# Protomelission

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> Source: https://en.wikipedia.org/wiki/Protomelission
> Source revision: 1292867768
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{{Short description|Contested Cambrian fossil}}
{{Automatic taxobox
| fossil_range = {{fossil range | Cambrian stage 3}}
| image = Wirrealpa_Protomelission.png
| image_caption = Microfossil of ''Protomelission'' from Wirrealpa. Reproduced from Zhang et al. 2021<ref>{{cite journal
 | doi = 10.1038/s41586-021-04033-w
| title = Fossil evidence unveils an early Cambrian origin for Bryozoa
| year = 2021
| last1 = Zhang
| first1 = Zhiliang
| last2 = Zhang
| first2 = Zhifei
| last3 = Ma
| first3 = Junye
| last4 = Taylor
| first4 = Paul D.
| last5 = Strotz
| first5 = Luke C.
| last6 = Jacquet
| first6 = Sarah M.
| last7 = Skovsted
| first7 = Christian B.
| last8 = Chen
| first8 = Feiyang
| last9 = Han
| first9 = Jian
| last10 = Brock
| first10 = Glenn A.
| journal = Nature
| volume = 599
| issue = 7884
| pages = 251–255
| pmid = 34707285
| pmc = 8580826
| bibcode = 2021Natur.599..251Z
}}</ref>
| taxon = Protomelission
| authority = Brock, G. A. & Cooper, B. J. 1993<ref name=Brock>{{cite journal | doi = 10.1017/S0022336000037045| title = Shelly fossils from the Early Cambrian (Toyonian) Wirrealpa, Aroona Creek, and Ramsay Limestones of South Australia| year = 1993| last1 = Brock| first1 = Glenn A.| last2 = Cooper| first2 = Barry J.| journal = Journal of Paleontology| volume = 67| issue = 5| pages = 758–787| s2cid = 132278189}}</ref>
}}

'''''Protomelission''''' is a [Cambrian](/source/Cambrian) fossil taxon of contested [affinity](/source/Affinity_(taxonomy)).  It comprises [cataphract](/source/cataphract) arrays of box-like chambers, forming a club-shaped [thallus](/source/thallus) surrounding a hollow central cavity.  It was first described from [phosphatized](/source/Phosphatization) microfossils whose individual chambers were interpreted as housing the [zooid](/source/zooid)s of a non-mineralized [bryozoan](/source/bryozoan), which would make it the only affinity representative of that phylum – implying that all animal [phyla](/source/phylum) originated in the [Cambrian](/source/Cambrian) period.<ref name=Zhang>{{Cite journal
 | doi = 10.1038/d41586-021-02874-z
| title = Bryozoan fossils found at last in deposits from the Cambrian period
| year = 2021
| last1 = Ernst
| first1 = Andrej
| last2 = Wilson
| first2 = Mark A.
| journal = Nature
| volume = 599
| issue = 7884
| pages = 203–204
| pmid = 34707263
| bibcode = 2021Natur.599..203E
| s2cid = 240073927
}}</ref>
The subsequent discovery of articulated macrofossils from the Xiaoshiba<ref>{{Cite web|url=https://www.mindat.org/paleo_loc.php?id=23464|title=Xiaoshiba, Kunming, Yunnan, China|website=www.mindat.org}}</ref> [biota](/source/biome) called into question the biological nature of the distal apertures, showing that the surface was instead covered with leaf-like triangular flanges.  This has led to the reinterpretation of the fossil material as a "seaweed", strictly as a [dasycladalean](/source/Dasycladales) green alga.<ref name=Yang>{{Cite journal
 | journal = Nature 
 | year = 2023
 | title = ''Protomelission'' is an early dasyclad alga and not a Cambrian bryozoan
 | doi = 10.1038/s41586-023-05775-5 | pmid = 36890226 | s2cid = 257425218 | last1 = Yang | first1 = Jie | last2 = Lan | first2 = Tian | last3 = Zhang | first3 = Xi-Guang | last4 = Smith | first4 = Martin R. | volume = 615
 | issue = 7952
 | pages = 468–471
 | url = https://durham-repository.worktribe.com/file/1182254/1/Accepted%20Journal%20Article
 }}</ref>

== History of description ==

''Protomelission'' was first described by Brock & Cooper in 1993 from limestones in [Wirrealpa](/source/Wirrealpa), Australia.  A bryozoan affinity was dismissed on the basis that its walls were too thin, among other things.<ref name=Brock/>
The fossil material was complemented by additional specimens from China, causing Brock and colleagues to revisit this earlier statement.  A key line of evidence in favour of the bryozoan affinity was the regular array of openings exhibited by each chamber.<ref name=Zhang/>  However, these openings were later argued to have arisen [taphonomically](/source/Taphonomy), i.e. by abrasion of an originally solid wall, or by enlarging a much smaller original hole.  Where a bryozoan affinity would denote the presence of a stalked ring of tentacles emerging from each module, the recovery of macrofossil material with soft tissue preservation demonstrated that each chamber was instead associated with a tapering conical flange, better suited to photosynthesis.<ref name=Yang/>  Authors of the original study are unconvinced by this reinterpretation, suggesting in media reports that the absence of tentacles may in turn be an effect of imperfect preservation.<ref>{{Cite news |last=Ashworth |first=James |date=8 March 2023 |title=New fossils challenge the identity of the oldest bryozoan |work=Natural History Museum |url=https://www.nhm.ac.uk/discover/news/2023/march/new-fossils-challenge-identity-oldest-bryozoan.html}}</ref>

== Available fossil material ==

''Protomelission'' is known from two distinct modes of preservation: [small shelly fossils](/source/small_shelly_fossils) from Australia and China, which are millimetric phosphatized fragments; and [Burgess Shale](/source/Burgess_Shale)-type macrofossils, which preserve more delicate anatomy.  The former are fully three-dimensional; the latter, squashed into a couple of planes of [mudstone](/source/mudstone).
These different preservational modes mean that the material from the two settings is not identical, and it is challenging to establish beyond doubt that the two forms of fossil belong to the same species, or even on a cynical view both to the same sort of organism.<ref>As emphasized by Paul Taylor in {{Cite news | url = https://www.newscientist.com/article/2363472-fossil-thought-to-be-earliest-bryozoan-animal-may-actually-be-seaweed/ | website=New Scientist| title=Fossil thought to be earliest bryozoan animal may actually be seaweed | date=8 March 2023 | first=Christa | last=Lesté-Lasserre }}</ref> 
Whether or not the two types of fossil are [conspecific](/source/Biological_specificity), Yang et al. argue that the similarity in gross morphology is sufficient to show that a [dasyclad](/source/Dasycladus) interpretation is plausible for both sets of fossil material, and that the material cannot be considered a ''bona fide'' bryozoan.<ref name=Yang/>

== References==
{{Reflist}}

==Further reading==
[https://www.haaretz.com/israel-news/science/2023-03-08/ty-article/.premium/a-hiccup-in-the-annals-of-animal-evolution-that-thing-was-a-plant/00000186-bce3-d247-a5ff-feef7d670000 A Hiccup in the Annals of Animal Evolution: That Thing Was a Plant - Science - Haaretz.com]

{{Taxonbar|from=Q117089942}}

Category:Ulvophyceae
Category:Fossil taxa described in 1993

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Adapted from the Wikipedia article [Protomelission](https://en.wikipedia.org/wiki/Protomelission) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Protomelission?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.