The males and females of many animals are easily distinguishable, lions for example or deer - most female deer (excluding most notably, reindeer) do not have antlers for example. In birds, the plumage of males and females is very distinctive, e.g. mallards, peacocks/peahens, chaffinches etc.
I knew about many of these examples before I became a zooarchaeologist. One gender difference that I did not know about, however, was that male carnivores have a penis bone or baculum! (os penis). On Irish sites this bone is most commonly present from dogs though examples from foxes and mustelids occur occasionally too.
Archaeologically, this is not hugely informative though it gives a bit of interest to the site to know the sex of an animal and potential pet. Knowing the gender, can also be of interest when stature and ‘breeds’ are being investigated.
Plate 1. A adult male dog skull, with it's baculum bone beneath it.