Bristolia colberti, Gapp, I. Wesley & Lieberman, Bruce S., 2014

Gapp, I. Wesley & Lieberman, Bruce S., 2014, New olenelloid trilobites from the Northwest Territories, Canada, Zootaxa 3866 (4), pp. 479-498 : 495-496

Bristolia colberti sp. nov.

Fig. 2.4

Type material. Holotype KUMIP 355552. Paratypes KUMIP 355553 and PWNHC 2013.23.35–37.

Etymology. In honour of actor and comedian Stephen T. Colbert.

Diagnosis. Width of interocular area approximately 0.5 times the width (tr.) of ocular lobe; L2 and L3 do not merge abaxially; prominent ocular furrow; width of the ocular lobe is equal to the width of the extraocular area abaxial to L2.

Description. Anterior cephalic border directly anterior of ocular lobes directed posteriorly 5-10 degrees, length (sag.) approximately 0.6 times length LO; anterior border furrow present; LA contacts anterior border furrow; length (sag.) of LA is approximately the combined length (sag.) of LO, LI, and L2; posterior half of LA constricts to width 0.6 times that of widest part of LA; furrow present where ocular lobes contact LA; ocular furrow present; ocular lobes wide, maximum width approximately equals width (tr.) extraocular area, extending posteriorly to L1; width of interocular area measured opposite L1 approximately 0.5 times the width (tr.) of ocular lobe; S3 convex anteriorly, conjoined adaxially; abaxial margins of L3 extend further adaxially than L2; L2 and L3 do not merge abaxially; S2 convex anteriorly, conjoined adaxially; L1 straight, not conjoined adaxially; abaxial margins of L1 directly anterior of LO; SO slightly convex posteriorly, not conjoined adaxially; posterior border of LO slightly convex posteriorly; posterior border between LO and intergenal angle straight, parallel to a transverse line; posterior border between genal angle and intergenal angle is deflected anteriorly approximately 70 degrees at intergenal angle; intergenal angle developed midway between genal angle and ocular lobe; intergenal swelling present; genal angle developed adaxial of anterior margin of ocular lobe; genal spines deflected posteriorly at approximately 45 degrees with an average width equal to the length (sag.) of LO.

Discussion. This species is assigned to the genus Bristolia based on a number of characters that it shares with other species within the genus. These include: a short (sag.) anterior cephalic border, prominently separated from the extraocular area by a furrow; the frontal lobe contacts the anterior border furrow; the ocular lobe contacts LA at the postero-lateral border; faint depression across entire region where ocular lobe hits frontal lobe (present in most Bristolia except for B. anteros Palmer in Palmer & Halley, 1979 and B. sp. [ Fritz 1972]); S3 is the same depth laterally as adaxially; lateral margins of L2 are constricted compared to the rest of the glabella; posterior edge of ocular lobe opposite adaxial part of margin of L1; long genal spines are present; a faint intergenal ridge is observed; extraocular area is flattened; and as with other species of Bristolia , this specimen has a prominent intergenal angle flexing anteriorly and genal spines that are positioned far anteriorly on the cephalon.

Unlike other species of Bristolia , this species has a prominent ocular furrow. Also the ratio of the width (sag.) of L3 to L2 is greater than in other species and the lateral furrows of LO and L1 are not as constricted anteriorly. Lastly, the width of the ocular lobe (measured perpendicular to the lobe axis at its midpoint) is equal to the width of the extraocular area abaxial to L2, whereas other species have narrower ocular lobes and wider ocular areas (sag.).

This species generally resembles the poorly preserved (known from a partial cephalon) Laudonia? sp. 1 Fritz, 1972, p. 27, pl. 9, fig. 21, treated as Bristolia sp. in Lieberman 1999, and also from the Sekwi Formation. For instance, they both have a prominent intergenal angle flexing anteriorly and genal spines that are positioned far anteriorly on the cephalon. However, they do differ in several features as well, primarily involving the shape and position of the ocular lobes, and are thus treated as distinct. In particular, in B. colberti : the posterior tips of the ocular lobes extend back to LO instead of L1; a line from the anterior to the posterior tips of the ocular lobe parallels a sagittal line, instead of forming a 20-30 degree angle relative to a sagittal line; and the interocular area and LA are less prominently inflated.

In southwestern Laurentia, species of Bristolia typically occur high up in the Dyeran stage ( Webster 2011a, 2011b; Webster et al. 2011). However, in northwestern Laurentia this genus occurs relatively lower down in the stage, especially relative to the position of other olenelloid genera.

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 4, 430– 435 m above the base of section.