Non-Avian Dinosaur Eats Avian Dinosaur

In life, Microraptor gui must have been an elegant dinosaur. This small, sickle-clawed dromaeosaurid was covered in plumage, including long feathers along its arms and legs. We know this thanks to the exquisite preservation of multiple Microraptor specimens found in the roughly 120-million-year-old strata of northeastern China. But feathers aren’t the only delicate dinosaur features that remained intact during the process of death, burial and fossilization. In at least one Microraptor specimen, paleontologists have found scraps of the dinosaur’s last meal.

Attendees to the 71st annual Society of Vertebrate Paleontology meeting in Las Vegas, Nevada earlier this month got a preview of the specimen during one of the conference’s poster sessions. Now the full paper describing the fossil, written by Jingmai O’Connor, Zhonghe Zhou and Xing Xu of Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology, has been published in PNAS. There are a few notable details of the feathery dinosaur.

The skeleton of this Microraptor, like others, is arched into the classic dinosaur death pose with the head arched back and the tail angled upwards. Whether the trigger for this posture turns out to be death throes, a result of immersion, or something else, the posture may be a clue to how the dinosaurs died or were rapidly buried. This Microraptor is also of interest because the dinosaur’s skull appears to be more complete and less crushed than some of the other specimens published so far, though the authors note that this specimen is relatively poorly preserved and therefore difficult to study. As for feathers, only a few tufts were preserved along the dinosaur’s head, neck and back. But the focus in the new paper isn’t on the dinosaur’s skeleton or outside appearance. The study is about what was inside the dinosaur’s body cavity when it died. There, hidden beneath the ribs, are parts of the wing and feet of a Cretaceous bird.

Exactly what genus of bird Microraptor consumed is impossible to say at the moment. Even so, anatomical characteristics of the bird feet allowed O’Connor and colleagues to classify the unfortunate avian as an enantiornithine, a form of archaic and now extinct bird. The position of this bird’s remains within the dinosaur is as good an indication as any that the feathered, non-avian dinosaur Microraptor at least sometimes consumed its distant avian cousins. But what happened just before the Microraptor swallowed the bird?

According to O’Connor and co-authors, the position of the bird bones within the Microraptor indicate predation rather than scavenging. The fact that the feet of the bird are closer to the front end of the dinosaur indicate that the prey was swallowed head first. The paleontologists cite this hypothesis as evidence that Microraptor was an arboreal dinosaur. Since the avian prey had anatomical specializations for life in the trees, and Microraptor supposedly caught the bird while the prey was still alive, then Microraptor must have been a skilled climber if not a regular tree-dweller.

Strangely, however, the paleontologists did not explore other scenarios for what might have happened in the moments before the Microraptor consumed the bird. Scavenging is briefly mentioned and dismissed as a possibility, but otherwise the idea that Microraptor scrambled up trees to catch birds is taken as the primary hypothesis. We know the facts—that a Microraptor swallowed a bird—but there is more than one pathway to that point.

Let’s assume that Microraptor truly did capture a live bird. But there is no indication whether the prey was caught on the ground or in the trees. In fact, as I sit here writing this, my cat Teddy is sitting in front of the window watching chickadees forage on the ground on my front lawn. Anatomically, the birds in my yard are specialized for life in the trees, but they do spend a considerable amount of time on the ground, and birds are often caught by cats and other terrestrial predators when the birds come down from their perches. Perhaps early birds also foraged on the ground, and when doing so they would have been vulnerable to attack by dinosaurs such as Microraptor.

Furthermore, there is nothing that tells us whether the bird was alive or dead when the dinosaur consumed it. Perhaps the bird died, fell to the ground, and the Microraptor was the recipient of a relatively fresh, free meal. All we know is that the bird was probably intact when the dinosaur ate it, but we can’t tell whether the bird was alive or recently deceased at the time.

We don’t know exactly what happened to the little bird, and therefore the association between the dinosaur and its prey can’t be cited as supporting either a ground- or tree-dwelling lifestyle for Microraptor. Nevertheless, the discovery that Microraptor ate birds adds one more piece to our understanding of this peculiar dinosaur, and I, for one, am a little tickled by the description of an avian dinosaur within a feathered non-avian dinosaur just prior to Thanksgiving. Turducken, anyone?

References:

O’Connor, J., Zhou, Z., & Xu, X. (2011). Additional specimen of Microraptor provides unique evidence of dinosaurs preying on birds Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1117727108

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.