This month I have chosen to look at the skull of the bat. I’ve always loved these animals and have an early memory of being intrigued by them when I visited the bat house at Cotswold Wildlife Park as a kid. Whenever I see them I always remark at how they look like small dogs (particularly the fruit bats which are common at zoos). I know some people are a little freaked out these creatures, I guess because of the myths and stories attached to them and the fact that they are a flying mammal, but I have a real soft spot for them!
As I want to find out more about bats I am going to start off by looking at the general skull of a bat, so nothing too specific. Perhaps during the month I’ll find out some interesting facts about particular species of bat, in addition to their evolutionary path.
So here’s a bit of an introduction to bats. There are over 100o species of bat making them the second largest group of mammal, with rodents being the first. Bats are an extremely diverse group which are spread across the globe, range in size and have a varied diet. The largest is the flying fox which has a wing span of up to 2 metres whilst the smallest is the Bumblebee bat weighing just 2 grams in weight.
Bats are split into two groups: megachiroptera and microchiroptetra. This split is based in the ability to echolocate and are also known as ‘true’ bats. The microchiroptetra possess this skill and most of the species that fall into this group are insectivorous. The other species of bats are megachiroptera and are either frugivorous or nectarivorous.
This variation in diet and feeding behaviour is evident in the skulls of bats. Frugivores have wider palates and molars which have sharp outer edges and flatter surfaces to crush food. Insectivores have narrower palates with sharp, spiky teeth for shearing and crushing. bats have 22 deciduous teeth which are curved to help to hold on to their mother’s fur when they are young. Alternatively adults will have 20 – 38 teeth depending on the species. An example dental formula of the fruit bat Rousettus is: I: 2/2, C:1/1, PM: 3/3, M:2/3 . There is a pretty cool video depicting the skulls of bats from each of the three different types of feeding ecology. It is a good way of understanding and seeing the differences in their teeth. To view it follow the link below to Smithsonianscience.org.
One interesting feature that I read out the bat’s skull is the way it is attached to the spine by a special vertebrae. These vertebrae differ depending on their roosting posture resulting in thinning of the neutral arches of microchiroptetra resulting in a higher degree of flexibility. This allows the bats to look around their surroundings when roosting upside down. The species of bats lacking this ability has had to develop a different roosting posture (Fenton & Crerar 1984).
Bats are interesting, varying mammals and I am intrigued with what I will find after a bit more reading! For example, the bite force of two speices has been investigated to examine the effect on skull morphology. Click here to see the summary and the originial article.
References and reading material:
Roosting posture: Fenton, M. B. and L. M. Crerar (1984). “Cervical Vertebrae in Relation to Roosting Posture in Bats.” Journal of Mammalogy 65(3): 395-403.
Frugivorous and animalivorous bats (Microchiroptera): dental and cranial adaptations: Freeman (1988)