A huge horde of mixed animal bones, including the remains of humans, has been found in an ancient lava tube in Saudi Arabia. The hollowed cave, called Umm Jirsan, is a sprawling lava conduit system underneath the volcanic fields of Harrat Khaybar in the northwest of the country. Umm Jirsan extends for a staggering 1.5 kilometers (almost a mile), making it the longest known reported lava tube in Arabia. Within those extensive shadows, wild creatures have been busy. In a new study, researchers report the discovery of hundreds of thousands of bones belonging to at least 14 different kinds of...