Tuleaspis jeneki, E.B & Adrain & Karim, 2018

E. B, Neo, Adrain, Jonathan M. & Karim, Talia S., 2018, The pliomerid trilobite Ibexaspis and related new genera, with species from the Early Ordovician (Floian; Tulean, Blackhillsian) of the Great Basin, western USA, Zootaxa 4525 (1), pp. 1-152 : 33-35

Tuleaspis jeneki n. sp.

Plates 44–46

1973 Protopliomerops sp. I; Demeter, p. 53, pl. 3, figs 3, 8.

2009 Ibexaspis sp. nov. 1; Adrain et al., p. 563, fig. 13Y.

Material. Holotype, cranidium, SUI 129505 (Pl. 44, figs 1, 4, 5, 7, 10), and assigned specimens SUI 115250, 129506–129532, from Section G 210.2, Fillmore Formation (Tulean, low Protopliomerella contracta Zone ), southern Confusion Range, Ibex area, Millard County, western Utah, USA. The species has also been sampled from the high P. contracta Zone at HC6 224.5 m, Garden City Formation, west side of Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho, USA.

Etymology. After Shane Jenek.

Diagnosis. Cranidium with long glabella compared to congeners, parallel-sided, and not highly convex (tr.), with wide lateral lobes; L1 only a little smaller in area than L2 and L3; genal spine very small and nub-like. Hypostome with longer posterior border than width of lateral border at shoulders (border not tapered posteriorly as in other members of Ibexaspis -group). Pygidium with five axial rings and four pairs of pleurae; narrow and deep axial furrow; short and deep inter-ring furrows; short, very deep interpleural furrows; and pleural spines closely spaced and backswept, not splayed.

Description. Cranidium strongly vaulted (sag., tr.), sub-semicircular in outline, with sagittal length 104.1% (97.9–107.1%) width across γ, 75.1% (71.3–77.0%) width across δ, 70.7% (65.6–74.5%) width across ε, and 50.0% (44.9–52.9%) maximum width across genal angles; anterior border lightly inflated, short, with length 4.4% (4.0–5.2%) sagittal cranidial length, broad, gently anteriorly bowed, densely covered in small tubercles; doublure only a rim ventrally, mainly expressed as anterior face of border; anterior border furrow very short, deep, incised, with small (narrow) lateral sections intersecting S3 and main part of furrow following arc of border; palpebral lobe situated with posterior margin slightly anterior from S1 and anterior portion of palpebral lobe level with mid-L3, with less distinct (better expressed in small specimens, e.g., Pl. 45, figs 22, 23), lobe elongate, fairly narrow, with broadest curvature approximately level with S2, sharply dorsolaterally elevated (anterior view), with sculpture of small tubercles and some effacement posteriorly and along lateral rim particularly in larger specimens, and with very narrow post-ocular ridge tapering down to fulcrum of fixigena; palpebral furrow narrow, very deep, anteromedially directed, sinuous, with very slight lateral flexure along main body of lobe, then curled sharply around posterior edge, not well-defined anteriorly; interocular fixigena subtriangular, fairly narrow, anteriorly tapered to a point at mid-L3, flat to slightly ventrolaterally sloped, densely tuberculate, with underlying granules and slightly longer tubercles opposite axial furrows; posterior fixigena short and very wide, with anteriorly curved anterolateral margin, very steeply downturned, with sculpture like that of interocular fixigena, and with some small pits on lateral portions and smaller tubercles near posterior border furrow; posterior border furrow short, deep, roughly transverse in course until anteriorly curved at genal angle; posterior border shortest adaxially, length approximately doubles to maximum at genal angle, moderately inflated, increasing toward genal angle and then slightly deflated again, finely granulose, with slightly larger granules lining border furrow and anterior from nublike small genal spine, with small cluster of spiny tubercles near axial furrow and scattered tubercles roughly following posterior margin; doublure only a rim until abruptly widened at genal angle, then anteriorly expanded until cut off by facial suture, smooth; axial furrows moderately narrow, very deep, roughly parallel, only very slightly laterally bowed, intersect all but palpebro-ocular furrows; LO broad, long medially, with sagittal length 14.7% (12.7–16.1%) sagittal cranidial length, shorter at exsagittal ends (mainly in larger specimens), moderately inflated, finely granulose, with small cluster of spinose tubercles on lateral margin extending into axial furrows, 4– 7 scattered small tubercles along posterior edge, and small median node at mid-length (effaced in larger specimens); doublure broad, long, pinched out laterally, elliptical; SO deep, very deep laterally, long medially, then shorter and overhung by posterior edge of L1, with broadly W-shaped course, middle portion anteriorly bowed in most specimens and lateral portions posteriorly bowed; glabella long and broad, parallel-sided with moderately anteriorly bowed anterior margin, posterior margin more weakly anteriorly bowed (especially on smaller specimens), subrectangular, with length excluding LO 107.2% (99.6–114.5%) maximum width across L2, mildly vaulted (sag., tr.), with distinct, independently inflated lateral lobes, and with dense sculpture of small tubercles; L2 and L3 very similar in shape and size, subrectangular, broader than long, occupy about 1/3 cranidial width, L2 slightly longer than L 3 in most specimens, lobes nearly transverse to somewhat anterolaterally directed; L1 a little smaller, shorter and narrower, more ellipsoidal, more anterolaterally directed, with a few elongate tubercles extending into SO from posterior edge; LF wedge-shaped, long medially and short laterally; S1–S3 short (sag.), deep, incised, S1 a little longer and shallower at sagittal end, all furrows gently anterolaterally directed.

Rostral plate and thorax unknown.

Hypostome with sagittal length 118.4% (113.7–123.2%) maximum width (excluding anterior wings) across posterior lobe of middle body; hypostomal suture broad, strongly anteriorly bowed, anterolaterally redirected along anterior wings; anterior border extremely short, just a rim along middle body, expanded laterally into small, posterolaterally placed, strongly upturned anterior wings; anterior border furrow short, incised, overhung medially by anterior margin of middle body in some specimens; middle body elliptical, moderately ventrally inflated anteriorly, much less inflated over posterior lobe, with large, ovoid, posteriorly tapered anterior lobe and short, Ushaped posterior lobe; anterior lobe densely covered in small tubercles except near posterior margin, posterior lobe effaced medially, but with small tubercles on lateral arms; middle body furrow mostly effaced medially, visible as indentation in lateral view, narrow and incised anterolaterally (with overlap of lateral border furrows); lateral border furrows strongly posteromedially directed along anterior lobe of middle body, wider, deeper, and less medially angled along posterior lobe; lateral border narrowest at lateral notch, abruptly widened just past notch and very slightly expanded posteriorly, moderately downturned, densely covered in small tubercles dorsally, with very fine granules on rim; posterior border furrow strongly posteriorly bowed, deep but slightly shallower than lateral furrows; posterior border long, with sculpture like that of lateral border; doublure incompletely preserved, but about half length/width of borders, smooth, sloped, with long, shallow lateral notch.

Librigena with width at midlength of eye 40.8% (37.9–43.5%) length of lateral border; ocular surface almost entirely unknown, with only raised adaxial margin of eye area preserved, with very narrow effaced patch extending onto anterior part of field (Pl. 46, fig. 4); anterior branch of facial suture short and very steep along field, longer with nearly flat slope along anterior projection of lateral border, sections form approximately 120° angle at anterior terminus of lateral border furrow; posterior branch of facial suture long and sloped along field, with slope decreasing after mid-width of field, short and nearly flat along posterior projection of border, with sections forming approximately 130° angle; librigenal field trapezoidal, widest under posterior end of eye, narrower anteriorly and posteriorly, with width at mid-length of eye 38.2% (35.4–40.3%) length along lateral border furrow, shallowly ventrolaterally sloped, somewhat laterally convex, with dense sculpture of mixed very small and tiny tubercles, and with small pits concentrated abaxially; lateral border furrow narrow, deeply incised, gently laterally bowed; lateral border almost as wide as anterior edge of field, narrower along anterior projection, tapered to a blunt point along posterior projection, moderately well inflated anteriorly, gradually deflated posteriorly, with very dense sculpture of very small tubercles, laterally bowed, with lateral margin more convex than border furrow, and with anterior projection anteroventrally rotated; doublure broad and smooth, discontinued along anterior projection, tapered to a point posteriorly, with triangular section of inner face visible externally (Pl. 46, fig. 1).

Pygidium with sagittal length from articulating furrow 67.7% width across anterior pleural band (ratio may be slightly distorted due to poor preservation); articulating half ring broad, short, with line of very fine granules on posterior edge; articulating furrow moderately long, very deep; axis composed of five rings and terminal piece, broad and well vaulted anteriorly, with width across first ring 55.3% pygidial width across anterior pleural band, strongly posteriorly tapered and flattened, with width across fifth ring 46.5% width across first ring; axial rings moderately long, fifth ring only slightly shorter than first ring, each ring independently well inflated, widest at midlength, with lateral margins rounded around dense sculpture of medium tubercles, with mix of smaller tubercles and granules dorsally and lining anterior and posterior margins; inter-ring furrows moderately long (more posterior furrows shorter), very deep; terminal piece small, triangular, less inflated than rings, with sculpture of small tubercles; axial furrows narrow (except at intersections with inter-ring and interpleural furrows), shallower along terminal piece, then merged with fourth interpleural furrow as single median furrow behind terminal piece; anterior pleural band present only on first segment, very short, effaced, with small anteriorly curved prong at tip; interpleural furrow very short and deep, slightly overhung by first posterior pleural band in dorsal view; four posterior pleural bands long (measured obliquely), well inflated, each more posteromedially directed, with second bands essentially parallel, with sculpture of medium tubercles and smaller tubercles at margins on first half of length (first band more sparsely sculptured), then effaced, then with collection of medium tubercles near tips of (posterior view) moderately long, blunt spines; posterior border expressed ventrally as V-shaped, raised posterolateral rim with fine terrace lines; doublure seen only in anterior view, not well preserved, but appears longest (tallest) medially, anterolaterally tapered, smooth.

Ontogeny. Ontogenetic differences in the known cranidia of T. jeneki are not dramatic, but comparison of the largest (Pl. 44, fig. 1) and smallest (Pl. 45, fig. 23) specimens show that they become broader overall; fixigenae develop pitting, and the tubercles along the axial furrows elongate into the furrows; the glabella broadens and deflates slightly while the lateral lobes inflate slightly; glabellar furrows lengthen (sag.) and shallow slightly at adaxial ends; glabellar sculpture becomes slightly finer; SO lengthens and shallows, particularly medially; LO changes mainly in sculpture: the median node becomes effaced, the tubercles on the posterior edge become finer, and the tubercles on the lateral edges grow into the axial furrows; tubercles on the posterior border become effaced, and the genal spine decreases to a nub.

The known hypostomes and librigenae are too close in size for meaningful ontogenetic comparison, except to note that the librigenal sculpture becomes slightly less dense and finer, and tubercles on the anterior lobe of the middle body of the hypostome decrease in size and number so that only fine tubercles remain on the anterior part of the lobe (cf. Pl. 46 fig. 10 with other specimens). The slight median indentation in the posterior margin of the hypostomal posterior border may also be an ontogenetic development, or it may be unique to the specimen of Pl. 46, fig. 10.

Notable ontogenetic changes in the pygidia of T. jeneki include finer tuberculation overall in the larger specimen, but with the addition of intercalated finer tubercles increasing the density of sculpture; and the terminal piece becomes much larger. Further comparison is hindered by the small sample size and incomplete preservation of the specimens.

Discussion. Tuleaspis jeneki is compared with Tuleaspis n. sp. A and Tuleaspis ? n. sp. B in the discussions of those taxa.