Abstract:
:The Late Devonian genus Ichthyostega was for many decades the earliest known tetrapod, and the sole representative of a transitional form between a fish and a land vertebrate. However, despite being known since 1932 (ref. 1) from a large collection of specimens, its morphology remained enigmatic and not what was expected of a very primitive tetrapod. Its apparent specializations led it to be considered as a "blind offshoot" or "sidebranch" off the tetrapod family tree, and recent cladistic analyses have disagreed about its exact phylogenetic position within the tetrapod stem group. In particular, its braincase and ear region defied interpretation, such that conventional anatomical terms seemed inapplicable. Using new material collected in 1998 (ref. 9), preparation of earlier-collected material, and high-resolution computed tomography scanning, here we identify and interpret these problematic anatomical structures. They can now be seen to form part of a highly specialized ear, probably a hearing device for use in water. This represents a structurally and functionally unique modification of the tetrapod otic region, unlike anything seen in subsequent tetrapod evolution. The presence of deeply grooved gill bars as in its contemporary Acanthostega suggest that Ichthyostega may have been more aquatically adapted than previously believed.
journal_name
Naturejournal_title
Natureauthors
Clack JA,Ahlberg PE,Finney SM,Dominguez Alonso P,Robinson J,Ketcham RAdoi
10.1038/nature01904keywords:
subject
Has Abstractpub_date
2003-09-04 00:00:00pages
65-9issue
6953eissn
0028-0836issn
1476-4687pii
nature01904journal_volume
425pub_type
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