Last week I gave you some detective work – I asked to work out what this was:

Unsurprisingly to me, most of you worked it out pretty quickly – it is indeed a bat. A fruitbat of the genus Pteropus to be more accurate.

It seems that you took a look at the sternum:

and rapidly worked out that whatever this animal is, it clearly had a large area for attachment of the pectoral muscles. This “keeled” look is something normally seen in birds (see A in image below), but they tend to have a much more strongly developed form:

A = strongly developed sternum "keel"

after all, birds beat the bats into the air by about 100 million years, so it is unsurprising that they have more extreme adaptations to flight. Some flightless birds have no “keel” on their sternum, but they still maintain a strongly developed, fused flat plate that is lacking in mammals. Another difference between bird and mammal ribs is the presence of “uncinate processes” (see B below):

B = Uncinate processes on ribs

 These processes brace the ribs and play a role in respiration and dispersing stress and strain forces more evenly during flight. All mammals lack these.

So, Friday’s Mystery Object has a somewhat keeled sternum, but no uncinate processes – so it belongs to a mammal with powered flight. That brings us to the bats, and by size alone we can say it’s almost certain to be a fruit bat.

Hope you enjoyed the deductive reasoning in that one!

For extra kudos, can anyone identify what bird I used in the labelled images above? It’s a comparative anatomy lab standard, so it shouldn’t be hard…