Lochmanolenellus bispinata, Harrington, 1956

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 : 18-21

Laudonia bispinata Harrington, 1956

Figs 3.2, 4.5, 4.6, 5.1–5.5

1956 Laudonia bispinata Harrington, pp. 60, 61, text-fig. 1f, pl. 15, figs. 4, 5.

1959 Laudonia bispinata Harrington; Harrington in Harrington et al., p. O 154, fig. 38c.

1959 Laudonia bispinata Harrington; Poulsen in Harrington et al., p. O 192, fig. 134.

1971 Laudonia bispinata Harrington; Hu, p. 79.

1972 Laudonia bispinata Harrington; Fritz, p. 27.

1978 Laudonia bispinata Harrington; McNamara, p. 642.

1992 Laudonia bispinata Harrington; Fritz, pp. 5, 7, 13, 16, 17, 26, 27, text-fig. 6c, pl. 12, figs. 4–8, pl. 13, figs. 1–8, pl. 14, figs. 1, 2.

1993 Laudonia bispinata Harrington; Palmer & Repina, p. 24.

1997 Laudonia bispinata Harrington; Palmer & Repina in Whittington et al., 1997, p. 412.

1998 Laudonia bispinata Harrington; Lieberman, pp. 62, 73, fig. 4.2.

1999 Laudonia bispinata Harrington; Lieberman (part), pp. 107, 110, 114, 140 only [not fig. 20.1, = Lochmanolenellus pentagonalis ].

1999 Laudonia bispinata Harrington; Smith & Lieberman, p. 462.

2002 Laudonia bispinata Harrington; Lieberman, p. 699.

2003 Laudonia bispinata Harrington; Lieberman, p. 63.

2003 Laudonia bispinata Harrington; Jell & Adrain, p. 396.

Diagnosis. Genal spine base transversely opposite lateral margin of LA; distal portion of posterior cephalic margin oriented slightly inwards at approximately 6° (range 10° to 3°) relative to an exsagittal line when traced toward base of genal spine. Distance (tr.) between genal spine bases approximately 189% (range 153% to 229%) of glabellar length (sag.), increasing through phase 5 of cephalic development. Angle between inner margin of proximal portion of genal spine and distal portion of posterior cephalic margin approximately 55° (range 50° to 66°). Width of anterior cephalic border (measured anterior to ocular lobes) 118% to 220% of length (exsag.) of LO, increasing through phase 5 of cephalic development. Ocular lobes divergent from exsagittal axis by approximately 52° (range 29° to 76°); posterior tip of ocular lobe transversely opposite lateral margin of L2, S2, or L3. Intergenal ridge with much narrower ridge running along summit, giving ‘ridge-on-ridge’ appearance.

Holotype. KUMIP 32400. This specimen was not examined first-hand during the present study, although morphometric data were extracted from published photographs ( Harrington, 1956, pl. 15, figs. 4, 5; Lieberman, 1998, fig. 4.2).

Other material. Detailed qualitative and/or morphometric data were recorded from first-hand examination of the following 16 specimens: USNM 137534, USNM 137630c (2 specimens), USNM 137630d, USNM 443757 (also figured by Fritz, 1992, pl. 12, fig. 4), USNM 443758 (also figured by Fritz, 1992, pl. 12, fig. 5), USNM 443759 (also figured by Fritz, 1992, pl. 12, fig. 5), USNM 443760 (also figured by Fritz, 1992, pl. 12, fig. 6), USNM 443761 (also figured by Fritz, 1992, pl. 12, fig. 7), USNM 443762 (also figured by Fritz, 1992, pl. 12, fig. 8), USNM 443763 (also figured by Fritz, 1992, pl. 13, fig. 1), USNM 443764 (also figured by Fritz, 1992, pl. 13, figs. 2, 3), USNM 443765 (also figured by Fritz, 1992, pl. 13, figs. 4–7), USNM 443766 (also figured by Fritz, 1992, pl. 13, fig. 8), USNM 443768 (also figured by Fritz, 1992, pl. 14, figs. 1, 2), and MCZ 110680 (tentatively assigned). MCZ 110680 was identifed as Laudonia bispinata by Lieberman (1998, p. 73; 1999, p. 114), and the anterior advancement of the genal spine bases and general cephalic outline are consistent with this identification. However, the ocular lobes of this specimen are chipped and their length and angle of divergence cannot be determined with precision. MCZ 110680 is therefore herein assigned to La. bispinata with reservation. An incomplete cephalon USNM 443767 (figured by Fritz, 1992, pl. 14, fig. 1) was also examined first-hand but qualitative and morphometric data were not recorded. Fritz (1992) recovered a single cephalon from GSC locality 87891 and ten cephala from GSC locality 90577, which were not figured and have not been examined during the course of this study. Lieberman (1998, p. 73; 1999, p. 114) also assigned MCZ 110679 to this species. However, MCZ 110679 is an almost complete individual of Lochmanolenellus pentagonalis , described herein.

Occurrence. CANADA: Mount Robson area, British Columbia and Alberta: GSC locality 90577, 138.1 metres above the base of the Mural Formation, Mumm Peak measured section, Alberta ( Fritz, 1992). Locality 61k, talus from the middle member of the Mural Formation on the western margin of Mumm Peak, Alberta (see Fritz, 1992). GSC locality 87891, 169.2 metres above the base of the Mural Formation, Cinnamon Peak-Whitehorn Mountain section, Mount Robson Provincial Park, British Columbia ( Fritz, 1992).

Discussion. Fritz’s (1992) description of Laudonia bispinata is generally adequate and, when complemented with the diagnosis provided previously, renders a full redescription of the species unneccesary. Fritz’s (1992) description did not mention the presence of the tropidium, however (Figs 3.2, 5.1, 5.2, 5.3, 5.4)—this omission is corrected herein by including the tropidium within the generic diagnosis. Differences between La. bispinata and La. amputata are discussed under the latter species.

Specimens of La. bispinata examined herein range from approximately 7.9 mm to more than 25 mm in sagittal cephalic length, and all represent morphologically mature individuals in phase 5 of cephalic development. Fritz (1992, p. 26) recovered specimens ranging from 4.5 mm to 9.5 mm in cephalic length, but these specimens were not examined herein. The trunk is known from two specimens (USNM 443764 and USNM 443768; Figs 4.5, 4.6, 5.5), both of which preserve the pygidium. (Several thoracic segments are also preserved scattered behind USNM 443766 [Fig. 5.4] and were probably associated with that cephalon in life, but the segments are disarticulated and their specific placement within the thorax cannot be determined.) Fritz (1992) reported a total count of 22 thoracic segments for the species, although no single known specimen unambiguously preserves this full complement. The posterior-most region of the thorax is not well preserved on USNM 443768 (Fig. 5.5), and the exact number of segments on the specimen cannot be precisely determined. Nineteen thoracic segments are clearly preserved, and an impression of the left pleura and fragmentary axis of at least one more segment is evident behind that. However, the pygidium lies somewhat behind that, and there is sufficient separation between T19 and the pygidium for three segments to have been present. USNM 443764 (Fig. 4.5, 4.6) preserves nineteen segments anterior to the pygidium (with some telescoping) but there is a displacement between the anterior-most preserved segment and the posterior margin of the cephalon, and the anterior few thoracic segments (including T3) are missing. By comparison with USNM 443768, the form of the anterior-most preserved segment on USNM 443764 is consistent with it representing T4, in which case USNM 443764 would have borne 22 thoracic segments (with T1 to T3 now missing).

Laudonia bispinata is the type species of the genus, and was included in cladistic analyses of the Olenelloidea by Lieberman (1998) and of the Bristoliinae by Lieberman (1999). Lieberman’s (1998, 1999) coding for La. bispinata was apparently based on first-hand examination of three specimens (KUMIP 32400, MCZ 110679, and MCZ 110680), one of which (MCZ 110679) is here reassigned to a different genus. The present study reveals several uncertainties, unrecognized polymorphisms, and errors in the character state coding of La. bispinata in Lieberman’s (1998) analysis. LA was coded as expanding dorsally ( Lieberman, 1998, character 10, state 1), but all available material has experienced compactional deformation and this character should be conservatively coded as state unknown. The preocular furrow (character 13) was coded by Lieberman (1998) as being oriented inward and backward from the glabellar margin (state 0). However, on many specimens the furrow runs inward and forward from the glabellar margin (state 2; e.g., Fig. 5.2, 5.3), and the character should therefore be coded as polymorphic (states 0, 2). The posterolateral margins of LA (character 17) were coded by Lieberman (1998) as being divergent anteriorly (state 1; e.g., KUMIP 32400). However, the posterolateral margins are sub-parallel on many specimens (state 2; e.g., Fig. 5.4), and the character should therefore be coded as polymorphic (states 1, 2). The ocular lobes were incorrectly coded by Lieberman (1998, character 20) as forming a 10°–20° angle with a sagittal line (state 0), but were correctly coded by Lieberman (1999, Bristoliinae analysis, character 5) as forming approximately a 40° angle (equivalent to state 2 in the 1998 analysis): angles of divergence measured during the present study averaged 52° (range 29° to 76°; n = 12). The posterior tips of the ocular lobes were coded by Lieberman (1998, character 23) as being developed transversely opposite the lateral margins of L2 (state 3; e.g., KUMIP 32400). However, the tips are developed transversely opposite S2 on several specimens (state 4; e.g., Fig. 5.3, 5.4), and the character should therefore be coded as polymorphic (states 3, 4). All available material has experienced compactional deformation, and the original dorsal convexity of the extraocular area ( Lieberman, 1998, character 44) is unknown (this had originally been coded as flattened [state 0] by Lieberman, 1998); similarly, the original ventral flexure of the distal tips of the thoracic pleurae ( Lieberman, 1998, character 71) is unknown (this had originally been coded as being in roughly the same dorsoventral plane as the medial portion of the pleurae [state 0] by Lieberman, 1998). An anterior ocular line ( Lieberman, 1998, character 46) was not seen on any specimen examined herein (state 1; this feature had originally been coded as visible [state 0] by Lieberman, 1998). A genal ridge ( Lieberman, 1998, character 47) was not seen on any specimen examined herein (state 1; this feature had originally been coded as prominently developed [state 0] by Lieberman, 1998). When traced abaxially, the posterior cephalic margin between the axial furrow and the adgenal angle ( Lieberman, 1998, character 56) is oriented at an angle ranging from 3° to 15° (average of approximately 8°; n = 11) posteriorly relative to a transverse line. The posterior cephalic margin is therefore variably more-or-less transverse (state 0, as originally coded by Lieberman, 1998; e.g., Fig. 5.1) to flexing posteriorly (state 1; e.g., Fig. 5.4). The thorax is not clearly differentiated into a prothorax and opisthothorax ( Lieberman, 1998, character 57, state 1; this had originally been coded as being divided into a prothorax and opisthothorax [state 0] by Lieberman, 1998 —see Terminology section [previous] for a discussion of this character). The posterior margin of every thoracic segment on both USNM 443764 and USNM 443768 is worn and/or not preserved (Figs 4.5, 4.6, 5.5), and the presence or absence of axial nodes on any thoracic segment ( Lieberman, 1998, character 66) cannot be determined with confidence (axial nodes had originally been coded as absent [state 1] by Lieberman, 1998; see also discussion under generic diagnosis). On at least T7 and more posterior segments, the pleural furrows ( Lieberman, 1998, character 67) extend a short distance onto the pleural spines (state 1; they had originally been coded as being confined to the inner pleural region [state 0] by Lieberman, 1998). However, state 0 applies to pleural furrows on more anterior segments (excluding T3), and this character as defined is accordingly polymorphic (states 0, 1). The width of the pleural spines on T5 to T8 at their midlength is not more than half of the length (exsag.) of the medial portion of the corresponding inner pleural region ( Lieberman, 1998, character 72, state 1; the spine widths had originally been coded as being more than two-thirds of the length of the corresponding inner pleural regions [state 0] by Lieberman, 1998). Finally, the posterior margin of the pygidium is not well preserved on either USNM 443764 or USNM 443768 (Figs 4.6, 5.5), and whether it bore a median notch ( Lieberman, 1998, character 79) cannot be determined with confidence. This character should accordingly be coded as uncertain (it had originally been coded as being transverse or weakly convex [state 0] by Lieberman, 1998). Given these coding issues, it remains to be seen whether the phylogenetic placement of Laudonia as determined by Lieberman (1998) is robust.