Pegasus, along with his brother Chrysaor, sprang straight from the bloodied neck of Medusa, being her children by Poseidon (their sexual liason was the cause of Medusa being turned into a monster). When Perseus flew over North Africa on his way home, the blood that dripped from the severed head became venomous serpents and scorpions - hence why there are so many in that part of the country.
It was Aphrodite who rose from the waves, much earlier, having been born from the blood spilt from Ouronus' genitalia that were cut off by Cronus.
Interestingly, the same instrument (an adamant sickle) used by Cronus was the same one used by Perseus. Perhaps it gave blood a special generative power?