A molecule present in 640-million-year-old rocks comes from a simple sea sponge, according to genetic analysis done by Massachusetts Institute of Technology (MIT) researchers. The time frame is well before the Cambrian Explosion 540 million years ago, in which most animals groups sprang up and took hold in a relatively short geologic stretch.
That makes the humble sea sponge a likely bearer of the title “first animal on Earth.”
That’s according to findings appearing in a paper just published in the journal Proceedings of the National Academy of Sciences by lead author David Gold and senior author Roger Summons, both from MIT.
True to its name, the Cambrian Explosion produced no shortage of fossils. But very few pre-Cambrian samples exist. That paucity has made it difficult for scientists to determine which animal was first.
The MIT researchers decided to look for the elusive first creature by studying molecular fossils –- trace molecules still present in ancient rocks after the animal that left them has long since decayed into nothingness.
Gold and Summons focused on a particular molecule: 24-isopropylcholestane, or 24-ipc. It had been found, through prior research, in the 640-million-year-old rocks.
They suspected the molecule was from a sea sponge, as some modern sponges are known to produce it. But, the rub was that some forms of algae also make 24-ipc. So they had to prove the molecule came from a sea sponge, while ruling out algae.
The researchers first identified the gene that made the molecule, observing that sea sponges and algae have an extra copy of the gene.
Then, after some evolutionary-tree detective work, they traced the extra-copy genetic behavior back to its oldest evolutionary carrier: the sea sponge. It turned out the sponge had evolved the extra gene copy well before algae, sometime around -- you guessed it -- 640 million years ago.
Read more at Discovery News
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