In Depth
Despite the fact that fossils of Palaeochiropteryx are dated all the way back to the Lutetian period of the Eocene, this bat is already almost like modern day bats are. In depth study of the cochlea of Palaeochiropteryx has revealed that it as an intermediate level of development, meaning that it was not as advanced as modern echolocating bats, but it was still substantially more developed that the cochlea of bats that do not echolocate. When you combine this observation with the discovery of insect remains (mostly moths and caddis flies) within the stomach of some specimens, it is clear that Palaeochiropteryx was capable of using echolocation to locate prey while on the wing.
The types of insects found inside the stomachs of Palaeochiropteryx are also of types that are mostly nocturnal (mostly does not mean exclusively, it is recognised that there are many types of daylight flying moth, but as a whole these are in the minority). This means that Palaeochiropteryx would probably emerge from where they were roosting for the day at dusk when the sun slipped beneath the horizon and the light started to fade, because this would be when their prey was becoming most numerous. As the night continued and total darkness set in, Palaeochiropteryx would have no light to see by, and this also reinforces the theory that Palaeochiropteryx was able to echolocate, as this would be the only way they would be able to detect insects like moths as they were flying about in the darkness.
The dental formulae for Palaeochiropteryx is 2.1.3.3. for the upper jaw and 3.1.3.3. for the lower. Each formula can be read by the number of specific kinds of teeth in one half of the jaw only, with the first number being incisors, second canines, third premolars and fourth molars. So altogether the upper jaw had four canines, two incisors, six premolars and six molars (across both sides), while the lower jaw had six incisors, two canines, six premolars and six molars for a combined total of thirty-eight teeth in the mouth. The dental formula for Palaeochiropteryx is identical to some modern bats, which again displays how little bats have changed in their overall form.
Palaeochiropteryx was still not quite a modern bat, and careful observation reveals some primitive features. Aside from the underdeveloped (but still functional for echolocation) cochlea, Palaeochiropteryx also retained claws on their index fingers.
The Messel Pit of Germany is what remains of what was once probably an ancient caldera (the crater of a volcano). Water eventually filled this crater to form a lake, exactly like what sometimes happens with volcanoes today. In the Eocene this caldera was still active, though eruptions seem to have been focused around the sudden release of volcanic gasses, such as Carbon Dioxide and Sulphur Dioxide. These gases would have erupted up out of the surface of the water and spread into the surrounding (at the time) tropical forests suffocating any animals that were living close to the ground. This would include low flying bats like Palaeochiropteryx that may have been suffocated by a sudden release of volcanic gases as they were flying low for insects. Losing consciousness from lack of oxygen they would have tumbled into the lake where they would have drowned and sunk to the bottom. This would explain why many seemingly healthy adult bats with full stomachs died, and also why they were so well preserved, since the low oxygen content of the water would have reduced the amounts of bacterium and scavenging animals capable of destroying the body before it was buried in sediment.
Further Reading
- Evolution of nocturnality in bats: Potential competitors and predators during their early history, J. Rydell & J. R. Speakman - 1995. - The evolution of flight and echolocation in pre-bats: an evaluation of the energetics of reach hunting, John R. Speakman - 1999. - Messel Pit Fossil site, Evelies Mayer - 2007.
