Exploring around on YouTube, I came across a video about the Ordovician/Silurian mass extinction that happen some 450 million years ago. The video was shown on the Animal Planet channel in 2009 and was called Animal Armageddon Episode 1 Death Rays. They speculate that the extinction was triggered by a massive gamma ray burst from a dying star. This radiation exposed the Earth to fatal levels of energy that wiped out 2/3 of species or 85% of animal life.
It is neat to see computer animations of the sea environment with creatures like straight-shelled cephalopods, Eurypterids sea scorpions, trilobites, Astraspis fish, and Acanthodian fish. Learn more at the Animal Planet web site for the show and on Wikipedia.org.
The total episode lasts 45 minutes and is shown below:
The second episode entitled Hell on Earth is about the Devonian extinction. They speculate that volcanic eruptions could have caused the extinction.