Lochmanolenellus primus

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 : 27-32

Lochmanolenellus primus (Lochman in Cooper et al., 1952)

Fig. 8

1952 Wanneria mexicana prima Lochman in Cooper et al. (part), pp. 96–98, pl. 18, fig. 3 only [not pl. 18, fig. 1, = Lochmanolenellus cf. primus 1; not pl. 18, fig. 2, = genus and species indet.].

1952 Wanneria mexicana prima Lochman ; Cooper & Arellano in Cooper et al., p. 19.

1956 Laudonia prima (Lochman); Harrington, pp. 56, 60, 61.

1971 Wanneria (“Laudonia”) mexicana prima Lochman; Hu, p. 79.

1972 Laudonia prima (Lochman); Fritz, p. 27.

1984 Wanneria mexicana prima Lochman ; Stewart et al., fig. 19.

1992 Laudonia? mexicana (Lochman) ; Fritz, pp. 5, 12, 26.

1998 Lochmanolenellus mexicana (Lochman) ; Lieberman, pp. 61, 62, 74, fig. 4.4.

1999 Lochmanolenellus mexicana (Lochman) ; Lieberman, pp. 116–118. 1999 Lochmanolenellus mexicana (Lochman) ; Smith & Lieberman, p. 462. 2002 Lochmanolenellus mexicana (Lochman) ; Lieberman, p. 699.

2003 Lochmanolenellus mexicana (Lochman) ; Lieberman, p. 63.

2003 Lochmanolenellus mexicana (Lochman) ; Jell & Adrain, p. 399.

Diagnosis. Cephalon pentagonal in outline; genal spine base transversely opposite posterior portion of lateral margins of L3; distal portion of posterior cephalic margin oriented anterolaterally at slightly less than 15° relative to an exsagittal line when traced toward base of genal spine. Distance (tr.) between genal spine bases approximately 152% of cephalic length (sag.). Angle between distal portion of posterior cephalic margin and outer margin of proximal portion of intergenal spine approximately 144°. Length (sag.) of LA approximately 65% of maximum width of LA. Posterior tip of ocular lobe transversely opposite area of contact between axial furrow and S1.

Description. Cephalic length of only known specimen approximately 9.7 mm (sag.). Cephalon pentagonal in outline, widest (tr.) at base of genal spines. Proximal portion of posterior cephalic margin oriented weakly posteriorly by approximately 10° relative to a transverse line when traced abaxially, flexing anteriorly at a rounded adgenal angle located slightly less than half way along cephalic margin from axial furrow to base of genal spine, distal portion of posterior cephalic margin oriented anterolaterally at slightly less than 15° relative to an exsagittal line when traced abaxially. Genal spine stout, broad-based; angle between distal portion of posterior cephalic margin and inner margin of proximal portion of spine approximately 75°, spines gently curving into slightly more posterior orientation along their length; tips not preserved but spine length estimated to be approximately one-half cephalic length (sag.); spine base at contact with distal portion of posterior cephalic margin transversely opposite posterior portion of lateral margins of L3. Distance (tr.) between genal spine bases approximately 152% of cephalic length (sag.). Intergenal spine slender, broad-based, angle between distal portion of posterior cephalic margin and outer margin of proximal portion of spine approximately 144°; tips not preserved but spine length estimated to be between one-third and one-half cephalic length (sag.); spine base slightly distal to adgenal angle. Cephalic border defined by broad, trough-like border furrow interrupted only by intergenal ridge as it merges with border at base of intergenal spine; border furrow somewhat shallower and narrower along proximal portion of posterior cephalic border. Anterior cephalic border narrowest at sagittal axis, broadens distally, width opposite junction of ocular lobes with LA approximately 15% length (sag.) of glabella; broadest portion of border located at confluence with genal spines; posterior border tapers to point adaxially, barely touches axial furrow at posterior-most portion of LO. Border well rounded dorsally anterior to LA, somewhat more broadly dorsally arched at and between bases of genal and intergenal spines. Preglabellar field absent; LA slopes anteriorly almost vertically into trough-like cephalic border furrow that is slightly wider than anterior border at sagittal axis. Plectrum not developed. Glabella club-shaped in outline, 83% of cephalic length (sag.), moderately dorsally convex (tr.), strongly dorsally arched (sag.), summit formed by posterior portion of LA and L3. Maximum width of LA 153% basal glabellar width (tr.). Posterior margin of glabella convex posteriorly. SO deep only abaxially, abaxial end slightly anterior to adaxial end. LO slightly subtrapezoidal, narrows slightly anteriorly (transverse width across SO approximately 95% basal glabellar width), length (exsag.) approximately 11% of glabellar length (sag.), very strongly dorsally convex (tr.). S1 deepest abaxially, approximately parallel to SO. L1 subquadrate, transverse width across S1 approximately 95% basal glabellar width; length (exsag.) approximately 15% of glabellar length (sag.). S2 deepest abaxially, connected to axial furrow, strongly arcuate (convex anteriorly) on either side of sagittal axis, adaxial portion slightly posterior to distal portion. L2 broadly V-shaped, lateral margins strongly diverging anteriorly, transverse width across S2 approximately 121% basal glabellar width, distance (exsag.) between contact of S1 with axial furrow and contact of S2 with axial furrow approximately 15% of glabellar length (sag.). S3 transglabellar, oriented anterolaterally away from axis until contact with ocular lobes where it contacts anteriorly converging axial furrow, the two together thus forming a strongly caret-shaped furrow on either side of sagittal axis, deepest at apex of each caret. L3 broadly M-shaped, lateral margins diverging anteriorly until contact with inner margin of ocular lobes, then converging anteriorly until contact with S3; transverse width of glabella at point of contact between axial furrow and inner margin of ocular lobes approximately 136% of basal glabellar width, distance (exsag.) between contact of S2 with axial furrow and contact of axial furrow with inner margin of ocular lobes approximately 4% of glabellar length (sag.). LA transversely oblate in outline, anterior margin bluntly rounded and rather bull-nosed; maximum width (tr.) at contact with outer margin of ocular lobes, length (sag.) approximately 65% of maximum width and 40% of glabellar length (sag.), maximum width (tr.) approximately 153% of basal glabellar width; moderately dorsally convex (tr.), strongly dorsally convex (sag.); prominently inflated relative to extraocular area, lateral margins clearly defined from anterior portion of extraocular area by axial furrow. Shallow, weakly arcuate (convex posteriorly) preocular furrow runs inwards and anteriorly from contact of LA with outer margin of ocular lobes; not incised over axis. Very shallow transocular furrow runs anterolaterally across ocular lobes from point of contact between S3 and axial furrow to preocular furrow, isolating ocular lobes from LA. Axis of LO chipped, but preserves base of axial node or spine. Prominent ovoid lateral swellings on L1, somewhat more subdued lateral swellings on L2, weak lateral swellings on anterior portion of LO; lateral swellings on LO merge into interocular area, interrupting axial furrow. Axial furrow broad, deepest at lateral margins of L2 and L3. Ocular lobes divergent from exsagittal axis by approximately 23°, crescentic; posterior tip transversely opposite area of contact between axial furrow and S1. Deep ocular furrow runs along length of ocular lobe; anteriorly, ocular furrow curves slightly outwards to merge into a “triple junction” of furrows at point where preocular furrow meets the axial furrow at the margin of LA, thus isolating outer band of ocular lobe from LA; posteriorly, ocular furrow curves slightly inwards to meet inner margin of ocular lobe so that posterior tip of ocular lobe is located on outer band. Inner band of ocular lobe convex dorsally (tr.). All but innermost lip of outer band of ocular lobe not preserved (worn or broken off); width (tr.) and dorsal convexity of outer band unknown. Circumocular suture defines large visual surface (not preserved) that occupied much of length of outer wall of ocular lobe; portion of outer wall of ocular lobe below circumocular suture forms prominent, steep eye socle approximately one-quarter of estimated vertical height of visual surface. Interocular area slopes down from inner margin of ocular lobe to axial furrow; surface convex upward, giving arched appearance; approximately half width (tr.) of inner band of ocular lobe opposite S2. Extraocular area climbs moderately steeply out of broad border furrow then arches to produce a moderately vaulted transverse profile. In vicinity of ocular lobe, extraocular area abruptly changes slope to form a steep-walled, horizontally topped (tr. and exsag.) extraocular platform upon which ocular lobe sits; extraocular platform subcrescentic in outline when viewed from above, width (tr.) of flat-topped portion of platform greatest at midlength of ocular lobes; anteriorly, extraocular platform narrows to a thin, subdued ridge that extends beyond anterior limit of ocular lobe, descending in vertical height and running parallel to lateral margin of LA then fading into anterior border furrow; posteriorly, extraocular platform progressively narrows (tr.) and wedges out against vaulted posterolateral portion of extraocular area just posterior to posterior tip of ocular lobe. Prominent intergenal ridge extends from interocular area opposite lateral margin of L1 to posterior cephalic border at base of intergenal spine; ridge broadens distally and merges smoothly into border, interrupting border furrow. Only known specimen exfoliated, so details of prosopon (if developed) unknown. Hypostome, rostral plate, thorax, and pygidium unknown.

Holotype. USNM 115681 ( Fig. 8 ; also figured by Lochman in Cooper et al., 1952, pl. 18, fig. 3 and by Lieberman, 1998, fig. 4.4).

Other material. Lochman (in Cooper et al., 1952, p. 97) listed USNM 115682, USNM 115683, and USNM 115684 as paratypes of “ Wanneria mexicana prima ”. All these specimens are poorly preserved in highly weathered limestone, and none can be unambiguously identified to the species level. They are herein treated as Lochmanolenellus cf. primus 1 and an indeterminate genus and species.

Lochman (in Cooper et al., 1952, p. 97) noted similarity between the Mexican material and Canadian specimens from USNM locality 61k at Mumm Peak, and suggested that the Canadian specimens were conspecific with Wanneria mexicana prima . However, those Canadian specimens represent Laudonia bispinata and Laudonia amputata ( Harrington, 1956; Fritz, 1992). Specimens originally identified as “ Laudonia ” by Nelson (1976, pl. 5) from the upper part of the Poleta Formation in the White-Inyo Mountains and Death Valley regions of Inyo County, California, were assigned to Lochmanolenellus primus by Lieberman (1998, p. 74; 1999, pp. 116, 118). However, these specimens are herein reassigned to Lo. trapezoidalis and Lo. cf. subquadratus 1. As a result of these reassignments, Lo. primus is definitively known only from the holotype.

Occurrence. MEXICO: Sonora State: USNM locality 801c, “ Wanneria Beds ” of upper portion of Puerto Blanco Formation, 180 metres (590 feet) above base of measured section and 113 metres (371 feet) below local base of Proveedora Quartzite, western flank of Cerros de la Proveedora, 11 kilometres (six to seven miles) west of Caborca (Cooper & Arellano in Cooper et al., 1952; Lochman in Cooper et al., 1952; Lochman-Balk, 1956).

Discussion. As can be seen from the synonymy list (see previous), there is some inconsistency in previous literature regarding the specific name of this taxon—it has variably been referred to as mexicana prima , mexicana , or prima. In her initial description of Wanneria mexicana, Lochman (in Cooper et al., 1952, p. 96) noted that “[i]n this species it is presumed that the long, medium-sized genal spines would lie at the posterolateral angles, and the intergenal spines would be small and in a short distance on the posterior margin”. She then proceeded to describe W. mexicana prima as a variety (subspecies) of that species. She noted that “(t)he cephalon of the variety is like that of the species in all proportions and details except for the position and size of the genal and intergenal spines which are placed as follows: At the posterolateral angle at the end of the strong posterior facial suture ridge lie mediumsized intergenal spines, projecting somewhat laterally; the long, heavy genal spines lie on a line with the first glabellar furrow, and the spine projects nearly straight outward at the side of the cephalon, with a slight upward flexure at the base” (Lochman in Cooper et al., 1952, pp. 96–97). In a subsequent paragraph, Lochman (in Cooper et al., 1952, p. 97) reiterated this distinction—she noted that several deeply weathered cephala co-occurred with W. mexicana prima at Locality 801c and that, although the glabella and ocular lobes of these specimens were too poorly preserved for definitive generic identification, their genal spines were located at the “posterolateral angle of the cephalon” and that they “may represent the normal form of the species, Wanneria mexicana ” (Lochman in Cooper et al., 1952, p. 97). No specimen of this “normal form” was figured, and W. mexicana is therefore a nomen nudum. However, it is clear that Lochman (in Cooper et al., 1952) intended the (sub)specific name prima to apply to the morphotype with the advanced genal spines. The type species of Lochmanolenellus is therefore here referred to as Lo. primus (Lochman in Cooper et al., 1952) rather than Lo. mexicana (Lochman in Cooper et al., 1952).

Lochmanolenellus primus was included in cladistic analyses of the Olenelloidea by Lieberman (1998) and of the Bristoliinae by Lieberman (1999). The present study reveals several coding inaccuracies for this species in both analyses. A plectrum is not present ( Lieberman, 1998, character 4, state 1; this had originally been coded by Lieberman [1998] as present [state 0]). LA is clearly separated from the anterior extraocular area by a furrow ( Lieberman, 1998, character 6, state 0) as was stated by Lieberman (1998) in his discussion for this character, although in his character-taxon matrix this is coded as not prominently separated (state 1). The sagittal length of LA ( Lieberman, 1998, character 9) is approximately 135% of the sagittal length of LO and L1, falling between states 0 (equal to the length of LO and L1) and 1 (150% of the length of LO and L1) as defined by Lieberman (1998; this was originally coded as state 0). A prominent shelf (the eye socle) separates the ocular lobe from the extraocular area ( Lieberman, 1998, character 16, state 0; this had originally been coded as state 1 [ocular lobe merges smoothly into extraocular area]). “Lateral lobes” (= lateral swellings herein) are developed on LO ( Lieberman, 1998, character 42, state 1; these had been coded as absent [state 0] by Lieberman [1998])—the lateral swellings on LO are subtle in comparison to those on L2 and especially on L1, but are comparable in development to those present on LO of Holmiella preancora Fritz, 1972 , for example. An anterior ocular line is not present ( Lieberman, 1998, character 46, state 1; this had been coded as visible [state 0] by Lieberman [1998]). A genal ridge is not present ( Lieberman, 1998, character 47, state 1; this had been coded as prominently developed [state 0] by Lieberman [1998]). The posterior tips of the ocular lobes ( Lieberman, 1998, character 23) were correctly coded as opposite S1 (state 5) by Lieberman (1998), but incorrectly as opposite L1 (equivalent to state 2) by Lieberman (1999, Bristoliinae analysis, character 3)—the 1999 Bristoliinae analysis included no equivalent state to 23(5) of the 1998 analysis. The genal spine angle ( Lieberman, 1998, character 52) was correctly coded as opposite L3 (state 3) by Lieberman (1998), but as opposite the distal tip of S3 by Lieberman (1999, Bristoliinae analysis, character 1, state 3)—the 1999 Bristoliinae analysis included no equivalent state to 52(3) of the 1998 analysis. A faint furrow is developed across the ocular lobe at the contact with LA (Lieberman, 1999, Bristoliinae analysis, character 7, state 1; this was coded as absent by Lieberman [1999]).

The holotype of Lochmanolenellus primus is easily distinguished from Lo. trapezoidalis and Lo. subquadratus by its pentagonal rather than subquadrate or trapezoidal cephalic outline (Figs 9.1, 9.2, 18.8) and by its less strongly anteriorly advanced genal spine bases (Fig. 9.3). However, Lo. primus is similar to Lo. pentagonalis in those traits (Figs 9.1–9.3, 18.8), and the two can be most readily distinguished by differences in (1) the relative location of the adgenal angle along the posterior cephalic margin, (2) the degree of lateral flaring of the intergenal spines, and (3) the proportional width of LA. The adgenal angle of Lo. primus is located proportionally more distally along the posterior cephalic margin than that of Lo. trapezoidalis and Lo. subquadratus , but slightly more proximally than that of Lo. pentagonalis (Fig. 9.4). The intergenal spines of Lo. primus flare outwards (relative to the orientation of the distal portion of the posterior cephalic margin) more strongly than do those of Lo. trapezoidalis and Lo. subquadratus , but slightly less strongly than do those of Lo. pentagonalis (Fig. 9.5). The glabella of Lo. primus is proportionally wider across LA (tr.) relative to basal glabellar width (tr.) than Lo. pentagonalis (Fig. 9.6). Another diagnostic feature of Lo. primus is the length of LA, which is slightly proportionally shorter (relative to glabella length, for specimens of that size) than in other species of the genus (Fig. 9.7). As a result, both L1 and L2 are typically slightly proportionally longer (relative to glabella length, for specimens of that size) in Lo. primus than in other species (Fig. 9.8; although some specimens of Lo. pentagonalis and Lo. trapezoidalis approach or match these proportions). Together these features serve to differentiate the only definitively known specimen of Lo. primus from all other congeneric species. The validity of these distinctions should be re-checked if and when additional material of Lo. primus is discovered.

Figures

FIGURE 8. Holotype cephalon of Lochmanolenellus primus (Lochman in Cooper et al., 1952); USNM 115681. 1, Dorsal view. 2, Anterior view. 3, Left lateral view. 4, Oblique anterolateral view. All x 4. From upper portion of Puerto Blanco Formation at USNM locality 801 c, Cerros de la Proveedora, Caborca area, Sonora, Mexico.