Saturday, 23 February 2013

The Pseudo-Vampires Of The Jurassic

In the second episode of Walking with Dinosaurs, we are given a view of a microscopic world as a collection of bloodsucking flies feed off of their gigantic dinosaur hosts. Fossils trapped in amber alongside more conventional specimens, preserved on the surface of slabs of stone, have confirmed that vampiric insects did exist hundreds of millions of years ago.

The 165 million year old fossils of mating strashilid flies
Mosquitoes have an ancient lineage as do fleas. For a while it was thought  that a small group of now extinct aquatic flies unearthed from 165 million year old Jurassic rocks in Inner Mongolia were also bloodsuckers. Recently, however, it has been shown that they have been falsely accused. The fossils, less than half a centimetre in length, appeared to have a proboscis similar to those found in fleas and mosquitoes, and grasping legs similar to those found in blood-feeding parasites.

Then 10 new specimens of the fly species, which belong to an insect group known as the strashilids, showed something rather unusual. A team of Chinese palaeontologists led by Diying Huang from the Nanjing Institute of Geology, noticed that a number of the specimens were in pairs. A closer examination revealed that the pairs consisted of a male and a female with the grasping legs of the male wrapped around the female.

These signs suggested that the fossils were in fact of mating pairs and the grasping legs were not to hold onto the feathers or skin of a dinosaur, but evolved for copulation. What is more, the needle mouth parts did not have the specializations needed for feeding and actually appeared to be vestigial rather than functional. Finally, the mating pairs lacked wings while the separate specimens still possessed large, membranous  wings. The overall image is that these creatures lived a lifestyle similar to that of a mayfly.

Some of the single specimen, showing wings and gills, suggesting that they lived at least a partially aquatic lifestyle
The rock surrounding the fossil was compacted sediment from a river supports this idea, suggesting that the insects emerged from their eggs, flew around to find a mate, lost their wings before mating, mated, laid the next generation of eggs and then died all in a very brief period of time, perhaps a day or two. This would explain the non-functional mouth parts. The ability to reconstruct lifestyles allows us to recreate inhabited ecosystems, giving us a glimpse beyond the creatures and into their world.