The Origins of Centaurs
Here is Pindar's account, from Pythian II:
Far were the Graces when Cloud
Bore him a monstrous issue,
She like nothing, and like nothing It;
Which found no favor among men, nor in
The company of the Gods.
She nursed It and called It Kentauros: and It lay
With the Magnesian mares on Pelion's foot-hills.
And a race was born
Prodigious, in the image of both parents,
Their nether parts of the mother, their father's above.
(tr. C.M. Bowra, from the Penguin Odes)
The word kentauros seems to mean bull-slayer. (My ancient Greek is very weak but consulting Donnegan seems to confirm this.) One can see what Pindar was getting at: the union of a human and a nymph could only produce something human in appearance; but if its monstrous nature (a produce of its monstrous conception) led it to mate with animals, the resulting offspring would partake of both parents.
But of Kentauros nothing else (that I can find) was said by any ancient source. Pindar's "far from the Graces" means that its birth was unblessed (the more literal Myers translation available from Perseus says "without favour of the Graces"), so that although he was nurtured by his mother, his cursed nature was recognized -- by a validating source whose authority was beyond appeal -- even before his birth. From this, we gather, came a life of solitude, including erotic solace found only among a herd of horses in Thessaly.
A potentially interesting figure, Kentauros. But I have never read anything else about him.