Carl Zimmer in The New York Times:
One of the greatest transformations in the history of life occurred more than 600 million years ago, when a single-celled organism gave rise to the first animals. With their multicellular bodies, animals evolved into a staggering range of forms, like whales that weigh 200 tons, birds that soar six miles into the sky and sidewinders that slither across desert dunes.
Scientists have long wondered what the first animals were like, including questions about their anatomy and how they found food. In a study published on Wednesday, scientists found tantalizing answers in a little-known group of gelatinous creatures called comb jellies. While the first animals remain a mystery, scientists found that comb jellies belong to the deepest branch on the animal family tree.
The debate over the origin of animals has endured for decades. At first, researchers relied largely on the fossil record for clues. The oldest definitive animal fossils date back about 580 million years, although some researchers have claimed to find even older ones. In 2021, for example, Elizabeth Turner, a Canadian paleontologist, reported finding 890-million-year-old fossils of possible sponges. Sponges would make sense as the oldest animal. They are simple creatures, with no muscles or nervous system. They anchor themselves to the ocean floor, where they filter water through a maze of pores, trapping bits of food.
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