Talk:Ikaria wariootia

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Created talk-page

Created the talk-page for the "Ikaria wariootia" article - Enjoy! :) Drbogdan (talk) 15:00, 24 March 2020 (UTC)[reply]

Age - dubious

The age 555 Ma has been widely published in media about Ikaria but is given in the discovery paper as an age that may post-date the genus:

"Trace fossils from Brazil, representing the activity of meiofaunal bilaterians, occur 30 to 40 m above a tuff dated at 555 Ma and in close association with Cloudina, indicating that they are likely younger than Ikaria"

A tentative upper limit on age may be inferred by another section of the same paragraph:

"are conservatively 560 to 551 Ma (21–24). The stratigraphic position of Helminthoidichnites suggests that the first appearance of Ikaria was likely within this age range or possibly earlier."

As such, I think it's best to label the age range as 560-555 Ma as a better indicator of the uncertainty in age. The authors specifically note that the age of the Ediacara Member is not well-defined currently. 00A86B (talk) 12:24, 15 August 2021 (UTC)[reply]

See the original article about Brazilian trace fossils - L. A. Parry et al., Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil. Nat. Ecol. Evol. 1, 1455–1464 (2017).

The brazilian trace fossils were collected from approximately 30–40 m above the base of the Tamengo Formation that also contains Сloudina fossils and two dates 541.85 ± 0.75 Ma and 542.37 ± 0.28 Ma. The Brazilian date 555.18 ± 0.3 Ma is derived from the underlying Bocaina Formation. The Tamengo Formation overlies the Bocaina Fm. with unconformity. Evans ' article says that the Brazilian trace fossils and Cloudina are younger than 555 Ma bed, not that Ikaria older 555 Ma. Worldwide, Cloudina fossils are known from deposits dated between 550-539 Ma.

The Australian deposits are not dated, but deposits with the similar fauna in Ukraine, Russia (White Sea and Ural) and China are well dated, about 10 U-Pb dates at 567 to 550 Ma. Key species (including Kimberella) common with Australia are known from age interval between 558-550 Ma, and the Australian fauna has maximum similarity with the White Sea fauna near tuff bed 555.36 ± 0.3 Ma (recently recalculated to 552.85 ± 0.77 Ma). Aleksey (Alnagov (talk) 21:59, 15 August 2021 (UTC))[reply]

It's entirely possible I've misinterpreted Evans et al here, my main complain was that the age range (given as precisely 555 Ma, not a range) seemed implausibly narrow for such a poorly understood species which the paper never gives an explicit age for, in a formation which is only comparatively dated. I think keeping the lower bound of ~560Ma makes sense but I am happy to remove references to 555 Ma as lower bound if this was an error on my part. If it's possible to back up a better age range then please do so. 00A86B (talk) 00:23, 18 August 2021 (UTC)[reply]

Features. 00A86B edits

Evans et al. 2020 write: "Given the simple morphology and preservation of both body and trace fossil in negative relief, even if Ikaria was preserved at the end of a trail, it is unlikely that it would be possible to confidently identify as distinct from that trace. We interpret the surprising discovery of Helminthoidichnites with nearby Ikaria (Fig. 2A) as the result of vertical movement from the bedding plane in the region between the end of its trace fossil and its final resting place. While this scenario was likely exceedingly rare, it may represent the only situation in which it would be possible to distinguish associated body and trace fossils and further corroborates interpretations of Ikaria as the progenitor of Helminthoidichnites."

There are no traces of vertical movement connecting this Ikaria specimen and this Helminthoidichnites trace specimen (Fig. 2A). They just sit side by side. About 100 Ikaria fossils and 600 Helminthoidichnites trace fossils were found together on one surface. It should be expected that, according to the theory of probability, some Ikaria fossil will randomly appear near Helminthoidichnites trace fossil. Such a single find is not a "surprising discovery" and cannot serve as any argument in support of the reasoning (fantasies) outlined in the article by Evans et al. 2020. Aleksey (Alnagov (talk) 17:10, 16 August 2021 (UTC))[reply]

I agree that the reasoning in the paper seems somewhat odd, but presently Evens et al (2020) is the only peer reviewed source on Ikaria. My edit leaves open the possibility that the appearance is coincidental, I think it's best to leave more definitive criticism until it can be cited from a credible source. If/when someone publishes a paper putting Evans et al into dispute then I'll have no issues with reporting that. 00A86B (talk) 00:16, 18 August 2021 (UTC)[reply]

Perhaps I will include a critical review of Evans et al. 2020 and Drosser et Gehling 2018 (about Helminthoidichnites) articles in one of my papers on new Ediacaran trace fossils from the White Sea area, or someone from paleoichnologists will do it before me. But this is a long process. Aleksey (Alnagov (talk) 13:38, 18 August 2021 (UTC))[reply]