Fossils are being used to reconstruct earth's ancient past, with discoveries including a 500-million-year-old fossil that sheds light on animal evolution and another that reveals a claw related to the origins of spiders. Other fossils, including a 275-million-year-old one with a twisted jaw, are also providing new insights into the history of life on earth. The findings appear to be focused on understanding how life adapted to extreme conditions and evolved over time.