Grape-sized protists make tracks
I think this is great, macroscopic single-celled organisms making tracks that can be confused with multicellular organisms:
DNA analysis confirmed that the giant protist found by Matz and his colleagues in the Bahamas is Gromia sphaerica, a species previously known only from the Arabian Sea.
They did not observe the giant protists in action, and Matz says they likely move very slowly. The sediments on the ocean floor at their particular location are very stable and there is no current—perfect conditions for the preservation of tracks.
Matz says the protists probably move by sending leg-like extensions, called pseudopodia, out of their cells in all directions. The pseudopodia then grab onto mud in one direction and the organism rolls that way, leaving a track.
He aims to return to the location in the future to observe their movement and investigate other tracks in the area.
Matz says the giant protists’ bubble-like body design is probably one of the planet’s oldest macroscopic body designs, which may have existed for 1.8 billion years.
“Our guys may be the ultimate living fossils of the macroscopic world,” he says.
The above excerpt suggests that these organisms are not in fact entirely new, but I wasn’t aware of such huge protists before this. It does indicate that evolution has more than one way to make larger organisms, although it does not seem likely that they would ever evolve into the many forms that multi-celled animals have.
Other than that, it appears that at least many Precambrian tracks are put into doubt by this, since multicellular organisms aren’t necessary to leave tracks behind. What is confusing is that the article implies that there may have been no multicellularity, and then there was a “Cambrian explosion”–ignoring the fact that there was an “Ediacaran explosion” before the Cambrian began.
Still, it could mean that the Ediacaran (presumably) multicellular organisms have no known precursors, and it’s still a good question whether or not any Ediacaran organisms left descendents. The appearance of multicellular life is not as mysterious as the anti-evolutionists pretend, but it continues to leave a lot of questions to be answered.