Fish On!

Dateline: The Third Culture

Neil Shubin has authored a "great" essay about that wacky fishapod Tiktaalik and the slippery slope of tetrapodia. It appears as part of a bolus of counter-intelligence designs offered up by Edge (not to be confused The Edge).

The essay uses the Tiktaalik for a model for how paleontology should "work": initial finds suggest a evolutionary sequence for a given trait, comparison of fossil and extant organisms allow us to make predictions about what transitional forms might look like, mapping work reveals unexplored rocks of the right age and depositional environments, hours of painstaking fieldwork are eventually rewarded with revealing fossils, the new discoveries generally raise more questions than they answer bringing us back to step one.

Of course, most major discoveries probably follow a more serpentine route than this express-tram to knowledge, but Shubin captures the major ideas in language easily appreciated by a reader with a limited science background. One bit of serendipity does come in the form of a forgotten map Shubin discovered in an old textbook (I knew I was saving mine for a reason). He even manages to bring the whole thing back to Mayr-cum-Darwin-cum-Lyell-cum-Hutton:

To get a glimpse of the water-to-land transition, we need to see the creatures that lived on Earth at that time, then we need to look at our world today. When we do this, we see something sublime: The ancient world was transformed by ordinary mechanisms of evolution, with genes and biological processes that are still at work, both around us and inside our bodies.

Shubin also touches on a number of other important points: the artificial nature of taxonomic groups (what exactly is a tetrapod now?), the importance of exaptation in the origin of major evolutionary changes (pre-existing limbs in aquatic creatures that later allowed them to take up terrestriality), the integration of new information from other fields into our understanding of evolution (DNA, developmental biology), and the non-directionality nature of evolutionary history (the "tree of life" is more of a bush). Here's Shubin's own words on that last point:

Only now, 370 million years later, do we see that one of those fish sat at the base of a huge branch of the tree of life—a branch that includes everything from salamanders to humans. It would have taken an uncanny sixth sense for us to have predicted this outcome when our time machine deposited us in the middle of the Devonian.

…

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.

Well put, too bad this graphic, from the multilingual Tiktaalik site hosted at the University of Chicago, is slightly misleading:

This figure and the Shubin picture above copyright University of Chicago, used without permission.

While it may be a simple function of single-point perspective, the image suggests Tiktaalik falling neatly (save for a border-breaking transgressive tail) along an ever-tapering path drawing fish inexorably up the chain of being toward tetrapods. Any guesses as to which species is to be found at the implied apex projecting some distance out of the Paleozoic?

Intelligently-designed graphics aside, the website has a lot of interesting information and is good way to learn Inuktitut/ᐃᓄᒃᑎᑑᖓᓪᓗᓂᓗ.

Unlike Tiktaalik, this ungainly post has been unravelling toward an ultimate telos,

Postscript: Here is a link to a perishable link to the Ted Daeschler/Colbert Report spot that Chelsea mentions in the comments below (thanks to Palaeoblog).  And here is a more metered response to the Shubin essay.  There's an old adage about politics and sausage making, does it hold for sonnets too? 

The amphibian Xipe Totec

Spring, as the frenzily copulating Swainson'ses across the street will tell you, is a time for reproduction, rebirth and regeneration. But Nature, scrupulous accountant that he-she is, demands competition, carnage and sacrifice in return for all that blooming Qi. As Darwin put it in The Origin:

We behold the face of nature bright with gladness, we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings are destroyed by birds and beasts of prey; we do not always bear in mind, that though food may be now superabundant, it is not so at all seasons of each recurring year.

And while, as Darwin notes, we may personally do our best to ignore the harsh realities of the season, our religious traditions do their darnedest to remind us. Some one billion or so practicing Catholics are fasting today, Good Friday, ostensibly to mark the date a dude was "nailed to a tree for saying how great it would be to be nice to people for a change" (in the words of Douglas Adams). Jews will be celebrating their own spring holiday, Passover, this weekend, remembering a spate of plagues, the decimation of a reproductive cohort, and a hasty flight into a forbidding desert.

The Mesoamericans had their own grisly spring rites, centered around this guy:

Xipe Totec, "Our Lord the Flayed One"…Sort of an Aztec cross between Demeter and Leatherface.

Which brings me to this article appearing in this week's issue of Nature, documenting an odd behavior observed in one species of a curious group of legless amphibian known as caecilians (you're breaking my heart). It seems that the devoted mommies offer up their own skin (amounting to up to 1/7th of their own body weight!) as a meal for their recently hatched young:

 

While this kind of parental investment is rather common in the animal kingdom (think milk and placentas), this is a rather dramatic example of motherly love to say the least. Interestingly, in other species of caecilian that give live birth, the young feed on the lining of their mother's oviduct during gestation, which the authors of the current study propose as a possible precursor behavior to the skin-snacking (I misread the abstract, the authors in fact suggest the reverse). As mentioned in this news article on the study it is fairly common for other amphibians to feed on their old skin after shedding.

Happy spring and don't forget to give mom a call this weekend!

Postscript:

Head on over to Rigor Vitae and Afarensis for much more. Carel's post is accompanied, as per usual, by some awesome art (this time a Scaphiopus couchii doing his/her best Gene Kelly impression).