Pseudoolenoides oilcreekensis, Adrain & Karim, 2012

Adrain, Jonathan M. & Karim, Talia S., 2012, 3467, Zootaxa 3467, pp. 1-97 : 30

Pseudoolenoides oilcreekensis n. sp.

Plate 12, figs 15, 20, Plate 20

1974 Pseudoolenoides acicaudus Hintze ; Shaw, p. 22, pl. 1, figs 13–22, 24.

1975 Pseudoolenoides acicaudus Hintze ; Derby, p. 26.

Material. Holotype, cranidium, OU 7939 (Pl. 20, figs 1, 4), from Section SP 1 126.8 m, and assigned specimens OU 7940–7947 , from Section SP 1 104.5 m and 126.8 m, Highway 77 section, Oil Creek Formation (Darriwilian), Carter County, Oklahoma, USA.

Etymology. From the Oil Creek Formation.

Diagnosis. Eye ridge with highly oblique course; fixigena relatively narrow; pygidium with raised pleural regions; anterior pleural band with distinct distal node.

Description. This species is very similar in cephalic morphology to P. acicaudus , with which it was originally identified ( Shaw, 1974). Hence, it is described via comparison with that species, noting all observable differences. Cranidium with eye ridge set more obliquely (very clear in Pl. 20, figs 1, 2, but Pl. 20, fig. 3 approaches the attitude seen in P. acicaudus ); interocular fixigenae distinctly narrower (transverse line from maximum lateral point of glabella to exsagittal line running through Ύ is 27–31% sagittal distance from front of LO to front of glabella in P. oilcreekensis , versus 35–40% in P. acicaudus ); anteromedian portion of LO set forward as distinct subtrapezoidal protrusion of anterior margin versus margin nearly transversely straight with only slight anterior projection in a few specimens (e.g., Pl. 17, fig. 17); pygidium with four versus five unreleased segments; raised pleural regions, anterior pleural band with swollen node on distal part, axis tapers more rapidly, rear of axis much narrower; posteromedian spine much more robust proximally and apparently longer.

Discussion. In cephalic morphology, P. oilcreekensis is differentiated from P. acicaudus to an extent which leaves no doubt it is a distinct species. The differentiation is still very subtle, and given the very close similarity of the cranidia and pygidia one would expect the pygidia also to be close. This is not the case, as the single pygidium occurring in the Oil Creek Formation with the cephalic material (Pl. 20, fig. 15) is quite radically different from that of P. acicaudus , and instead more closely resembles those of P. carterensis and P. fossilmountainensis . Given this, one must at least consider the possibility of misassociation. There is apparently no cephalic material associated with the pygidium other than figured herein, but the overall sample size is very small and the possibility exists that the pygidium belongs to a second, rare, species. For this reason we have selected one of the larger heads (Pl. 20, fig. 1) which displays the cranidial differentia well as the holotype, even though if correctly associated the pygidium is the much more distinctive sclerite. Pseudoolenoides oilcreekensis occurs a comparable distance beneath P. carterensis in the Oil Creek Formation (48.8 m at the Highway 77 section) as P. acicaudus does beneath P. fossilmountainensis in the Kanosh Formation (approximately 68 m) and the pairs of species are each other's closest comparison.