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Fish fingers: digit homologues in sarcopterygian fish fins
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Physiology and Developmental Biology, Evolutionary Organism Biology.
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2007 (English)In: Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, ISSN 1552-5007, Vol. 308B, no 6, 757-768 p.Article in journal (Refereed) Published
Abstract [en]

A defining feature of tetrapod evolutionary origins is the transition from fish fins to tetrapod limbs. A major change during this transition is the appearance of the autopod (hands, feet), which comprises two distinct regions, the wrist/ankle and the digits. When the autopod first appeared in Late Devonian fossil tetrapods, it was incomplete: digits evolved before the full complement of wrist/ankle bones. Early tetrapod wrists/ankles, including those with a full complement of bones, also show a sharp pattern discontinuity between proximal elements and distal elements. This suggests the presence of a discontinuity in the proximal-distal sequence of development. Such a discontinuity occurs in living urodeles, where digits form before completion of the wrist/ankle, implying developmental independence of the digits from wrist/ankle elements. We have observed comparable independent development of pectoral fin radials in the lungfish Neoceratodus (Osteichthyes: Sareopterygii), relative to homologues of the tetrapod limb and proximal wrist elements in the main fin axis. Moreover, in the Neoceratodus fin, expression of Hoxd13 closely matches late expression patterns observed in the tetrapod autopod. This evidence suggests that Neoceratodus fin radials and tetrapod digits may be patterned by shared mechanisms distinct from those patterning the proximal fin/limb elements, and in that sense are homologous. The presence of independently developing radials in the distal part of the pectoral (and pelvic) fin may be a general feature of the Sarcopterygii.

Place, publisher, year, edition, pages
2007. Vol. 308B, no 6, 757-768 p.
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-16283DOI: 10.1002/jez.b.21197ISI: 000251331100006PubMedID: 17849442OAI: oai:DiVA.org:uu-16283DiVA: diva2:44054
Available from: 2008-05-19 Created: 2008-05-19 Last updated: 2010-02-11Bibliographically approved
In thesis
1. The Origin of Tetrapod Limbs and Girdles: Fossil and Developmental Evidence
Open this publication in new window or tab >>The Origin of Tetrapod Limbs and Girdles: Fossil and Developmental Evidence
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Around 375 million years ago, the first tetrapods appeared, marking one of the most important events in vertebrate evolutionary history. The fin to limb transition saw the appearance of fingers and a weight bearing pelvic girdle. While very little research has been done on the evolution of the tetrapod pelvic girdle, a fair amount has been done on the origins of fingers but some aspects remained controversial. A combination of palaeontology, developmental biology and comparative morphology was therefore used in this thesis to better understand the fin to limb transition. The pectoral fin of Panderichthys, a sarcopterygian fish closely related to tetrapods was CT-scanned and modeled in three dimensions and its pelvic girdle and fin were examined with traditional techniques. This information from the fossil record was integrated with comparisons of the development of the Australian lungfish, Neoceratodus forsteri, our closest living fish relative and the axolotl (Ambystoma mexicanum), a salamander representing well the condition of early tetrapods. Development of bone and cartilage was studied through clearing and staining and development of skeletal muscles through immunostaining. In situ hybridizations were performed on the lungfish to study the expression of Hoxd13, associated with the formation of digits in tetrapods.

This work shows that the late expression phase of Hoxd13 is present in Neoceratodus and is associated with the formation of radials. Redescription of the pectoral fin of Panderichthys reveals that distal radials are present, which, in addition to other information, lead us to conclude that digits are not novelties in tetrapods but rather have evolved from the distal radials present in the fins of all sarcopterygian fish. The earliest tetrapods lack a full set of wrist + carpals/ankle + tarsal bones. Here, we propose that this region of the limbs evolved after fingers and toes through an expansion of the region between the proximal limb bones and the digits. As for the pelvic girdle, it is very primitive in Panderichthys but comparison of its development in Neoceratodus and Ambystoma suggest that the ischium evolved through the posterior expansion of the pubis and the ilium, through an elongation of the iliac process already present in sarcopterygian fishes.

The results of this thesis help to better understand the fin to limb transition and show that it is more gradual than previously believed.


Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 53 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 613
National Category
urn:nbn:se:uu:diva-98911 (URN)978-91-554-7448-5 (ISBN)
Public defence
2009-04-09, Lindhalsalen, EBC, Norbyvägen 14, Uppsala, 13:00 (English)
Available from: 2009-03-13 Created: 2009-03-04 Last updated: 2009-04-03Bibliographically approved

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