The Four-Winged Dinosaur: DVD Review

This is a 2008 Nova (PBS) program on a dinosaur (Microraptor) that is still the subject of breaking news, so in some ways it is pretty dated. But it also gives a good view of how scientific controversies are resolved (or not) and some of the tools of paleontology.

Most people, thinking of dinosaurs, think big. Tyrannosaurus. Stegosaurus. Triceratops. Even the raptors of Jurassic Park were large, though not overwhelmingly so.

But how much of that is due to a combination of publicity (the biggest of anything is news) and preservation bias? How many of today’s birds ever fossilize?

Luckily there are formations in which fossils are preserved with extraordinary fidelity. One such formation, in China, has yielded numerous specimens which retain vestiges of fur or feathers, leading to the recognition that feathers were widespread on dinosaurs. Most of the feathers seem to have been more for warmth or display than for flying, as they lack the aerodynamic asymmetry seen in the flight feathers of today’s birds.

This is not the case for Microraptor, which had asymmetric flight feathers on all four limbs.

But how were those limbs used in flight? Could the animal actually have spread its rear limbs horizontally, as first suggested by Xu Xing when he initially described it?

The controversies explored in this DVD are twofold: how did Microraptor use its extraordinary feathered hind limbs, and are birds in fact dinosaurs?

Birds have all of the skeletal features used to state that a fossil is a dinosaur. Given the evidence of many other feathered dinosaurs from the same Chinese formation, I have problems seeing birds as anything other than flying dinosaurs. The origin of flight — from gliding out of trees or scrambling up from the ground — is a completely separate question, and should have been separated in this way by the scientists involved.

One argument repeatedly made by one of the scientists strikes me as as based on a rather poor assumption. This is that “dinosaurs didn’t climb trees, so flight could not have originated by dinosaurs gliding down from trees.” Who says dinosaurs couldn’t have climbed trees? Certainly the big ones couldn’t have, but there is increasing evidence that some dinosaurs were considerably smaller than a turkey, and turkeys (the original wild ones, not their domesticated descendants) certainly roost in trees. Lack of evidence the dinosaurs climbed trees is not the same as evidence that they did not climb trees.

Leaving that aside, the bulk of the DVD follows experimental work trying to reconstruct the 3-dimensional skeleton of Microraptor from the fossils (often flattened in the fossilization process) followed by wind tunnel work to asses the probable way in which it used its limbs to fly or glide.

The DVD is worth watching for this experimental work, though none of the work shown should be considered conclusive. It is worth pointing out the actual fossils are still giving up more information, the latest being evidence that this animal probably had iridescent blue-black feathers. Neither this DVD nor the microraptors shown in Prehistoric Park show this color.

Sky Monsters (DVD Review)

No, they weren’t dinosaurs. True, model sets of extinct animals often include saber-tooth cats, sail-backs (which were mammal-like reptiles and more closely related to us than to dinosaurs) and extinct marine reptiles as well as pterosaurs, but none of these are actually dinosaurs. Pterosaurs did, however, live alongside dinosaurs and are of great interest as the largest animals ever to fly on their own.

This DVD, another of the National Geographic series, looks at the mystery of pterosaur flight. As usual, the animation is not very exciting, but the scientific work and the attempt to build a mechanical pterosaur more than makes up for that.

The big questions are, how large did pterosaurs grow and how did they fly?

One of the threads of the program is the rather controversial discoveries of trackways and fossils suggesting even larger pterosaurs than Quetzalcoatlus, which itself had a wingspan of 10 meters (33 feet.) That’s three times larger than an albatross, the largest flying bird alive today. Forget the giants; how did even the ones we’re reasonably sure of fly?

The meat of the DVD, as far as I was concerned, was an attempt to build a robotic pterosaur, controlled like a model airplane. The result was not wholly successful, but a great deal was demonstrated about pterosaurs in the process.

First, pterosaur wings were a good deal more complicated than the sailcloth that was first tried. They had oriented stiffening fibers, muscles within the wing membrane, a good blood supply to the wings, a furry covering that (like the dimples on a golf ball) helped aerodynamically, and some kind of built-in sunscreen. (Bats are nocturnal in part because their wings would sunburn too badly in daylight.)

Control was incredibly sophisticated, certainly more so than could be mimicked by a model airplane controller. Much of the maneuvering of a real pterosaur was probably as automatic as keeping your balance is to you – possibly more so, if the speculation that baby pterosaurs were born knowing how to fly is correct. Changing the shape of the wings and the tilt of the head would have been automatic for a real pterosaur. Not so for the model, and it is hardly surprising that it was not fully successful, even aside from the problems of finding components and power sources of sufficiently light weight. Pterosaurs, like birds, had very light bone structures.

As entertainment this DVD falls short. But as documentation of a fascinating experiment, it is worth watching.