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Gogo fish sheds light on tetrapod origins take 2
Hopefully without "---REMAINDER OF MESSAGE TRUNCATED---" this time...
Nature advance online publication =
for pretty pictures =
An exceptional Devonian fish from Australia sheds light on tetrapod
John A. Long, Gavin C. Young, Tim Holland, Tim J. Senden and Erich M. G.
The transition from fishes to tetrapods was one of the most dramatic
events in the evolution of vertebrates, but many pivotal fossils are
incomplete, resulting in gaps in the data that are used for phylogenetic
reconstruction. Here we present new observations from the most complete,
acid-prepared Devonian tetrapodomorph fish yet discovered, Gogonasus,
which was previously placed just crownward of Kenichthys and
rhizodontids, the most primitive taxa on the tetrapod lineage.
Unexpectedly, Gogonasus shows a mosaic of plesiomorphic and derived
tetrapod-like features. Whereas the braincase and dermal cranial
skeleton exhibit generalized morphologies with respect to Eusthenopteron
or Panderichthys, taxa that are traditionally considered to be
phyletically close to tetrapods, the presence of a deeply invaginated,
wide spiracle, advanced internal spiracular architecture and
near-horizontal hyomandibula are specialized features that are absent
from Eusthenopteron. Furthermore, the pectoral fin skeleton of Gogonasus
shares several features with that of Tiktaalik, the most tetrapod-like
fish. A new phylogenetic analysis places Gogonasus crownward of
Eusthenopteron as the sister taxon to the Elpistostegalia. Aspects of
the basic tetrapod limb skeleton and middle ear architecture can now be
traced further back within the tetrapodomorph radiation.
Vertebrate palaeontologist and illustrator
website = www.geocities.com/ozraptor4
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