31. |
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32. |
- Ahlberg, Per Erik, 1963-, et al.
(author)
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Pelvic claspers confirm chondrichthyan-like internal fertilization in arthrodires
- 2009
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In: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 460:7257, s. 888-889
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Journal article (peer-reviewed)abstract
- Recent finds(1,2) demonstrate that internal fertilization and viviparity (live birth) were more widespread in the Placodermi, an extinct group of armoured fishes, than was previously realized. Placoderms represent the sister group of the crown group jawed vertebrates (Gnathostomata)(3,4), making their mode(s) of reproduction potentially informative about primitive gnathostome conditions. An ossified pelvic fin basipterygium discovered in the arthrodire Incisoscutum ritchiei was hypothesized to be identical in males and females, with males presumed to have an additional cartilaginous element or series forming a clasper. Here we report the discovery of a completely ossified pelvic clasper in Incisoscutum ritchiei (WAM 03.3.28) which shows that this interpretation was incorrect: the basipterygium described previously(1) is in fact unique to females. The male clasper is a slender rod attached to a square basal plate that articulates directly with the pelvis. It carries a small cap of dermal bone covered in denticles and small hooks that may be homologous with the much larger dermal component of the ptyctodont clasper.
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33. |
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34. |
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35. |
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36. |
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37. |
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38. |
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39. |
- Ahlberg, Per
(author)
-
Science set in stone
- 2007
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 447, s. 37-38
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Review (pop. science, debate, etc.)
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40. |
- Ahlberg, Per, et al.
(author)
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The axial skeleton of the Devonian tetrapod Ichthyostega.
- 2005
-
In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 437:7055, s. 137-140
-
Journal article (peer-reviewed)abstract
- Ichthyostega was the first Devonian tetrapod to be subject to a whole-body reconstruction and remains, together with Acanthostega one of only two Devonian tetrapods for which near-complete postcranial material is available. It is thus crucially important for our understanding of the earliest stages of tetrapod evolution and terrestrialization. Based on extensive re-examination of original material, augmented by recently collected specimens, we present a new reconstruction of Ichthyostega that differs substantially from those previously published and reveals hitherto unrecognised regionalization in the vertebral column. Ichthyostega is the earliest vertebrate to show obvious adaptations for non-swimming locomotion. Uniquely among early tetrapods, the presacral vertebral column shows pronounced regionalization of neural arch morphology, suggesting that it was adapted for dorsoventral rather than lateral flexion.
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