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Life history of the stem tetrapod Acanthostega revealed by synchrotron microtomography
Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology. European Synchrotron Radiat Facil, 71 Ave Martyrs,CS 40220, F-38043 Grenoble, France..
European Synchrotron Radiat Facil, 71 Ave Martyrs,CS 40220, F-38043 Grenoble, France..
Univ Cambridge, Univ Museum Zool, Dept Zool, Downing St, Cambridge CB2 3EJ, England..
Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
2016 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 537, no 7620, 408-+ p.Article in journal (Refereed) Published
Abstract [en]

The transition from fish to tetrapod was arguably the most radical series of adaptive shifts in vertebrate evolutionary history. Data are accumulating rapidly for most aspects of these events(1-5), but the life histories of the earliest tetrapods remain completely unknown, leaving a major gap in our understanding of these organisms as living animals. Symptomatic of this problem is the unspoken assumption that the largest known Devonian tetrapod fossils represent adult individuals. Here we present the first, to our knowledge, life history data for a Devonian tetrapod, from the Acanthostega mass-death deposit of Stensio Bjerg, East Greenland(6,7). Using propagation phase-contrast synchrotron microtomography (PPC-SR mu CT)(8) to visualize the histology of humeri (upper arm bones) and infer their growth histories, we show that even the largest individuals from this deposit are juveniles. A long early juvenile stage with unossified limb bones, during which individuals grew to almost final size, was followed by a slow-growing late juvenile stage with ossified limbs that lasted for at least six years in some individuals. The late onset of limb ossification suggests that the juveniles were exclusively aquatic, and the predominance of juveniles in the sample suggests segregated distributions of juveniles and adults at least at certain times. The absolute size at which limb ossification began differs greatly between individuals, suggesting the possibility of sexual dimorphism, adaptive strategies or competition-related size variation.

Place, publisher, year, edition, pages
2016. Vol. 537, no 7620, 408-+ p.
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-305454DOI: 10.1038/nature19354ISI: 000383098000055OAI: oai:DiVA.org:uu-305454DiVA: diva2:1038665
Funder
EU, European Research Council, 233111Swedish Research Council, 201504335
Available from: 2016-10-19 Created: 2016-10-18 Last updated: 2016-10-19Bibliographically approved

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Sanchez, SophieAhlberg, Per E.
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