Lochmanolenellus amputata, Fritz, 1992

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 : 22-25

Laudonia amputata Fritz, 1992

Fig. 6

1992 Laudonia amputata Fritz, pp. 26–27, text-fig. 6d, pl. 11, figs. 1–5, pl. 12, figs. 1–3. 1993 Laudonia amputata Fritz; Palmer & Repina, fig. 4.4.

1997 Laudonia amputata Fritz; Palmer & Repina in Whittington et al., p. 412, fig. 259.2. 1999 Laudonia amputata Fritz; Lieberman, pp. 3, 107, 114, 115.

1999 Laudonia amputata Fritz; Smith & Lieberman, p. 462.

2002 Laudonia amputata Fritz; Lieberman, p. 699.

2003 Laudonia amputata Fritz; Lieberman, p. 63.

Diagnosis. Genal spine base transversely opposite lateral margin of L3 or S3; orientation of distal portion of posterior cephalic margin ranging from 4° inwards to 7° outwards relative to an exsagittal line when traced toward base of genal spine. Distance (tr.) between genal spine bases approximately 162% (range 140% to 174%) of glabellar length (sag.), increasing slightly through phase 5 of cephalic development. Angle between inner margin of proximal portion of genal spine and distal portion of posterior cephalic margin approximately 45° (range 42° to 49°). Width of anterior cephalic border (measured anterior to ocular lobes) 104% to 156% of length (exsag.) of LO. Ocular lobes divergent from exsagittal axis by approximately 15° (range 11° to 22°); posterior tip of ocular lobe transversely opposite lateral margin of L1 or distal tip of S1.

Lectotype. USNM 443754 (figured by Fritz, 1992, pl. 11, fig. 4; Palmer & Repina, 1993, fig. 4.4; Palmer & Repina in Whittington et al., 1997, fig. 259.2), designated by Lieberman (1999, p. 115). This specimen had been labelled USNM 137533d prior to the study by Fritz (1992).

Other material. Detailed qualitative and/or morphometric data were recorded from first-hand examination of the lectotype (see previous) plus the following nine specimens: USNM 137533, USNM 137533c, and USNM 137533f (all stored in the biological collections); USNM 443752 (also figured by Fritz, 1992, pl. 11, fig. 1); USNM 443753 (also figured by Fritz, 1992, pl. 11, figs. 2, 3); USNM 443755 (also figured by Fritz, 1992, pl. 11, fig. 5); USNM 443756 (also figured by Fritz, 1992, pl. 12, figs. 1–3); an unnumbered specimen in the biological collections of the USNM; and MCZ 113773. MCZ 113773 is an incomplete cephalon (part and counterpart) partially obscured by matrix, but shows a morphology consistent with Laudonia amputata ; this specimen is tentatively assigned to this species.

Occurrence. CANADA: Mount Robson area, British Columbia and Alberta: Locality 61k, talus from the middle member of the Mural Formation on the western margin of Mumm Peak, Alberta (see Fritz, 1992). Laudonia amputata was not found in situ during Fritz’s (1992) restudy of Walcott’s (1913) “61k fauna”, and the precise stratigraphic provenance of the species remains uncertain. Nevertheless, it is assumed to occur within the lower portion of the Dyeran Stage, Waucoban Series ( Fritz, 1992, p. 27; see previous).

Discussion. The original description of Laudonia amputata was based on examination of five specimens from Walcott’s locality 61k ( Fritz, 1992). All of those specimens, plus five additional specimens (listed previously), were studied first-hand during the present work. Cephalic lengths of the suite of specimens examined herein range from 6.4 mm to 38.2 mm, and all represent morphologically mature individuals in phase 5 of cephalic development. Fritz’s (1992) description of La. amputata is generally adequate and only a species diagnosis is provided herein. However, the presence of the tropidium ( Fig. 6 )—here included within the generic diagnosis—was not mentioned by Fritz (1992).

Laudonia amputata differs most obviously from La. bispinata by having ocular lobes that are proportionally longer (posterior tips developed transversely opposite the lateral margin of L1 or rarely S 1 in La. amputata , opposite the lateral margins of L2, S2, or L 3 in La. bispinata ; Fig. 7.1) and less strongly divergent (Fig. 7.2), and in having genal spines that are less anteriorly advanced (bases developed transversely opposite the lateral margin of L3 or S 3 in La. amputata , transversely opposite the lateral margin of LA in La. bispinata ; Fig. 7.3) and that flare less strongly laterally from the distal portion of the posterior cephalic margin (Fig. 7.4). The species also differ in orientation of the distal portion of the posterior cephalic margin (Fig. 7.5): on all specimens of La. bispinata examined herein, the margin is consistently oriented slightly inward when traced towards the base of the genal spine; while the margin of La. amputata is typically directed very slightly outward when traced towards the base of the genal spine—on only the largest known specimen of La. amputata is the margin directed inward and forward (USNM 443753; see Fritz, 1992, pl. 11, fig. 2), and on that specimen the inward orientation is not as strong as in large specimens of La. bispinata . Relative to La. bispinata , La. amputata also typically has a proportionally slightly narrower anterior cephalic border (Fig. 7.6) and a proportionally narrower (tr.) extraocular area (Fig. 7.7, 7.8), although the two species show some overlap in values for those traits. The intergenal ridge of La. amputata lacks the ‘ridge-on-ridge’ structure that is developed in La. bispinata . In the thorax, the inner pleural regions of La. amputata are slightly proportionally narrower (tr.) relative to width (tr.) of the axis than are those of La. bispinata (presumably related to the interspecific difference in width of the extraocular area), and the pleural spines of La. amputata are slightly shorter than the spines on equivalent segments of La. bispinata . Fritz (1992) claimed that the species also differed in the degree of constriction of the glabella at S1, although such a supposed difference was not supported by the morphometric analyses conducted herein (data not shown).

Laudonia amputata was not included in the cladistic analysis of the Olenelloidea presented by Lieberman (1998). However, the species was subsequently used as an outgroup taxon in the cladistic analysis of Bristoliinae by Lieberman (1999), where it was assumed to form a clade with La. bispinata . Character states for La. amputata were coded correctly, with the possible exception of character 7. Lieberman (1999, Bristoliinae analysis, character 7) coded La. amputata as lacking a “faint ventral depression across entire region where ocular lobe hits frontal lobe”. However, if this faint ventral depression refers to a transocular furrow, then it is mis-coded. (The same holds true for coding of that character for La. bispinata .)

Figures

FIGURE 6. Morphologically mature specimen of Laudonia amputata Fritz, 1992. Cephalon and incomplete thorax, latex peel of external mold; USNM 443752, x 4. From middle member of Mural Formation at Locality 61 k, Mumm Peak, Mount Robson area, Alberta.