Half-billion-year-old sea squirt could push back origins of vertebrates, including humans

In 2019, a finger-size fossil landed on the desk of Karma Nanglu, a paleontologist at Harvard University who specializes in the Cambrian and Ordovician periods, when many of today’s animal forms made their entrance. The specimen had sat for years in the drawer of a Salt Lake City museum; its finders, who had pulled it from a fossil-rich layer of Cambrian limestone in western Utah, thought it might be a sea squirt or tunicate—a marine invertebrate that shares a distant ancestor with all vertebrates. Nanglu was excited but cautious at the prospect of a very ancient tunicate: “That’s a group for which there is essentially no fossil record for the entire 500 million years of recorded history.” Now, in a paper published today in Nature Communications , Nanglu and his co-authors report that the exquisitely-preserved 500-million-year-old fossil is a dead ringer for some tunicates today, with two siphons to filter organic particles from the water and complex musculature controlling the siphons. “It looks like a tunicate that died yesterday and just happened to fall down on some rock,” says Nicholas Treen, a developmental biologist at Princeton University who wasn’t involved in the work. The discovery offers clues to the timing and development of early tunicates and could even push back the date for the origin of tunicates’ sister group, the vertebrates, including humans. Today, some 3000 species of tunicate live in almost every habitat of the o...
Source: ScienceNOW - Category: Science Source Type: news