Fish fingers: Digit homologues in Sarcopterygian fish fins

Zerina Johanson*, Jean Joss, Catherine A. Boisvert, Rolf Ericsson, Margareta Sutija, Per E. Ahlberg

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    96 Citations (Scopus)


    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 radiais in the lungfish Neoceratodus (Osteichthyes: Sarcopterygii), 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 radiais 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.

    Original languageEnglish
    Pages (from-to)757-768
    Number of pages12
    JournalJournal of Experimental Zoology Part B: Molecular and Developmental Evolution
    Issue number6
    Publication statusPublished - 15 Dec 2007


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