Protopliomerella kerouaci, Adrain, 2011

Adrain, Jonathan M., 2011, Revision of the Lower Ordovician (lower Floian; Tulean) pliomerid trilobite Protopliomerella, with new species from the Great Basin, western USA 3144, Zootaxa 3144, pp. 1-113 : 19-23

Protopliomerella kerouaci n. sp.

( Plates 20–30)

1951 Protopliomerops contracta Ross , p. 136, pl. 33, figs 18, 19, 23–32 (only; pl. 33, fig. 15 = Protopliomerella seegeri ; pl. 33, figs 16, 17, 22 = P. contracta ). 1953 Protopliomerops sp. indet.; Hintze, p. 31. 1973 Genus and species undetermined A; Demeter, p. 64, pl. 5, fig. 15 (only; pl. 5, figs 2–4, 7, 8 = Cybelopsis ? spp.; pl.

5, fig. 9 = Protopliomerella seegeri ; pl. 5, fig. 13 = gen. and sp. indet.). 2009 Protopliomerella sp. nov. 2; Adrain et al., p. 561, fig. 11M.

Material. Holotype, cranidium, SUI 126209, from Section G 168 T m, and assigned specimens SUI 126206– 126208, 126210–126246 from Section G 168 T m and 174.0 m, Fillmore Formation (lower Floian; Tulean; Psalikilus typicum Zone ), southern Confusion Range, Ibex area, Millard County, western Utah, USA.; SUI 115214, 126146–126205 from Section HC6 202 T m, 203.0 m, and 203.5 m, Garden City Formation (lower Floian; Tulean; Psalikilus typicum Zone ), west side of Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho, USA. Also known from Locality YH E, Yellow Hill Limestone (lower Floian; Tulean; high Psalikilopsis cuspidicauda Zone ), Yellow Hill, near Pioche, Lincoln County, eastern Nevada, USA.

Etymology. After Jack Kerouac.

Diagnosis. Fixigenae with sparse granules concentrated around edges of pits; thoracic segments dorsally effaced; pygidium nearly effaced, with transverse line of pits on axial rings and down center of pleurae.

Description. Cranidium with strongly vaulted fixigenae, moderately vaulted axis, narrow anteriorly and very wide posteriorly, with sagittal length 48.4% (44.6–52.9%) width across genal angles; anterior border narrow, short, subrectangular, very slightly anteriorly curved, moderately inflated, with U-shaped cross-section, densely granulose, more effaced dorsally, with line of pits at mid-length echoing curvature; doublure expressed as anterior face, exposes bottom half of outer face of inner wall of border, scalloped with shallow median arc of rostral suture, only a rim ventrally; anterior border furrow short, very deep, incised, with short anterolateral branches angled at about 30º above horizontal and broad median section with slight anterior convexity; glabella long, narrow, strongly anteriorly tapered, with maximum width across L1 94.9% (81.6–106.1%) sagittal length, moderately arched, with convexity higher posteriorly, with four well-defined lateral lobes, and with dense granulose sculpture medially (effaced on larger specimens) and some perforate tubercles or pits, lateral lobes with sculpture extending exsagittally from middle lobe along mid-length and mid-width, but surrounded by short and narrow effaced rim on dorsal face (lobes totally effaced on larger specimens), lobes also outlined by granules on edge extending into lateral and axial furrows; L1 largest, subtriangular, with L2 and L3 slightly shorter and sub-square, L4 short, narrow, triangular, median lobe long, narrow, roughly rectangular, LF just a very short arc behind anterior border furrow; all lateral furrows short, deep, and incised, progressively narrower anteriorly, with S4 about 1/3 width of S1, S1–S3 strongly anterolaterally directed, about 30-40º above horizontal, S1 with slightly elongated adaxial end, S4 very strongly anteromedially directed about 50º above horizontal, branching from near exsagittal tip of S3; SO short, slightly longer medially and behind outer halves of L1, deep, shallower medially and deeper laterally, with gently wavy course curved behind L1, lined anteriorly and posteriorly with granules just inside rim; LO wide, about as long as L2, rectangular, with slightly wavy anterior margin, effaced; doublure fairly short, slightly laterally tapered, with a fine transverse ridge at midlength; axial furrows moderately wide, wider at triangular intersections with lateral glabellar furrows, very deep, subparallel along LO, bowed outward around L1, then steadily anteriorly convergent, framed by granulose margins of glabella and fixigenae; palpebro-ocular ridges opposite L3–LF, short, narrow, with strongly arcuate outer margin and very narrow, rapidly tapered posterior ridge, highly elevated at about 50–60º above horizontal (anterior view), densely granulose; palpebro-ocular furrows narrow, deep, incised, except effaced along extreme anteromedian section of ridge, with gently sigmoid course; interocular fixigenae triangular, narrow, short, a little less than 1/3 maximum length of fixigena; posterior fixigenae long, wide, subrectangular, with broadly curved anterior margin, all fixigena with fairly sparse sculpture of tiny granules, concentrated only on rims of pits in larger specimens, densely scattered small pits, and effaced zone along axial and posterior border furrows; posterior border furrow short, slightly longer toward genal angle, then constricted again, deep, incised, roughly transverse until mid-course, then anteriorly curved (lateral view), rimmed with granules anteriorly and posteriorly; posterior border short medially, expanded laterally to maximum at genal angle, then strongly tapered to point at tip, moderately inflated, mostly effaced, but with scattered granules on posterior edge (concentrated near genal angle), and small nubby spine at genal angle; doublure very short adaxially, turned outward into articulating tongue near axis, longer and wider toward genal angle, cut shallowly by facial suture at anterior corner of genal angle.

Rostral plate unknown.

Hypostome narrow and elongate, with width across shoulders 70.2% (65.8–73.0%) length; hypostomal suture broad, very slightly anteriorly convex; anterior border vanishingly short, especially medially, nearly overhung by middle body, expanded laterally into long, fairly wide, wedge-shaped anterior wings with small, deep wing process pits located very close to lateral margin, with granulose sculpture and some larger granules medially; anterior bor- der furrow narrow arc, strongly anteriorly bowed, extremely short, especially medially, deep anteriorly, then abruptly shallowed at connection with lateral border furrow; anterior lobe of middle body long, wide, ovoid, strongly ventrally inflated, with inflation decreasing anteriorly and posteriorly from maximum about even with anterior end of lateral notch (lateral view), with sculpture of dense tiny tubercles over anterior half, becoming much less dense posteriorly; middle body furrow ill-defined, moderately long, shallow, strongly posteriorly convex, merged with lateral border furrow at about half length of middle body; posterior lobe of middle body U-shaped, short, tapered anterolaterally, somewhat inflated, with inflation decreasing posteriorly, effaced; lateral border furrows narrow, deep, gently laterally bowed, anteriorly and posteriorly convergent; lateral border very narrow at lateral notch, much expanded at shoulders, and gradually expanded posteriorly to maximum width at posterolateral corners, moderately downturned (lateral view), densely granulose, with small nubby spines at shoulders, small pointed spines between shoulders and posterolateral corners, and larger pointed spines at corners; posterior border furrow moderately long and deep medially, short and shallow laterally, strongly posteriorly convex; posterior bor- der long, narrow, strongly downturned (lateral view), with granulose sculpture and short, triangular median spine; doublure long and wide, reaches slightly inside lateral border furrows and nearly to posterior border furrow, rotated anterolaterally at lateral notch out into anterior wings, posterior section moderately raised and posteroventrally sloped, lateral notch broad and moderately deep.

Librigena long and narrow, strongly posteriorly tapered, wedge-shaped with moderate lateral curvature (ventrolateral view); anterior branch of facial suture very short along eye and field, sharply posteriorly angled to make narrow angle with border, then long and steeply anteroventrally sloped to end of anterior projection of border; posterior branch of facial suture very long, steeply sloped from eye to about mid-length of librigenal field, then more shallowly sloped down to border (about 35º and 15º below horizontal, respectively); eye small, elliptical, moderately raised above field on socle (ventrolateral view); librigenal field fairly wide anteriorly, strongly tapered posteriorly, with width of field under midpoint of eye 17.0% (14.5–19.4%) length of lateral border furrow, moderately ventrolaterally and anteroposteriorly sloped, with dense sculpture of tiny granules and moderately densely distributed small pits; lateral border furrow narrow, deep, deeper anteriorly and slightly shallower near posterior end, very gently laterally bowed and posteriorly sloped in course; lateral border very wide, posteriorly tapered to fine point, with long anterior and posterior projections, anterior anteroventrally rotated, with bluntly squared termination, posterior triangular, rapidly tapered and strongly posterodorsally curved, border well inflated, with dense sculpture of medium granules; doublure wide, reaches about 3/4 to lateral border furrow, slightly tapered anteriorly, then terminated as border rotates to form anterior projection, with inner face exposed along tip of posterior projection in external view.

Total number of thoracic segments unknown; individual segments highly arched both axially and pleurally, generally short and broad, with width of axis 39.5% (31.3–80.7%) width across posterior pleural band, posterior segments narrower and more strongly arched, segments nearly effaced dorsally, very finely granulose on other surfaces; articulating half ring short, laterally tapered, somewhat lens-shaped, anterodorsally raised such that anterior margin is roughly equal in elevation with axial ring, anterior rim effaced, posterior half granulose (best seen as change in tone from bright light gray to medium gray in dorsal view); articulating furrow moderately long, very deep laterally in apodemal pits, shallower but still deep medially, transverse medially, with anterolaterally curved ends; axial ring short and broad, slightly wider posteriorly, with small, shallow indent at about midlength of each lateral margin, ring lightly inflated, with inflation stronger near axial furrows (posterior view), with clusters of coarse granules at each corner; doublure short, laterally tapered, semilunate, with several very fine transverse ridges; axial furrows narrow posteriorly, slightly wider at lateral indent of axial ring, and a little more than doubled in width after intersection with pleural furrow, deep, very deep posteriorly, anteriorly convergent in course; inner pleurae and outer pleurae (excluding spine) roughly equally wide in anterior segments, inner pleurae decrease in width posteriorly, joined by steep fulcral angle varying from approximately 45º to approaching subvertical; anterior pleural band as wide as posterior band (excluding spines), very short, with extremely short articulating shelf running along anterior margin and with small hook structure projecting anteriorly from ventral tip, with dense granulose sculpture concentrated posteriorly; pleural furrow very short and very deep, transverse to posterolaterally directed for most of course, anteriorly curved near tips; posterior pleural band slightly longer than axial ring, moderately inflated, higher near axial furrows and just past fulcrum, ventrolateral part of pleurae and pleural spine anterolaterally rotated and somewhat laterally flattened, with fine granules lining all edges and concentrated on anterior face just past fulcrum, and on edges of spine, spine wide (tr.), moderately long, tapered to single fine point on some specimens (Pl. 23, fig. 24; Pl. 28, fig. 21), split by small notch into two blunter tips on others (e.g., Pl. 23, fig. 15; Pl. 29, figs 4, 23), gently anteriorly curved except on far posterior segments (e.g., Pl. 28, fig. 21); doublure wide, covers all of spine, with rounded notch centered over posterior pleural band, posterior rim wider than anterior rim, folded posterodorsally to form very short articulating shelf on inner pleurae of posterior pleural band (posterior view).

Pygidium made of five segments and terminal piece, strongly pleurally vaulted and moderately axially vaulted, slightly longer than wide, with width measured across tips of anterior pleural band 107.9% (99.7–118.7%) sagittal length excluding articulating half ring; articulating half ring short, laterally tapered, semilunate, slightly narrower than first axial ring, with anterior effaced strip and posterior finely granulose strip similar to thoracic articulating half rings; articulating furrow fairly short, deep, somewhat shallower medially; axis conical, broad anteriorly, strongly posteriorly tapered to point at end of terminal piece, moderately vaulted anteriorly, decreasing posteriorly to gently inflated terminal piece; anterior axial rings roughly equal in length, posterior rings slightly shorter, first ring very wide, fifth ring about 2/3 as wide, each ring independently inflated, shape of rings transverse to somewhat anteriorly bowed due to embayment by inter-ring furrows, mostly effaced dorsally, but with some dense granules (mainly on smaller specimens), and tiny pits in transverse line at midlength of rings, also outlined with small granules, especially noticeable at corners; inter-ring furrows lens-shaped, long medially and laterally constricted (anterior furrows) to moderately short (posterior furrows), very deep, especially laterally in apodemal pits; terminal piece triangular, long, wide anteriorly, gradually tapered to point even with or just above base of pleural spines, anterior portion gently inflated, falling along posterior taper, with pits and granules like axial rings, and with complex impression on most specimens varying from two furrows connected to last inter-ring furrow to large, roughly hexagonal pit; axial furrows fairly narrow, wider at intersections with inter-ring furrows, very deep, widely anteriorly divergent, well impressed over fifth segment, then overlapped with fifth interpleural furrows along terminal piece; anterior pleural band expressed on first segment only, extremely short in dorsal view, overhung laterally by posterior pleural band, longer ventrolaterally (lateral view), as wide as posterior pleural bands (without spine), with vanishingly short articulating tongue on anterior margin, and small anteriorly pointed hook at ventrolateral tips; pleural furrow also extremely short in dorsal view and overhung by posterior pleural band, very deep, backturned; posterior pleural bands long, wide, increasingly backturned, with pleurae 1–3 subparallel and 4–5 posteriorly convergent, each pleural rib moderately inflated near axis, increasingly inflated posteroventrally (lateral view), ribs somewhat laterally flattened toward base and spine, mostly effaced dorsally, rimmed with granules on anterior, posterior, and adaxial faces, and with line of widely spaced small pits on midline of each rib; spines with strongly posteroventrally curved ventral margin (lateral view), spines fairly short and wide, tapered to blunt point, closely spaced but with free tips, with granules on ventral margin, and small pit close to tip of spine; interpleural furrows short and very deep, posterior furrows shallower on smaller specimens, strongly backturned like pleurae; pygidial border located ventrally, formed from joined spine bases, short and narrow, with raised anterior rim; doublure seen best in anterior view, very long and pointed medially, sharply anterolaterally tapered, smooth.

Ontogeny. Cranidia of Protopliomerella kerouaci become wider overall, and all sculpture becomes increasingly effaced; the anterior border narrows and develops pits; the palpebro-ocular ridges move anteromedially, widen, and lose the slight postocular ridge; the glabella widens slightly posteriorly and tapers anteriorly; the lateral furrows lengthen and deepen, and S4 develops; LO lengthens, particularly laterally and becomes more rectangular; the median LO tubercle disappears; and the genal spine is reduced.

The hypostome lengthens; the anterior wings expand somewhat and rotate ventromedially to better expose the wing process pits in ventral view; the anterior border shortens to near absence medially; the lateral notch deepens (lateral view); the middle body furrow deepens anterolaterally and fades medially; the middle body sculpture reduces in coarseness and becomes restricted to the anterior part of the anterior lobe; the lateral border widens slightly and the posterior border lengthens; and the border spines become shorter and narrower.

Librigenal changes include overall elongation and increase in convexity (ventrolateral view); the anterior branch of the facial suture becomes slightly longer as the anterior part of the field widens and increases the distance between the eye and the lateral border; the librigenal field decreases in posterior taper and its pits enlarge and spread posteriorly; and the lateral border becomes more laterally curved. Thoracic ontogenetic changes cannot be accurately assessed because of variation in size and shape of pleurae by position.

The pygidium becomes longer and laterally rounded; the sculpture changes from coarse granules and small tubercles to nearly complete effacement; the axis narrows slightly relative to the pleurae; the axial rings become shorter medially as the inter-ring furrows lengthen; the axial furrows deepen and widen; the pleurae become longer, wider, and more posteromedially directed; and the tips of the pleural spines become blunter and more closely spaced.

Discussion. The terminal piece of one pygidium (Pl. 30, fig. 1) is marked with a large, deep, roughly hexagonal impression. One librigena (Pl. 28, fig. 1) has a small rounded excursion of the posterior librigenal field interrupting the slope of the posterior branch of the facial suture. Some cranidial specimens, e.g., those of Pl. 28, appear more effaced, and this is likely a combination of ontogenetic and preservational differences. The cranidia in question are both larger and more damaged overall than the more granulose specimens.

All but three sclerites figured by Ross (1951, pl. 33, figs 16–19, 22–32) as Protopliomerella contracta represent P. kerouaci , which we have also sampled from the Garden City Formation. Protopliomerella kerouaci is compared to P. stegneri , P. bowlesi , P. seegeri , and briefly to P. contracta in the discussion sections of those species.