Lochmanolenellus cf. subquadratus

Webster, Mark & Bohach, Lisa L., 2014, Systematic revision of the trilobite genera Laudonia and Lochmanolenellus (Olenelloidea) from the lower Dyeran (Cambrian Series 2) of western Laurentia, Zootaxa 3824 (1), pp. 1-66 : 52-53

Lochmanolenellus cf. subquadratus 1

Fig. 19.1

1966 Laudonia sp.; Nelson & Durham, pl. 2, fig. 9.

1976 Laudonia sp.; Nelson (part), pl. 5, top right and lower left “ Laudonia ” specimens only [not top left “ Laudonia ” specimen, = Lochmanolenellus trapezoidalis ].

Material. Two of the three specimens illustrated as “ Laudonia ” by Nelson (1976, top right and lower left specimens only; one of which was also illustrated by Nelson & Durham, 1966, pl. 2, fig. 9) are herein reassigned to Lochmanolenellus cf. subquadratus 1. Quantitative morphometric and qualitative descriptive data were recorded from first-hand examination of one of those specimens (LACMIP 7401); the whereabouts of the second specimen is unknown (M. Stecheson, personal communication to M. Webster, March 2012), and it therefore was not examined during the course of the present study.

Occurrence. U.S.A.: Magruder Mountain, Esmeralda County, Nevada: Upper portion of the middle member of the Poleta Formation at LACMIP locality 26828, SW ¼, SW ¼, SW ¼ of Section 22, T6S, R40E. The second specimen, illustrated by Nelson (1976, pl. 5, lower left specimen), was collected from the middle member of the Poleta Formation in either Esmeralda County, Nevada, or Inyo County, eastern California, but more precise details of geographic and stratigraphic provenance for this specimen are unknown. Both occurrences are assumed to be in the lower portion of the Dyeran Stage, Waucoban Series based on the range chart provided by Nelson (1976, fig. 5).

Discussion. The two specimens show the subquadrate cephalic outline, strongly anteriorly advanced genal spine bases, and ocular lobe length (posterior tip located transversely opposite the lateral margin of L1) typical of Lochmanolenellus subquadratus . Both exhibit genal and intergenal spines that are slightly less strongly laterally flared relative to the typical condition for this species, but this probably results from the slight tectonic deformation experienced by both specimens. The broader anterior cephalic border of one of the specimens (Fig. 19.1) relative to Lo. subquadratus is probably attributable to a combination of tectonic deformation plus taphonomic compaction (this specimen is preserved in shale, all other specimens of Lo. subquadratus are preserved in limestone). Given the preservational differences, assignment of these two specimens to Lo. subquadratus must remain tentative, and they are conservatively treated herein as Lo. cf. subquadratus 1.

The sagittal axis of LACMIP 7401 was oriented parallel to the major axis of the tectonic strain ellipse (as revealed by weak lineations within the shale matrix). This orientation relative to tectonic strain accounts for the unusually large length:width ratios evident on this specimen. The sagittal cephalic length of the specimen (14.1 mm) might have been slightly exaggerated by the deformation.