Talk:Yarravia

Tims and Chambers on the location of Cookson's fossils

On p. 265 (the first page) of Tims & Chambers (1984) – full reference in the article – they write "The Lower Plant Assemblage material ... None of this material had been included in Lang and Cookson's papers. ... The Upper Plant Assemblage material illustrated by Lang and Cookson (1935) was collected from Killingworth Road, Yea." Thus they are saying that all of the material described by Lang and Cookson was actually from Yea. If you look at Lang and Cookson's paper, it seems clear that they were not familiar with the geography of the area. So I had put: "Tims and Chambers say that the material described by Lang and Cookson was from near Yea, some distance from the location originally given." This was removed with the comment that it wasn't supported by the source; I have now restored it. I accept that the second half of the sentence isn't in the original; it's a simple geographical inference, but if other editors aren't happy it can be removed. However the first part does appear to me to be supported by the source given. Peter coxhead (talk) 20:00, 20 December 2011 (UTC)

You are correct that Lang & Cookson (1935) had some fossil plants from Yea. It does not include Yarravia, as can easily be ascertained from their paper, where it is explicitly stated on p. 447 that all the Yarravia material came from the Yarra Track, and the captions with the illustrations again state this. Tims & Chambers (1984) p. 265 statement is not speaking about Yarravia, but about an assemblage of early land plants, the so-called "Upper Plant Assemblage", and specifically about the specimens of this which were collected by the Harris & Thomas party in 1929, which did not include Yarravia. I hate to bombard with references, but this last point can easily be checked, as Cookson in 1949 published a list of all Siluro-Devonian plant records which she was aware of ("Records of plant remains from the Upper Silurian and Early Devonian Rocks of Victoria", Proceedings of the Royal Society of Victoria vol. 56, 119-122). So IMHO bringing Yea into the picture gives a misleading picture of Yarravia, the subject of the article, however much it may be valid for other early land plants such as Baragwanathia. If you have a public email address I can give you chapter and verse on any other references you may come up with, the early land plants of Victoria have been the cause of much wrangling over the years which it would be a pity to propagate to Wikipedia. MisterCDE (talk) 09:19, 21 December 2011 (UTC)

BTW, the text in the "Taxonomy" section appears to duplicate text in other sections. Perhaps this can be removed? MisterCDE (talk) 09:25, 21 December 2011 (UTC)

Ok, well I've removed the sentence again (for the present), although I think that other people have picked up Yea as the location for Yarravia (I don't have access to all my sources over the holidays). Note that the reference should be there as it supports all the material from "The shale in which they were found ..." to the end of the paragraph. The issues, I think, are not whether Lang & Cookson said that it came from the Yarra Track, but (a) were they right (b) what is the age of the deposits in which Yarravia was found? As you say, it's clear from the literature that there is uncertainty about the age of the early land plants of Victoria, and I'm certainly no expert. So what is the evidence about the age of Yarravia if it did come from the Yarra track? Peter coxhead (talk) 10:12, 21 December 2011 (UTC)

The age of the Wilson Creek Shale, which is the geological unit at the Yarra Track locality, is given by a graptolite which occurs there. In fact Lang & Cookson (1935) carefully chose their plant specimens only from graptolite localities to demonstrate the age, as they say in their paper. They believed the graptolites to be Silurian, but Jaeger (1966) (the reference is cited by Tims & Chambers) showed them to be a new Early Devonian species Monograptus thomasi. Since Jaeger's paper the age of the graptolites has been refined by many other studies too numerous to mention, and is now believed to range from kindlei zone of the Pragian to the lowest conodont zone of the currently defined Emsian (soon to be redefined). The latest synthesis of graptolite ages that I'm aware of is Jaeger (1993) "Graptoloidea" in Devonian of the World vol. 3, 431-438 (CSPG, Calgary); see also the paper by Lenz in the same volume on Canadian graptolites, as the species also occurs in N. America where dating is easier. The reason I do not want to bring Yea into the picture in an article about Yarravia is that other, Silurian, graptolites are claimed to occur at several Yea early plant localities (but not the Killingworth locality from which Lang & Cookson's specimens came - that is much higher stratigraphically) and it is this claim that is controversial; but Yarravia has not been said to occur at those localities. MisterCDE (talk) 20:11, 21 December 2011 (UTC)

You obviously know much more about this subject than I do. (I just decided that the coverage of paleozoology was disproportionate to paleobotany and set about adding articles on Silurian/Devonian plants; it's not my area of expertise.) I was initially surprised at a comment that I added something not in the source, because normally I'm very careful about this. It seems that I mis-interpreted Tims & Chambers, although I think that I got their paper initially from a secondary source which says what I did – however I may be wrong.

On the issue of repetition, you're right. It comes from trying to have the same structure for articles on Siluro-Devonian plants. I think a little bit is ok in the interests of making it easier for readers to find specific topics within an article, but I agree there's too much here. I'll make a few changes, but feel free to make more! Peter coxhead (talk) 07:52, 22 December 2011 (UTC)

No problem. Thanks for your contribution, I seldom have the time these days to compose articles like that. MisterCDE (talk) 08:18, 22 December 2011 (UTC)