Getting to the beach early... 397 million years early.

[Update 01/07/10: OK, this result is more exciting than I first appreciated. Matthew Cobb at Why Evolution is True discusses this finding in a much better way than the BBC article did]

The BBC has a nice (accessible) story about a fossil trackway from was a muddy beach dated at 397 million years ago. What is interesting it is that it appears to record the tracks of a four legged creature about 2 metres long, which is slightly older than the famous Tiktaalik fossil (from ~375 million years ago, which is not a direct ancestor of tetrapods) and quite a bit older than the classic early tetrapod Ichthyostega (from ~360 Myr before present).

Some slight re-arrangement of the timeline of when tetrapods arose is not earth-shattering, but it pushes things back a bit, and incremental improvements in knowledge are still nice (to be fair the Nature News & Views article mentioned below thinks this a big deal).

For the genuinely interested:

• "Tetrapod trackways from the early Middle Devonian period of Poland", Niedźwiedzki, Nature 463, 40-41 (7 January 2010) (doi:10.1038/463040a; Published online 6 January 2010). et al, 2010,
  
• The Nature News & Views article by Janvier & Clément discussing Niedźwiedzki etal.
  

The age of the previously identified Devonian tetrapod trackways (short green bars) contrasts with the 397-Myr-old Zachemie tracks identified by Niedźwiedzki and colleagues¹. These newly discovered tracks generate a mismatch between the currently accepted tree of tetrapodomorph fishes (lobe-finned fishes with internal nostrils) and its timing based on the body-fossil record (shown by solid red lines). The temporal mismatch implies the existence of long 'ghost ranges' (dashed red lines) among Devonian tetrapodomorphs. The divergence between elpistostegalian fishes and tetrapods with limbs and digits must have occurred much earlier than previously thought, perhaps during the 10-Myr-long Emsian stage, from which only few tetrapodomorph fishes are recorded. 1, Earliest articulated tetrapod skeletons with limbs and digits (Ichthyostega, Acanthostega)²; 2, earliest isolated tetrapod bones; 3, earliest tetrapodomorph fish (Kenichthys)⁵; 4, possible earlier tetrapodomorph fish⁶.

[Figure and caption from Palaeontology: Muddy tetrapod origins, Philippe Janvier & Gaël Clément, Nature 463, 40-41(7 January 2010), doi:10.1038/463040a]