Microraptor: Beast of the Week

This week we shall check out a tiny dinosaur that has taught us more than we ever could imagine we'd learn about any fossil animal.  Enter Microraptor gui!

Microraptor was a small, feathered, meat-eating dinosaur that lived in what is now China, during the early Cretaceous, 120 million years ago.  Adults ranged in size between 2.5 and 3 feet long from snout to tail.  The genus name, Microraptor, translates to "Small Hunter/Thief".

Microraptor was a tiny member of the dromaeosaurid family of dinosaurs, and therefore was related to creatures like Deinonychus and Velociraptor.  Like it's larger cousins, Microraptor had and long thin tail for balance, three long claws on each hand and of course, the signature retractable "killer claw" on the second toe of each foot.  Microraptor had large eye sockets, indicating it had good vision, and a mouth armed with pointed teeth, some of which were serrated.

Watercolor life reconstruction of Microraptor gui  hunting a scorpionfly by Christopher DiPiazza.

Microraptor's real claim to fame is the fact that its feathers were preserved during the fossilization process, giving us a much clearer vision of what it looked like when alive.  Microraptor would have been as covered in feathers as most modern birds, and even had proportionally very long primary feathers growing out of its arms and hands, forming wings.  More amazing, Microraptor also had long wing feathers on its legs and feet!  There were actually other kinds of dinosaurs that evolved to have primary feathers on their lower limbs we now know of, like Anchiornis or Changyuraptor, but Microraptor was the first of these to be discovered and described back in 2003.

So why the extra set of wings?  At first it was proposed that Microraptor would have lived in trees and glided from branch to branch with its legs outstretched behind it, like a modern flying squirrel, using the leg wings to form a kite-like shape as it did so.  It was later determined that despite the fact that the fossilized skeleton had the legs in this position, that it was crushed flat in a position not true life during the decomposition and fossilization process.  Other known dromaeosaurs and living birds can't position their legs that way without breaking them, and Microraptor likely was the same.  Instead, it is possible Microraptor's leg feathers could have provided extra lift when jumping or taking off.  Many paleontologists now think that Microraptor may have been capable of actual powered flight, and not just gliding.  It had a fused sternum, like most modern flying birds have, and its wing feathers were extremely long to the point where they, combined with its leg wings, almost certainly could have provided Microraptor the ability to get and stay off the ground if it needed to.  It's arm sockets, however, prevented Microraptor from lifting its arms above its shoulders, unlike modern flying birds can to perform a strong upstroke when flapping.  This doesn't mean that Microraptor still couldn't fly, it just means it wasn't as adept a flier as a lot of modern flying birds.  It would have been common to see Microraptor flying short distances, possibly from tree to tree, or from the ground to a tree to roost, but probably not soaring up in the sky like an eagle.

There are many specimens of Microraptor on the fossil record and several of them actually preserved food that had been ingested shortly before the Microraptor died.  Because of this wealth of fossil information, we know that Microraptor was a meat-eater, but wasn't picky or specialized in going after one kind of prey.  Among the known last meals include lizards, mammals, birds (yes, there were true modern-style birds back then) and even fish.

Cast of the skeleton and feathers of Microraptor gui on display at the American Museum of Natural History for their Dinosaurs Among Us seasonal exhibit.

For a long time, we always assumed that no matter how many fossils we found, we'd never know what colors prehistoric animals were.  Not the case with Microraptor!  Microraptor's feathers preserved so well, that when viewed under a microscope, organelles called melanosomes were found to still be present.  Melanosomes are responsible for determining what color waves reflect back when light hits the feather.  Whichever waves are reflected is the color we see.  Even though the color, itself, was not visible anymore, by comparing the shape of the fossilized Microraptor melanosomes to melanosomes of modern bird feathers, paleontologists were able to deduct what colors Microraptor would have had when it was alive.  As it turns out, Microraptor feathers were iridescent blackish bluish, like those of modern crows, grackles, and starlings!  Since the iridescence of feathers like these can only be noticed in the sunlight, this also supports the idea that Microraptor would have been active during the day and not at night, otherwise there wouldn't have been a reason for it to have evolved such reflective colors.  This being said, keep in mind these melanosomes were only observed in one specimen of Microraptor.  This doesn't mean that all Microraptors were this color throughout their whole lives.  It is entirely possible that only adults, or one sex was this color.  Or maybe Microraptor molted feathers, becoming a different colors depending on the season.  There is still room for imagination!

Modern Boat-Tailed Grackles have feathers that may have been similar to those of Microraptor.  Notice the shiny blue-black coloration.

That is all for this week!  As always feel free to comment below!

References

Chatterjee, S.; Templin, R.J. (2007). "Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui"(PDF). Proceedings of the National Academy of Sciences. 104 (5): 1576–1580.

Jingmai O'Connor; Zhonghe Zhou & Xing Xu (2011). "Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds". Proceedings of the National Academy of Sciences of the United States of America. 108 (49): 19662–19665. 

Li, Q.; Gao, K.-Q.; Meng, Q.; Clarke, J.A.; Shawkey, M.D.; D'Alba, L.; Pei, R.; Ellision, M.; Norell, M.A.; Vinther, J. (2012). "Reconstruction of Microraptor and the Evolution of Iridescent Plumage". Science. 335 (6073): 
1215–1219. 

 Lida Xing; et al. (2013). "Piscivory in the feathered dinosaur Microraptor". Evolution. 67: 2441–2445.

Senter, P (2006). "Scapular orientation in theropods and basal birds, and the origin of flapping flight". Acta Palaeontol. Pol. 51: 305–313.

Xu, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F. and Du, X. (2003). "Four-winged dinosaurs from China." Nature, 421(6921): 335-340, 23 Jan 2003.