• A Survey of Precambrian Animals

    Over the last few days, I’ve been doing some research into Precambrian animals.  This is a direct effort to refute the claims of Meyer that all these forms appeared in the Cambrian explosion.  This is the status of my efforts to date.

    Age (mya) Reference Event Notes
    3,500 Schopf 1993 microfossils resembling cyanobacteria (Australia)  
    2,100 Han & Runnegar 1992 Algal cysts with cells largers than any known in modern prokaryotes  
    1,500 Javaux et al 2001 complex specrical and spinose forms of eukaryotes  
    1,100   red and green algae appeared  
    1,000 Wray 1996 Time of divergence of inverts and verts; molecular data A literal reading of the fossil record suggests that the animal phyla diverged in an ‘explosion’ near the beginning of the Cambrian period. Calibrated rates of molecular sequence divergence were used to test this hypothesis. Seven independent data sets suggest that invertebrates diverged from chordates about a billion years ago, about twice as long ago as the Cambrian. Protosomes apparently diverged from chordates well before echinoderms, which suggests a prolonged radiation of animal phyla. These conclusions apply specifically to divergence times among phyla; the morphological features that characterize modern animal pbody plans, such as skeletons and coeloms, may have evolved later.
    635-580 Budd, 2007 Doushanto Fm. The significance of these dates is that all of the Doushantuo fossils would predate the oldest of the famous Ediacaran fossils such as Dickinsonia, and thus would provide an independent record of the animal life during a period of time that no large body or trace fossils are known. Indeed, the overlying Dengying Fm does yield Ediacaran-type fossils, which could be said to support this contention.
    630 Budd, 2007 Stem Group Animals Present  
    600   no multicellular prior to this  
    590 Xiao et al 1998, 2002 brown algae; highly diverse multicellular algae  
    590 Xiao et al 1998, 2002 probably microscopic embryos in stages of cleavage with 2, 4, or 8 cells Ediacaran
    590 Li et al 1998 sponges with monaxonal spicules and preserved soft tissue  
    590 Chen et al 2008 Bilaterian fossils appear Furthermore, the organization of these fossils, taken together with their provenance, indicates that the genetic tool kit and pattern formation mechanisms required for bilaterian development had already evolved by Doushantuo times, long before the Cambrian. Therefore, the diversification of body plans in the Early Cambrian followed from the varied deplument of these mechanisms once conditions permitted, not from their sudden appearance at od just before the Cambrian boundary.
    575 Narbonne & Gehling 2002 Mackenzie Mountains, Canada: organisms in disc, trianle, and fronds  
    late Precam Fedonkin 1997 Kimbrella – a bilateral mollusc-like organism http://www.nature.com/nature/journal/v388/n6645/full/388868a0.html
    541   Cambrian Period Begins  
    505 Caron 2006   Odontogriphus omalus was originally described as a problematic non-biomineralized lophophorate organism. Here we reinterpret Odontogriphus based on 189 new specimens including numerous exceptionally well-preserved individuals from the Burgess Shale collections of the Royal Ontario Museum. This additional material provides compelling evidence that the feeding apparatus in Odontogriphus is a radula of molluscan architecture comprising two primary bipartite tooth rows attached to a radular membrane and showing replacement by posterior addition. Further characters supporting molluscan affinity include a broad foot bordered by numerous ctenidia located in a mantle groove and a stiffened cuticular dorsum. Odontogriphus has a radula similar to Wiwaxia corrugata but lacks a scleritome. We interpret these animals to be members of an early stem-group mollusc lineage that likely originated in the Neoproterozoic Ediacaran Period, providing support for the retention of a biomat-based grazing community from the late Precambrian until at least the Middle Cambrian.

     

    Notice that last entry “Cambrian period begins”.  All of the stuff on this list is Pre-Cambrian.  We have the presence of bilateral organisms.  Indeed according to the Wray paper, we have the majority of the animal forms already present.  That being said, specific features may have appeared later, but the genetic plan for those phyla are already present.

    The Wray paper is particularly interesting as it also opens with a brief discussion of Darwin and how the appearance of the sudden development of animal fossils posed a problem for natural selection.  The paper describes the use of molecular divergence rates for a large number of taxa.  They used seven different genes for this process and the results are pretty interesting.

    The existence of an extended but cryptic Precambrian history of metazoans also has some interesting implications for understanding the origin and diversification of animal body architecture. In particular, the rapid appearance of diverse skeletonized taxa in the fossil record during the middle Early Cambrian may reflect an exceptional period of simultaneous morphological innovation within distinct lineages rather than a rapid branching of phyla. It has long seemed likely, for example, that mineralized skeletons evolved independently in several phyla at this time (39). It is unlikely, however,that all “body plan” features evolved during the Cambrian. A cephalized, bilaterally symmetrical body composed of three germ layers predates the protostome-deuterostome split (28, 40, 41) and thus probably evolved much earlier than is generally recognized. Coeloms are shared by the two deuterostome phyla we examined and may predate the Cambrian by several hundred million years (the coeloms of protostomes may have an independent origin, and dating their appearance will require more
    information about the divergence times of the various protostome phyla) .

    Four of the major ‘innovations’ in body plans are in place well before the Cambrian.  Radial anatomy, bilateral anatomy (with a specific head and rear), three germ-layers (we have three germ layers, it’s basically a difference in cell types that make up the outside layer, the inside tube (intestines, stomach , etc) and everything between those two layers (in humans things like the heart, skeleton, etc), and coeloms (a fluid-filled body cavity between the intestines and the body wall of some higher metazoans) were present long before the Cambrian.

    We also have molluscs (Caron 2006) and cnidarians (Chen 2002) well before the Cambrian.  We also have segmented organisms (Valentine 1989) and worms.

    So, what’s Meyer’s issue here? Aside from the fact that there’s only four of these articles listed as references in his book (they are bolded below) and he draws completely opposite conclusions from them than the authors do.

    Meyer’s book, even the Kindle edition, isn’t crosslinked from references back to text, so we’ll just have to see what he says when we find them.

    A final note is that this isn’t even close to all the material on precambrian organisms.  This is just a sample… i.e. what was available in PDF for free or via Science.

    We’ll talk about Meyer’s “diagrams” in the next installment.  Suffice to say that he must not have actually read the papers he referenced in his book, because his diagrams are nothing like what is actually in the papers.

    _______________________________

    References:

    Battison, Leila, and Martin D. Brasier. “Remarkably preserved prokaryote and eukaryote microfossils within 1Ga-old lake phosphates of the Torridon Group, NW Scotland.” Precambrian Research, 2012. Available: http://dx.doi.org/10.1016/j.precamres.2011.12.012.

     

    Budd, Graham . “The earliest fossil record of the animals and its significance.” Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 26 Apr. 2008. Available: http://www.ncbi.nlm.nih.gov/pubmed/18192192.

     

    Caron, Jean-Bernard et al. “A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale.” Nature, 12 Jul. 2006. Available: http://dx.doi.org/10.1038/nature04894.

    Chen, Jun-Yuan et al. “Precambrian animal life: probable developmental and adult cnidarian forms from Southwest China.” Developmental biology, 31 Jul. 2002. Available: http://www.ncbi.nlm.nih.gov/pubmed/12142030.

     

    Chen, Jun-Yuan et al. “Small bilaterian fossils from 40 to 55 million years before the cambrian.” Science (New York, N.Y.), 8 Jul. 2004.

     

    Cunningham, John et al. “Distinguishing geology from biology in the Ediacaran Doushantuo biota relaxes constraints on the timing of the origin of bilaterians.” Proceedings. Biological sciences / The Royal Society, 21 Jun. 2012.

     

    Dzik, Jerzy. “Anatomical information content in the ediacaran fossils and their possible zoological affinities.” Integrative and comparative biology, 31 Jan. 2003.

     

    ———. “Possible ctenophoran affinities of the Precambrian ‘sea-pen’ Rangea.” Journal of morphology, 31 May. 2002. Available: http://www.ncbi.nlm.nih.gov/pubmed/11948678.

     

    Gehling, James G, and J Keith Rigby. “Long expected sponges from the Neoproterozoic Ediacara fauna of South Australia.” Journal of Paleontology. JSTOR, 1996. Available: http://www.jstor.org/stable/10.2307/1306383.

     

    Holmer, Lars E., Christian B. Skovsted, and Alwyn Williams. “A Stem Group Brachiopod From The Lower Cambrian: Support For A Micrina (Halkieriid) Ancestry.” Palaeontology, 2002.

     

    Peterson, K, M McPeek, and D Evans. “Tempo and mode of early animal evolution: inferences from rocks, Hox, and molecular clocks”, 2005. Available: http://www.psjournals.org/doi/abs/10.1666/0094-8373(2005)031%5B0036%3ATAMOEA%5D2.0.CO%3B2.

     

    Schopf, J . “Microfossils of the Early Archean Apex chert: new evidence of the antiquity of life.” Science (New York, N.Y.), 29 Apr. 1993. Available: http://www.ncbi.nlm.nih.gov/pubmed/11539831.

     

    Shu, D-G et al. “Lower Cambrian vendobionts from China and early diploblast evolution.” Science (New York, N.Y.), 4 May. 2006. Available: http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=16675697.

     

    Shu, Degan et al. “A new species of yunnanozoan with implications for deuterostome evolution.” Science (New York, N.Y.), 27 Feb. 2003. Available: http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=12610301.

     

    Stephen, Dornbos et al. “Precambrian animal life: Taphonomy of phosphatized metazoan embryos from southwest China.” Lethaia, 2005.

     

    Valentine, J . “Bilaterians of the Precambrian-Cambrian transition and the annelid-arthropod relationship.” Proceedings of the National Academy of Sciences of the United States of America, 31 Mar. 1989. Available: http://www.pnas.org/cgi/pmidlookup?view=long&pmid=16594022.

     

    ———. “Late Precambrian bilaterians: grades and clades.” Proceedings of the National Academy of Sciences of the United States of America, 18 Jul. 1994. Available: http://www.pnas.org/cgi/pmidlookup?view=long&pmid=8041693.

     

    Wray, G, J Levinton, and L Shapiro. “Molecular evidence for deep Precambrian divergences among metazoan phyla”, 1996. Available: http://www.sciencemag.org/content/274/5287/568.short.

     

    Xianguang, H, D Siveter, and M Williams…. “Appendages of the arthropod Kunmingella from the early Cambrian of China: its bearing on the systematic position of the Bradoriida and the fossil record of the  …”, 1996. Available: http://www.jstor.org/stable/10.2307/56180.

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    Article by: Smilodon's Retreat

    • Nicholas J. Matzke

      Hiya! Good post, but it’s a little hazardous in this topic to take stuff from different decades and stick it together. The molecular dating, the geological dating, and the interpretation of fossils have each changed substantially between the earliest efforts and updated work with improved data and methods.

      My sense of things is:

      – The developing embryo fossils in the Doushantuo formation are pretty well-accepted as at least metazoan embryos of sponge grade, but the larger bilaterians alleged by Chen et al. in the Doushantuo have been strongly disputed by Budd and others as geological artifacts.

      – Kimberella is now well-accepted to have bilaterian traits, and could be a mollusc, but it could also be on the stem below molluscs, or even on the stem below crown bilaterians.

      – The molecular dating in the 1990s used very simple “strict clock”
      models and calibrated the clock using fossils without much consideration
      of the uncertainty in moving from the dates of fossil specimens, to the
      dates of nodes on the tree. The number of genes doesn’t matter very much, the determining factor in the dates one gets is the fossil calibrations one uses. With relaxed-clock models, more & better fossil calibrations, etc., the dates of the bilaterian crown, the deuterostome crown, and the “phyla” crowns have come much closer to the Cambrian, perhaps 50-100 my before the Cambrian for the deepest animal nodes. Many of the crown phyla divergence times might even be in the Cambrian. E.g., the vertebrate-cephalochordate divergence might well be in the Cambrian, certainly the earliest claimed “vertebrates”, even if they technically are on the vertebrate branch, look a lot more like lancelets than than like fish.

      • SmilodonsRetreat

        Thanks Nick. I’m stilling learning all this deep research stuff. Usually, I pick one paper apart, now I’m trying to keep 15-20 running in my head. Not easy.

        Even with your specifics the general seems to remain, that body plans and major phyla have developed prior to the Cambrian explosion. At least, it seems reasonable to me.*

        * That and $4.50 will get you a cup of coffee at Starbucks.

    • Christine Janis

      Small comment. The brain is derived from ectoderm (via infolding of the neural tube), not mesoderm. Otherwise, great post

      • SmilodonsRetreat

        Fixed. Thanks

    • Frankly, both Nick and you are both “whoosh” over my head. But that, itself, is a criticism of Meyer. He is not trying, as a good science populizer does, to simplify concepts to make it easier for the uninitiated to understand complex things, he is ignoring the complexities in order to make the uninitiated think they are simple.

      We’ll talk about Meyer’s “diagrams” in the next installment.

      Looking through the book, I was struck at how amateurish many of the illustrations are. I can imagine “Research Director” Casey Luskin late at night hunched over actual scientific books and papers at some library, tracing paper in hand, tip of his tongue sticking out of the corner of his mouth, trying to copy some illustration. (Indeed, he is given partial credit for two of the worst in Ch. 11).

      • SmilodonsRetreat

        That’s a good point, I probably do need to tone it down. And what’s going on, but that’s a book in and of itself… one I’m not qualified to write.

        RE: the diagrams.

        I’d be embarrassed to publish a book like this with what appears to be hand drawn diagrams. Especially ones that are so obviously NOT like what appear in the scientific literature that Meyer is supposed to be referencing.

        Right now, I’m having an issue with images uploading into WordPress, so I’m on hold until that gets resolved. Hopefully soon.

        • I think it is ok for you to lay out the complexities, in the nature of a “sidebar” separate from the actual review, especially when you have commenters like Nick and Christine to help with the technicalities. The tricky part is, getting back to the review, to give a good balance between laying out the evidence for the history without drowning the lay person in scientific jargon and minutia. We (cough) laity need 1) a broad overview of the evidence and 2) references where we can find the evidence if we feel moved to delve deeper.

      • Nicholas J. Matzke

        There is some Discovery Institute artist they use on these projects, you can see the same style in other books, e.g. some of Jonathan Wells’s stuff. Jody Sjogren? I forget.

        What’s weird is how they accumulate tidbits over the decades — the “phylogenetic lawn” version of the Cambrian phyla, the California Academy of Sciences display from 1990 that no one except the ID movement remembers — and then toss them together as croutons in their word salad…

        • The person most often credited for the diagrams is Ray Braun, usually with the phrase “based on information from …” In short, without obtaining the right to reproduce someone else’s diagram.

    • Nicholas J. Matzke

      Also, the Odontogriphus specimens are in the Burgess shale, which has a date of 505 Ma (Middle Cambrian), not 555 Ma (Precambrian). Its lineage might have diverged back in the Precambrian, but that’s a different thing than the date of the fossil specimens.

      Odontogriphus
      Odontogriphus
      Odontogriphus
      Odontogriphus

      • Nicholas J. Matzke

        LOL now I guess I know where “Odontogriphus” went when I was trying to paste it and it wasn’t showing up…

    • GubbaBumpkin

      All your references are about the fossils themselves. There are a couple global chemical changes which are also relevant. The rise of an oxygenated atmosphere is one, a change in sea conditions which may have favoured the rise of mineralized body parts is another. The timing of these two changes meshes with the type of fossils found in different periods.

      • SmilodonsRetreat

        I saw a little bit about that. Do you have any references?

        • Nicholas J. Matzke

          The Marshall 2006 paper and Erwin & Valentine book review these pretty well

    • Christine Janis

      “There are a couple global chemical changes which are also relevant. The
      rise of an oxygenated atmosphere is one, a change in sea conditions
      which may have favoured the rise of mineralized body parts is another.
      The timing of these two changes meshes with the type of fossils found in
      different periods.”

      Which, as I have pointed out many times on the Amazon reviews (at least the first one) are nowhere to be found in Meyer’s book.

      • Christine Janis

        I mean the first point about oxygen, not the first Amazon review!

    • Christine Janis

      Hey, I’m really looking forwards to the next posting —- don’t disappoint us!

    • This is some impressive (& V’ Interesting) stuff, i look forward to your next post. I’ve long felt that due to the timescales involved the phrase “Cambrian Explosion” could easily turn out to be a bit of a misnomer as imo it’s likely there are many earlier intermediates that may never be found in any Fossil record & genetics is limited by (as i already said) how long ago it all happened.