 All post @-@ 1638 depictions appear to be based on earlier images , around the time reports mentioning dodos became rarer . Differences in the depictions led authors such as Anthonie Cornelis Oudemans and Masauji Hachisuka to speculate about sexual dimorphism , ontogenic traits , seasonal variation , and even the existence of different species , but these theories are not accepted today . Because details such as markings of the beak , the form of the tail feathers , and colouration vary from account to account , it is impossible to determine the exact morphology of these features , whether they signal age or sex , or if they even reflect reality . Dodo specialist Julian Hume argued that the nostrils of the living dodo would have been slits , as seen in the Gelderland , Cornelis Saftleven , Crocker Art Gallery , and Ustad Mansur images . According to this claim , the gaping nostrils often seen in paintings indicate that taxidermy specimens were used as models . 
