What Did the Earliest Animals Look Like?
Published:30 May2023 Source:University of California - Berkeley
Searching among today's most primitive-looking animals for the earliest branch of the animal tree of life, scientists gradually narrowed the possibilities down to two groups: sponges, which spend their entire adult lives in one spot, filtering food from seawater; and comb jellies, voracious predators that oar their way through the world's oceans in search of food.
Although the researchers determined that the ctenophore lineage branched off before sponges, both groups of animals have continued to evolve from their common ancestor. Nevertheless, evolutionary biologists believe that these groups still share characteristics with the earliest animals, and that studying these early branches of the animal tree of life can shed light on how animals arose and evolved to the diversity of species we see around us today.
Researchers found a relic of a very ancient chromosomal signal. It took some statistical detective work to convince that this really is a clear signal and not just random noise. But the signal is there and strongly supports the 'ctenophore-branched-first' scenario. The only way the alternative sponge-first hypothesis could be true would be if multiple convergent rearrangements happened in both sponges and non-ctenophore animals, which is very unlikely.