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Tuesday, June 18, 2013
Meet the Original Birds in a Field Guide to Winged Dinosaurs
Has any paleontological discovery of the 21st century been so transformative as the fact that dinosaurs were feathered? Sure, biologists still have academically foundational arguments over the proper positions of various protoplasmic goos at the tree of life's trunk, but what shakes the trunk doesn't always sway the branches. Not like dinosaurs — the charismatic megafauna of our collective childhood imaginations, now with feathers.
The dinosaur history books have literally been redrawn, and among the artists is Matthew Martyniuk. Inside, using the field guide format that's introduced so many people to nature, he introduces readers to dozens of dinosaurs that lived in the strange evolutionary junction between dino and bird.
"I've always been interested in bird evolution. It seemed there were so many books illustrating prehistoric animals, but none focusing on bird origins," said Martyniuk. "A lot of their characteristics go pretty deep into what were traditionally considered dinosaurs, and are really making us rethink how they would have looked in real life."
After its discovery in 2005, Jinfengopteryx was thought by some paleontologists to be the oldest bird of all, a forerunner of Archaeopteryx, the original first-bird title-holder. New studies suggest that's not the case, but it's still a fantastic creature.
The name translates to "elegant golden phoenix feather," and rightly so: Jinfengopteryx is among the most beautiful fossils in existence, and so well-preserved that the remains of its last meal can be seen in its stomach.
Coloration is a matter of some conjecture, but patterns in the fossil impressions do suggest an alternation between light and dark hues, Martyniuk said.
Boluochi Gracing the cover of Mesozoic Birds are a pair of squabbling Boluochia, which lived 120 million years ago in what is now northeastern China. The region is home to fantastically preserved fossil deposits that have yielded most of the feathered specimens to date. Boluochia was among the first of these.
Aurornis As with many early bird fossils, scientists know that Aurornis -- which was announced late in May, and may be the earliest known bird -- had feathers, but their exact shape and distribution is a matter of inference.
Though dinosaur species are often known from a bone or two, Hongshanornis remains are complete enough to know that it had a crest on its head and long, spindly legs perhaps suited to wading. "It seems to be analogous to a sandpiper," said Martyniuk. "It shows that a lot of these birds we have around today had some kind of parallel in the Mesozoic. It's not just pterodactyls flying around."
Living 70 million years ago in what is now Romania, Balaur was originally thought to be a close relative of velociraptors, but is now considered to be an early flightless bird. Martyniuk is fascinated with its double-sickle-clawed feet, which seem to have been one of the original bird traits, he said.
Also visible on Balaur are what appear to be claws protruding from its wings. Called spurs, they're thought to be leftovers of the reptile hands from which bird wings evolved, and can still be found in some birds today.
Vestigial as they might have been, the spurs were likely quite useful for preening and prey capture. Martyniuk's own hypothesis is that the spurs helped proto-birds land. "Species with non-aerodynamic tail fans couldn't slow down and basically smacked into tree trunks or brush, simultaneously grabbing on with the wing claws, and so would have landed quadrupedally, sort of like flying squirrels or gliding lizards," he said.
Pigments decay over time — but if a fossil preserves the microscopic physical structures that generate iridescent color, its hues can be inferred after millions of years. Such was the case with Microraptor, which appears to have possessed dark, iridescent plumage. "I went with dark blue, like a grackle," said Martyniuk. Microraptor's feathers also appear to have been adapted to flight, though its skeleton was not. "Feathers seem to be more malleable in terms of evolutionary selection," he said. "It's a creature that was just starting to adapt to living in trees or flying. The skeleton has yet to catch up with the feathers."
"There's a conception that different birds emerged from different dinosaurs, that there are, say, ostrich dinosaurs, and that's where ostriches evolved from," Martyniuk said. "But when you get down into the nitty-gritty anatomy, all modern birds probably evolved from something like Ichthyornis, a generalist seabird that managed to make it through the big extinction at the end of the Cretaceous."
Wulatelong, depicted here with lizard prey, was described for the first time in May in the little-known journal Vertebrata PalAsiatica.
Many new dinosaur species, especially those from China, are reported in this fashion, with no fanfare and little public attention. Martyniuk and other enthusiasts scan the journals, sifting for discoveries like paleontologists hunt for bones.
"That's one of my favorites," said Martyniuk. "I didn't know much about this bird before I did the research for my book. It almost got cut from the book because the paper describing it is so hard to get. It's only published in Chinese so far. I'm surprised that I haven't seen more depictions, because it had these long tail feathers."
Many dinosaur bird species had long tail feathers, Martyniuk said, but they're only found in about half the fossils. That ratio suggests they were a sex-linked trait, perhaps found only among males, like the fantastic tails of modern birds of paradise.
Scheduled to be published in the upcoming second edition of Mesozoic Birds, Ningyuansaurus was an early oviraptor, or egg-stealing dinosaur. One lineage of its own descendants would eventually become birds.
Some Anchiornis fossils are so exquisitely preserved that the coloration patterns of its entire body can be discerned with the naked eye.
"There's a little controversy brewing over whether these were the natural colors, but it's cool that we can at least get an idea of it," said Martyniuk. "And it's cool that it contradicts what we learned as kids: that we'd never have an idea what the colors of dinosaurs were."