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Let’s Help “Professor Dave” Understand the Precambrian

Namacalathus and Cloudina fossils
Photo: Namacalathus and Cloudina fossils, collection of Redpath Museum, McGill University, by Daderot / CC0, via Wikimedia.

I have been responding to a video attack (Farina 2022) on Stephen Meyer and Darwin’s Doubt by popular YouTuber Dave Farina, aka “Professor Dave.” We have much to teach the non-professor, and I trust that he is grateful for the education being rendered to him here. This is the fourth post in my series. Find the earlier installments here, here, and here. I have inserted timecodes throughout to make it easier to track with this individual’s video.

[TC 25:38] Farina concludes that at this point it would be completely ridiculous to even imply that there are no animals in the Precambrian. Well, as we have already seen in this series, Farina is wrong for three reasons:

  1. Dr. Meyer explicitly acknowledges the existence of Precambrian animals, which alone makes Farina’s rant totally fallacious. He’s attacking Meyer for a claim Meyer did not make.
  2. Most alleged Precambrian animals are highly disputed among mainstream experts, and many of those scholars indeed think that there simply were no animals in the Precambrian (e.g., Daley et al. 2018).
  3. Even if some relatives of sponges, cnidarians, stem (eu)metazoans, and maybe even stem bilaterians should be present in the Ediacaran, this would do absolutely nothing to explain the sudden appearance of the many different bilaterian animal body plans in the Cambrian Explosion. They do appear as if out of nowhere, and that is not just a claim by Stephen Meyer. Here is what the great apostle of Darwinism, Richard Dawkins, has said: “The Cambrian strata of rocks, vintage about 600 million years, are the oldest in which we find most of the major invertebrate groups. And we find many of them already in an advanced state of evolution, the very first time they appear. It is as though they were just planted there, without any evolutionary history” (Dawkins 1986: 229; repeated by Dawkins 2009: 147–148, who complained about the quote mining of this sentence without revoking its message).

[TC 25:57] Farina also claims that Meyer must have been aware of all the papers he mentioned, which is absurd as almost all of them were published years after Meyer’s book Darwin’s Doubt. Thus, even if those claims for Ediacaran animals were correct, which they most likely are not, Meyer can hardly be faulted for not being able to have clairvoyance into future research. Everything he said was well supported by mainstream up-to-date science at the time of the writing his book, and it still is well supported today. To say that Meyer tried to hide the existence of Ediacaran animals is ludicrous, as he discussed several candidates known at that time like Kimberella and the Doushantuo fossils and even acknowledges their status as Ediacaran animals, which in my view may have been far too generous (Bechly 2020c, 2020d). In my article on the myth of Precambrian sponges (Bechly 2020c) I went through all the literature on the alleged Doushantuo animal embryos and showed that they are not sponges according to most experts (also see my earlier discussion of the Doushantuo fossils).

[TC 26:14] Farina’s next claim is based on Wood et al. (2019). He says that the Ediacaran fossils exhibit a gradual stepwise evolution of animals, and suggests a progression from embryos, to soft bodied, to organic walled, to biomineralized SSF, to trace fossils documenting a “wormworld.” Let’s look at these alleged evolutionary steps:

We already addressed the alleged embryos, so what about the other points such as the Small Shelly Fauna (SSF) and the trace fossil record (wormworld)?

Small Shelly Fauna to the Rescue?

Does the Small Shelly Fauna (SSF) really help to solve the problem of the Cambrian Explosion? Farina is not the first critic of Meyer’s book to mention the SSF as alleged evidence for a smooth transition from the Ediacaran to the Cambrian fauna (Marshall 2013, Matzke 2013). This critique has been addressed before (Luskin 2015, Meyer 2015). By the way: Meyer was not at all oblivious of the SSF and even briefly commented on this issue in a footnote of his book (footnote 39 of chapter 4). Anyway, the claim that the SSF establishes some kind of evolutionary continuity between the Ediacaran and the Cambrian Explosion is based on a fallacy of equivocation. Why? Because there are two distinct types of small shelly faunas that are unrelated except for the name. The first type is the Ediacaran small shelly fauna, which mainly consists of the three taxa Cloudina, Namacalathus, and Namapoikia. I discussed the doubtful animal affinity of these three genera in several prior articles (Bechly 2020a, 2020c, 2020e, 2020f, 2021a, 2021b). The second type is the Lower Cambrian Small Shelly Fauna (SSF) proper, which was most prominent in the Cambrian Stage 2 or Tommotian. This SSF is generally considered as index fossils for the beginning of the Cambrian period. It simply consists of fragments from exoskeletons and shells of the well-known Cambrian animal phyla. These two faunas are distinct and neither overlap nor grade into each other. The only elements of the Cambrian SSF that are very rarely found in the terminal Ediacaran, right at the border to the Cambrian, are the problematic protoconodont Protohertzina and the likewise problematic angustiochreids Cambrotubulus and Anabarites (Zhu et al. 2017) The latter have been either considered as diploblastic-grade metazoans similar to cnidarians (Kouchinsky et al. 2009), or as late survivors of the Ediacaran clade Trilobozoa (Val’kov 1987), and thus are not closely related or ancestral to the Cambrian bilaterian animal phyla. At best, terminal Ediacaran small shelly fossils like Protohertzina could suggest a slightly earlier onset of the Cambrian Explosion, but they do not establish any kind of evolutionary continuity with the genuine Ediacaran small shelly fauna.

Farina quotes Erwin et al. (2011) on the SSF issue, but fails to mention that these authors acknowledge on the very same page, which he shows in screenshot, that “although Ediacaran phosphate deposits are common, they lack SSF, suggesting that bilaterian clades acquired skeletons during the Cambrian.” Does anyone need further proof that Farina is not to be relied upon?

Turning to Trace Fossils

Let’s look at whether the trace fossil record changes the picture. Ediacaran trace fossils, which often look like the creeping traces of worms or the crawling traces of polychaetes or even arthropods, indeed represented an interesting and valid argument for the existence of Ediacaran bilaterian animals until a few years ago. Then a seminal new study by Mariotti et al. (2016) changed everything. The scientists did some interesting experiments based on the fact that the Ediacaran biota were characterized by microbial mats covering the sea floor. Mariotti et al. cultivated such microbial mats in aquariums, stirred them up, and looked at what kind of artifacts are formed by the settling mats. Lo and behold, all of the complex Ediacaran traces known at that time could be identically reproduced as artifacts of such microbial mats. This refuted most of the Precambrian ichnofossil record as invalid or at least unconvincing evidence for animal activity. Another crucial argument was presented by Matz (2008), based on the discovery that bilaterian-like traces are today produced on the deep-seafloor by giant protists, so that similar Ediacaran traces cannot be considered evidence for metazoan activity either. Nevertheless, some new evidence for Ediacaran traces has been presented since then (and after publication of Meyer’s book). I critically discussed those traces attributed to Dickinsonia and Kimberella in previous articles (Bechly 2018c, Bechly 2020g), and I also discussed the putative bilaterians Yilingia (Chen et al. 2019) and Ikaria (Evans et al. 2020) and their associated trace fossils (Evolution News 2019, Bechly 2020b; also see Watson 2020). Other prominent examples with seemingly convincing evidence are the studies by Oji et al. (2018), Chen et al. 2013, Chen et al. (2018), Chen et al. (2019), and Evans et al. (2020), who all described trace fossils that strongly suggest a bilaterian animal as producer.

However, there are multiple problems with the latter studies, of which the most striking is that none of them even mentions the alternative microbial interpretation suggested by the work of Mariotti et al. (2016) and Matz (2008). A notable exception is Mángano & Buatois (2020), who mentioned several alternative interpretations (Matz 2008, Retallack 2013, Mariotti et al. 2016) and emphasized that “a case-by-case evaluation is invariably needed before affirming the bilaterian origin of any alleged trace fossil.” Even though they suggested five evolutionary phases for the Ediacaran-Cambrian transition, their figure 5 clearly shows a dramatic and non-gradual increase in ichnodisparity and ichnodiversity with the beginning of the Cambrian, nothing even remotely looking gradual or continuous. For their phase 3, which aligns with the earliest Cambrian (Fortunian), they found that it “is characterized by the appearance of novel architectures reflecting the evolution of novel body plans.” That sounds like something Meyer would have said.

The widely cited study by Chen et al. (2013) was criticized by Retallack (2013), who suggested that several features of the traces are incompatible with bilaterian worms as producers of the traces and instead suggested a protist origin. This criticism is valid independent of the questionable validity of some other of Retallack’s hypotheses.

Newer work by Oji et al. (2018), who described U-shaped burrows from the Ediacaran of Mongolia, has a different problem: the authors did not consider the fact that these burrows correspond in size, shape, dating, and geographical distribution to the described tube-like fossils of Gaojiashania (Cai et al. 2013). These fossils were initially described as possible annelid worms, but Cai et al. (2013) considered them to be problematic fossils with unresolved phylogenetic affinity. The stacked composition of the sclerotized tubes with ring-bucket-like elements in my view suggests that they could be related to cloudinids (note the funnel-in-funnel structure of the tubes) that are widely considered to be putative cnidarians, thus not bilaterian animals (Bechly 2020a). I consider these U-shaped tubes and the associated trace fossils as burrowing cnidarians of the extinct clade Cloudinomorpha, which may also include other biomineralized tubular fossils like Sinotubulites (tube-in-tube structure) and Conotubus (annulated structure) (Cai et al. 2011, Cai et al. 2015, Yang et al. 2022). Recently, this hypothesis of mine was strongly reinforced by the discovery that similar phosphatized and annulated tube-like fossils from the Cambrian were not worms but indeed cnidarians (Zhang et al. 2022). The authors concluded that “early annulated tubular exoskeletons from the latest Ediacaran and Cambrian are better understood as variations on cnidarian exoskeletons rather than early annelids”, which removes much of the alleged evidence for a hypothetical late Ediacaran “wormworld”.

Claims for even more ancient bilaterian trace fossils from Uruguay (Pecoits et al. 2012), allegedly more than 585 million years old, have recently been debunked as incorrectly dated and shown to be of Carboniferous/Permian origin (Gaucher et al. 2013, Verde et al. 2022). This is just one of countless examples suggesting that in evolutionary biology and paleobiology the evidence is often quite controversial and weak, so that some healthy skepticism is always better than a simplistic call to blindly “trust the science.”

That said, the current trace fossil evidence suggests that a few problematic bilaterian animals may well have existed in the latest Ediacaran, and the existence of Ediacaran worm burrows and four groups of bilaterians was clearly acknowledged by Meyer in his book (also see Evolution News 2019). However, the potential presence of a few problematic and simple (stem) bilaterians in the Ediacaran does not solve the mystery of the sudden appearance of more than twenty complex new animal body plans during the Cambrian Explosion!

The Ominous-Sounding “Wormworld”

Since the small shelly fauna and trace fossils fail to support Farina’s claims, what about this ominous “wormworld”? This hypothesis would at least require the positive demonstration of a very diverse wormworld during the latest Ediacaran period that includes soft-bodied putative ancestors and missing links for many of the Cambrian bilaterian animal phyla. But such an Ediacaran menagerie only exists in the wishful thinking of some Darwinists. Actually, the very term “wormworld” is only found in two scientific papers by the same lead author (Schiffbauer et al. 2016, Schiffbauer 2016) and in an unpublished thesis from a member of the same research group (O’Neil 2020). The traces fossils and tube-like fossils (e.g., Gaojiashania and Conotubus) are all problematic and could as well have been produced by tube-like coelenterates as has been postulated by most experts for the similar cloudinids. That actual fossil record and modern paleontologists disagree with an alleged Ediacaran menagerie is clear from the following statement by Daley et al. (2018) published in the prestigious journal PNAS: “BSTs [= Burgess Shale Type localities] from the latest Ediacaran Period (e.g., Miaohe biota, 550 Ma) are abundantly fossiliferous with algae but completely lack animals, which are also missing from other Ediacaran windows, such as phosphate deposits (e.g., Doushantuo, 560 Ma).” It could hardly be more in your face that Meyer’s position is far from contradicting modern science.

Next, “Dave Farina Criticizes Intelligent Design but Doesn’t Understand It.”