A protist is a single celled eukaryotic organism, and they are usually pretty small. You can often see them, though! Before you put that sample of pond water under the microscope, take a close look: Many protists are at the boundary of visibility for humans.
Then, there are the giant protists, grape size, living on the bottom of the sea where they roll around in the mud. It has been known for some time that there are giant deep sea protazoans that are not mobile. Here, though, is a bit of film of giant mobile protists.
A recent paper in Current Biology links these creatures to very ancient trace fossils. In so doing, a beautiful hypothesis is slaughtered by a small, grape size muddy amoeba thingie.
This is from the abstract of the paper:
One of the strongest paleontological arguments in favor of the origin of bilaterally symmetrical animals … prior to their obvious and explosive appearance in the fossil record in the early Cambrian, 542 million years ago, is the occurrence of trace fossils shaped like elongated sinuous grooves or furrows in the Precambrian … these traces … are commonly attributed to the activity of the early nonskeletonized bilaterians or, alternatively, large cnidarians such as sea anemones or sea pens. Here we describe macroscopic groove-like traces produced by a living giant protist and show that these traces bear a remarkable resemblance to the Precambrian trace fossils, including those as old as 1.8 billion years. This is the first evidence that organisms other than multicellular animals can produce such traces, and it prompts re-evaluation of the significance of Precambrian trace fossils as evidence of the early diversification of Bilateria. Our observations also render indirect support to the highly controversial interpretation of the enigmatic Ediacaran biota of the late Precambrian as giant protists…
Here’s a picture of one cleaned up, from the paper:
In case you were wondering how much these creatures move …. well, you can’t tell from the film above because it is a film of still photos. Here is some moving pictures of the giant protists:
So, there you have it. One of the most exciting finds of the century, and one of the most boring finds of the century, all wrapped up in one!
M MATZ, T FRANK, N MARSHALL, E WIDDER, S JOHNSEN (2008). Giant Deep-Sea Protist Produces Bilaterian-like Traces Current Biology DOI: 10.1016/j.cub.2008.10.028