I have been reviewing and responding to popular YouTuber Dave Farina’s recent video (Farina 2022) attacking Stephen Meyer and Darwin’s Doubt. This is the third post in my series. Find the first two here and here. I have provided timecodes in square brackets throughout for ease of following Professor Dave’s (as he styles himself) assertions.
[TC 15:43] Mr. Farina claims that Dr. Meyer’s central thesis is that “Animals appear in the Cambrian explosion with no predecessors! Nothing!” Farina calls this “caught lying on the Internet” and says it exposes one of Meyer’s biggest and most persistent lies. This is ludicrous, as Farina himself admits in the same video that Meyer in Darwin’s Doubt explicitly acknowledges the existence of Precambrian animals like sponges, cnidarians, and even a possible bilaterian (Kimberella). Farina then goes into various cases of alleged Ediacaran animals. This is supposed to debunk Meyer, or rather Farina’s straw man of Meyer’s argument.
[TC 16:54] Farina starts with sponges and cites the biomarker study of Gold et al. (2016) as evidence for Precambrian sponges. First, as I’ve already emphasized, Meyer acknowledges the possible presence of sponges in the Ediacaran and as Farina himself recognized before, Meyer clearly refers to the origin of bilaterian animal body plans as the problem of the Cambrian Explosion. Therefore, fossils of putative sponges, ctenophores, and cnidarians from the Ediacaran are totally irrelevant. However, even these claims are highly disputed. I have discussed and debunked all this evidence for Precambrian sponges (Bechly 2020c). And in a comment on Facebook, Joe Botting, one of the world leading experts on fossil sponges, agreed with all the points in this article (apart from the conclusion to ID).
In the description of his video on YouTube, Farina links to two new papers (Zumberge et al. 2018, Love et al. 2020), by the same team of authors, about steroid biomarker evidence for Cryogenian animals about 650 mya. Nettersheim et al. (2019) challenged the identification of demosponges as likely producers of the Cryogenian biomarkers because they found these putative typical sponge biomarkers to be common among unicellular organisms (Rhizaria) and concluded that “negating these hydrocarbons as sponge biomarkers, our study places the oldest evidence for animals closer to the Cambrian Explosion.” Love et al. (2020) briefly responded and disputed the results of Nettersheim et al. as possible artifacts and again suggested that demosponges are currently the only known biological source for the found sterane biomarkers. But another even more recent study by Maldegem et al. (2021) demonstrated that these particular steranes can form via geological alteration of common algal sterols. Here is what the press release by the Australian National University (2020) said: “Scientists have resolved a longstanding controversy surrounding the origins of complex life on Earth. The studies found molecular fossils extracted from 635-million-year-old rocks aren’t the earliest evidence of animals, but instead common algae.” Thus, the alleged conclusive evidence for Cryogenian animals has evaporated. Farina is either unaware of the more recent research, and thus did not do his homework, or he is misleadingly cherry-picking older studies to support his case.
In Search of Ediacaran Animals
[TC 17:41] Are there Ediacaran animals 635-541 mya? Farina claims that it is in this period that we find the first animal body fossils. This is of course possible, even though controversial even among the mainstream experts, but it is irrelevant unless we were to find bilaterian animals and putative ancestors of the Cambrian bilaterian animal phyla. Here is what Telford et al. (2015) concluded: “Even if bilaterians were tiny in the Precambrian, they would be capable of being preserved in the microfossil record, suggesting that their absence is real.” Meyer cites Budd and Jensen (2003) forcefully pointing out the lack of Precambrian bilaterian fossils:
As Graham Budd and Sören Jensen state, “The known [Precambrian/Cambrian] fossil record has not been misunderstood, and there are no convincing bilaterian candidates known from the fossil record until just before the beginning of the Cambrian (c. 543 Ma), even though there are plentiful sediments older than this that should reveal them.” Thus they conclude, “The expected Darwinian pattern of a deep fossil history of the bilaterians, potentially showing their gradual development, stretching hundreds of millions of years into the Precambrian, has singularly failed to materialize.”
[TC 17:50] Farina mentions Lantianella as a putative Ediacaran cnidarian, so not a bilaterian animal but a member of one of the animal groups that Meyer acknowledges to occur in the Ediacaran. But the case for Lantianella as a cnidarian is far from conclusive. Actually, the fossils described as Lantianella were originally considered to be problematica, possible animals, or taphonomic variations of macroalgae (Yuan et al. 2011, 2013). Van Iten et al. (2013, 2014) and Wan et al. (2016) suggested that Lantianella might be a cnidarian animal, but this was only based on the superficially conulariid-like habitus with presence of a holdfast and tentacle-like structures. Therefore, even the latter authors admitted that “these animal interpretations are intriguing possibilities, but definitive evidence for an animal affinity is lacking.” Nevertheless, without further study or arguments, most subsequent authors have tentatively accepted or at least considered this possibility (e.g., Bowyer et al. 2017, Cunningham et al. 2017b, Dunn & Liu 2017, Dzik et al. 2017, Wood et al. 2019, Cordani et al. 2020, Zhao et al. 2021). Of course they did. Why should they question such convenient hypotheses? The recently described alleged Ediacaran cnidarian Auroralumina (Dunn et al. 2022) is very similar to Lantianella, which surprisingly is not even mentioned in this publication. Maverick paleontologist Gregory Retallack, who considers most Ediacaran organisms as terrestrial lichens, suggested in a comment on Facebook that Auroralumina is similar to the podetium and soredia of the living lichen Cladonia chlorophaea. I don’t believe this fringe view either, but it shows how much room for very different interpretations these fossils leave. These organisms may have been conulariid-like cnidarians, or not. It is a lot of guesswork based on superficial similarities of relatively poorly preserved fossils without much in the way of diagnostic features. For the time being, I think that Lantianella and Auroralumina would be better considered as related forms of Precambrian problematica or macroalgae, especially since similar uncontroversial macroalgae abound in the Ediacaran localities from China (Wang et al. 2020). Anyway, as I have already said, Meyer did not dispute the existence of Ediacaran cnidarians and their (potential) existence is irrelevant for his case about the Cambrian Explosion of bilaterian animal phyla.
[TC 17:54] Concerning the phosphatized animal embryos from Doushantuo, Farina had boldly claimed that Meyer lied about them, but now at least acknowledges briefly that they have been the subject of intensive debate. However, he thinks that Megasphaera, Caveasphaera, Helicoforamina, and Spiralicellula are genuine animal embryos rather than algae or protists. This is based on the recent papers by Yin et al. (2019, 2022), but they only talk about holozoan affinity, total-group metazoans, and metazoan-like development. That’s fine (even though likely wrong), but again irrelevant in the absence of a strong case that these putative animal embryos belonged to bilaterian animals rather than stem animals. There is no such case, though, even according to the champions of the embryo-interpretation. There is wide agreement that the Doushantuo fossils are not crown-group animals (e.g., Butterfield 2011, Kaplan 2011, Chen et al. 2014b) and thus not bilaterians (the bilaterian animal nature of Vernanimalcula was thoroughly debunked by Bengtson et al. 2012). Telford et al. (2015) therefore said that none of the Doushantuo fossils “can be confidently assigned to bilaterians.” But are those fossils even animal embryos in the wider sense at all?
Like numerous previous studies (see Bechly 2020c and 2020d for a brief review and references), a brand-new study by Zhang & Zhang (2022) strongly disagrees and concludes that Megasphera’s developmental “features are inconsistent with the embryogenesis of living animals, and therefore do not support the metazoan-embryo interpretation.” Tang (2015) reviewed the controversy around the interpretation of Megasphera and the other genera and concluded that they are algae rather than animal embryos. Spiralicellula was first suggested as possible metazoan embryo by Xiao et al. (1998). Just two years later the authors themselves admitted that the interpretation is problematic (Xiao & Knoll 2000). Later studies suggested that Spiralicellula and Helicoforaminacould instead be of algal (Zhang & Pratt 2015) or mesomycetozoan-like protist (Huldtgren et al. 2011) origin. Xiao et al. (2014) suggested that all these genera are likely multicellular eukaryotes but could not decide if they are algae or stem-animals. Cunningham et al. (2017a) concluded that “although the Weng’an Biota includes forms that could be animals, none can currently be assigned to this group with confidence.” Ouyang et al. (2019) therefore still classified Megasphera, Helicoforamina, and Spiralicellula as acanthomorph acritarchs. Farina does not care about such scientific “subtleties” and presents these problematic and highly controversial taxa as proven evidence of Ediacaran animals.
By the way: Just this year, another of the alleged Doushantuo animal embryos, called Tianzhushania, was debunked and identified as an algal cyst (Moczydłowska & Liu 2022), which is the most likely fate for all the others.
At best a few forms like Caveasphaera could be stem-metazoans with animal-like development (Yin et al. 2019), but this is far from established. New York Times science writer and ardent evolutionist Carl Zimmer was not convinced either and quoted numerous eminent scientists who strongly dispute such an animal affinity (Zimmer 2019). Another scientific study from the same year accordingly classified Caveasphera among acanthomorph acritarchs like the other genera mentioned above (Ouyang et al. 2019).
Wondering about Acritarchs
[TC 18:26] Farina mentions a diversification of acritarchs as possible indirect evidence based on co-evolution with eumetazoans. This seems dubious, because we have no clue what acritarchs even are, and which ecological role if any they might have played for early metazoans. Acritarchs are problematic microfossils that could represent an artificial assemblage of algal cysts, moss pollen, and planktonic protists. Farina’s statement is likely based on the study by Peterson & Butterfield (2005), which found no evidence at all for acritarchs as metazoans or for any metazoans. Instead, they simply correlated molecular clock dates for the origin of metazoans, which we know are highly unreliable and disputed, with detected regime changes in the Proterozoic acritarch record, and boldly concluded in favor of co-evolution. That’s hardly science but more like reading tea leaves. Yet even if true, these early metazoans would most likely have been stem metazoans or non-bilaterian metazoans and thus would be totally irrelevant to the Cambrian Explosion. Nothing in this argument explains the abrupt appearance of the bilaterian animal phyla and body plans in the Early Cambrian.
[TC 18:59] Farina also mentions the low-oxygen requirements of sponges and ctenophores (Mills et al. 2018) as relating to the fact that only the ocean surface was oxygenated until the middle Ediacaran. So what? Unlike me, Meyer did not even dispute the existence of Ediacaran sponges and coelenterates like ctenophores and cnidarians. So this is yet another red herring from Farina that has nothing to do with the real problem of the Cambrian Explosion.
[TC 19:20] Farina refers to the three assemblages of the typical Ediacaran biota that exhibit increasing ecological complexity (Eden et al. 2022):
- Avalon Assemblage 771-555 mya
- White Sea Assemblage 560-551 mya
- Nama Assemblage 555-541 mya
Apparently, he wants to give the impression that Ediacaran biota progress towards the Cambrian animal phyla. However, this is false. No phylogenetic link has been established between the organisms of these Ediacaran biota and the Cambrian animal phyla, and the very existence of any Ediacaran animals is highly controversial among experts to say the least (see further).
[TC 19:58] Farina misleads his viewers by claiming that the interpretation of the Ediacaran biota as enigmatic problematics, multicellular protists, fungi, and lichens, was just due to an early lack of knowledge, from the time of their discovery in the 1940s to Stephen Jay Gould’s time in the 1980s. Farina maintains that modern research has changed this picture in favor of an animal interpretation, which he seems to base on Liu et al. (2015).
[TC 20:39] He quotes a study by Wan et al. (2016) on alleged animal fossils from the Lantian Formation in China and does not conceal their admission that Ediacaran candidate animals represent “frustrating cases for animal affinities.” Farina uncritically accepts this study and does not recognize that it is highly problematic. Here is just one example: the authors speculated that Xiuningella could be a bilaterian worm but admitted that alternatively it “could be an epibenthic algal organism, with the bulbous structure being a holdfast, the stalk being a stem, and the cylindrical tube representing a coenocytic siphonous thallus.” Since macroalgae totally dominate the Lantian biota and clear animals are lacking, this seems like a much more reasonable interpretation. The authors even admitted that for all their discussed candidate organisms “definitive evidence for an animal affinity is lacking.” We’ve already discussed in this series the problematic nature of Lantianella, but what if it should indeed be a cnidarian as speculated by Wan et al.? So what? I hate to say it another time, but Meyer has acknowledged the possible existence of Ediacaran cnidarians, so this would be just another one. The problem of the Cambrian Explosion is the abrupt appearance of numerous different body plans of bilaterian animal phyla, and cnidarians are not one of them. Farina is here again shooting down caricatures of Meyer’s arguments, which shows that this wannabe “professor” cannot refute the actual arguments.
[TC 21:08] Farina briefly addresses the claim by maverick paleontologist Gregory Retallack that Ediacaran communities were terrestrial rather than marine, and that Ediacaran organisms likely were lichens. Farina correctly identifies this as a highly disputed fringe position, but thereby gives the misleading impression that modern skepticism about an animal affinity is restricted to fringe scientists. Nothing could be further from the truth as you will see in my discussion further on of the various examples mentioned by Farina.
[TC 22:07] Farina talks about the frond-like taxa and their controversial placement, but reports that recent work by Dunn et al. (2021) has identified the frond-like rangeomorphs Charnia as stem-eumetazoans. Correct, and Runnegar (2022) agreed but considered them as a “far simpler organism than previously thought.” However, one problem with the Dunn et al. study is the very low statistical support of the data. If you look at their figure 6 you will find that the support in terms of posterior probability for the position of Charnia is the lowest in the whole tree. Many other topologies that are still considered uncertain, e.g., the precise positions of Cnidaria and Ctenophora, are still better supported. As Farina is apparently ignorant of Bayesian phylogenetic methodology, he also fails to recognize that statistical support of only 77 percent is basically considered worthless in this field of science, where good support begins above 98 percent. This would be like a physics paper claiming the discovery of a new particle with a sigma 3 support. It is also clear from the study that the animal affinity is just based on multicellularity, body tissues, and anatomical polarity. All these character states are also known from macroalgae and thus not diagnostic for metazoans. The only remaining point is the developmental mode with indeterminate growth of a predictable pattern of maintained differentiation of elements, which the authors claim is otherwise known only from within Metazoa. The crucial problem hides in the little word “within”, because such a developmental mode does not belong to the ground plan (see here for a precise definition of this technical term of cladistics) of Metazoa or Eumetazoa, and not even a homology within Metazoans has been established. Furthermore, the fractal growth (Seilacher 1992, Gehling & Narbonne 2007) of the Ediacaran frond-like taxa differs from anything we know in metazoans. Taken together, this evidence suggests a convergence and shows that Dunn et al. (2021) definitely presented a case of invalid phylogenetic reasoning even from the viewpoint of mainstream evolutionary cladistics. But I can only repeat the same thing ad nauseam: Even if Charnia were a stem-metazoan, if would contribute absolutely zilch to solving the problem of the Cambrian Explosion of bilaterian animal phyla.
Please, Not Again
[TC 22:55] Farina introduces Haootia quadriformis as almost certainly a cnidarian. Please, not again. Meyer acknowledges Ediacaran cnidarians, thus it is irrelevant if there is another one. Maybe Haootia indeed is a cnidarian, but not so fast: A recent paper (Dunn et al. 2022) about Ediacaran cnidarians is not so confident and even excludes Haootia from their phylogenetic analysis because of its uncertain position. This study instead suggested that the new fossil Auroralumina from Charnwood Forest is a putative Ediacaran crown group cnidarian, which is problematic as well (see my earlier comments). Even if Haootia and Auroralumina are Ediacaran cnidarians, they would just confirm what Meyer acknowledged anyway and that does nothing to explain the sudden appearance of bilaterian animal phyla in the Cambrian Explosion. This is getting ridiculous!
[TC 23:07] Farina shows a screenshot from the study of Evans et al. (2021), which places Tribrachidium, Dickinsonia, Ikaria, and Kimberella in the Eumetazoan tree with the latter two taxa as putative Bilateria. Well, at least the latter two taxa are a bit more interesting as they have been claimed to be bilaterian animals. I discussed this paper in a previous article (Bechly 2021c), and have critically discussed all four genera in great detail in others (Bechly 2018c, 2020b, 2020g, 2021c, 2022e). Therefore, I will refer to those articles and just include a few notes here:
[TC 23:18] Farina first presents Tribrachidium of the extinct phylum Trilobozoa as another stem-eumetazoan, which allegedly was a benthic, sessile, suspension feeder. In my article series on trilobozoans (Bechly 2021c) I showed that the suspension feeder interpretation by Rahman et al. (2015) is dubious and controversial, judging from up-to-date mainstream science that contradicts this interpretation. The authors even admit that the related genera within Trilobozoa or Triradialomorpha “appear to lack the apical ‘pits’ that we hypothesize are key to this method of feeding in Tribrachidium,” which basically debunks their hypothesis as emphasized by McMenamin (2016: 60-62). New research has also revealed the internal anatomy of trilobozoans (Taylor et al. 2017, Zakrevskaya & Ivantsov 2020) and it is incompatible with the suspension feeding hypothesis and unlike any known animal body plans. Many experts therefore still consider the enigmatic trilobozoans as a “failed evolutionary experiment in multicellular eukaryote body plans” (Droser et al. 2017, Hall et al. 2018). Even Rahman et al. (2015) admitted that “Tribrachidium is best understood as a multicellular eukaryote with uncertain relationships to crown Metazoa.” Trilobozoans were very aberrant and clearly not ancestral to any of the Cambrian animal phyla and thus are completely irrelevant for solving the problem of the Cambrian Explosion.
[TC 23:33] Second in Farina’s list is Dickinsonia, which he introduces as a stem-bilaterian, based on alleged strong ichnological, developmental, and biomarker evidence. The ichnological (trace fossil) evidence is not strong but controversial, and some leading experts think that the alleged traces are just successive imprints of passively drifting specimens (McIlroy et al. 2009), and conclude that “there is no evidence from within material of Dickinsonia from Ediacara, or from any other material yet known, of true escape trails, faecal trails or locomotion traces” (Brasier & Antcliffe 2008). New results suggest that the developmental evidence is not only weak, but actually incompatible with an animal nature for Dickinsonia (Retallack 2022). Another recent study by Runnegar (2022) showed “that the biomarker evidence supports a lifestyle based on poriferan-style phagocytosis rather than bilaterian extracellular digestion.” The absence of a gut was also suggested by the biomarker study of Bobrovskiy et al. (2022). Runnegar also confirmed that at least some dickinsoniids had glide symmetry rather than bilateral symmetry and suggested that “Seilacher’s characterization of them as fluid-filled ‘pneus’ may serve as the current null hypothesis.” Cabey (2020) concluded that “the phylogenetic relationships of the genus Dickinsonia remain still undetermined.” This all supports my critical discussion of Dickinsonia and its rejection as a bilaterian animal (Bechly 2018c, Bechly 2022e).
[TC 23:54] Third is Ikaria which Farina describes as a worm-like bilaterian. That is indeed what the original description claimed (Evans et al. 2020). However, as I have shown in my article on Ikaria, the association with the Helminthoidichnites trace fossils and the bilaterian nature are far from established and even contradicted by the sedimentological evidence (Bechly 2020b). Evans et al. (2020) failed to properly address the possibility that Ikaria could be a protist and only said that modern protists “are typically smaller than Ikaria.” Yes, they are typically smaller but not always smaller, and exactly those modern protists that create traces similar to Helminthoidichnites on the deep-seafloor (Matz et al. 2008) are even much bigger than Ikaria (Gooday et al. 2000). The authors also failed to even mention the possibility that Ikaria could be a cnidarian planula larva or a cnidarian worm like the modern Buddenbrockia. Ikaria is just a dubious fossil looking like imprints of grains of rice without any structure. It could be anything. Its sensationalist description was a clear case of overinterpretation driven by wishful thinking.
[TC 24:13] Fourth and last in the list is Kimberella. Farina acknowledges that it is a contentious taxon with suggested affinities ranging from cnidarian to mollusk, but he correctly reports that most recent studies have tended towards stem-mollusk or stem-spiralian affinities. I discussed Kimberella in intricate detail in a 14-part article series (Bechly 2020g), where I showed that Kimberella is almost certainly not a stem mollusk but possibly a stem bilaterian. I also showed with mainstream research that an interpretation as a coelenterate grade animal cannot be ruled out, especially since there is evidence for sclerotization and very diverse body plans in early Cambrian comb jellies (Scleroctenophora), as well as evidence for ancestral bilateral symmetry in Cnidaria. Cabey (2020) agrees that “whether Kimberella is a bilaterian or a coelenterate-grade animal is still unresolved.” Again, my critique was recently confirmed by Runnegar (2022), who agreed that Kimberella “might be an animal of cnidarian grade” and even thinks that “it is possible to regard Kimberella as some kind of foraging anemone.” Of course, it is also possible that Kimberella and Yilingia will still turn out to document the existence of two bilaterian groups of uncertain affinity prior to the Cambrian period, as suggested by a very recent biomarker study (Bobrovskiy et al. 2022), which suggested the presence of a gut based on molecular signatures of supposed gut content. However, their unique specializations strongly suggest that they could only represent extinct side branches but could not be directly ancestral to any of the numerous Cambrian animal phyla, and thus do not resolve their enigmatic origin. Meyer in Darwin’s Doubt also discusses Kimberella and generously acknowledges that it could be a bilaterian. What is Farina’s problem, then? Meyer can hardly be blamed for not having discussed Yilingia, which was described years after his book was published.
The Nama Assemblage
[TC 24:33] Farina turns to the Nama assemblage and mentions three fossil taxa: Cloudina, Yilingia, and Namacalathus.
[TC 24:48] Concerning the tubular fossil Cloudina he correctly says that it has recently been argued to be likely an annelid. I disputed this attribution in an earlier article (Bechly 2020a) based purely on mainstream science. He immediately acknowledges that other cloudinomorphs were rather attributed to cnidarians, but instead of doubting one of the two attributions, he suggests that cloudinomorphs might not be a natural group of related organisms.
[TC 25:12] He describes Yilingia (Chen et al. 2019) as a segmented bilaterian, possibly either an annelid or a panarthropod. That’s indeed what the paper and the accompanying media reports suggested. However, there is a big problem because annelids (belonging to lophotrochozoans) and panarthropods (belonging to ecdysozoans) are not closely related and their similar body plan is generally considered to be a convergence. This makes it very weak evidence because another convergence could be quite likely. Farina also says that a relationship with panarthropods would be supported by the trilobed structure as in trilobites. However, this structure does not even belong to the ground plan of Panarthropoda and is absent in basal groups such as Cambrian lobopods. Farina seems to get his information from Wikipedia (https://en.wikipedia.org/wiki/Yilingia) and other unreliable sources. Also, the metameric pattern of Yilingia is very different from any known panarthropod or annelid (Evolution News 2019, Bechly 2020b).
[TC 25:29] Finally, he claims that Namacalathus appears to be an early relative of brachiopods and bryozoans. I criticized this attribution on many grounds (Bechly 2020e, 2020f, 2021a, 2021b), not the least of which is that brachiopods and bryozoans are of questionable relationship and the homology of the used similarities has been disputed and refuted by the experts even for these two living groups. The phylogenetic attribution of Namacalathus was therefore objectively based on invalid arguments. A lot of nonsense gets published in peer-reviewed scientific articles (just think of the replication crisis) and it requires a bit of expertise to separate the wheat from the chaff and to recognize poor arguments. Farina clearly lacks any expertise to do this.
Next, “Let’s Help ‘Professor Dave’ Understand the Precambrian.”