The Myth of Precambrian Sponges – Discovery Institute
♫ Wednesday, May 13th, 2020Sponges are sessile marine invertebrates that are considered to be the most basal and most primitive branch of the multicellular animals (Metazoa). Therefore, evolutionists would expect to find such sponges as the earliest animals in the fossil record. Also, immunological evidence (Wilkinson 1984) and especially molecular clock data placed the origin of sponges long before the Cambrian and even before the Ediacaran era (Peterson et al. 2004,Sperling et al. 2007,Sperling et al. 2010,Erwin et al. 2011,Cunningham et al. 2017a). Consequently, the alleged discovery of sponge-like fossils from layers prior to the Cambrian explosion, which gave rise to all the more complex animal phyla, was welcomed by evolutionary biologists as clear confirmation of Darwins theory. When the branching order of reconstructed phylogenetic relationships agrees well with the stratigraphic order of appearance in the fossil record, evolutionary biologists speak of so-called stratigraphic fit. The existence of Precambrian fossil sponges was accepted as established fact in many textbooks and academic articles (e.g.,Debrenne & Reitner 2001,Reitner 2005,Budd 2008,Mller et al. 2009). A perfect example isCarrera & Botting (2008), who confidently stated that it is fairly clear that sponges possess a long record back to the Proterozoic, represented in the Ediacara fauna. The evidence seemed convincing enough that even most critics of Darwinian evolution acknowledged the existence of sponges prior to the Cambrian explosion (e.g.,Meyer 2013,Evolution News2016).
I will show that this concession was premature and much too generous. Lets see how good or rather how embarrassingly bad the case for Precambrian sponges really is and have an exhaustive look at all the potential candidates in alphabetical order.
Ausia fenestratais known from a few specimens from the Ediacaran of Namibia and Russia. These about 5 cm small fossils look like a triangular bag with numerous ovate depressions or openings in it. It has been considered to be a cnidarian sea pen by its original describers (Hahn & Plug 1985), or a halkieriid stem mollusk (Dzik 2011), or a chordate tunicate (ascidian) (Fedonkin et al. 2007, 2008,2012), or a sponge-like animal related to the Cambrian Archaeocyatha or even as a true sponge (Fedonkin 1996, McMenamin 1998: 38-39). This shows that the preserved characters are totally insufficient for any definite placement. Unsurprisingly,Antcliffe et al. (2014)consideredAusiaas failing to meet the diagnostic criteria of sponges, andMuscente (2015)commented that such interpretations of aspiculate organisms are inherently subjective, and the affinities of the fossils remain disputed. Interestingly, another genus and species that has been attributed to the same family Ausiidae,Burykhia huntifrom the Ediacaran of Russia, was considered by its describers (Fedonkin et al. 2012) as a possible tunicate, but no possible relation to sponges was even mentioned.
Coronacollina aculais a very strange Ediacaran organism described byClites et al. (2012)from Australia. The fossil is a triradial cone-like mound with four 37 cm long radial spicules, which has been considered as resembling the Cambrian demosponge genusChoia.Coronacollinahas been called the oldest organism with a skeleton and in this way considered as a precursor to the Cambrian explosion (UC Riverside 2012). Serezhnikova (2014) accepted the similarity withChoiaand stated that records of Coronacollina supported the Precambrian origin of sponges and their ability for biomineralization in the Late Proterozoic. In their revision of Ediacaran tri-radial body plans,Hall et al. (2018)excludedCoronacollinafrom the otherwise monophyletic group Trilobozoa or Triradialomorpha, but did not propose any other relationships.Muscente et al. (2015)refuted any structural similarity of the spicules with those of sponges.Cunningham et al. (2017a)observed that there is not even a definite association with the putative spicules and concluded: As such, neither Palaeophragmodictya nor Coronacollina are considered to reflect poriferans, or even metazoans, on the basis of current evidence. None of the recent exhaustive revisions of putative Precambrian sponges still consideredCoronacollinaworthy of discussion (Antcliffe et al. 2014,Botting & Muir 2017).
Cucullus fraudulentusis a bag-like or tube-like fossil and represents the most abundant and largest organism from the Neoproterozoic Miaohe biota of the Doushatuo Formation in China. It was described by Steiner (1994: 125) as a putative cyanobacterial colony or mega-alga of uncertain affinity. Chen et al. (1994) suggested that their new species,Sinospongia hubeiensis, later been synonymized withCucullus fraudulentus, is a poriferan. Therefore, Li et al. (1996) and Hu (1997) attributedCucullusto demosponges, whileSteiner & Reitner (2001)still considered them as microbial colonies. Due to poor preservation, its morphology and affinities remained unclear. ThusXiao et al. (2002)still could not decide if it was a sponge or a siphonous green alga. Finks et al. (2004) rejected an affinity ofCuculluswith sponges in their revised edition of the prestigiousTreatise on Invertebrate Paleontology.Xiao & Dong (2006)consideredCucullusto be a protoarenicolid, which these authors do not identify as an animal but as dasycladacean algae. When new and better preserved material became available from the Doushantuo Formation in China,Wang & Wang (2011)resurrected an affinity to demosponges based on the observation of assumed organic walls formed by non-mineralized spongin fibers.Antcliffe et al. (2014)disagreed and concluded:
There is however, no unequivocal morphological evidence to support assignment to the Porifera. Furthermore, no spicules have been described in association with Cucullus. We conclude that assignment to the Porifera is highly speculative and that Cucullus fails the diagnosis test as the possibility that the specimens are microbialites seems to us much more likely.
Lets repeat this in plain English:Cucullusis not a sponge but rather of microbial origin.Serezhnikova (2014)also found that the interpretation ofCucullusandSinospongiaas sponges and their comparison withVaveliksiaare difficult to support.Muscente (2015)basically agreed with that skeptical position.
Eocyathispongiaqianiawas described byYin et al. (2015)after a single specimen from the Early Ediacaran Doushantuo Formation in China, as a sponge grade fossil with cellular resolution. Of course, it was immediately celebrated in the popular media as the discovery of the oldest sponge (Yirka 2015).Cunningham et al. (2017a)remarked:
It represents the most plausible report of a sponge from the Precambrian. However, more analyses and specimens are needed to test this hypothesis. In particular, high-resolution tomographic analysis of the walls of the specimen could reveal whether pores are present, and therefore whether Eocyathispongia could have functioned as a sponge.
Cunningham et al. (2017b)commented, Eocyathispongiais considered to be one of the strongest candidates for a Precambrian sponge. However, although it could be a sponge, it has no convincing sponge apomorphies such as pores or spicules, just a generalized sponge gestalt.Bottjer et al. (2019)rather suggested that although it contains no characters that are exclusive to crown group sponges , if not a stem group sponge it could be an extinct organism between the last common ancestor of metazoans and the last common ancestor of living sponges. However,Botting & Muir (2018)in their review of early sponge evolution mention a severe problem for the sponge hypothesis:
Eocyathispongia is an extremely interesting fossil, but several features are not easily compatible with sponge biology. The morphology is problematic for a sponge, especially a very small one, as it appears to actively minimise the available surface area for incurrent pores, on which it would depend for feeding.
In my view this tiny fossil, which is only about a single millimeter in size, represents just another vase-shaped encysting protist from the Doushantuo layers (Li et al. 2008).
Namapoikiarietoogensisis a calcified reef-building organism of up to one meter size, discovered in the Ediacaran Nama group of southern Namibia. In the original description its affinities have been considered to be with either cnidarians or sponges (Wood et al. 2002).Zhuralev et al. (2012)agreed thatNamapoikiais only of a cnidarian or poriferan grade of organisationAntcliffe et al. (2014)clarified in their large revision of alleged Precambrian sponges that diagnostic poriferan morphological characteristics are lacking and that such a structure could arrive from the calcification of microbial colonies.Wood & Curtis (2015)still considered it to be of uncertain affinity, though resembling chaetetid sponges or simple colonial cnidarians.Cunningham et al. (2017a)said thatNamapoikiapossesses no characters diagnostic of any particular eukaryotic group.Wood & Penny (2018)finally placed its probable affinity within total-group poriferans, mainly based on similarities in growth pattern and (inferred!) biomineralization. They concluded that such an interpretation confirms the presence of poriferans, with calcareous skeletons, in the terminal Ediacaran. However,Tang et al. (2019)remained unconvinced and offered the qualification that Namapoikiahas been interpreted as an encrusting poriferan, but more work is needed to confirm that it is a calcified encrusting sponge rather than a microbial structure, which strongly suggests thatNamapoikiastill fails to meet the diagnostic criteria required byAntcliffe et al. (2014).
Curiously,Wikipediaclaims thatZhuralev et al. (2015)instead proposed an affinity with lophophorate bilaterian animals or their stem group. However, this is total nonsense and factually incorrect as this paper does not even remotely make such a claim. This example shows how utterly unreliableWikipediais as source for scientifically accurate information.
Otavia antiquais an irregular spheroid microfossil found in 760-550 million year old layers in Namibia, of which some predate the Ediacaran and even the assumed neoproterozoic snowball earth period called Cryogenian. It was described as a sponge-like fossil byBrain et al. (2012), and again celebrated by the press as Namibia sponge fossils are worlds first animals (AFP 2012,Gess 2012).Antcliffe et al. (2014)rejected its identification as a sponge and remarked that alternative hypotheses have not been sufficiently explored and/or have been rejected without sufficient reason. They even raised severe doubts thatOtaviais a genuine fossil of biogenic origin at all, or maybe of microbial origin rather than an animal. Antcliffe et al. concluded that no features are presented that are diagnostic of sponges. We interpret these objects as calciphosphate grains that have been pitted by sediment reworking. This sounds much less spectacular and thus did not hit the news headlines. Even the more recent textbook byJain (2016: page 7),Fundamentals of Invertebrate Palaeontology,ignored the refutation and still teaches gullible students the obsolete story thatOtaviais a calcareous sponge and the oldest animal.
The type speciesPalaeophragmodictya reticulatawas described byGehling & Rigby (1996)as long expected sponges from the Neoproterozoic Ediacara fauna of South Australia. The very title of their work shows how eagerly Darwinists longed for an empirical confirmation of their theoretical expectations. The sponge affinity was accepted by most other authors (e.g.,Seilacher 1999, Finks et al. 2004,McCall 2006). About ten years later a second speciesP. spinosawas discovered bySerezhnikova (2007)in the White Sea region of Russia and demolished these expectations again. She did not identifyPalaeophragmodictyaas sponge at all, but recognized that it is just a holdfast of an unknown sessile organism (again affirmed bySerezhnikova 2014) that might have been a cnidarian. Nevertheless, the story was apparently too nice to be spoiled by stupid facts, so that the sponge interpretation was retained in many recent articles (e.g.,Maloof et al. 2010,Brain et al. 2012,Dohrmann et al. 2013,Stearley 2013). But the truth could not be ignored forever. Antcliffe et al. (2014)
agree with Serezhnikova (2007a) that some of the material is likely to represent the holdfast of other Ediacaran-age organisms, we question whether these specimens represent sponges of any kind. No compelling arguments are presented that Palaeophragmodictya should be considered separately from other disc-like structures of Ediacaran age.
Furthermore, Antcliffe et al. present extensive evidence and arguments that these fossils indeed represent holdfasts of the typical Ediacaran frond-like organisms.Cunningham et al. (2017a)acknowledged thatPalaeophragmodictyais perhaps the most widely recognized candidate for a sponge within the Ediacaran macrobiota but the taxon may be more readily interpreted as decayed attachment discs from an organism of uncertain affinity.Likewise,Botting & Muir (2018)remarked that this fossil taxon was a misidentified holdfast of an Ediacaran frond and bears little resemblance to extant or early fossil sponges. Finally, the only potential sponge character inPalaeophragmodictyaand some other alleged Precambrian sponges, the presence of apparent skeletal nets, has been discredited by a new study byLuzhnaya & Ivantsov (2019), who documented such structures in the characteristic Ediacaran fronds, which were never considered as sponges and certainly are not because they have no openings for water circulation.
Rugoconites enigmaticusis another circular organism from the Ediacaran biota of Australia described byGlaessner & Wade (1966).Gehling & Rigby (1996)mentioned thatRugoconiteshas some characters in common withPalaeophragmodictya, but recognized that the lack of evidence of a spicular framework prevents a clear assignment of Rugoconites to the poriferans. Some authors considered them to be jellyfish (Cloud & Gessner 1982,Sepkoski 2002), while others considered them as possible sponges (Darroch et al. 2018). Nevertheless, the consensus among specialists today generally tends to classifyRugoconitesas member of the Ediacaran monophylum Trilobozoa or Triradialomorpha with a tri-radial body plan (Ivantsov & Fedonkin 2002,Xiao & Laflamme 2009,Hall et al. 2018).
The genusSinospongiais known from two species,S. typicaandS. chenjunyuani, from the Miaohe biota of the Doushantuo Formation in China (a third speciesSinospongia hubeiensiswas synonymized withCucullus fraudulentus, see above). It was considered as mega-algae by Steiner (1994), as microbial colonies bySteiner & Reitner (2001), and as Protoarenicolidae byXiao & Dong (2006), which these authors do not identify as animals but as dasycladacean algae with holdfasts.Xiao et al. (2002)suggested three possible interpretations: sponge, cnidarian, or siphonous green alga, because no convincing sponge spicules have been found in association with these fossils, and alternative algal interpretations are possible and alternative interpretations, such as a cnidarian-grade organism or a siphonous green alga (especially of the order Dasycladales), should be entertained. As already mentioned above,Serezhnikova (2014)concluded, Therefore, the interpretation of Cucullus and Sinospongia as sponges and their comparison with Vaveliksia are difficult to support. The more recent revisions of alleged Precambrian sponges byAntcliffe et al. (2014),Muscente et al. (2015), andBotting & Muir (2018)did not even bother to further discussSinospongiaas a putative sponge.
Thectardis avalonensisis a conical organism of about 9 cm length and 3 cm diameter, known from numerous specimens from the Ediacaran Mistaken Point locality in Newfoundland (Clapham et al. 2004). It is believed to have been attached with its pointed end to the bacterial mat sea floor as a suspension feeding mat sticker, but it lacks any visible holdfast structures. In the original description no affinity to sponges or any other group was suggested.Sperling et al. (2011)proposed a most likely attribution to sponges, only based on the habitat beneath the photic zone (which precludes photosynthesis) and because its body plan would be consistent with the hydrodynamics of the sponge water-canal system. This is a very weak level of argumentation for the far-reaching conclusion that the recognition of sponges in the Mistaken Point biota provides some of the earliest body fossil evidence for this group, which must have ranged through the Ediacaran based on biomarkers, molecular clocks, and their position on the metazoan tree of life, in spite of their sparse macroscopic fossil record. Consequently,Antcliffe et al. (2014)correctly pointed out that such poor indirect criteria could at best exclude certain affinities, but not confirm any. They concluded that the interpetation ofThectardis avalonensisas a fossil sponge is therefore highly problematic. They even elaborated that the fossil might rather be just the misinterpreted remains of the decay process of an unknown larger organism.Muscente et al. (2015)concluded Thectardisfrom Newfoundland have been interpreted as sponges based on inferences regarding soft tissue anatomy, biomechanics, and taphonomy. However, such interpretations of aspiculate organisms are inherently subjective, and the affinities of the fossils remain disputed. Christian paleontologist RalphStearley (2013)still affirmed that the conical fossilThectardisfrom the Avalon assemblage is also probably a sponge, but this was just in a book review.Serezhnikova (2014)agreed that the general body plan ofThectardisis similar to the sponge-like archaeocyaths, but offered the qualification that the affinity of the Precambrian taxa to Porifera is limited by a lack of data on their possible filtering structures.Liu & Conliffe (2015)remarked that until more informative specimens are found, this taxon will likely remain of uncertain biological affinity.Botting & Muir (2018)remarked that although it is theoretically possible that some alleged Ediacaran Biota sponges (e.g., the featureless triangle-shaped objectThectardisClapham et al., 2004; Sperling et al., 2011) are in fact genuine, there is no evidence to that effect. Let that sink in: NO EVIDENCE! There seems to be a pattern here: desperate attempts to fulfill Darwinian expectations in the absence of any convincing evidence.
A 3-10 cm large sac-shaped organism of radial symmetry with a perforated body wall and an attachment disc, the type speciesVaveliksia velikanoviwas described by Fedonkin (1983) from the Ediacaran of Ukraine. A second species,Vaveliksia vana,was described from the Vendian of the White Sea region in Russia byIvantsov et al. (2004). They concluded: From the above observations and assumptions, one may propose thatVaveliksiahas the same level of organization as archaeocyaths or sponges.McCall (2006)suggested possible coelenterate and hydrozoa affinities instead.Serezhnikova (2014), who co-described the second species ofVaveliksia, listed it as problematic lower metazoans with a levelof organization of parazoa (?).Antcliffe et al. (2014)mentioned the possibility thatVaveliksiacould rather be an agglutinated amoebozoan, thus a colonial protist, and concluded that Vaveliksia vanalacks any definitive poriferan characteristics and fails the characters and diagnosis criteria.
Malloof et al. (2010)reported unnamed ellipsoidal fossils as sponge-grade metazoans from the Neoproterozoic of Australia. Paleontologist ChrisNedin (2010)was not convinced and commented on his respected Ediacaran blog that Proterozoic Sponges Claim Doesnt Hold Water. Well, blogs dont count in science, butAntcliffe et al. (2014)came to the same conclusion and remarked that
no characteristics that are distinctive for sponges are presented by the authors. These fossils have no morphology that is diagnostic of sponges and should in our view be more readily ascribed to the calcimicrobes that abound at these localities.
Finally,Wallace et al. (2014)described unnamed chambered structures from Cryogenian reefs, for which they pose the question of whether they could be the oldest sponge-grade organisms. However, they concluded:
The closest morphological analogues for the structures are: a) some types of reef-dwelling sponges; and b) some complex microbialites from Archean and Paleoproterozoic carbonates. The structures lack spicules and ostia found in sponges, ruling out a true Poriferan origin. However, it is plausible that they are proto-sponges, sponge-grade organisms, or complex microbial precursors to sponge-grade organisms. Whatever their affinity, we suggest these structures record a significant evolutionary event on the path towards organic complexity.
It is very clear from their conclusions that these fossils also fail all three criteria ofAntecliffe et al. (2014)for an identification as sponges and thus have to be considered as problematic fossils of uncertain affinity, but more likely of microbial origin.
That was the last candidate. But what about more indirect evidence from alleged sponge embryos, sponge needles, and sponge biomarkers? Here comes the story of their demise.
Phosphatized microfossils from the 609-million-year old Doushantuo Formation in China, which were originally interpreted as colonial green algae, were later re-interpreted as alleged animals (Xiao et al. 1998) and especially sponge embryos and sponge larvae (Li et al. 1998a,1998b, Chen et al. 1999,Chen et al. 2000,Xiao & Knoll 2000,Xiao et al. 2000, Chien et al. 2001,Chen 2012). This interpretation was immediately disputed by other Chinese researchers (Zhang et al. 1998, Xue et al. 1999), who alternatively identified these fossils as collapsed acritarch protists, thus not sponges at all but unicellular organisms. Even thoughCao & Zhu (2001)disagreed with this, they acknowledged that whether or not they are larvae of sponges, it is not determined as yet.Hagadorn et al. (2006)showed that the absence of epithelialization is consistent only with a stem-metazoan affinity for Doushantuo embryos, thus rejecting any sponge affinities.
Bailey et al. (2007)suggested that the alleged embryos are giant actually vacuolate sulphur bacteria close to the recent genusThiomargarita. However, this was convincingly rejected byDonoghue (2007),Xiao et al. (2007),Yin et al. (2007),Cunningham et al. (2012), andIgisu et al. (2014), even though these authors did not all agree on the embryo nature of the fossils.
After careful synchrotron-tomographic studies, which included a team of the most eminent paleontologists like Philip Donoghue and Stefan Bengtson,Huldtgren et al. (2011)concluded that the alleged embryos are neither metazoans nor embryos but just encysting eukaryotic protists (also seeButterfield 2011, who commented that wherever the Doushantuo fossils eventually end up, it will clearly not be within crown-group Metazoa, andKaplan 2011, whose comments are titled, Enigmatic fossils are neither animals nor bacteria).Xiao et al. (2012)readily disagreed in a response to this article, but were again refuted byHuldtgren et al. (2012). But then, in a study byChen et al. (2014), co-authored by Shuhai Xiao, the authors came to the same result that the available evidence also indicates that the Doushantuo fossils are unlikely crown-group animals.
Even the alleged and much celebrated oldest bilaterian animalVernanimalculafrom the Doushantuo Formation was debunked byBengtson et al. (2012)in an article titled A merciful death for the earliest bilaterian, in which the authors came to the scathing conclusion that there is no evidential basis for interpretingVernanimalculaas an animal.
Yin et al. (2016)presented new evidence in the form of meroblastic cleavage patterns for the identification of Doushantuo fossils as metazoan embryos, but acknowledged that their phylogenetic affinity cannot be established. Just recently,Yin et al. (2019)described gastrulation-like cell division in the fossilCaveasphaerafrom this locality, which they said foreshadows animal-like embryology. However, it was not considered as a sponge or even a metazoan by these authors. CarlZimmer (2019)commented in theNew York Timesthat these balls of cells may be the oldest animal embryos or something else entirely.
Cunningham et al. (2017b)reviewed all the published evidence from the Wenan biota of the Doushantuo Formation and concluded that although the Wengan Biota includes forms that could be animals, none can currently be assigned to this group with confidence. If there are not even definite animals, there can be no sponge embryos either.
Independent of the doubtful nature of the Doushantuo embryos, recently a multicellular organism was described as a microfossil from the Ediacaran Nyborg Formation in Norway (Agi et al. 2019). It was namedCyathinema digermulenseand the authors considered it as sharing characteristics with extant and fossil groups including red algae and their fossils, demosponge larvae and putative sponge fossils, colonial protists, and nematophytes. Even though sponge affinities are not ruled out, they have not been demonstrated either.
Even if all the body fossils discussed above fail to establish the presence of sponges prior to the Cambrian era, maybe we could at least find their most durable parts as microfossils: sclerotized needles, so-called spicules, that form the skeleton of sponges and are made of silica or calcite.
Indeed, several works described alleged sponge spicules from Precambrian deposits, mainly in China (Dunn 1964, Tang et al. 1978, Ding et al. 1985, Zhao et al. 1988,Allison & Awramik 1989,Brasier 1992,Steiner et al. 1993,Gehling & Rigby 1996,Brasier et al. 1997,Li et al. 1998a,Tiwari et al. 2000,Xiao et al. 2000,Du & Wang 2012, andDu et al. 2015). Even elaborate scenarios for the presumed evolution of sponge skeletons in the Proterozoic have been proposed based on this evidence (Mller et al. 2007).
Steiner et al. (1993)questioned the Doushantuo spicules andGehling & Rigby (1996)mentioned that of the many reported spicules from Proterozoic sediments most have proven to be volcanic shards or other inorganic crystals (Pickett, 1983).
Zhou et al. (1998) considered the spicule-like structures from the Doushantuo Formation described byLi et al. (1998)as nothing but pseudo-fossils, whileZhang et al. (1998)considered them as detached spines of collapsed acritarch protists.Cao & Zhu (2001)disagreed and remarked that based on the observation of extant specimens they tend to the interpretation of the sponges as monaxial spicules.
Yin et al. (2001)showed that the alleged sponge spicules from the Doushantuo Formation in China are indistinguishable from coexistent diagenetic crystals, thus inorganic artefacts rather than fossil remains. They found that the evidence for a sponge spicule interpretation of the Doushantuo spicular structures are at best ambiguous at present, but strangely added the inconsistent disclaimer (likely for political reasons) that despite our initial questioning the proposed interpretation of Doushantuo spicular structures as demosponge microscleres, we do not deny that sponges spicules do exist in Doushantuo cherts.
Antcliffe et al. (2014)reviewed all the published evidence for alleged sponge spicules from the Precambrian and dismissed all of them, mostly as abiogenic artifacts (e.g., the once oldest, widely accepted hexactinellid spicules from Mongolia, which were shown to be cruciform arsenopyrite crystals by EDX analysis). They found that the earliest reliable sponge fossils are hexact spicules from Iran dated to c. 535 Ma.
Muscente et al. (2015)used the most modern analytical techniques like scanning electron microscopy and synchrotron nanotomography to decisively assess the veracity of assumed Precambrian sponge needles, especially from the Doushantuo Formation. They found that their new data invalidate the oldest and only Precambrian demosponges with mineralized spicules. Thehighlightssection in their article says it all:
Finally,Botting & Muir (2018)agreed in the most recent review of early sponge evolution that there are no definite records of Precambrian sponges: isolated hexactine-like spicules may instead be derived from radiolarians. AndTang et al. (2019)likewise stated that the oldest spicules are Cambrian in age, but hypothesized based on a new Cambrian fossil that potential Ediacaran sponges might have lacked biomineralized spicules (also seeTang 2019). So, when alleged Precambrian spicules were found they were naturally considered as evidence for Darwinian evolution, and now since they are consistently lacking, Darwinian evolution is invoked to explain their absence. Whatever the evidence says, Darwinists always claim victory.
The latest claim was made recently byChang et al. (2019), who reported alleged sponge spicules from the Ediacaran-Cambrian boundary of the Yanjiahe Formation in China. However, in the actual article they only say that monaxon spicules and spicule-like structures in the lower Yanjiahe Formation might putatively be interpreted as demosponge remains, thus acknowledging a high degree of uncertainty. They also acknowledged that their interpretation of the monaxon spicules would be incongruent with the evolutionary scenario ofBotting & Muir (2018), who suggested a hexactine-based ground plan. In the Yanjiahe Formation non-monaxon spicules only appear just beneath the Lower CambrianProtohertzina anabariteszone (see their Figure 6).
The fact is this: Despite the multiple premature claims of success, genuine sponge needles from the Precambrian era thus not only have proved to be elusive like the proverbial needles in a haystack but indeed seem to be non-existent.
Based on chemical analyses of sediments it has been suggested that fossil steroids (24-isopropylcholestane and 26-methylstigmastane) are lipid biomarkers that provide indirect evidence for the existence of demosponges in the Precambrian (McCaffrey et al. 1994, Moldowan et al. 1994,Love et al. 2009,Sperling et al. 2010).Antcliffe (2013)questioned the evidence for sponge biomarkers because 24isopropylcholestane is also produced by marine algae or their diagenetic alteration, and claimed that it seems more likely that these compounds represent algal biochemical evolution at a time when algal burial occurred in great quantity with well-known coeval algal fossils but no sponge fossils. This was reasonably rejected byLove & Summons (2015), and even very recent studies byGold et al. (2016a),Gold et al. (2016b),Brocks et al. (2017),Sperling & Stockey (2018), andZumberge et al. (2018)still considered this so-called sponge biomarker hypothesis to be validated by the most up-to-date evidence. The popular science media reported Sponges on ancient ocean floors 100 million years before Cambrian period (UC Riverside 2018). However,Nettersheim et al. (2019)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. Ooops!
In a thorough revision of all twenty potential Precambrian sponge fossils, including most of the taxa discussed above (exceptEocyathispongia) as well as all the other unnamed candidates for sponge-grade metazoans,Antcliffe et al. (2014)came to the conclusion that that no Precambrian fossil candidate yet satisfies all three of these criteria to be a reliable sponge fossil. The authors suggested that molecular clocks should be recalibrated accordingly to a Lower Cambrian age of sponges and metazoans (such a recalibration is just a euphemism for using a fudge factor to get the desired outcome).Muscente et al. (2015)confirmed this result that no unequivocal sponge fossils occur below the EdiacaranCambrian boundary. Another recent study about the early history of sponges (Botting & Muir 2018) also found that there are no definite records of Precambrian sponges. Just a year later,Nettersheim et al. (2019)refuted the only remaining biomarker evidence (see above), so that all the empirical evidence for Precambrian sponges had finally evaporated. Maybe new fossil finds will come up with something better, but considering the track record so far, we probably dont have to hold our breath.
We can safely conclude that, contrary to common misconception, there exists zero compelling evidence for the existence of any genuine Precambrian fossil sponges. Unambiguous sponges only appear in the Cambrian explosion together with the other animal phyla. The oldest reliable fossil record for sponges is represented by siliceous spicules from the basal Cambrian of Iran (Antcliffe et al. 2014) and China (Chang et al. 2017,Chang et al. 2019) (the latter are slightly older, just below theProtohertzina anabariteszone). With an age of about 535 million years these are even two million years younger than the oldest trace fossil evidence for crown-group arthropods like trilobites recently dated to 537 million years ago (Daley et al. 2018). The first complete body fossils of sponges only appear even somewhat later in the Lowermost Cambrian (Steiner et al. 1993,Yuan et al. 2002.Flgel & Singh 2003). Only after 525 million years ago sponges became more common (Antcliffe et al. 2014), and crown group demosponges do not appear before 515 million years (Botting et al. 2015).
Having sponges appear after arthropods is not only a very bad stratigraphic fit, but indeed rather a temporal paradox like in many other cases (e.g., the oldest tetrapods and birds). If a good stratigraphic fit is considered to be confirmation for Darwins theory, then a poor stratigraphic fit (as well as a mismatch between molecular clocks and fossil record) has to count as conflicting evidence, even if evolutionists can fudge boldad hocexplanations (like 200-million-year-long ghost lineages,Sperling et al. 2010) to accommodate and explain away such unwelcome data.
Interestingly, the most comprehensive revision of the early fossil record of sponges, byAntcliffe et al. (2014), came to a conclusion very similar to that of intelligent design proponent Stephen C. Meyer in his seminal bookDarwins Doubt. Here is what they said in their conclusion: The Cambrian explosion was an evolutionary event of great magnitude and closely connected to the origin of animals. Science deniers like Jerry Coyne, Donald Prothero, and Nick Matzke, who downplayed the Cambrian explosion in their polemical reviews of Meyers book, should read the actual specialists to learn about the significance and abruptness of the origin of animal body plans in the Cambrian explosion, including the body plan of the most primitive animals, sponges.
Photo: Living Guantanamo sponge, by Timothy W. Brown / Public domain.
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The Myth of Precambrian Sponges - Discovery Institute