Olenellus

Gapp, I. Wesley & Lieberman, Bruce S., 2014, New olenelloid trilobites from the Northwest Territories, Canada, Zootaxa 3866 (4), pp. 479-498 : 482-483

Olenellus sp. aff. getzi Dunbar, 1925

Fig. 2.1, 2.2

? Olenellus sp. 1 Fritz, 1991, p. 16, pl. 2, figs. 7, 8.

Material examined. KUMIP 355557 and PWNHC-2013.23.2.

Discussion. These specimens most closely resemble O. getzi . Key diagnostic features that they share include: broadly convex anterior cephalic border; the absence of a preglabellar field; S2 and S1 are not conjoined adaxially; and the ocular lobe has a prominent furrow that is present across the entire margin. Fritz (1991) and Whittington (1989) both noted strong similarities between O. getzi and O. thompsoni ( Hall 1859) , and this close relationship was further supported by phylogenetic evidence ( Lieberman 1999). The specimens presented here can be distinguished from O. thompsoni based on characters identified by Lieberman (1999) that include: lateral margins of LA directly anterior of lateral margins of LO; the lateral margins of L2 do not bulge laterally relative to L1; the posterior margins of the ocular lobes extend back to the abaxial tips of SO; and the anterior margins of T3 are deflected anteriorly relative to a transverse line. However, these specimens do not share the same characteristics as O. getzi . For instance, in the specimens illustrated herein S3 is conjoined adaxially. The material available is too incomplete to merit description of a new species.

Olenellus sp. 1 in Fritz (1991) represents relatively early ontogenetic stages, yet it shares several characters with O. sp. aff. getzi . These include the lack of a preglabellar area, S3 strongly convex and conjoined adaxially, S2 not conjoined adaxially, and an extraocular area that is gently convex. Due to these similarities, we suggest that Fritz’s (1991) specimens may be an early ontogenetic stage for the species identified here.

In southwestern Laurentia, this genus typically occurs high up in the Dyeran stage ( Webster 2011a, 2011b; Webster et al. 2011). However, in northwestern Laurentia at least these specimens of Olenellus (which are inferred to be closely similar to a species previously known only from northeastern Laurentia) occur stratigraphically relatively low down in the stage. However, it is worth noting that the early Cambrian stratigraphy of northeastern Laurentia has not been comprehensively revised to the extent that it has been in southwestern Laurentia.

Occurrence. Olenellus zone or Waucoban Series, Dyeran stage, sensu Webster (2011a, b) and Webster et al.

(2011), early Cambrian, Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada, Section 2, 260 – 280 m above the base of section, and also questionably from Illtyd Formation, Wernecke Mountains, Yukon Territory, Canada (Unit 3) (see Fritz 1991).