The Burgess Shale fauna was around a lot longer than we thought

We all know the Burgess Shale fauna from Steve Gould’s book Wonderful Life, which described it as a group of fantastic animals lacking any affinity with modern-day animals.  Gould suggested that they went extinct without issue in the Cambrian, about 505 million years ago, but could easily have given rise to modern animals if the “tape of life” had been rewound.

Later work by Simon Conway Morris and others, of course, showed that the Burgess Shale fauna, although weird, did have affinities with modern groups like arthropods, lobopods (Onychophora) and annelids. Indeed, some of the fauna could have been ancestors of modern groups, although there still seem to be bizarre forms—called the “problematica”—without affinities to modern animals.

Related to the Burgess Shale fauna is the even better collection of animals in the Chengjiang Fauna of China, also in the Cambrian but earlier—about 525 mya.  Here we see clear representatives of echinoderms, arthropods, annelids, sponges, and even what seems to be a chordate.

The Burgess Shale fauna did disappear from the fossil record about 505 mya.  Maybe they suddenly went extinct, or perhaps they lived on but just weren’t preserved, since many of them were soft bodied and wouldn’t have fossilized easily. The next major fauna we see is in the Ordovician period (488-443 million years ago), whose beginning shows mostly shelly or hard-bodied creatures: trilobites, echinoderms, gastropods, brachiopods, and, hard-shelled arthropods like barnacles.  What happened to the Burgess shale animals?

A new paper in Nature by Peter Van Roy et al. gives the answer: those animals were there all along.  They didn’t go extinct in the Cambrian, as long thought, but hung on for at least twenty million years more, perhaps giving rise to more forms that were ancestral to modern life.  Their disappearance in the later Cambrian reflected not extinction but poor preservation.

Van Roy et al. describe a remarkably preserved fauna from a valley in southeastern Morocco (the “lower Fezouata Formation”) that dates to the lower Ordovician.  Remarkably, the Fezouata fauna contains not only Burgess-Shale type creatures (Fig. 1), but also later and typical Ordovician creatures (Fig. 2)  Clearly, the Burgess fauna persisted for millions of years after they were supposed to have gone extinct.

Here are figures from the Nature paper showing both the Burgess fauna and more typical Ordovician fauna.  They’re lovely fossils, colored from the oxidation of the pyrite that infused them:

Fig. 1.  Burgess-Shale type organisms from the Fezouata fauna.  a, b Demosphonges; c, annelid; d, halkieriid?; e), armored lobopod?; f, g, and h, arthropods; i, arthopod appendage.

Fig. 2.  Ordovician elements of the Fezouata fauna.  a and b, arthropods; c, stalked barnacle?, d, Xiphoshuran (chilcerate resembling modern horseshoe crabs); e, another Xiphosuran.

Now this finding is not “revolutionary” in the sense of telling us more about the ancestry of modern phyla.  That revolution occurred back when Simon Conway Morris et al. realized that, contrary to Gould’s—and Conway Morris’s own initial— suggestion, the Burgess creatures were not one-offs with no affinities to modern life, but belonged to extant groups.  What the new finds show is simply that there wasn’t a mass extinction that destroyed Cambrian life, but a more gradual replacement that lasted millions of years. And it leaves the Burgess Shale creatures as good candidates for ancestors (or at least relatives) of many modern groups.

Fig. 3.  Workers in the Draa Valley.  Left to right:  Jakob Vinther, Peter Van Roy, and Derek Briggs. Photo copyright Patrick Orr.

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P. Van Roy, P. J. Orr, J. P. Botting, L. A. Muir, Jacob Vinther, B. Lefebvre, K. el Hariri, and D. E. G. Briggs.  2010.  Ordovician faunas of Burgess Shale type.  Nature 465:215-218.

17 Comments

  1. Florian M
    Posted May 13, 2010 at 1:36 pm | Permalink

    These fossils are great, but Jerry correct me if I’m wrong: If I remember Gould’s book right (some time ago that I read it), it was mainly Whittington/Briggs/Morris who actually showed that contrary to Walcott’s initial classification a lot of the Burgess shale fossils could NOT be grouped with extant phyla (while some still could)…

    • whyevolutionistrue
      Posted May 13, 2010 at 1:39 pm | Permalink

      Indeed; I left that part of the story out. Gould accepted the initial assessment of the animals by WBM as not belonging to modern phyla, and popularized that. Later, Conway Morris did find affinities to modern phyla, and changed his mind. But then C-M attacked Gould for saying in Wonderful Life what Conway Morris had originally said himself!

      Here is the published exchange between Gould and Conway Morris on this, in which Gould, I think, comes off as the winner. Here’s where Gould does the most damage:

      (I must also ask readers’ indulgence for a paragraph that Robert’s Rules of Order would call a “point of personal privilege”: Conway Morris has chosen, less in this article than in his book, to be imperiously dismissive of my ideas, as if no sensible or experienced person could ever advocate such prejudiced nonsense. But he never tells us that Wonderful Life treats him, in his radical days as a graduate student, as an intellectual hero. I developed my views on contingency and the expanded range of Burgess diversity directly from Conway Morris’s work and explicit claims, and I both acknowledged my debt and praised him unstintingly in my book. I even suggested—although it’s surely none of my business—that Whittington, Conway Morris, and Briggs should receive the Nobel Prize for their exemplary work. Conway Morris is certainly free to change his mind, as he has done. Indeed, such flexibility can only be viewed as admirable in science. But it is a bit unseemly never to state that you once held radically different opinions and to brand as benighted, in some obvious and permanent sense, a colleague who holds the views you once espoused. I do therefore object to Conway Morris’s strategy of working out his own ontogenetic issues at my expense. Lest readers think I am being either peevish or idiosyncratic, may I cite our British colleague Richard Fortey, who generally sides with Conway Morris on the scientific debate, from the October 10 issue of the London Review of Books: “What is peculiar about [The Crucible of Creation] is that the casual reader…would never guess from it that Conway Morris ever entertained views different from those he now holds.…It is this selective amnesia which accounts for the passion of his disillusion with Gould, for Gould has preserved in the print of a best-seller ideas that Conway Morris…now repudiates. He is furious that his past misinterpretations have been so eloquently placed on record.…The way Conway Morris goes about biting the hand that once fed him would make a shoal of piranha seem decorous.”)

  2. Thanny
    Posted May 13, 2010 at 2:21 pm | Permalink

    Now all we need to do is wait for someone to find a Burgess Shale-like deposit for the late Precambrian, so we can see the (probably) tiny and shell-free ancestors of Cambrian fauna, evolving at a quite normal pace, and finally be shot of the Cambrian “explosion” notion.

  3. NewEnglandBob
    Posted May 13, 2010 at 2:46 pm | Permalink

    What, no 475 mya movies of the fauna? 😉

    • Notagod
      Posted May 13, 2010 at 6:17 pm | Permalink

      Sadly enough, only the movies from that time that depict the christian christ-god-son-incestuousfather thingy exist. It is likely that the christian burned all other films and pictures. 😉

    • Matthew Cobb
      Posted May 14, 2010 at 2:44 am | Permalink

      Oh yes, Bob! Copy the link below and you can see a very pretty computer-generated video of the Burgess Shale fauna, complete with many relatives of the animals just reported from 40My later, in Morocco. Towards the end, you’ll see Anomalocaris, a load of scared trilobites and Marrella, related to the animal in Figure 1g above. NB the file is rather large, so you need to be patient if you’re on a slow internet connection. And if you want to see the whole movie, go to the Field Museum in Jerry’s Chicago!

      http://www.phleschbubble.com/album/movies/cambrian_movie.html

    • NewEnglandBob
      Posted May 14, 2010 at 4:01 am | Permalink

      Thanks, Matthew. That is a great CG video.

      “…Jerry’s Chicago” – now he has taken over the entire city??? I knew these New Atheist scientists had designs on taking over the world! Give them a card and they take a city.

      • Torbjörn Larsson, OM
        Posted May 14, 2010 at 5:32 am | Permalink

        Ditto re video.

        PS. Shouldn’t that be “Discuss cards and how they are necessary to explain the creation and management of cities as discussed in the “Book of Cards – Old and New collection”, and they tell you they don’t believe in cards; then they take the city”?

  4. Kirth Gersen
    Posted May 13, 2010 at 3:20 pm | Permalink

    I’m just holding my breath, waiting for the yellow journalism headlines of “Evolutionists Yet Again Admit They Were Wrong All Along!”

  5. Posted May 13, 2010 at 3:27 pm | Permalink

    “new paper in Nature” link does not link to the new paper in Nature.

  6. Torbjörn Larsson, OM
    Posted May 13, 2010 at 4:05 pm | Permalink

    Now I’m impressed all around.

    First, that Wikipedia was on top of this.

    Second, that the diversity distribution (which I eagerly await an update on, lest the paper did one; paywall sucks) goes up for another ~ 20 My (looking at a diagram of the purported productive periods of the whole Fezouata Formation). At least on the one side; hope Thanny’s scenario will play out.

    Third, that those layers are ~ 10 times thicker than the Burgess Shale, reflecting the longer period covered. That must be a haven for curious biologists.

  7. Posted May 13, 2010 at 4:43 pm | Permalink

    Though many of Gould’s phylogenetic assessments (or rather the initial assessments of “WBM” that he relied upon) may be in error, I’m not certain that the central thesis of Wonderful Life must necessarily be scrapped. Gould admitted that some elements of the Burgess Fauna had affinities with living phyla indeed “christmas tree” model with a handful of lineages persisting beyond the Cambrian depended upon it. Gould makes this point eloquently in the epilogue of his book using the Burgess Fauna’s celebrated putative stem-chordate Pikaia, though ironically this taxonomic assignment has been questioned in the past by Nick Butterfield, I’m not sure where things stand today.

    This week’s undercelebrated description of a Cambrian Bryozoan means that all major Phyla were present by the latest Cambrian. Therefore these Ordovician oddballs do represent late holdouts of apparently stable morphotypes that persisted for millions of years after diverging from extant lineages and then vanished without leaving any descendants. This extinction obviously occurred later than we thought, and it might have occurred more gradually, but neither of those facts really contradict Gould’s picture of a modern fauna that is far less disparate at the “bauplane” level than it was in early Paleozoic.

    Of course, there are many other criticisms that can be leveled at this scenario: taxonomic practices and geologic/preservational biases being among the more serious. But I think Gould probably would have seen the Fezouata fauna as lending support to his vision of this history of life, albeit requiring a chronological revision.

  8. articulett
    Posted May 13, 2010 at 5:40 pm | Permalink

    I’m confused… the link to the “new paper in Nature” is a 1999 article in Science News.

    • whyevolutionistrue
      Posted May 13, 2010 at 5:48 pm | Permalink

      Fixed. Thanks!

  9. theshortearedowl
    Posted May 14, 2010 at 10:09 am | Permalink

    I want Fig. 1-g on a t-shirt.

    • Matthew Cobb
      Posted May 14, 2010 at 10:26 am | Permalink

      Me too! Love that Marrellomorph!

    • Posted May 14, 2010 at 11:53 am | Permalink

      Me three — I’m thinking about getting it in ink to join my Marrella splendens. Though perhaps it would be best to wait until it is formally described.


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