Animals appear as fossils c.570 million years ago, back in the Ediacaran, but there are trackways preserved in old mud going back nearly 2 billion years. The trackways look somewhat like worm-trails, but no worm has been identified in the fossils from then, or known specimen from the present, as a likely culprit. Now it seems a new suspect is on offer and it’s not an animal…
Discovery Of Giant Roaming Deep Sea Protist
Single-celled giant upends early evolution
Deep-sea protists may explain trace fossils
Discovery of giant roaming deep sea protist
…a giant Protist, as big as a grape apparently, makes trails on the sea-floor just like the old fossil trails. This would neatly explain why “animal” trackways can appear in PreCambrian sediments from the PaleoProterozoic (2.5-1.6 Gya) and makes protists even more dynamic than anyone had previously imagined. Macroscopic colonies of microbes are well known as fossils – stromatolites can be gigantic, for example – but few had imagined mobile microbial colonies. Which is a bit sad since we Animals are effectively very large bacterial/Archeal colonies. Our mitochondria were once purple bacteria, while our centrioles and undulipodium were once bacteria related to spirochetes. And even now your body contains at least 10 times more bacterial than living animal cells. In a real way land animals are life-support suits for bacteria trying to live on land.