#preadaptation

A new feathered dinosaur suggests that most dinosaurs had feathers Evolutionary biologist Jerry Coyne comments on a recent paper:   Godefroit, P., et al. [25 July] 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. 2014.  Science 345:451-455.

What better evidence that birds arose from dinosaurian reptiles than the discovery of a fossil with both scales and feathers? Further, the fossil comes from the right time period: after reptiles had already evolved but before we see modern flying birds with fully-developed feathers.

Of course, we already knew that birds are the only living descendants of dinosaurs—some biologists classify them as dinosaurs—but as we go earlier and earlier back into the evolution of dinos, we’re beginning to find that many, perhaps most, had feather-like structures. That is what we call a “preadaptation”—a feature that could be co-opted later for a different useful function: in the case of birds, gliding and then flight.

(“Preadaptations,” of course, didn't evolve because they’d be useful in the future, for natural selection doesn't anticipate future needs; it produces features that enhance reproduction in the here and now. But those features can be hijacked for other things later, like penguins’ vestigial wings that became modified for swimming.)

The earliest feathers, as we’ll see on the specimen I’ll show shortly, are small, filamentous structures that occur along with scales. They were of no possible use for flying or gliding, but they wouldn't evolve unless they enhanced the animal’s reproduction (or its proxy, survival). What were they for? The authors of the paper we’re discussing today suggest this (my emphasis):

"Here we report a new ornithischian dinosaur, Kulindadromeus zabaikalicus, with diverse epidermal appendages, including grouped filaments that we interpret as avianlike feathers. This suggests that all Dinosauria could have had feathers and that feathers arose for purposes of insulation and signaling and were only later co-opted for flight."