November 28, 2012
How did feathered dinosaurs take to the air? Paleontologists have been investigating and debating this essential aspect of avian evolution for over a century. Indeed, there have been almost as many ideas as they have been experts, envisioning scenarios of dinosaurs gliding through trees, theropods trapping insects with their feathery wings and even aquatic Iguanodon flapping primitive flippers as flight precursors (I didn’t say that all the ideas were good ones). The biomechanical abilities of bird ancestors and their natural history has always been at the center of the debate, and a new Current Biology paper adds more fuel to the long-running discussion.
At present, hypotheses for the origin of avian flight typically fall into one of two categories. Either bird ancestors accrued the adaptations necessary for flight on the ground and, through evolutionary happenstance, were eventually able to take off, or small tree-dwelling dinosaurs used their feathery coats to glide between trees and, eventually, flapped their way into a flying lifestyle. There are variations on both themes, but feathers and the characteristic avian flight stroke are at the core of any such scenario. In the case of the new paper, Yale University paleontologist Nicholas Longrich and colleagues draw from the plumage of early bird Archaeopteryx and the troodontid Anchiornis to examine how feathers changed as dinosaurs started to fly.
In modern flying birds, Longrich and coauthors point out, the wing arrangement typically consists of “long, asymmetrical flight feathers overlain by short covert feathers.” This pattern creates a stable airfoil but also lets the flight feathers separate a little during the upstroke of a wing beat, therefore reducing drag. When the paleontologists examined the fossilized wings of Archaeopteryx and Anchiornis, they found different feather arrangements that would have constrained the flight abilities of the Jurassic dinosaurs.
Both prehistoric creatures had long covert feathers layered on top of the flight feathers. Anchiornis, in particular, appeared to have an archaic wing form characterized by layers of short, symmetrical flight feathers and similarly shaped coverts. Archaeopteryx showed more specialization between the flight feathers and the coverts but still did not have a wing just like that of a modern bird. As a result, Longrich and collaborators hypothesize, both arrangements would have stabilized the wing at the cost of increased drag at low speeds, making it especially difficult for Anchiornis and Archaeopteryx to take off. As an alternative, the researchers suggest that these dinosaurs might have been parachuters who jumped into the air from trees, which might hint that “powered flight was preceded by arboreal parachuting and gliding.”
The trick is determining whether Anchiornis and Archaeopteryx actually represent the form of bird ancestors, or whether the dinosaurs, like Microraptor, were independent experiments in flight evolution. At the Society of Vertebrate Paleontology conference in Raleigh, North Carolina last month, flight expert Michael Habib quipped that all that was needed to make dromaeosaurs aerially competent was the addition of feathers. If Habib is right, and I think he is, then there could have been multiple evolutionary experiments in flying, gliding, wing-assisted-incline-running and other such activities. There’s no reason to think that flight evolved only once in a neat, clean march of ever-increasing aerodynamic perfection. Evolution is messy, and who knows how many ultimately failed variations there were among flight-capable dinosaurs?
The three-step Anchiornis-Archaeopteryx-modern bird scenario of wing evolution fits our expectations of what a stepwise evolutionary pattern would look like, but, as the authors of the new paper point out, shifting evolutionary trees currently confound our ability to know what represents the ancestral bird condition and what characterized a more distant branch of the feathered dinosaur family tree. We need more feathery fossils to further investigate and test this hypothesis, as well as additional biomechanical and paleoecological information to determine whether such dinosaurs really took off from trees. We must take great care in distinguishing between what an organism could do and what it actually did, and with so much up in the air, the debate on the origin of flight will undoubtedly continue for decades to come.
Longrich, N., Vinther, J., Meng, Q., Li, Q., Russell, A. 2012. Primitive wing feather arrangement in Archaeopteryx lithographica and Anchiornis huxleyi. Current Biology DOI: 10.1016/j.cub.2012.09.052
December 23, 2011
When it came time for my wife and me to pick this year’s Christmas ornament, there was no question what it had to be: We needed a dinosaur. After all, this year we left New Jersey to settle in the fossil-rich state of Utah, and so it was only appropriate to celebrate our successful move with a dinosaurian decoration. We settled on an Allosaurus pendant from Dinosaur National Monument. This Late Jurassic theropod—one of my favorite dinosaurs—is the official state fossil of my new home, and my first visit to the geologically wonderful national park two years ago was what inspired me to head west. Perfect.
But my wife and I aren’t the only ones to adorn our tree with dinosaurs. Friends have been sending me snapshots of their own tannenbaum dinosaurs over the past few weeks, and yesterday I put out a call for more merry Mesozoic ornaments. I was not disappointed.
Long-time reader Michael Barton tweeted this Cretaceous scene wherein a Triceratops faces off against a Tyrannosaurus. C’mon, guys—don’t you know that this is the time of year for peace on earth and goodwill towards dinosaurs?
Among other dinosaurs, John Pomeranz nestled this particularly colorful Triceratops among the branches of his Christmas tree. With no predators around, this dinosaur clearly doesn’t need camouflage.
Even though pterosaurs aren’t dinosaurs, I couldn’t say no to this photo of one of the flying archosaurs decked out in a Santa hat, sent by Aline McKenzie.
What’s flashier than a Stegosaurus? A sequin-covered Stegosaurus ornament, of course. Thanks to freelancer Helen Fields—who has written about dinosaurs for Smithsonian herself—for this one.
Those sparkly stegosaurs sure do get around. This one, tweeted by Matthew Cobb, had been shuffling around the Christmas tree since 1986.
A vintage theropod reaches out from @scurvygirl’s Christmas tree.
Given their probable diet of conifers, I’m surprised there aren’t more holiday sauropods in the mix. Fortunately for us, though, @ArtfulMagpie has shared this lovely pink sauropod from her Christmas tree. She says “He was a brontosaurus when I got him as a child. I suppose he’s an apatosaurus now!”
A cute little Triceratops lives in Alexandra Witze’s Christmas tree, but where there’s Triceratops…
…Tyrannosaurus is not far behind. Though, based upon the lipstick, I’d say this one is ready to make love, not war.
Of course, the fellows at Love in the Time of Chasmosaurs have unique dinosaur decorations, too. These two dinosaurs, sent by Marc Vincent, are out for a nice winter sleigh ride…
… and LITC founder David Orr has this fuzzy Spinosaurus, crafted by his wife.
Even museums have jumped in. This tree—inhabited by many origami dinosaurs—is on display at the American Museum of Natural History in New York. I think this tree wins the category of “most dinosaurs per square inch.” Thanks to fellow science writer Alexandra Witze for the tip about this one.
Do you have holiday dinosaurs in your home? Don’t hesitate to send them to us at firstname.lastname@example.org. We will create an end-of-the-year roundup for whatever other dinosaurs might appear. Until then, all of us here at Dinosaur Tracking want you to wish you warm and happy holidays, wherever you are.