Tiktaalik roseae - new tetrapod-like vertebrate (Nature)

[Tim Williams <twilliams_alpha@hotmail.com>]

In today/tomorrow's _Nature_, a new missing-link-that-is-no-longer-missing 
between lobe-finned fishes and tetrapods.  Named _Tiktaalik roseae_ (genus 
name based on a local Inuktitut name for a large, freshwater fish) , it is a 
close relative of _Elpistostege_, and is even closer to the origin of 
tetrapods than _Panderichthys_ is.  Best of all, it shows a well-preserved 
forelimb skeleton.  _Tiktaalik_ is even granted the honor of appearing on 
the _Nature_ cover page.

Edward B. Daeschler, Neil H. Shubin, and Farish A. Jenkins, Jr (2006).  A 
Devonian tetrapod-like fish and the evolution of the tetrapod body plan.  
Nature 440: 757-763.

Abstract: "The relationship of limbed vertebrates (tetrapods) to lobe-finned 
fish (sarcopterygians) is well established, but the origin of major tetrapod 
features has remained obscure for lack of fossils that document the sequence 
of evolutionary changes. Here we report the discovery of a well-preserved 
species of fossil sarcopterygian fish from the Late Devonian of Arctic 
Canada that represents an intermediate between fish with fins and tetrapods 
with limbs, and provides unique insights into how and in what order 
important tetrapod characters arose. Although the body scales, fin rays, 
lower jaw and palate are comparable to those in more primitive 
sarcopterygians, the new species also has a shortened skull roof, a modified 
ear region, a mobile neck, a functional wrist joint, and other features that 
presage tetrapod conditions. The morphological features and geological 
setting of this new animal are suggestive of life in shallow-water, marginal 
and subaerial habitats."

Neil H. Shubin, Edward B. Daeschler, and Farish A. Jenkins, Jr (2006). The 
pectoral fin of _Tiktaalik roseae_ and the origin of the tetrapod limb. 
Nature 440: 764-771.

Abstract: "Wrists, ankles and digits distinguish tetrapod limbs from fins, 
but direct evidence on the origin of these features has been unavailable. 
Here we describe the pectoral appendage of a member of the sister group of 
tetrapods, _Tiktaalik roseae_, which is morphologically and functionally 
transitional between a fin and a limb. The expanded array of distal 
endochondral bones and synovial joints in the fin of _Tiktaalik_ is similar 
to the distal limb pattern of basal tetrapods. The fin of _Tiktaalik_ was 
capable of a range of postures, including a limb-like substrate-supported 
stance in which the shoulder and elbow were flexed and the distal skeleton 
extended. The origin of limbs probably involved the elaboration and 
proliferation of features already present in the fins of fish such as 
_Tiktaalik_."

There's also a nice summary:

Per Erik Ahlberg and Jennifer A. Clack (2006).  Palaeontology: A firm step 
from water to land.  Nature 440: 747-749.

Cheers

Tim