Report Abuse. An egg lives for around 12 hours after ovulation. Sperm can live for about five days inside the uterus, so providing those two time frames collide, it can be pretty soon after sex.
The tail arrangement is believed to have been a defensive weapon against predators. The term thagomizer was coined by Gary Larson in a 1982 Far Side comic strip, in which a group of cavemen in a faux-modern lecture hall are taught by their caveman professor that the spikes were named for the late Thag Simmons.
The spiked tail of Stegosaurus (Wikimedia Commons). Way back in 1982, a famous Far Side cartoon depicted a group of cavemen clustered around a picture of a Stegosaurus tail; one of them points to the sharp spikes and says, Now this end is called the thagomizer...after the late Thag Simmons..