scale is constructed two distinct type of growth patterns: a linear polarized pattern in the initial stage and a gap-filling pattern in the later stage. In the crown of Psarolepis scale the second odontode is most peculiar, with a the enamel covering penetrated by several pores, while the primordia odontode is almost morphologically identical with that of Andreolepis scale. A developmental shift following the formation of the primordia odontode may be the key step of the evolution of cosmoid scales, and Psarolepis scale is explained as a transitional form between the Andreolepis-type scale and the typical cosmoid scales in more derived sarcopterygians such as Osteolepis. Comparison of the entire canal system among Andreolepis, Psarolepis and more derived sarcopterygians show that the pore-canal system and cosmine-like construction are already present in Psarolepis scales, although the construction is different from typical cosmine as in Osteolepis. A stepwise scenario of the origin of pore-canal system and cosmine is proposed according to the new data.
New characters are composed based on the in situ 3D data and could be incorporated into phylogenetic analysis in the future when more taxa have been studied using similar imaging method and 3D histology obtained. The 3D histology study of skeletal fossils using PPC-SRµCT could provide more informative and reliable phylogenetic data.
Place, publisher, year, edition, pages
3D histology, cosmine, characters, cladistics
Research subject Earth Science with specialization in Historical Geology and Palaeontology
IdentifiersURN: urn:nbn:se:uu:diva-213350OAI: oai:DiVA.org:uu-213350DiVA: diva2:681776
The Second International Symposium on Paleohistology (ISPH.2013), Bozeman,July 18 - 20, 2013
ProjectsERC Advanced Investigator Grant 233111
FunderEU, European Research Council, 233111