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More Admissions of Cambrian Explosiveness

Evolution News

In these days of anti-ID “consensus,” don’t expect to find science journals publishing overt statements like, “Well, what do you know! Stephen Meyer and the intelligent design people were right!” Darwinian natural selection must remain omnipotent. Observational evidence, however, is more powerful than the language used to suppress it. Here are a couple of examples.

Rapid Arthropods

We reported two years about Marble Canyon, a remarkable Cambrian fossil deposit in British Columbia that rivals the famous Burgess Shale in significance. More extensive and detailed than its famous neighbor 26 miles to the northwest, Marble Canyon will likely provide years of discoveries to illuminate the Cambrian explosion. The site is of special interest because it was announced a year after Darwin’s Doubt (2013) was published.

Meet Tokummia, a creature found at Marble Canyon. The Calgary Sun calls it an “ancient arthropod with gnarly claws.” By all appearances, this four-inch animal was highly complex, possessing over 50 pairs of jointed legs, a shell, antennae, pincers, eyes, and mouth parts (implying a gut). Undoubtedly it was capable of sexual reproduction and partial metamorphosis, as are other arthropods. It is assigned a date of 508 million years old.

Jean-Bernard Caron, the discoverer of the Marble Canyon fossil trove (who also found a vertebrate fish there), with colleague Cédric Aria from the University of Toronto, studied 21 specimens of Tokummia. They tried to figure out where it fits in the evolutionary scheme. Writing in Nature, they conclude that it might have represented the start of the taxon Mandibulate (“biting things”). The Editor’s Summary offers hope that a gap has been partially filled:

Fossils from the famous 508-million-year-old Burgess Shale in Canada have been vital for shaping our understanding of the origin and early evolution of arthropods, the group of invertebrate animals recognized by their segmented bodies with jointed limbs and an exoskeleton. In recent years, research has found support for a single group of arthropods known as mandibulates that comprises insects, crustaceans and myriapods (centipedes and millipedes) but excludes chelicerates (spiders, scorpions and their allies). Few fossils have been found to illuminate the earliest mandibulates. Cédric Aria and Jean-Bernard Caron now show that this gap is partially filled by the arrival of the Burgess Shale fossil Tokummia katalepsis, whose anatomy allows the reconstruction of the anatomical and evolutionary history of this important animal group. [Emphasis added.]

It’s hard to find, however, more than mere suggestions that certain protrusions on the face of this animal might suffice to “partially” fill the gap. They present a theory story that modern mandibulates emerged from larval forms:

The presence of crustaceomorph traits in the Cambrian larvae of various clades basal to Mandibulata is reinterpreted as evidence for the existence of distinct ontogenetic niches among stem arthropods. Larvae would therefore have constituted an important source of morphological novelty during the Cambrian period, and, through heterochronic processes, may have contributed to the rapid acquisition of crown-group characters and thus to greater evolutionary rates during the early radiation of euarthropods.

Pause to understand what they are saying. This statement does nothing more than push the lucky mutations into the larva instead of the adult. Instead of the adult constituting “an important source of morphological novelty” (i.e., body luck), the larva becomes the source. Then, through “heterochronic [different-time] processes,” some things evolved more rapidly than others. Presto! You “greater evolutionary rates” in the Cambrian, speeding up the “acquisition” of arthropod traits. A more vacuous suggestion could hardly be concocted: basically, “some things happened, and some of them happened faster.” Now, watch how some things happened over and over:

The integration of larval taxa in the phylogeny (Extended Data Fig. 10 and Supplementary Discussion) suggests that morphological traits typically associated with crustaceans or their larvae (large labrum, segmented cephalic exopods, antennule-like frontalmost appendages) have occurred across multiple euarthropod clades (Cheiromorpha, Artiopoda, Pycnogonida) with non-mandibulate adult morphologies.

From there, they launch into full-bore storytelling mode. Putting the lucky mutations into the larvae open up wondrous possibilities:

This implies that crustacean-like characters appeared early in the evolution of euarthropods, as a result of adaptation to ecological niches specific to ontogenetic stages, and may have persisted across the ancestors of major clades before their paedomorphic appearance in adult mandibulates. Because ontogenetic niches create new characters upon which natural selection can act intraspecifically, the emergence of specialized larval forms may have constituted an important catalyst for the rapid evolution of euarthropods during the Cambrian period, and a notable source of morphological novelty for the first mandibulates.

Imagine that lucky mutations appeared in larvae, which exposed them to new “ecological niches” where natural selection could act. Those that stayed young-looking as adults (paedomorphs) “emerged” as new kinds of arthropods. That “emergence” triggered “rapid evolution.” This explanation is indistinguishable from magic. It should be dismissed as a non-scientific affirmation of presumptive Darwinian belief.

What’s more interesting for design advocates is their admission of “rapid evolution of euarthropods during the Cambrian period,” and “rapid acquisition of crown-group characters,” viz., the Cambrian explosion. You can’t hide an explosion in post-hoc distractions like “emergence” and “acquisition” and “arrival”. Like all the other Marble Canyon fossils, Tokummia appears in the rock record fully formed as a complex, successful animal.

Elsewhere in their paper, they admit to serious problems in the evolutionary story of arthropods, the most diverse and successful animals in all of nature:

  • Retracing the evolutionary history of arthropods has been one of the greatest challenges in biology.
  • Protocaridids are retrieved with Canadaspis and Odaraia (in Hymenocarina, emended) as part of an expanded mandibulate clade, refuting the idea that these problematic bivalved taxa, as well as other related forms, are representatives of the basalmost
  • The origin of the mandibulate body plan, …which encompasses myriapods, crustaceans and hexapods, has remained poorly documented.
  • These results, which had been influenced by an interpretation of the heads of large bivalved Cambrian arthropods as two-segmented, have fuelled a number of macroevolutionary hypotheses about the emergence of arthropod body plans and the evolution of frontal appendages, most notably with the objective to resolve the arthropod head problem.
  • The only fossil taxa put forward as the earliest crown mandibulates have been euthycarcinoids, historically problematic Palaeozoic centipede-like arthropods with multisegmented legs.
  • How the morphological characters and anatomies of the most successful animal body plan came into place has thus remained largely unknown.

(Regarding the “arthropod head problem,” see here.)

It’s clear that putting lucky mutations into larvae is not going to solve any of these problems. Meyer’s book stands unanswered.

Unrelated Ediacarans

What about earlier Ediacaran organisms? Can they be considered ancestral? Meyer dealt with one called Parvancorina on page 89, refuting suggestions that it had superficial resemblances to an ancestral trilobite-like body plan.

A new paper in Nature Scientific Reports focuses on another topic, a suggestion that Parvancorina displayed an early instance of rheotaxis (active alignment with a fluid current). The evidence, however, is circumstantial and admittedly open to interpretation. The authors do not present any evidence of organs, genes, or tissues capable of controlling movement.

Of more interest to us is their affirmation of Meyer’s view, that the Ediacaran animals bear no ancestral relationship with the Cambrian animals. Here, in regard to one of the leading candidates of such a relationship, these authors say, “Apart from possessing a bilaterally symmetrical body, there are no unequivocal morphological characters to support placement of Parvancorina within the Euarthropoda or even the Bilateria.”

These papers show that four years after Meyer’s book, and 13 years after his paper in the Smithsonian journal, evolutionists are still failing to come up with plausible evolutionary hypotheses for the sudden appearance of the Cambrian animals. As paleontologists hold these stunning fossils in their hands, they need to stop the storytelling about magic appearances, the desperate attempts to force-fit the fossils into mythical evolutionary trees, and take seriously Meyer’s proposal that intelligent design provides the best explanation.

Photo: Parvancorina fossils, Australia, compared with a size of a coin, by EOL Learning and Education Group [CC BY 2.0], via Wikimedia Commons.