I've written here before about unusual paleontological discoveries -- illustrations of the fact that Darwin's lovely phrase "many forms most beautiful and most wonderful" has applied throughout Earth's biological history.
We could also add the words "... and most weird." Some of the fossils paleontologists have uncovered look like something from a fever dream. A while back I wrote about the absolutely bizarre "Tully Monster" (Tullimonstrum spp.) that is so different from all other life forms studied that biologists can't even figure out whether it was a vertebrate or an invertebrate. But Tully is far from the only creature that has defied classification. Here are a few more examples of peculiar organisms whose placement on the Tree of Life is very much up for debate.
First, we have the strange Tribrachidium heraldicum, a creature of uncertain relationships to all species at the time or afterward. It had threefold symmetry -- itself pretty odd -- and its species name heraldicum comes from the striking resemblance to the triskelion design on the coat of arms of the Isle of Man:
Despite superficial similarities to modern cnidarians (such as jellyfish) or echinoderms (such as sea urchins and starfish), Tribrachidium seems to be neither. It -- along with a great many of the Ediacaran assemblage, organisms that dominated the seas during the late Precambrian Era, between 635 and 538 million years ago -- is a mystery.
The Ediacaran is hardly the only time we have strange and unclassifiable life forms. From much later, during the Carboniferous Period (on the order of three hundred million years ago), the Mazon Creek Formation in Illinois has brought to light some really peculiar fossils. One of the most baffling is Etacystis communis, nicknamed the "H-animal":
It's an invertebrate, but otherwise we're still at the "but what the hell is it?" stage with this one. Best guess is it might be a distant relative of hemichordates ("acorn worms"), but that's speculative at best.
Next we have Nectocaris. The name means "swimming shrimp," but a shrimp it definitely was not. It next was thought to be some kind of primitive cephalopod, perhaps related to cuttlefish or squid, but that didn't hold water, either. They had a long fin down each side that they probably used for propulsion, and a feeding tube shaped like a funnel (that you can see folded to the left in the photograph below):
All of the Nectocaris fossils known come from the early Cambrian. It's possible that they were a cousin of modern chaetognaths ("arrow worms"), but once again, no one is really sure.
Another Cambrian animal that has so far defied classification is Allonnia, which was initially thought to be related to modern sponges, but their microstructure is so different they're now placed in their own order, Chancelloriidae. You can see why the paleontologists were fooled for a while:
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At the moment, Allonnia and the other chancelloriids are thought to represent an independent branch of Kingdom Animalia that went extinct in the mid Cambrian Era and left no descendants -- or even near relatives.
Last, we have the bizarre Namacalathus hermanestes, which has been found in (very) late Precambrian shales in such widely-separated sites as Namibia, Canada, Paraguay, Oman, and Russia. Check out the reconstruction of this beast:
It's been tentatively connected to lophophorates (which include the much more familiar brachiopods), but if so, it must be a distant relationship, because they look a great deal more like something H. P. Lovecraft might have dreamed up:
The early Cambrian seas must have contained plenty of nightmare fuel.
And those are just five examples of organisms that would have certainly impelled Dr. McCoy to say, "It's life, Jim, but not as we know it." Given how infrequently organisms fossilize -- the vast majority die, decay away, and leave no traces, and the vagaries of geological upheaval often destroy the fossil-bearing strata that did form -- you have to wonder what we're missing. Chances are, for every one species we know about, there are hundreds more we don't.
What even more bizarre life forms might we see if we actually went back there into the far distant past?
I guess we'll have to wait until someone invents a time machine to find out.
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