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- Johanson, Zerina, et al.
(författare)
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Fish fingers : digit homologues in sarcopterygian fish fins
- 2007
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Ingår i: Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. - : Wiley. - 1552-5007 .- 1552-5015. ; 308B:6, s. 757-768
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Johanson, Zerina, et al.
(författare)
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Phylogeny of lungfishes
- 2010
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Ingår i: The Biology of Lungfishes. - Enfield, N.H. : Science Publishers. - 1578084318 - 9781578084319 ; , s. 43-60
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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- Johanson, Zerina, et al.
(författare)
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The braincase and palate of the tetrapodomorph sarcopterygian Mandageria fairfaxi: morphological variability near the fish-tetrapod transition
- 2003
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 46:2, s. 271-293
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Tidskriftsartikel (refereegranskat)abstract
- The braincase of the Late Devonian tristichopterid sarcopterygian Mandageria fairfaxi, from Canowindra, NSW, Australia, differs radically from the conservative pattern present in other 'osteolepiforms' (stem–group tetrapodomorph fishes) and non–dipnoan sarcopterygian fishes in general. The basioccipital region is short, displaced anteriorly, and either unossified or loosely articulated to the exoccipital, leaving most or all of the notochordal tunnel open ventrally. The exoccipital complex, which is developed into a large saddle that would have rested on top of the notochord, carries large, triangular articular facets on its posterior face and appears to have formed part of a functional neck joint, a synovial articulation between the skull and vertebral column that allows the former to rotate against the latter. Such a joint is characteristic of post–Devonian tetrapods, but unknown in other sarcopterygians. We infer that the ventrally open notochordal tunnel allowed gentle flexion of the cranial notochord during (predominantly vertical) rotational movement at the occiput; this is a mechanically unique solution to the problem of creating a mobile neck. Other unusual features of Mandageria include a posteriorly located lateral commissure, and structures on the entopterygoid and lateral commissure that may have been associated with an elaborate spiracular tract.
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