Cybantyx sp. (Lane & Thomas 1978)

@Ludwigia I would wager this is Bumastus ioxus since this is Silurian material.  

Looks more like a bumastus than a faelleana

28 minutes ago, Kane said:

@Ludwigia I would wager this is Bumastus ioxus since this is Silurian material.  

3 minutes ago, Malcolmt said:

Looks more like a bumastus than a faelleana

Thanks guys. Somebody who knows more than me about trilobites suggested Failleana, so I took him at his word. But I think you guys know even better, so I'll rectify this in a minute. Thanks for your input.

Holloway 2021 has recently reclassified Bumastus ioxus as a junior synonym of Bumastus barriensis. The pygidium of B. barriensis should be approximately 1.25 times wide as long. The width to length ratio of this pygidium appears to be more equalized suggesting a different illaenid similar to Cybantyx sp.

Remarks: Historically widely reported both stratigraphically and geographically, Bumastus was restricted by Holloway & Lane (1998: 872) to three named species in addition to the type; one of those species, B. ioxus (Hall, 1867) is a junior subjective synonym of B. barriensis (see following remarks on that species). The genus has a stratigraphic range of Wenlock to possibly Ludlow and a geographical distribution in eastern and central North America (Illinois, Wisconsin, Indiana, New York, Ontario, Tennessee, Arkansas, Oklahoma) and the Welsh Borderlands of England.

‘Illaenus’ ioxus was proposed by Hall (1867: 378) for specimens from the Racine Formation of Wisconsin that in the first half of the same paper (p. 332), printed a couple of years before the remainder, he assigned to ‘Illaenus (Bumastus)’ barriensis. Also assigned to the new species were specimens he had earlier (Hall 1843; Hall 1852) identified as barriensis, from the Rochester Formation (Sheinwoodian) of New York. Hall (1867) recorded ioxus in Wisconsin from ‘Racine, Waukesha, Wauwatosa, and other places’.

I can identify no significant morphological differences between the Wisconsin and British specimens, and consequently regard B. ioxus as a junior synonym of B. barriensis. I have not examined any specimens of the Bumastus species attributed to B. ioxus from the Rochester Formation, and the specimens illustrated have all been crushed (e.g. Levi-Setti 1975: pl. 77; Levi-Setti 1993: pl. 171; Whiteley et al. 2002: pl. 11; Lawrance & Stammers 2014: fig. on p. 356). Weller (1907: 223) suggested that they are not conspecific with the specimens from Wisconsin; however, like Raymond (1916: 21), I can see no evidence to support this view, and hence I assign the Rochester Formation specimens also to B. barriensis.

text from:

Holloway, D.J. 2021. Middle Silurian Trilobites from Arkansas and Oklahoma, USA. Order Corynexochida.

Palaeontographica Abteilung A, 319(1-6):1-55

figure 8. Cybantyx anaglypte from:

Thomas, A.T. 1978. British Wenlock Trilobites. Part 1. Monograph of the Palaeontographical Society, 132(552):1-56

Coincidentally, here is another Cybantyx sp. from Ontario that was posted in a short video back in 2016. Dave Rudkin of the ROM provided the ID.

@piranha

So, if Bumastus is restricted to the Silurian what genera did all the Ordovician species migrate to?

Don

12 minutes ago, FossilDAWG said:

@piranha

So, if Bumastus is restricted to the Silurian what genera did all the Ordovician species migrate to?

 

Don

I (likely wrongly) assume the Ordovician ancestor would be Bumastoides. 

Bumastus and similar Silurian trilobites are phyletic derivatives of Ordovician bumastines and not effaced scutelluids as claimed recently by Lane & Thomas. Revised diagnoses of Illaeninae and Bumastinae are presented... ...Specifically, our purpose in preparing this paper is threefold: (a) To demonstrate the integrity of the taxonomic unit we designated Failleana calva and to elucidate the ontogeny of this species in response to recent criticisms by Lane & Thomas (1978). (b) To suggest an Early Ordovician origin of the illaenines and bumastines from the styginids and a Middle Ordovician origin of the scutelluids from the bumastines. (c) To advance the view that Bumastus and similar Silurian trilobites are phyletic derivates of Ordovician bumastines and not effaced scutelluids as suggested by Lane & Thomas (1978) and Thomas (1978).

Ludvigsen, R., Chatterton, B.D.E. 1980. The Ontogeny of Failleana and the Origin of the Bumastinae (Trilobita). Geological Magazine, 117(5):471-478

***Holloway 2021 and Holloway & Lane 2016 continue to designate the Subfamily Bumastinae as:   "Family uncertain"

Holloway, D.J., Lane, P.D. 2016. Trilobites of the Suborder Illaenina from the Silurian of North Queensland, Australia. Journal of Paleontology, 90(3):433-471

Thanks Scott.

Don