Anomalies Like Anomalocaris

Joyce Havstad writes...

Since we’ve been talking about paleoart and paleoaesthetics, I’ll start by saying that all of what I consider to be the most splendid fossils I’ve ever seen are relatively small specimens preserved in either Hunsrück Slate from the Devonian Period or Burgess Shale from the Cambrian.  It’s hard to do justice to the dark pieces from these Lagerstätten without a serious photographic set-up, but here are some shots from inside the Field Museum of Natural History’s collection of fossil invertebrates (click to enlarge):

Crinoidea and Medusaster specimens in Hunsrück Slate from Bundenbach, Germany—Devonian Period.  (Photographs by the author, with special thanks to Scott Lidgard and Paul Mayer at FMNH.)

It’s hard to see this in the shots, but both of these Bundenbach pieces have experienced some pyritization—in other words, some permineralization has occurred, with iron sulfide replacing organic tissue.  Actually, maybe some close-ups will help:

Two enhanced views of Crinoidea specimens in Hunsrück Slate from Bundenbach, Germany—Devonian Period.  (Photographs by the author, with special thanks to Scott Lidgard and Paul Mayer at FMNH.)

These fossils literally sparkle.  In the right light, it looks like some crazed bedazzler with a gold glitter stick broke into the collection and decided to delicately enhance a few pieces that were already pretty spectacular to begin with.  It’s positively outrageous!  Now, although they are also exceptionally-well preserved and stunningly beautiful, fossil specimens from the Burgess Shale can be totally outrageous in a completely different way—for their own, rather strange reasons:

Anomalocaris, Waptia, and Peytoia specimens from the Burgess Shale in British Columbia—Cambrian Period.  (Photographs by the author, with special thanks to Scott Lidgard and Paul Mayer at FMNH.)

Friends of paleontology will likely recognize what I mean here, as well as most if not all of the specimens depicted just above.  In the middle we have the holotype of Waptia fieldensis, one of the first Burgess Shale fossils discovered by Charles Doolittle Walcott in August of 1909.  It’s one of the most abundant kinds of arthropod (or arthropod-like) fossil types to be found amongst the Burgess Shale specimens, and Waptia looks rather obviously like a shrimp—yet, paleontologists are still not sure whether it is a member of the crustacean crown group.  Waptia might merely be a member of the crustacean stem group instead; it might barely be a member of even the arthropod stem group.

And then we have Anomalocaris—plus its related components, like Peytoia (depicted above) and Laggania (not pictured).  This story has been told many times already (e.g., Whittington & Briggs 1985; Gould 1989; Collins 1996; Conway Morris 1998; Daley & Budd 2010), so I won’t go into great detail with the set-up here.  But the gist of it is that this gigantic apex predator (perhaps the very first apex predator!) was initially discovered (part of it, at least) nearly 100 years before it (the part, and the whole organism it belonged to) even began to be understood.  Anomalocaris as we understand it today is an organism composed of what were at first thought to be several independent organisms in their own right, but which turned out to be mere components of a much larger whole.  A supposed crustacean turned out to be a frontal appendage; a purported jellyfish turned out to be a mouthpiece; and what was variously interpreted as a sea cucumber, a bristle worm, and then a sponge turned out to be the trunk (a.k.a., the body) of an anomalocaridid.

Paleontologists were tricked into thinking that such mere components of assorted anomalocaridids were their own, individual organisms for various reasons.  For one, these components were often found by themselves—though now that result is explained as a result of disarticulation, common during the process of fossilization, along with the varying potentials for fossilization among the organism’s softer to harder body parts.  For another, the pieces often looked a lot like very familiar kinds of organisms which paleontologists expected and tended to find—though sometimes the organisms the pieces looked like were kinds of organisms that paleontologists “recognized” but didn’t actually expect or tend to find in the particular locale in which they found them.  And conversely—perhaps most importantly—what Anomalocaris turned out to look like, along with the rest of the anomalocaridids, was nothing like what paleontologists expected and tended to find.

Earlier I described Anomalocaris as a “gigantic” apex predator—but this is a relative term.  Next to other more familiar and massive prehistoric apex predators, like Tyrannosaurus rex (up to 13 meters long) and Carcharodon megalodon (up to 18 meters long), even the unusually large, recently-discovered Moroccan anomalocaridids from the Ordovician (which may have reached over 2 meters in length) seem incredibly tame.  But when you compare the relative size of these predators to their prey, Anomalocaris is genuinely gigantic—it dwarfs everything else that paleontologists tend to find alongside it.  And that’s why paleontologists had such a hard time recognizing it: in addition to being often fragmented, and deceptively “recognizable,” and anomalous in a whole bunch of other ways, Anomalocaris existed on a totally different scale (size-wise) than what paleontologists expected and got used to finding amongst all the other Cambrian specimens from within the Burgess Shale.  As a result, it took close to 100 years for its various components to be recognized and put together into a single, cohesive type of organism: the anomalocaridid.

One of my colleagues here at Extinct (hello again, Derek!) calls this kind of lingering, widespread, and serious error a deep mistake in scientific practice (Turner 2007, pg. 90).  He describes this particular deep mistake—failing to properly interpret Anomalocaris specimens—as a result of scientists being “misled by observable analogues for prehistoric creatures” (ibid.).  Then Derek uses this problem—the potential for observable analogues to mislead in paleontological interpretation of unknown prehistoric creatures—as a way of reviving Larry Laudan’s well-known and influential pessimistic meta-induction for realism about reconstruction in historical sciences like paleontology.

Whether, how, and to what degree the pessimistic meta-induction works against historical realism (in contrast with realism about the experimental sciences) is a fascinating question, and one that deserves sustained attention in a future post.  But for now, I just want to close by noting the interesting and surprising way in which such deep mistakes—once we finally see and correct them—can supply unexpected and potentially otherwise-unobtainable information that can aid in ongoing scientific investigation.  Here’s what I’m proposing: that when we realize that we, or paleontologists, or whoever have made a deep mistake, this realization can—in addition to correcting the particular error—also be a way of alerting us to undetected presumptions and / or scotomas which led to the original error.

In the case of Anomalocaris, correcting the various reconstructive errors revealed not just a new, surprisingly large apex predator from the Cambrian; it also revealed certain prevalent assumptions about the way in which new discoveries were likely to resemble the old (this is Gould’s main point, I think, in Wonderful Life [1989]).  It further revealed scotomas of various magnitudes: such as the way in which repeatedly encountering specimens of a certain size can lull us into forgetting to consider potential reconstructions at other scales, or the way in which repeatedly encountering specimens of certain shapes can make it hard for us even to imagine what something radically different might look like.  In sum, it seems to me as if—at least some of the time, and in these sorts of ways—our deep mistakes might be deeply productive, and I think there is something really heartening about that.

Aside from their beauty, this is what I find so splendid about the mysterious Burgess specimens like Anomalocaris and Peytoia and Waptia—along with many other troublemakers from various locales that have and haven’t been figured out yet.  Paleontologists originally called Escumasia “a problematic organism” (Nitecki & Solem 1973) and Etacystis “a fossil of uncertain affinities” (Nitecki & Schram 1976).  Before it was (relatively) figured out, Anomalocaris was called “the enigmatic metazoan” (Conway Morris 1985), and even afterwards it was deemed “the largest Burgess oddball” (Gould 1989).  Opabinia has been called “another Burgess Shale conundrum” (Collins 1999).  And altogether—with characteristic Gouldian flair—the assorted cryptic finds from this Lagerstätte in British Columbia have been called “the Burgess ‘unclassifiables’” (Gould 1989).  Such specimens are simultaneously a source of great puzzlement and promise.  They don’t sparkle, but these fossils—I guess I’ll bow to tradition, and call them problematica—are absolutely splendid in their own way.



Collins, D. (1996), “The ‘Evolution’ of Anomalocaris and Its Classification in the Arthropod Class Dinocarida (nov.) and Order Radiodonta (nov.),” Journal of Paleontology 70(2): 280–293.

Conway Morris, S. (1985), “Cambrian Lagerstätten: Their Distribution and Significance,” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 311(1148): 49–65.

Conway Morris, S. (1998), The Crucible of Creation: The Burgess Shale and the Rise of Animals (Oxford: Oxford University Press).

Daley, A. C. & G. E. Budd (2010), “New Anomalocaridid Appendages from the Burgess Shale, Canada,” Paleontology 53(4): 721–738.

Gould, S. J. (1989), Wonderful Life: The Burgess Shale and the Nature of History (New York: W. W. Norton & Co).

Laudan, L. (1981), “A Confutation of Convergent Realism,” Philosophy of Science 48: 19–49.

Nitecki, M. H. & F. R. Schram (1976), “Etacystis communis, a Fossil of Uncertain Affinities from the Mazon Creek Fauna (Pennsylvanian of Illinois),” Journal of Paleontology 50(6): 1157–1161.

Nitecki, M. H. & A. Solem (1973), “A Problematic Organism from the Mazon Creek (Pennsylvanian of Illinois),” Journal of Paleontology 47(5): 903–907.

Turner, D. (2007), Making Prehistory: Historical Science and the Scientific Realism Debate (Cambridge: Cambridge University Press).

Van Roy, P., D. E. G. Briggs & R. R. Gaines (2015), “The Fezouata Fossils of Morocco; An Extraordinary Record of Marine Life in the Early Ordovician,” Journal of the Geological Society 172: 541–549.

Whittington, H. B. & D. E. G. Briggs (1985), “The Largest Cambrian Animal, Anomalocaris, Burgess Shale, British Columbia,” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 309(1141): 569–609.