From the time I used to read the Amar Chitra Kathas, I have wondered why Buddha did not tonsure his head - apparently, all his disciples did, including the women. And since his 'sangha' was reputed to be an 'egalitarian' organization, such a distinction, even for the Master, was rather puzzling...
Not very long back, I happened to read that Buddha had a small protuberance (called the 'usnisa') on top of his head - one of the many legendary 'Mahapurusha Lakshanas' that mark out enlightened masters. That triggered the following thought: "Perhaps it would be odd to show Buddha with a shaven head with a little bump on top. So, what is shown as a nice top-knot of hair in pictures actually is a 'cover'!". There the matter rested, for a while (I did remember seeing some statues showing Buddha's hair as not hair at all, but a mass of squares or spirals packed together; but I decided they were 'mere' stylizations).
A few days back, I came to know about the Buddha's alleged debt to snails from this page
, which I referred to in an earlier post here
as well. In brief, this is the story: during a severe summer, a group of snails crept onto Buddha's head and shielded him from sunstroke - and gave up their lives in the process; and as a mark of gratitude, the Master bore their shells on his head for the rest of his life. Oh, yes, then, what looked like a mass of spirals on some statues was indeed a mass of spirals, all those snail shells sticking to his head! And of course, there was no special problem due to protuberance on the head - some of the the snails had sat on top of that as well. And but for the snails his head would have been bare - devoid of hair. So, it looked plausible that someone in comparatively recent times mistook those snails shown in ancient statues for hair and the modern 'topknot Buddhas' came to be made.
However, things were not so simple; for there indeed are many ancient statues of Buddha which show him with actual hair tied in a graceful topknot. And some of these were Gandhara-style statues and the earliest of Buddha images - (with coiffure resembling that of the famous Greek statue of 'Apollo Belvedere'). The hair versus shells issue is thus not quite resolved.
The plot thickened further when I read yesterday that the word 'kaparda' in Sanskrit means either a small shell (a cowrie shell) or hair worn in a top-knot shaped like such a shell (source: the online Monier-Williams dictionary). Where does that leave us? Buddha wore a 'kaparda' but that could be (a mass of) shells or a topknot. It could be either - or both!
And things got murkier when I found that there were somewhat divergent legends on what Buddha did to his hair when he renounced the world. One story says he cut his hair down to two inches length (very modern!) and another says he got rid of them totally!
Some speculations: Buddha grew up a prince. And princes and royals in those days used to tie their hair in kaparda style. Perhaps, when, a few centuries after his passing, people thought of making his statues (the earliest known Buddha images *post date* him by at least 3 centuries) they showed him as basically a prince who chose to be a monk. Hence the hairstyle of the Gandhara images (this implies that his being of royal lineage did count for something - and the Sangha was not purely 'socialist' - at least in those days). Then, someone came along and thought up the snail story, smartly using the 'ability' of the word kaparda to mean 'shell' and this new story became popular and so the hair turned to a mass of shells in subsequent Buddha images.
And it appears that just like Buddha's own life-trajectory, the legends surrounding him got 'de-elitized' over time - he came be seen to have completely abandoned all princely attributes to lead a purely ascetic life. And simultaneously, these legends incorporated superhuman and supernatural elements as well.
For the proper academic take on Buddha's 'hairstyle' and its artistic representations, here are some links (yes, this has been a subject of very intense study and many, including Ananda Coomaraswamy, have written at length on the matter):
Note 1: Just like 'kaparda', the Sanskrit word 'usnisa' is ambiguous as well. It could literally mean a turban-like headdress (again a royal trapping) and it is an 'esoteric' matter to interpret it as a cranial prominence. (Strangely, the Monier-Williams dictionary does not contain this word). Indeed some more of the Mahapurusha Lakshanas are 'royal' - for instance, the elongated ear-lobes - these can be attributed to the heavy golden earrings worn by Buddha when he was a prince.
Note 2: These 'Lakshanas' are also part of Jain mythology. The Tirthankaras are often shown with a something like a topknot (or a stylization thereof) and elongated ear-lobes (and unlike the Buddha, they are also sometimes shown with a tonsured 'plain' head). Of course, tradition says many of the Jinas also were princes. The snail story, of course, seems an exclusively Buddhist invention.