I was just re-reading a Scientific American article from 1982 about the Burgess Shale, and taking close note of the lovely artwork accompanying the story, a reconstruction of several Burgess Shale animals. The reconstruction is already known to be out of date - it shows Peytoia as a jellyfish, when it has since been discovered to be the mouth structure of Anomalocaris, and it shows Hallucigenia in its old, spines-down orientation.
Hallucigenia has always struck me as a danger zone in Burgess Shale research. Everyone focuses on how weird it is, yet for the longest time no one could actually make the animal work. Scientific American showed it walking on the spines (complete with little dot-trails of "spineprints") - which I always thought was... not right. To walk on inflexible spines, you'd need the spines to be spaced well apart and have EXTREMELY flexible muscles at the body end, so as to be able to lift the points off the ground and move them, else all you're doing is dragging points along in the silt. (An animal COULD move like this, by moving, say, 1/3rd of its legs forward at a time - it would be slow and inefficient.) Not to mention a strong current would knock the animal over and leave it with no way to right itself.
Research has since indicated that Hallucigenia was probably a velvet worm. The model has been turned upside down, letting it walk on its "tentacles" and have the spines pointed in the air - this makes much more sense, and I honestly don't know why it wasn't considered as a possibility in the first place. But even here I have my doubts: scientists still don't know which end is the head and which is the tail.
Which makes me tend to side with the theory that Hallucigenia is actually the broken-off appendage of a larger, yet undiscovered animal. This is precisely what happened with Anomalocaris, where its arms were classified as shrimp, its body as a sponge, and its mouth as a jellyfish, before someone noticed they all belonged to the same animal.
(Speaking of Anomalocaris: it went by real fast, but on Tenchi Muyo today I noticed Washu keeps an Anomalocaris in one of the tanks in her lab...)
The Sci American article mentioned that there's a fossil in a collection at Harvard showing several Hallucigenia "associated with" a large worm - "leaving little doubt" that H was feeding on the worm. Me, I read that and wondered if maybe the worm isn't the body and the associated Hallucigenias are appendages. I wish I could find a picture of the fossil in question.
Either way, it brings something to mind: the Burgess Shale, in addition to being one of the most famous faunas in paleontology, also tends to be the one most subject to reclassification. The whole of the Burgess Shale fauna was grouped by its discoverer (Walcott) into just two orders: polychaete worms and "trilobitoides" (trilobite-like things); modern reevaluation of the fauna has left maybe one polychaete worm and two genuine trilobites, the rest scattered around some 20 different phylums. Fine-tuning in recent years has moved Hallucigenia from its own phylum into the onycophorans, Peytoia into nonexistence, etc. This is to be expected when dealing with such a weird assortment of critters. Or should it?
It seems to me the problem is that paleontologists just aren't used to soft body preservation. We know what vertebrates look like as fossils - we know what to expect because a) they're so common, and b) we've found fossils of living species. Same with hardshelled fauna. But when it comes to soft body parts, the paleontologists are in brand new territory.
Particularly with the Burgess Shale, some of these phylums (the ones that exist today) are known ONLY from living animals and the Burgess Shale, nothing in between. The Burgess-only phylums (weirdos like Opabinia, Anomalocaris etc) may well be related to modern phylums, but without the continuity of the intervening few hundred million years, there's no way to match them up. Conversely, animals in the Burgess Shale may LOOK like modern creatures, but might have different enough internal workings that, were we to go back in time and catch one, we'd be able to see from the actual nonfossil animal that it isn't related all that closely after all. (What, after all, would we make of dolphins, sharks, and ichthyosaurs if we only had their OUTSIDE appearances to work with?) Suppose Pikaia isn't a chordate after all, suppose it's just an annelid worm with fins - and Nectacaris is the true chordate. Suppose Anomalocaris is the ancestor of something living today - maybe it's an echinoderm, or the weirdest damn sea slug ever. Indeed, what's to say Anomalocaris wasn't still living until say, 10,000 years ago, in some peculiar niche? We have the Burgess Shale to show us what invertebrates looked like in the Cambrian and... not a whole hell of a lot since then.
It's to be expected, of course - it's the nature of fossils that soft parts rarely get preserved. But maybe the paleontologists should be more, I dunno, proactive about keeping that fact in mind. Paleontology has its biases, just like any field of human endeavor (look how biased the computer industry is toward digital devices, even though analog might be a better way to work) - so I can't really fault the bulk of the work that's been done on the Burgess Shale - but still, there's that crazy little Hallucigenia sitting there, daring me to figure out which end is which, daring me to even figure out if it's a complete animal or a piece broken off a bigger one. Is there more to learn from the known fossils? Is ALL Burgess Shale research prejudiced by our limited understanding of the intervening 540 million years? Is there a tendency to "try too hard" to make fossils into complete animals, as in the case of Anomalocaris' disparate parts?
In marine biology, it's common to learn of the juvenile form of a species being misidentified as a whole new species. Over time, though, marine biologists have grown cautious. Should paleontologists also? Or are we better served by having them go too far, lest we end up with another Burgess Shale fauna classified as "trilobitoides"?
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