Protopliomerella okeeffeae, 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 : 24-27

Protopliomerella okeeffeae n. sp.

( Plates 34–40)

1953 Protopliomerops aff. P. contracta Ross ; Hintze, p. 31, 207, pl. 22, figs 18, 20 (only; pl. 22, figs 11, 19 = Protopliomerella bowlesi ).

? 1953 Protopliomerops sp. ; Hintze, p. 35.

? 1953 Protopliomerops contracta Ross ; Hintze, p. 35, 36.

1973 Protopliomerella contracta (Ross) ; Demeter, p. 59, pl. 4, figs 6, 11, 12 (only; pl. 4, fig. 2 = Protopliomerella bowlesi ).

1973 Pseudocybele cf. altinasuta Hintze, 1953 ; Demeter, p. 62, pl. 4, fig. 7.

1973 Pseudocybele sp. ; Demeter, p. 62, pl. 5, figs 1, 6, 11.

2009 Protopliomerella sp. ; Adrain et al., p. 567, fig. 14L.

2009 Protopliomerella sp. nov. 3; Adrain et al., p. 567, fig. 15Y, CC.

Material. Holotype, cranidium, SUI 126291, from Section G 258.2 m, and assigned specimens SUI 126290, 126292–126307, 126319, 126320, 126325–126336, from Section G 238.3 m and 258.2 m, Fillmore Formation (lower Floian; Tulean; Heckethornia hyndeae Zone ), southern Confusion Range, Ibex area, Millard County, western Utah; SUI 115287, 115288, 126272–126289, 126308–126318, 126321–126324, 126337–126345, from Section H 93.4 m and H 127.1 m, Fillmore Formation (lower Floian; Tulean; Heckethornia bowiei Zone ), southern Confusion Range, Ibex area, Millard County, western Utah, USA; SUI 115263, from Section YH 128.9 m, Yellow Hill Limestone (lower Floian; Tulean; Heckethornia hyndeae Zone ), Yellow Hill, near Pioche, Lincoln County, eastern Nevada, USA.

Etymology. After Georgia O'Keeffe.

Diagnosis. L1 smaller than L2 and L3; S3 short and shallow; axial furrows very wide and strongly laterally bowed around glabella; librigenae with relatively very narrow field and wide lateral border; terminal piece with complex W-shaped impression; pygidial pleural spines strongly ventrally directed, with small pit on posterior face marking angle.

Description. Cranidium long medially, tapered laterally, narrow anteriorly, very wide posteriorly, with sagittal length 48.2% (43.0–53.1%) width across genal angles, highly vaulted pleurally and axially; anterior border moderately short, longer medially and slightly tapered laterally, with lateral edges truncated by palpebro-ocular ridges, narrow, gently anteriorly bowed, with posterior margin less curved than anterior margin, moderately inflated, very densely granulose; doublure present as a rim ventrally, mainly shown as anterior face of border, with narrow, shallow, semicircular median arc of rostral suture about 1/3 width of border, bottom half of anterior side of posterior wall of border exposed; anterior border furrow short, very deep, longer and deepest in apodemal pits at junctions with axial furrows, course gently anteriorly bowed medially, but with lateral branches projecting anterolaterally at about 30º above horizontal; palpebro-ocular lobes fairly short, narrow, posteriorly tapered, located opposite mid- L3–LF, steeply raised at about 50–60º (anterior view), granulose; palpebro-ocular furrows short, narrow, deep along most of course, but abruptly shallowed at anteromedial end of ridge, slightly sigmoidal in course, with inner end even with S4 on some cranidia (e.g., Pl. 34, figs 1, 2); interocular fixigenae triangular, very short, very narrow anteriorly and slightly expanded posteriorly; posterior fixigenae very long and wide, with gently anterolaterally curved anterior margin, steeply downturned post-fulcrum (occurs roughly in line with palpebro-ocular ridge; see anterior views), with dense sculpture of very fine granules and small pits, except effaced along axial and posterior border furrows; posterior border furrow moderately long, tapered adaxially and anterolaterally, deep, roughly transverse for most of course, then sharply anteriorly curved at genal angle, rimmed by tiny tubercles; posterior border very wide, short medially, expanded laterally to maximum length at genal angle, then anteriorly tapered, most of border effaced or with scattered tiny granules, but with some tiny tubercles on posterior margin, and with very short articulating tongue set off by extremely short, deep furrow on posteromedian margin (Pl. 34, fig. 19; ventral views); doublure very short proximally, with transverse furrow for articulation, lengthened toward genal angle, cut by facial suture at genal spine; axial furrows wide to very wide, somewhat lacunate in larger specimens, deep, anteriorly convergent, strongly laterally bowed around glabella, subparallel along LO, lined by granules on glabella, and inner margins of fixigenae, LO and posterior border; glabella long, narrow anteriorly and wide posteriorly, with width across L1 92.2% (80.8–103.8%) sagittal length, strongly inflated (sag., tr.), with convexity higher posteriorly, with three well-defined lateral lobes and less distinct L4, and with densely granulose sculpture, especially medially, but also on lateral lobes of some specimens; L1 ellipsoid, short, narrow, small, steeply anterolaterally directed; L2 and L3 small, subsquare, also anterolaterally directed but at lower angles, slightly larger than L 1 in area; L4 more prominent in larger specimens (e.g., Pl. 34, fig. 2), small triangular, open-ended exsagittally; LF long, wide and nearly semicircular on cranidia without L4, just a short arc on cranidia with L4, has line of fine granules on anterior edge (e.g., Pl. 36, fig. 10, Pl. 37, fig. 17) hidden by anterior border in most specimens; S1 long, deep, anterolaterally directed, with posteriorly elongated inner end; L2 slightly shorter, deep, anterolaterally directed similarly to L1 at about 30º above horizontal; L3 short, moderately shallow, disconnected from axial furrows, anteromedially curved; S4 short, shallow, positioned far anterolaterally, disconnected from axial furrows, does not intersect S3; SO moderately long, deep, longer and deeper laterally in apodemal pits, lined by tubercles on posterior edge of glabella and far lateral edges of LO; LO wide, moderately long, slightly tapered laterally behind apodemal pits in SO, gently inflated, very slightly raised posteriorly (lateral view), with sculpture of small tubercles mainly on posterior edge, and with prominent median node nearly at posterior edge in small specimens (e.g., Pl. 36, figs 22, 27); doublure fairly long medially, nearly reaches SO, gently laterally tapered, semilunate.

Rostral plate unknown.

Hypostome long, narrow, widest across anterior wings, posteriorly tapered, with width across shoulders 72.1% (70.1–74.2%) sagittal length; anterior border sharply downturned (lateral view), short, laterally expanded into short, narrow, triangular anterior wings with deep, relatively large, wing process pits; anterior border furrow short, deep, incised, gently anteriorly convex; middle body long, narrow, posteriorly tapered, with lobes ill-defined by nearly effaced middle body furrow; anterior lobe ovoid, reaches to about 3/4 middle body length, strongly ventrally inflated, with inflation decreasing slightly anteriorly and posteriorly (lateral view), mostly effaced, with dense cluster of fine tubercles anteromedially; posterior lobe U-shaped, short and narrow, with anterolaterally tapered arms, moderately inflated anteriorly, nearly flat toward posterior border, effaced; lateral border furrows narrow, with alternating moderately deep and shallow segments: shallow far anteriorly along anterior wings, then deep opposite lateral notch, with shallow length near anterolateral limits of posterior lobe of middle body, then deep again from just past shoulders to junction with posterior border furrow; lateral border very narrow at lateral notch, slightly expanded at shoulders, then gradually further expanded (as middle body tapers) to maximum width at posterolateral corners, strongly downturned, with dense granulose sculpture and small nubby spines at shoulders, slightly larger and more conical spines at posterolateral corners, and small, spine in between; posterior border furrow very shallow, moderately short, U-shaped; posterior border short, narrow, strongly downturned (lateral view) with short median triangular spine; doublure slightly longer and wider than posterior and lateral borders, upturned, rotated anteroventrally over anterior part of very shallow lateral notch into anterior wings.

Librigena long, narrow, slightly anteroposteriorly curved (external view), strongly laterally curved (ventrolateral view); anterior branch of facial suture very short along eye and field, directed steeply ventroposteriorly to make angle of about 40º with lateral border, then somewhat longer and anteroventrally directed about 30º below horizontal along anterior projection of lateral border; posterior branch of facial suture very long, with break in slope at about half length of librigenal field, anterior slope about 35–40º below horizontal, posterior slope much shallower at about 5º; eye small, elliptical, highly inflated, raised above field on tall, narrow platform, with very shallow, narrow circumocular furrow (ventrolateral view); librigenal field very long and narrow, posteriorly tapered, with width at midpoint of eye 16.1% (12.1–19.4%) length along lateral border furrow; densely granulose, with small pits concentrated near eye and along posterior branch of facial suture; lateral border furrow narrow, deep, incised, nearly transverse to slightly ventrolaterally bowed in course; lateral border wide, sharply tapered along posterior projection to point with doublure showing, anterior projection roughly equal in length to posterior, ventrolaterally rotated, with blunt margin, border strongly inflated, densely covered in large granules; doublure moderately wide, gently anteriorly tapered near anterior edge of field, then truncated and turned anteroventrally into anterior projection.

Thorax with total number of segments unknown; segments highly arched both axially and pleurally, short, fairly wide (varies with thoracic position; posterior segments narrower), with relatively narrow axis of width 40.3% (34.0–54.2%) width across posterior pleural band; articulating half ring fairly long medially, laterally tapered, semilunate, anterodorsally raised, but not quite as high as axial ring (lateral view), anterior half of ring mostly effaced, posterior half densely granulose; articulating furrow fairly long and moderately deep medially, shorter and very deep anterolaterally in apodemal pits, broadly U-shaped in course; axial ring relatively short, slightly shorter than articulating half ring, wide, strongly inflated, slightly higher posteriorly, densely granulose, with line of small tubercles along posterior margin, small slightly elongate tubercles along sides and anterolateral corners, an elongate tubercle at each antero- and posterolateral corner (anterior and posterior view), and with arch of axial ring outlined posteriorly by slightly larger granules; axial furrows narrow and deep along axial ring, wider at meeting with pleural furrow, then narrow and very deep along articulating half ring, lined by tubercles and granules on axial ring and pleurae; inner pleurae and outer pleurae about same width on anterior segments, inner pleurae narrower on posterior segments, joined by steep fulcral angle of about 45–50º; anterior pleural band short, about half length of posterior band, as wide as posterior band excluding pleural spine, densely granulose, with extremely short articulating tongue and furrow on anterior margin, and small articulating hook structure at ventrolateral ends; pleural furrow short, deep, incised, abruptly shallowed and gently anteriorly curved near posterolateral tip; posterior pleural band about same length as axial ring, moderately inflated, highest near axis and just past fulcrum, densely finely granulose, with line of small tubercles at midlength, with larger granules and more tubercles scattered on some segments, and with large pleural spine; spine long, wide, laterally flattened, anterolaterally rotated, ventrally tapered, some spines with notch separating two pointed tips, with coarse granules along posterior edge and near spine tips.

Pygidium of five segments and terminal piece, relatively short and wide, with width across anterior pleural band of first segment 103.1% (91.2–114.1%) sagittal length from articulating furrow, strongly vaulted axially and pleurally; articulating half ring moderately long, laterally tapered, semilunate, anterior half effaced, posterior half finely granulose; articulating furrow short, deep, incised; axis moderately wide, conical and posteriorly tapered to point, strongly convexly vaulted anteriorly, convexity falling posteriorly to nearly flat terminal piece; axial rings each independently inflated, with first ring moderately well inflated, fifth ring very gently inflated, and terminal piece nearly uninflated, first ring moderately long and wide, fifth ring slightly shorter and a little less than 2/3 width of first, rings with rounded lateral margins, background sculpture finely granulose (specimens from H 93.4) to nearly effaced (specimens from G 258.2), rings rimmed by granules in furrows, and with some larger tubercles and pits in rough transverse line across midlength of ring; inter-ring furrows moderately long and deep, somewhat shallower and longer medially, with first and fifth inter-ring furrows particularly long; terminal piece triangular, fairly narrow anteriorly, long, tapered to point, with sculpture like axial rings and with complex W-shaped impression; axial furrows narrow, slightly wider at junctions with inter-ring furrows, deep anteriorly, not well impressed over fifth segment of most pygidia, unimpressed over fourth segment of some pygidia (e.g., Pl. 40, figs 5, 30, 33), overlapped with fifth interpleural furrows along terminal piece; anterior pleural band strongly posterolaterally directed, very short, as wide as posterior pleural band excluding spine, but not well exposed in dorsal view, with extremely short articulating tongue on anterior edge and small hook-like articulating structure at ventrolateral limits; pleural furrow short, deep, incised, with slight anterior curvature near tip; posterior pleural bands very strongly backturned, subparallel to posteromedially convergent, long, wide, strongly independently inflated, somewhat laterally flattened, with inflation and flattening increasing posteroventrally into pleural spines, with granulose sculpture overlain by larger granules on margins and with some small pits running down middle of pleurae; spines fairly long, strongly posteroventrally curved, with small pit at angle (posterior view), laterally flattened, tapered to blunt points, granulose, with rim of coarser granules on ventrolateral margin (lateral view); interpleural furrows short, deep, incised, with posterior furrows shorter and shallower; pygidial border (ventral view) short and narrow, posteromedially tapered, with slight raised anterior margin near anterolateral corners, granulose; doublure moderately long in ventral view, tall medially, semilunate, strongly anterolaterally tapered in anterior view, smooth.

Ontogeny. Cranidial ontogenetic changes include relative shortening and widening of the cranidium overall (sagittal length:width across genal angles); lengthening, especially medially, and narrowing of the anterior border; narrowing of the interocular fixigenae and slight posteromedial movement of the palpebro-ocular ridges; widening of the posterior glabella (and LO) and development of the anterior taper; lengthening and deepening of the glabellar furrows, particularly S1 and S2; development of S4; widening of the axial furrows; effacement of the fixigenae bordering the axial and posterior border furrows; lengthening of SO and the posterior border furrow; shortening of the posterior fixigenae; reduction of the genal spine and median LO tubercle to nubs; and overall reduction in the coarseness of the granulose background sculpture.

Librigenae lengthen and narrow overall; the elevation of the eye increases (ventrolateral view); the anterior part of the posterior branch of the facial suture decreases in slope, and the posterior branch increases in slope; the anterior part of the field shortens (measured under the eye); the posterior part (after change in slope) widens slightly; the pits deepen; the lateral border furrow deepens; and the lateral border narrows, while the anterior and posterior projections increase in length. The two known hypostomes are too similarly sized to observe ontogenetic change, and the thoracic segments also lack the necessary range of sizes.

Pygidia are relatively close in size and less well preserved than the other sclerites. Major changes include overall lengthening relative to width; an increase in the angle of the backturned pleurae; elongation of the pleurae and inflation of the axis (lateral view); elongation and increased ventral direction of the pleural spines; and a decrease in tuberculate sculpture (cf. Pl. 40, figs 3, 30).

Discussion. The left first posterior pleural band of one pygidium (Pl. 39, fig. 15) has a furrow separating the inner pleural and outer pleural parts of the band. The fifth axial ring of one pygidium (Pl. 40, fig. 5) is split roughly in half by an excursion of the final inter-ring furrow. The posteromedian section of one pygidium (Pl. 40, fig. 1) seems to be merged and effaced.

Protopliomerella okeeffeae is compared to the most morphologically similar species, P. contracta , in the discussion section of the latter. It occurs with a new species of Lemureops McAdams and Adrain, 2009 , at Section H 127.1 m. The taxa are somewhat morphologically similar, and both are relatively poorly preserved at this horizon. However, the species of Lemureops possesses a very wide, lacunate axial furrow which easily distinguishes it from P. okeeffeae , as well as a shorter and relatively wider hypostome with nubby spines, and a strongly posteriorly tapered pygidium.