We now know that birds evolved from small, feathered dinosaurs. It’s easy to think that since birds are still around today, they must have come after their dinosaur* cousins, but that’s not true. In the Cretaceous period, dinosaurs were still around while their descendants flitted through the skies. And some dinosaurs made meals of their flighty relatives. Jingmai O’Connor from the Chinese Academy of Sciences has uncovered the remains of a small dinosaur called Microraptor that has the bones of small bird in its gut.
O’Connor analysed the fossil with Xing Xu, a Chinese scientist who has made a career from discovering beautiful feathered dinosaurs. Microraptor is one of his most important finds. This tiny animal, about the size of a pigeon, had four wings, with long feathers on both of its legs as well as its arms. It was, at the very least, a very competent glider, if not a true flier.
The specimen that O’Connor and Xu have studied isn’t the best preserved Microraptor around. However, it does clearly have the remains of a small bird in its gut, including the left wing and both feet. There aren’t enough bones to tell which species it was, but the distinctive shape of its leg bone singles it out as one of the enantiornithines, an extinct group of early birds. They were, after all, one of the most common groups of birds in the forests of China, where Microraptor hunted.
The bird wasn’t just buried alongside Microraptor, for its bones are enclosed by the larger animal’s ribs. It must have been eaten, and O’Connor thinks that Microraptor probably killed the bird, rather than scavenging one that was already dead. Many of its bones are still found in the right orientation, and the animal facing down towards Microraptor’s hips. The dinosaur probably caught it and swallowed it head-first, just like many modern birds of prey do.
If O’Connor is right, then this unique bird-within-a-dinosaur fossil has implications for the origin of flight. Some argue that the powerful flapping stroke of modern birds evolved in ground-living dinosaurs, to help them flap over obstacles. Others suggest that the stroke originated in trees, to help dinosaurs to glide between branches and control their descent. The four-winged Microraptor has always been acted as a star witness in this debate, and O’Connor’s specimen confirms that it was indeed at home in the trees.
All of the Jehol enanthiomithines lived in trees. Their legs and feet were clearly adapted for perching rather than running or swimming. If its prey lived among the branches, then that’s where Microraptor must have hunted. And since its prey was an adult, rather than a chick, it must also have been a fairly agile predator. “[The fossil] lends further support to interpretations that Microraptor gui was spending a substantial amount of time in the trees,” says O’Connor.
This new Microraptor joins a brief but distinguished line of fossils-within-fossils, that provide conclusive evidence about who ate whom in our prehistoric planet. Based on similar gut fossils, we know that the first feathered dinosaur Sinosauropteryx often ate small mammals and lizards. Turning the tables, the early mammal Repenomamus sometimes made meals of dinosaurs, like a baby parrot-beaked Psittacosaurus. And predators themselves would often become prey – the abdomen of Sinocalliopteryx included the leg of a meat-eating dromaeosaur (the group that includes Microraptor and Velociraptor).
Reference: O’Connor, Zhou & Xu. 2011. Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds. PNAS http://dx.doi.org/10.1073/pnas.1117727108
*Throughout this piece (and indeed, in the title of the new paper), “dinosaur” refers to the “non-avian” kind.
Reconstruction by Brian Choo; fossils photographed by Li Yutong and Gao Wei
November 21st, 2011 at 4:32 pm
Happy to see this in published form (please be open access–DAMMIT)! I saw the abstract in the SVP abstract book and was intrigued. It’s rather irritating that this is only the third specimen of Microraptor to be published–I’ve read elsewhere that there’s a wealth of fossils for this taxon. As one of the more important dinobirds discovered in the last decade, you’d think more of the material would be published!
Excellent article as usual, Ed. Thanks for the writeup!
November 21st, 2011 at 4:59 pm
Very cool. I do take issue with author’s idea that because Microraptor caught a perching bird it must have been partly arboreal. Maybe, but I have seen a red fox with a perching bird and they don’t seem to climb so well (or often). Cats are another good example. They can climb, but not well (compared to a squirrel or martin) and I think that most of the perching birds they catch a caught from the ground.
November 21st, 2011 at 5:16 pm
It is not exactly rocket science to guess that “the Jehol enanthiomithines” refers to the Chinese forests, or to google and find out that it is more specifically a specific biota of a time and place.
But FWIW it would have saved some perusing to make it “the Jehol forests of China”.
Interesting article for an interested layman! Some of the claims seems overconfident (say, “must have hunted” instead of “likely have hunted” seeing that some perching birds may visit forest floors ADDED IN POSTING: What MattK said), but YMMV.
November 21st, 2011 at 5:51 pm
In addition to MattK. About some more than a year ago I’ve seen a jackdaw murdering and eating a sparrow on the street, just by jumping [from some nearby small bushes] in the middle of a group of about 5 of them sitting there for their own lunch. So, even a modern predatorbird doesn’t always use flight.
November 21st, 2011 at 11:46 pm
Others have already mentioned this and I’ll add my two cents. It is a bit of a leap to assume that the Microraptor must have hunted in the branches because it had a small bird in its stomach. Many small passerines that live in trees can be found feeding on the ground, and at times in large numbers. E.g. White-throated and White-crowned Sparrows, Dark-eyed Juncos, Fox Sparrows, Veerys, Hermit and Wood Thrushes, American Robins, and even Northern Flickers (‘woodpeckers’). Some of these are in the open, many are on the ground in the underbrush kicking up leaves. M. gui may indeed have spent a substantial amount of time in trees, but I would argue that the fossil does not lend further (or any) support to that interpretation.
On another note did the authors mention if M. gui possessed a gizzard? The eaten fossil seems a bit far back for a gizzard placement although it could have been passed from the gizzard to the stomach at that point–although I would have thought the gizzard would have broken the bones up more (maybe that is why there are only a few bones left).
November 22nd, 2011 at 12:16 am
Mr. Yong does not seem to have been internalized the cladist mindset yet; he quaintly refers to birds as if they were somehow not dinosaurs…
November 22nd, 2011 at 7:32 am
Of course, I actually address that in a footnote, but please don’t let what I write get in the way of your snark.
November 22nd, 2011 at 7:41 pm
My apologies, I meant no offense; snarkily is just how I write!
Yes, you made the distinction between avian and non-avian dinosaurs clear; but the piece does read as if Birds are a different ‘thing’ from dinosaurs; as opposed to merely a subset of dinosaurs. I was making more a commentary on how strict cladistics leads one to read even the title of the piece ‘Microraptor ate Birds’ as anachronistic… the line between Avialae and Aves remains blurry. If I saw a M. gui gliding overhead, my first thought would be ‘huh, weird bird’. But I’m well aware you know what’s up.
It’s affected me quite deeply, I know can’t even eat chicken without saying out loud “mmm, dinosaur!”
November 22nd, 2011 at 7:50 pm
It’s like saying “Lions – the four legged mammal that ate Zebras”
November 23rd, 2011 at 4:24 am
Reminds me of another fossil, from 2001, that also involved birds being eaten by something that may well have been a dinosaur (but in that case we don’t know if it actually was). This is memorable to me because I used it in the scientific trivia quiz I compiled a couple of years ago.
http://www.abc.net.au/science/articles/2001/03/05/253801.htm
I’m wondering how the ages of these fossils compare, and who currently holds the record for oldest known fossil of an avian lunch.
November 24th, 2011 at 4:32 am
Actually, the whole feathered dinosaurs thing is a controversy over a human-developed taxonomy, and has nothing to do with whether one evolved from the other.
January 9th, 2012 at 4:03 pm
There is one other possibility re the finding of the bird bones within the ribcage- you have, no doubt, seen the movie ‘Alien’….