Saturday, December 26, 2009

Wings on its Fingers

It is of course an easy matter to get excited about the latest fossil find. A new species that supplies a previously-missing piece to the puzzle of where to fit what into the scheme of things deserves the attention that it receives in scientific circles and beyond. By way of contrast, other fossil specimens which might have been discovered decades ago, and which represent now-familiar fossil animals, perhaps run the risk of losing their edge through simple familiarity.

Recently I obtained (via the Internet, naturally!) a museum-quality cast of one of the best-known of all fossil pterosaur specimens (the original fossil, above). This is the species Pterodactylus kochi, which was no larger than a common garden bird of today. The slender toothed skull is just 73mm (almost 3 inches) long, and in life the delicate animal would have had a wing span of some 40cm (16 inches). The fossil is one of the best-preserved of its kind; not only every bone can clearly be seen, but the fleshy outline of the animal, and even the indication of the wing membranes, have been preserved.

The extended fourth digit which formed the leading edge of the wing ('pterodactyl' means 'wing-finger') is perfectly articulated in the fossil, and even the sclerotic ring (the tiny circle of bony plates that supported the eyeball, below) is clearly visible. In life, the animal would have been covered with a thin layer of integuments similar to hairs in structure (my life reconstruction drawing, above), and the tiny teeth would have grasped and held insects on the wing.

Since dragonflies (below) have been found in the same fossil beds, it is reasonable to speculate that these would have been on the menu of this small pterodactyl. This pterosaur fossil comes from the famed deposits of Solnhofen limestone in Bavaria: the same fossil site where Archaeopteryx was discovered. Together with the small dinosaur Compsognathus and other species of pterosaurs, these creatures formed a community of Jurassic animals living in what was then an archipelago of islands lying in warm tropic seas.

It was among these islands that the pterosaur which my fossil cast portrays hunted and caught insects on the wing, living out its life until - for whatever reason - it died. The small body sank into the sheltered waters of a coastal lagoon, where, in the layer of oxygen-starved water lying in the deepest part of the lagoon, the body was hardly touched by the processes of decay - or by the actions of scavenging crustaceans - before being covered by silt. The covering of finely-compacted sediments provided further ideal conditions for fossilization to take place, and for the little pterosaur to begin its one hundred and fifty million year-long journey to our own time.