A remarkable fossil hidden in a museum collection for decades is helping scientists rethink one of the biggest mysteries in early animal evolution. The discovery of a 500-million-year-old arthropod in eastern Canada suggests that a period once thought to be marked by declining biodiversity may have been far richer and more complex than researchers believed. The newly described species, named Magnicornaspis garwoodi, comes from the late Cambrian Period and belongs to a rare group of extinct arthropods known as corcoraniids. These ancient creatures are considered important relatives of the lineage that eventually gave rise to modern chelicerates, a group that includes spiders, scorpions and horseshoe crabs. Researchers say the fossil provides valuable evidence from a poorly understood interval known as the Furongian, a period spanning roughly 497 million to 485 million years ago. For decades, paleontologists have puzzled over why relatively few fossils appeared to come from this time. The new findings suggest the apparent shortage may not reflect a true collapse in life on Earth. Instead, it may reveal gaps in where scientists have …