Not So Much Head in the Sand

It has always been claimed that ostriches and emus etc (the so-called ratites), differ from other birds, in that their males achieve penile erection by engorging the organ with blood (as do mammals). A recent detailed study (http://www.bbc.co.uk/nature/16112188 ) has, however, confirmed that these birds, like the rest of the Aves, actually use lymph in this process. This suggests that the mechanism evolved early in this vertebrate Class.