This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
While we transition from paleontology back to protistology, let's make a short stop along the way. A stop in downtown Chicago, of all places. You know, the ideal place for finding living critters and fossils, right? Well, actually, it's not all that bad -- after the Great Chicago Fire of 1871, fear of fire encouraged the entire city to be built of stone or brick. Several states' worth of quarries were employed for the rebuilding, including those tapping into the Salem limestone around Bloomington and Bedford, south-central Indiana. Incidentally, much of the wealth here in Bloomington came from the late 19th and early 20th century construction boom and rising demand for quality limestone. While the industry isn't doing so hot anymore, the masonry and stonework make for some pretty architecture both in Bloomington and a few major cities in eastern US. What is this limestone predominantly composed of?
Millions upon millions of years of foram rain, eventually compressed along with a few bryozoans and crinoids (but not many in this particular formation -- hence why the quality of stone is so high). If you crawl around some buildings in Chicago, New York, DC with a hand lens, you can find a trove of relics of marine life long past -- while passerbys find yet another city creep doing inexplicable things.
As cool as Salem limestone is (I cannot offend it too much as I'm literally sitting above it as I write this; limestone can always fight back with sinkholes), there are more dramatic variants of it -- especially in the foraminiferan department. In fact, arguably the first historical note of protists (besides seaweeds) is of the surreal extinct amoebae in the following rock.
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In downtown Chicago there is this Chicago Tribune building, renown for its neogothic architecture (which is indeed not hard to look at!). But little do architectural aficionados know that the building is way cooler than they thought. Another relatively well-known feature of the building is the preponderance of random (stolen?) chunks of temples and monuments from around the world, shoved into the outer walls at street level. Rome, Ankgor Wat, forts, etc. Among them, a piece of the Egyptian pyramids at Giza:
Naturally, I got really excited. As a biologist. I immediately stopped to examine it. If you look closer, you may notice the rock isn't exactly compressed sand, and has weird "lentil-shaped" (as ancient Greeks described it) bits in it. Just left of centre in the following picture:
Those layers are remnants of chambers... of an extinct group of giant forams called Nummulites. Some were as big as a few centimetres across -- remember, built by entirely unicellular amoebae! It is thought that the compartmentalisation allows the forams to get this big, but imagine how large the reticulopodial (net-like pseudopod) network stretched out for feeding! It probably took a few days for proteins to make their way from the nucleus (or nuclei) at the centre of the test to the periphery of the pseudopods. The above was a longitudinal section, but now let's look at a cross section. This guy was about a centimetre in diameter.
You should see the chambers arranged in a spiral. This is a quick note, but someday I'll go over some foram architecture -- the tests are even more complex than they look, often filled with ridges, channels and alcoves, not always with an obvious function. While Nummulites are sadly now extinct, there are still plenty of massive foram genera left to admire.
Ancient Egyptians doubtlessly saw those while hewing the stone for pyramids. I wonder what they thought. Single-celled organisms were millennia away from being a concept. So were fossils and evolution. One wonders what sort of explanations a parent gave to an annoyingly inquisitive kid who noticed those. Did they know the "lentil-shaped" objects once housed living organisms?
Why should they have? It's still tantalising to imagine how long we have lived with these ancient forams, to only recently discover who they really were. (and we still know little about them, as soft tissue seldom gets preserved). Oh, and GIANT FORAMS! How can that not be awesome??
The coolest thing in Chicago, outside the Field Museum.