Niedźwiedzki’s Gap

6 January 2010

Mudskipper (Periophthalmus) at the California Academy of Sciences

So yeah, just wanted to go on record and coin that one really.  An early contender for Top Paleo Story of 2010 is hitting the media shores like a flotilla of stem-tetrapods:

Nice (if rather breathless) promotional video from Nature

Detailed post on Nature editor Henry Gee’s blog

And the paper (Niedźwiedzki et al., 463, 43-48, 7 January 2010) here

Tetrapod tracks 20 million years before we would expect to find them.  Dude.

One interesting implication of this paper is that it may force us to rethink the environmental context of the water-to-land transition of early tetrapods.  The newly discovered trackways were left on exposed marine tidal flats, suggesting the “Tangled Bank” picture of the earliest tetrapods clambering around in vegetation-choked streams and rivers before taking to the land may not be exactly the entire story.  The role of freshwater as an avenue for sea>land and land>sea evolutionary transitions is an interesting subject in its own right, remind me to blog about it some time.

Another interesting angle is how this story contrasts with the last big “origins of tetrapod story”. The discovery of Tiktaalik has been relentlessly touted as an example of how we can make “predictions” about when (stratigraphically) and where we expect to find important fossils based on what we already know about the history of life and then go look for them.  That is true, to a point.  However there is also a very important place for unexpected discoveries in paleontology despite the fact that they don’t fit in as nicely with fairy tales about how “THE” scientific method is supposed to work.  Granted, it’s difficult to write successful grant applications along the lines of “well, I have no idea what the eff I’m going to find, but I’m sure it will transform what we think about evolutionary history.”  Still, I’ve always that old line (usually attributed to Asimov, perhaps apocryphally)–“the most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s funny…’–was particularly true in paleontology.

What will get the most attention however, is that the new discovery pushes back the divergence of true tetrapods and elpistostegids like Tiktaalik by 20 million years or so.  So, news flash to everyone who went ga-ga over Tiktaalik as THE missing link, it isn’t.  But you already knew that.  Before you feel to sorry for Tiktaalik getting summarily kicked to the curb though, it’s good to remember Neil Shubin’s words back in 2006 when the discovery of “the fishapod” was first announced:

Mudskippers and the other walking fish are all very interesting, but are they extraordinary in an evolutionary sense? No, they are not, and the reason is instructive. Hopping, climbing, and breathing fish are just animals that have evolved to live in different kinds of aquatic and subaereal habitats. They are able to breathe air, hop, or climb because of subtle changes to their bodies; no revolutionary changes are needed…If paleontologists 300 million years from now dig up the remains of a mudskipper, they will write chapters about its role in a “great” transition only if its part of the evolutionary tree has branched into many twigs. The mudskipper will get extra special treatment if one of its evolutionary branches leads to the paleontologists’ own species. (Shubin 2006 “The ‘Great’ Transition”)

Hear that Mudskipper?  Nice try.  We’re not impressed.

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