Cambrian Trilobite ID

[JesseKoz]

Below is a Trilobite fossil from the Arthur Creek Formation (middle Cambrian) I found some months ago. This formation is located in the Southern Georgina Basin in Central Australia, in a remote location between Northern Territory and Queensland. I hadn't attempted preparing a fossil before and decided to finally give it a try. I wanted to see if the Cephalon was present and still intact and if I could carefully uncover it. I'm quite pleased with how it turned out, as the fossil is comprised of a very dense sandstone and I was told it could be a challenge. 

 

Now I have it fully uncovered I wanted to see if anyone could help with identification.

 

From the reading I've done I'm thinking it's Xystridura Templetonensis. The two circular sections either side of the Glabella, which itself is quite circular line up with other examples I see of Templetonensis. I find it hard to get an accurate thorax segment count, but I believe I see 13, which would also line up with what I thought. Thanks for any help!

[JesseKoz]

I took some more detailed measurements of the specimen, comparing to a chart on Templetonensis.

 

Chart: https://d28rz98at9flks.cloudfront.net/92/Bull_121.pdf (Page 47, Table 2. Xystridlira templetonensis (Chapman), trends in holaspid morphogenesis.)

 

My Measurements

Total Length = 61mm
Cephalon Length = 22mm
Cephalon Width = 39mm

Length, cephalon:length, total = 0.37
Length, cephalon = 10 segments of thorax
Total width (max):total length = 0.63

 

The total length is my estimate as the last few segments of the Pygidium are missing.

[Monica]

I'll tag @piranha - he's the trilobite guy 

 

(Nice find, by the way!)

[Fossildude19]

Nice fossil and good prep job!

Thanks for posting it here.  

[FossilNerd]

Nice bug, and for a first prep job I’d say you did rather well! 

 

I wish I could help with the ID, but I don’t have a clue on this one. Hopefully Monica’s tag to Piranha will get you some results.  

[piranha]

X. templetonensis looks like a match ... nice find!

[fifbrindacier]

Nice find, thanks to share it with us @JesseKoz

[Tidgy's Dad]

Lovely bug and a very good prep job too, especially for a first go. 

[JesseKoz]

Thanks everyone for the replies!

 

Very pleased with the specimen, as it's one of the only finds from this location I found containing nearly the entire Trilobite, letting me take measurements.

 

The other species that I was considering was X. Saintsmithi, the description of this was very similar to X. Templetonensis. Also I found that a specimen in Victoria Museum is listed as X. Templetonensis on their website, with the image displaying a tag of X. Saint-Smithi. So, maybe I'm not the only one struggling to tell the two apart haha. (https://collections.museumvictoria.com.au/specimens/1362374)

[piranha]

1 hour ago, JesseKoz said:

The other species that I was considering was X. Saintsmithi, the description of this was very similar to X. Templetonensis. Also I found that a specimen in Victoria Museum is listed as X. Templetonensis on their website, with the image displaying a tag of X. Saint-Smithi. So, maybe I'm not the only one struggling to tell the two apart haha.

 

 

Xystridura saintsmithi was described from a single specimen.  Accordining to Öpik 1975, it is a synonym of Xystridura templetonensis.

 

 

The type species of Xystridura Whitehouse, 1936, is Milesia templetonensis Chapman, 1929 and not Olenellus browni Etheridge Jr, 1897, as hitherto quoted in the literature; the species name Xystridura templetonensis (Chapman) prevails over its subjective synonyms, including perhaps the commonly used X. saintsmithi.

 

Whitehouse (оp. cit. p. 200) gave his preference for the name saintsmithi because it was the first species described by Chapman; the application of the page precedence rule in Whitehouse (1939), however, was too late: three years earlier, the first reviser Whitehouse (1936, p. 74, footnote) in replacing Milesia Chapman by the new name Xystridura tacitly acknowledged the validity and the priority of the species name Milesia templetonensis, which is the holotype of the monotypical genus Milesia Chapman.

 

The species name Xystridura saintsmithi adheres to a single specimen - the holotype of Bathyuriscus saintsmithi Chapman, 1929, plate 21, figure 7. Whitehouse (1939) in assuming the synonymy of all species of Chapman (оp. cit.) gave priority to the name saintsmithi, which is, however, not accepted here (see p. 29). lt appears that the holotype of saintsmithi may represent either an individual variant of X. templetonensis or X. dunstani or a separate species. lt is presented here as such because the synonymies are inconclusive and may be only apparent.

 

Öpik, A.A. 1975
Templetonian and Ordian Xystridurid Trilobites of Australia. 
Australia Bureau of Mineral Resources, Geology and Geophysics Bulletin, 121:1-84  PDF LINK

[JesseKoz]

@piranha Great information! Thank you very much.