Cambrian Explosion: Namacalathus refuted ; no slope (Introduction)

by David Turell , Thursday, January 21, 2021, 01:05 (1403 days ago) @ David Turell
edited by David Turell, Thursday, January 21, 2021, 01:29

A scathing criticism by Gunter Bechly about our slope discussion in 'miscellaneous':

https://evolutionnews.org/2021/01/namacalathus-revisited-not-much-to-see/

"Shore et al. also speculate that “the generally six, large lateral lumens point to either a colonial organization for Namacalathusor a solitary organism in which lumens might correspond to brood chambers formed by external body wall invaginations, as found in bryozoans.” Again, there is much uncertain speculation here with “either/or” and “might.” Nevertheless, they boldly reconstruct Namacalathus with such brood chambers (compare Fig. 5 in Shore et al. 2021).

"There are numerous problems with this reconstruction, apart from the fact that the very existence of such brood chambers in Namacalathus is speculative and uncertain:

"Such brood chambers are not hexameric in bryozoans.
Such brood chambers neither belong to the ground plan of lophotrochozoans nor to that of lophophorates and thus cannot establish a relationship. The authors would have to document a bryozoan relationship of Namacalathus, which they neither provide nor even claim.
The authors do not provide a comparison of the detailed structure of the assumed brood chambers with that of bryozoans to document any specific similarities that would suggest homology.

***

"However, this statement is pretty much nonsensical, as the pores in these taxa are not considered to be homologous anyway, as is indicated by the term “pseudopunctae” in bryozoans. Also, these taxa do not even form a monophyletic group or clade. The authors themselves acknowledge this non-homology just a page later when they say that the “‘punctae’ have multiple origins across the brachiozoan total group.” But just another sentence later they again emphasize the similarity with the sensory pores in lophophorates. Such sloppy reasoning is embarrassing and is simply poor science.

***

{"In the abstract the authors affirm the presence of a “probable J-shaped gut” as supporting a lophotrochozoan affinity. That is strange, because lophotrochozoans do not have a J-shaped gut as a defining character. However, it gets worse: in the actual description of the preserved traces the authors clearly say that “Alternatively, this may represent a retractor muscle band …or body cavity extension.” So, obviously it could be something totally different from a gut. But the authors prefer to think (without offering further evidence) that it is “more likely a gut” and boldly suppose that it is “potentially a partially preserved U-shaped gut” (emphasis added). The reason the authors want the gut to be U-shaped is that such a gut is one of the diagnostic features of lophophorates, including the supposed Cambrian stem lophophorate Cotyledion from the famous Chengjiang locality (Zhang et al. 2013). Here we have the next fatal problem: a J-shaped gut, as preserved in the fossils, would not represent a similarity with lophophorates at all. Therefore, the authors have to invoke a completely ad hoc hypothesis: an exceptionally preserved gut that is incompletely preserved in all studied specimens, to make a U-shaped gut look like a J-shaped gut. But there is no evidence as to why just the rest of the U-shaped gut should always be unpreserved. The uncertainty is revealed in the authors’ other statements, where they speak about “a J- or U-shaped inferred gut” or a “possible J- or U-shaped gut.” So maybe it is a J-shaped gut, unlike in lophophorates, after all, and maybe the inferred gut is not a gut at all. Thus is not exactly what I would call compelling evidence.

***

"What they conveniently fail to mention is that these comparisons are outdated and obsolete, because Dinomischus and Siphosauctum have been recognized by Zhao et al. (2019) as a group of sclerotized stem ctenophorans (comb jellies) and thus do not even belong to bilaterian animals. Moreover, Namacalathus shares even more similarities with Siphosauctum(not just a stalk and calyx, but also the hexaradial symmetry with a ring of six lateral openings), which suggests a ctenophoran relationship of Namacalathus as well. Since Shore et al. cited the work of Zhao et al., they must have been aware of these issues.

"To Sum Up
There is not much to see here. The new evidence is very ambiguous and totally inconclusive. No far-reaching conclusions should be drawn from such dubious material and such a deficient and sloppy scientific study. Namacalathus remains what it was before — a problematic organism of uncertain affinity. And whatever Namacalathus ultimately turns out to be, the Cambrian Explosion also remains what it always was — fatal conflicting evidence against any theory of unguided evolution.

"As a concluding note: Lophotrochozoa is a higher taxon of invertebrate animals, including lophophorates (brachiopods, horseshoe worms, and moss animals) and trochozoans (molluscs, annelids and ribbon worms), which has been postulated mainly based on phylogenomic data. Entoprocts are enigmatic living invertebrates that have a much debated and strongly disputed position within Lophotrochozoa."

Comment: We've met the highly trained Bechly before. The slope we discussed between Ediacaran and Cambrian under 'miscellaneous' may still be just a gap. Darwinists sure try hard to get rid of it.