Love and Flying Dinosaurs

In Solnhofen, Germany, there is a stone quarry that has supplied limestone for centuries. This stone had many uses: for example, Romans had paved roads and constructed buildings with it. In the 1700s, a new market for limestone emerged when lithography – an image-making technique -became popular. Limestone used in making lithographs had to be free of blemishes. Otherwise, the resulting images were imperfect. Solnhofen's limestone was now inspected for cosmetic blemishes.

As the limestone was examined closely, many types of fossils were found in them. A stone with fossils was useless for lithography but useful for scientific collections. Most of these fossils were well-known, but in 1861, the fossilized skeleton of an unknown creature was found. It had feathers and wings for flight! This was the first evidence of a flying dinosaur. But the Archaeopteryx - as it was named - also had some characteristics of reptiles including a long bony tail.

This discovery strongly hinted that birds had evolved from dinosaurs. But what was the path followed during this evolution? The link between the older, larger dinosaurs and the Archaeopteryx was unclear.

Then, in 1962, the scientist John Ostrom found another important fossil in the American West. Three and a half feet tall, it was like other dinosaurs with one exception: one claw in its foot was clearly designed to cut and slash. So this beast was a swift killer, not a lumbering gentle giant. Ostrom named it Deinonychus (terrible claw.) Studying its anatomy further – including its long tail and sharp teeth – Ostrom found similarities to ground birds such as emus and cassowaries. This class of dinosaurs was named theropods.

Ostrom then went on to study Archaeopteryx fossils and made a startling discovery. He found many similarities between Deinonychus and Archaeopteryx. For example, the wrists of both had bones useful for up and down movements of wings. He argued that the carnivorous Deinonychus was a predecessor of the flying Archaeopteryx.

(Incidentally, before making Jurassic Park, Michael Crichton spoke with Ostrom. The movie featured a predatory dinosaur modelled after Deinonychus, but since it is a difficult name, they decided to call it Velociraptor.)

Many scientists today think that birds descended from theropods such as Deinonychus by way of the Archeopteryx. But mysteries remain. How did feathers come about? How did they become flight feathers? How did wings evolve?

The role of feathers is pivotal. A bird's flight feathers are incredibly sophisticated – much more so than airplane wings which exploit the same physical principles. To withstand the force of oncoming air, flight feathers are asymmetrical with a thin and stiff leading edge. The network created by the threadlike barbs in the feather makes it strong yet light.

There are several theories about how feathers came about. They may have evolved from scales of reptiles such as crocodiles. Another theory hints at love: feathers evolved to be seen. A recently unearthed dinosaur called the Anchiornis had way too many colourful feathers for practical purposes such as running and chasing, so it is conjectured they were for amorous purposes. Those feathers helped it find a mate, like many birds today that seasonally change to breeding plumage.

Another key question dinosaur to bird evolution: was it bottom-up or top-down? Some scientists argue that birds evolved from feathered dinosaurs that flapped their feathered arms as they ran, evolving into flight. Others think that feathered dinosaurs leaped from treetops and glided, evolving into flying creatures using their feathers.

It seems that every time we learn something new about this topic, new questions are also raised. And so we find that nature does not easily give up her secrets.

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