Shake your tail feathers

My wife and I reset some pavers in our front sidewalk a couple of days ago.  In our area, most of the stone used for paving and wall-building is native slate and limestone, which make up the majority of the bedrock in this part of upstate New York; and given slate's tendency to fracture naturally along parallel planes, it makes an obvious good choice for paving stones.

We used a pry-bar to pull up one big stone -- maybe a meter across and two meters long -- and a piece of it sheared off.  Unfortunate but unavoidable.  When I stopped and picked up the chunk, a flat, triangular piece a little larger than the palm of my hand, I noticed something interesting about it.  It had ripple marks, the clear signature of the muddy environment where it formed.

Seeing this sort of thing always makes me imagine what things were like back then.  The rocks in this area are Devonian in age, on the order of four hundred million years old, at which time this whole area was at the bottom of a shallow sea.  So those ripple marks in my sidewalk paving stone were created by water movements that occurred so long ago it's hard to imagine.  At that point, there was virtually no terrestrial life -- a few plants and insect species had colonized the land, but everything else was still aquatic.  The first dinosaurs were still a good 150 million years in the future.

It's kind of cool the way these sorts of moments thrill me from two different perspectives.  Being a biology teacher (retired now), I find it absolutely fascinating to ponder the grand panorama that is the history of life on Earth, and to consider evolution's role in creating what Darwin famously called "endless forms most beautiful and most wonderful."  As a novelist, it never fails to fire my imagination -- to picture what it would be like to stand there on the beach with the bare, treeless Devonian landscape stretching out behind me, looking out over oceans where swam trilobites and bizarre armored fish (ostracoderms) and ammonites, all of which went extinct long, long ago.

The reason this comes up -- besides finding signs of four-hundred-million-year-old ocean waves in my slate sidewalk paver -- is a link sent to me (once again) by the indefatigable Gil Miller, about a fossil discovery found in northeastern China recently.  It's the fantastically well-preserved remains of a little feathered dinosaur from 120 million years ago called Yuanchuavis kompsosoura, which was about the size of a blue jay -- but had a thirty-centimeter-long tail, which is longer than its entire body.

Yuanchuavis kompsosoura

Extravagant tails like this are an interesting case of an evolutionary trade-off.  Modern birds like peacocks have tails so long they're actually a hindrance to flying, but apparently the disadvantages of having such a clumsy appendage are outweighed by the advantage in terms of attractiveness to potential mates (sexual selection).  It's theorized that having elaborate plumage is a way of advertising your overall genetic health.  "Look at me," they say.  "I am so genetically superior I can throw away all sorts of energy and resources on something completely frivolous.  I am totally who you want to have sex with."

Kind of the bird version of driving a Jaguar.

That sort of teleological reasoning, however, is always thin ice when you're talking about evolutionary drivers.  None of that selection is being done because of any kind of conscious weighing of options.  But whatever its basis, we see similar kinds of wild tails in a great many bird species today -- swallowtailed kites, African widowbirds, paradise flycatchers, quetzals, drongos, and a lot of hummingbirds, as just a few examples.  The fact that so many relatively unrelated species have gone down the same path supports the conjecture that whatever is propelling this selection, it's pretty powerful.

Reading the article about this fascinating little dinosaur immediately switched on the other mode, which led me to imagining what it actually looked like when alive, and wondering about its behavior and environment.  Of course, even most well-preserved fossils give you only a hint about what the living creature looked like; all the spots and patterns and colors in movies like Jurassic Park are guesses, as are the behaviors (like the dinosaur with the toxic spit that killed Dennis Nedry).  But here, the preservation is on such a fine scale that the paleontologists do have an idea of what color it was -- traces of pigment-producing cells suggest that the fan part of its tail was gray, and the two long banner feathers in the middle were jet black.

Here, we actually can visualize what it looked like when he was shaking his tail feathers in the early Cretaceous forests.

So that's our imagined trip into deep time for today.  I know I've quoted it here before, but the lines from Tennyson's "In Memoriam" are so poignant and so apposite that I will end with them anyhow:

There rolls the deep where grew the tree.
O Earth, what changes hast thou seen?
There where the long road roars hath been
The stillness of the central sea.

The hills are shadows, and they flow
From form to form, and nothing stands;
They melt like mist, the solid lands,
Like clouds, they shape themselves and go.

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