Protopliomerella bowlesi, 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 : 16-19

Protopliomerella bowlesi n. sp.

( Plates 14–19)

1953 Protopliomerops sp. 6 ; Hintze, p. 31, 209, pl. 22, fig. 12.

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

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

2009 Protopliomerella sp. nov. 1; Adrain et al., p. 560, fig.10V, Z.

Material. Holotype, cranidium, SUI 115195 , and assigned specimens SUI 115196 , 126096–126145 , from Section G 162 T m, Fillmore Formation ( lower Floian ; Tulean ; low Psalikilopsis cuspidicauda Zone ), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. After Paul Bowles.

Diagnosis. Glabella long and narrow; glabellar sculpture very fine and concentrated medially; palpebro-ocular ridges long, with posterior end even with S2; LO with very small median tubercle; effaced six-segmented pygidium, with very long first and second inter-ring furrows.

Description. Cranidium long and very wide posteriorly, narrow anteriorly, with sagittal length 53.3% (48.0– 57.4%) width across genal angles, strongly vaulted; anterior border short, moderately narrow, slightly anteriorly bowed, moderately inflated, with U-shaped cross-section, densely covered in fine granules; doublure expressed as anterior face of border, exposes roughly bottom 1/3 of outer face of inner wall of border, with broad, very shallow median rostral suture arc (anterior view), and doublure also present ventrally as very short rim; anterior border furrow short, very deep, with large, deep apodemal pits at junctions with axial furrows, somewhat overhung by inflation of anterior border, broad median section gently anteriorly bowed, lateral sections between border and palpebro-ocular ridges anterolaterally directed at about 30º above horizontal; glabella long, narrow, anteriorly tapered, with maximum width across L1 88.3% (79.5–100%) sagittal length, moderately arched (sag., tr.) with convexity decreasing anteriorly, formed of four distinct lateral lobes separated by sulci, densely granulose, with sculpture mostly confined to median lobe, but also branched into center of lateral lobes on some specimens (Pl. 14, figs 10, 15), and with a few very small perforate tubercles located at mid-length of each lateral lobe even with ends of sulci, additional tubercles scattered on some specimens, e.g., Pl. 15, fig. 2; Pl. 16, fig. 19; glabellar lobes weakly independently inflated, reach to about 1/3 glabellar width on each side, L1–L3 large, roughly equal in area, but L1 subtriangular, L2 and L3 sub-square, L4 less well defined, short, narrow, triangular, and LF present only as very short band echoing curvature of anterior border; S1–S3 short, deep, with courses about about 45º, 30º, and 45º above horizontal, with sagittal ends of S2 and especially S1 slightly posteriorly elongated, S4 very narrow, directed opposite other sulci, branches anteromedially from just inside abaxial end of S3, with junction angle of roughly 90º; SO short, moderately deep medially, very slightly longer and much deeper along L1, with course transverse medially and gently posteriorly bowed laterally; LO wide, moderately long, subrectangular, slightly inflated, with sculpture of dense granules concentrated medially, and small median node located slightly posterior from 2/3 length; LO doublure short, hardly laterally tapered, smooth; axial furrows narrow, a little wider at junctions with glabellar sulci, very deep, subparallel along LO, then steadily anteriorly convergent after bulge around L1; palpebro-ocular ridges long and moderately narrow, extend from anterior border to about even with base of L3, with widest part opposite S3, arcuate to gently sigmoid in shape, strongly raised laterally and steeply sloped anteroventrally (anterior view), with finely granulose rims; palpebro-ocular furrows narrow, deep, incised for most of course, effaced anteriorly from S3 forward and far posteriorly, shallowly sigmoid; interocular fixigenae small, triangular, anteriorly tapered, slightly longer than wide, with sculpture identical to posterior fixigenae; posterior fixigenae long and very wide, strongly downturned from fulcrum roughly even with posterolateral end of eye ridge (anterior view), with broadly anterolaterally bowed anterior margin, and with fairly dense sculpture of small pits and tiny granules, except for a border along glabella and in front of posterior border lacking pits, and a rim of granules on all furrows; posterior border furrow short, deep, incised, with broadly anterolateral course nearly transverse adaxially, and strongly anteriorly curved by genal angle; posterior border moderately short adaxially, expanded ventrolaterally to maximum length slightly before genal angle, then tapered anteriorly, with fine granulose sculpture and small, nubby genal spine; doublure fairly short laterally, cut by facial suture at anterior tip, very short medially, until slightly before genal angle, as doublure is posterodorsally rotated outward to form articulating tongue near LO.

Rostral plate unknown.

Hypostome long and narrow, widest across anterior wings, with width across shoulders 68.2% (67.2–68.6%) sagittal length; hypostomal suture fairly broad, slightly anteriorly bowed; anterior border extremely short medially, flared laterally into short, narrow, triangular anterior wings with relatively large, deep wing process pits; anterior border furrow very short, deep medially, shallowed laterally along posterior half of anterolateral wings, narrow, strongly anteriorly convex; middle body long, narrow, roughly ovoid but with gradual posterior taper; anterior lobe of middle body long (about 3/4 length of middle body), ovoid with rounded posterior margin, strongly ventrally inflated, inflation decreases slightly anteriorly and significantly posteriorly, with fairly dense sculpture of small tubercles concentrated on anterior half, and some scattered small pits (e.g., Pl. 16, fig. 2) on posterior half; anterolateral branches of middle body furrow overlapped with strongly impressed lateral border furrows, furrow illdefined medially, mostly effaced and more present as break in slope between lobes of middle body, strongly posteriorly bowed; posterior lobe of middle body U-shaped, lateral branches long and very narrow, middle short and narrow, gradually posteriorly tapered in width, moderately ventrally inflated, effaced; lateral border furrows narrow, deep and incised, anterior part posteromedially directed, posterior part gently laterally bowed, with anterior portion separated from posterior portion by anterolateral tips of posterior middle body branches; lateral border narrowest anteriorly along lateral notch, gradually expanded posteriorly (as glabella also narrows) to maximum width at posterolateral corners, moderately downturned (lateral view), with dense sculpture of small granules, and with small nubby spines at shoulders, corners, and roughly halfway between those points; posterior border furrow narrow, moderately long and deep, posteriorly curved; posterior border moderately downturned (lateral view) short, but slightly longer than maximum width of lateral border, posteriorly tapered to tip of small, slightly elongated median spine; doublure turned outward into wings anteriorly from moderately long, shallow lateral notch, short and narrow posteriorly, but reaches nearly to lateral and posterior border furrows, gently dorsally raised, smooth.

Librigena long and narrow, moderately laterally convex (ventrolateral view); anterior branch of facial suture very short along eye and field, then about double length and anteroventrally directed along anterior projection of border; posterior branch of facial suture very long, posteroventrally sloped, with change from about 27º to about 10º below horizontal at a little less than half length, then upturned along posterior projection; eye small, ovoid, slightly raised above field (ventrolateral view); librigenal field long and narrow, posteriorly tapered, wedge-shaped, with width under midpoint of eye 20.8% (17.0–23.8%) length along lateral border, with sculpture of fairly densely spaced small pits, and small granules on raised area below eye (Pl. 16, fig. 26); lateral border furrow long, narrow, deep, slightly laterally bowed; lateral border wide, very slightly posteriorly tapered along field, then more strongly tapered to point along posterior projection, strongly inflated, with long, wide, ventrolaterally directed anterior projection with bluntly squared end, posterior projection slightly shorter, strongly tapered, triangular, with strongly upturned end; doublure moderately wide, tapered to sharp point posteriorly, with narrow strip visible behind tip of posterior projection in external view, slightly tapered and terminated anteriorly at anterior edge of librigenal field, then anteroventrally rotated into anterior projection.

Total number of thoracic segments unknown; segments short and relatively wide, with width of axis 38.9% (33.1–50.5%) width across posterior pleural band, highly vaulted in axis and pleurae, with dense sculpture of fine granules all over, including in furrows; articulating half ring short, tapered laterally, relatively wide, raised to about even with axial ring (lateral view); articulating furrow moderately long, deep medially, deeper laterally, very broadly U-shaped in course; axial ring short, approximately same length as posterior pleural band, wide, slightly wider posteriorly than anteriorly, mildly inflated, granulose, with slightly larger granules medially and projecting into axial furrows from corners; doublure very short, very slightly laterally tapered, with extremely fine parallel transverse ridges; axial furrows narrow and very deep along axial ring, slightly wider and shallower after intersection with pleural furrow, anteriorly convergent, more steeply so over anterior pleural band; inner pleurae and outer pleurae approximately same width (excluding pleural spine) on more anterior segments (Pl. 17, fig. 22), outer pleurae longer on more vaulted posterior segments (Pl. 17, fig. 21), pleural angle steep, from about 45º below horizontal to subvertical; anterior pleural band very short medially, slightly expanded ventrolaterally, with extremely short articulating tongue on anterior edge defined by extremely short furrow, and with small anteriorly directed hook structure at tips of band; pleural furrow very short, deep, incised, course posterolateral until just before tips, then gently anteriorly curved; posterior pleural band fairly long, equally broad as anterior band (excluding pleural spine), gently inflated, highest just past fulcrum (anterior view), anterolaterally rotated and somewhat laterally flattened toward abaxial end and through spine, densely granulose, with long, wide, somewhat bladed genal spine, spine with notch separating two bluntly pointed tips in some specimens, and some specimens with concentration of coarser granules lining tip(s) (Pl. 17, figs 17, 27), spine anteriorly curved in most specimens, but posteriorly directed similar to pygidial spines in more posteriorly positioned segments (Pl. 17, fig. 17); doublure very short proximally, turned out posteriorly into very short articulating tongue, long and wide ventrolaterally over spine, with notch at pleural furrow.

Pygidium of six segments and terminal piece, relatively short and broad, with width across anterior pleural band 120.3% (111.9–132.1%) length, highly vaulted, more pleurally than axially, mostly effaced; articulating half ring short, wide, semilunate; articulating furrow short and deep; axis very wide anteriorly, strongly tapered posteriorly to point at tip of terminal piece, moderately vaulted anteriorly, with convexity decreasing toward nearly flat terminal piece; axial rings subrectangular with rounded margins, broad and long anteriorly, tapering to about half width and half length posteriorly, each independently moderately inflated, with paired tiny pits located at about 1/3 and 2/3 width (e.g., Pl. 18, fig. 4; Pl. 19, figs 2, 4), and with additional smaller pits and tiny tubercles on some smaller specimens (Pl. 19, fig. 22); terminal piece triangular, narrow, highly posteriorly tapered, long, very slightly inflated; inter-ring furrows deep, short laterally, longer medially, with first 2-3 furrows much longer; axial furrows narrow, wider at intersections with inter-ring furrows, deep, strongly anteriorly divergent, slightly laterally bowed, discontinuous over sixth pleurae on most but not all specimens (cf. Pl. 18, figs 3, 13), rapidly convergent toward tip of terminal piece, then merged into single sixth interpleural furrow; inner pleurae narrow and increasingly so posteriorly; fulcral angle very steep (anterior view); outer pleurae very wide and strongly downturned; anterior pleural band present only on first segment, broad, very short, with extremely short articulating tongue on inner half set off by extremely short, fairly shallow furrow (lateral view), and with small hook-like articulating structure at lateral tips; pleural furrow short, deep over most of course, but somewhat shallowed near tips of pleurae; posterior pleural bands long, wide, strongly backturned, with fourth pair roughly parallel, and fifth and sixth pairs increasingly posteriorly convergent, moderately inflated like axial rings, with inflation lessening toward tips, ventrolateral portion somewhat laterally compressed into buttress shape (lateral view), effaced except for tiny, widely spaced line of pits centered on ribs (posterior view); pleural spines long, tapered to blunt point, laterally flattened, triangular, gently posteroventrally curved, with very tips slightly recurved dorsally, effaced except for continuation of line of pits on pleurae, and with small tubercles lining ventral margin (lateral view); interpleural furrows short, deep, incised, posterior furrows slightly shallower, backturned to follow pleurae; ventral pygidial border short and narrow, with raised inner rim; doublure moderately long medially, strongly anterolaterally tapered (anterior view).

Ontogeny. Cranidial ontogenetic changes (cf. Pl. 14, figs 3, 15; Pl. 15, figs 10, 23) include overall reduction in coarseness and density of sculpture; narrowing of the anterior border; posterior expansion and anterior tapering of the glabella; lengthening of LF and development of S4; development of perforate glabellar tubercles; reduction of the median LO tubercle; and reduction of the genal spine.

Hypostomal changes (cf. Pl. 16, figs 2, 20) include overall shortening and widening; slight widening of the anterior wings; deepening of the lateral notch; shortening and widening of the anterior lobe of the middle body; shortening of the lateral branches of the posterior lobe of the middle body; reduction in coarseness and extent of middle body sculpture; and increased taper of the lateral border.

Librigenae (cf. Pl. 16, fig. 28; Pl. 17, fig. 1) elongate and widen anteriorly; the eye develops a slightly raised socle; the librigenal field pits spread and enlarge; and the lateral border curves more (especially posteriorly). Thoracic segments are not comparable due to variation based on thoracic position.

Pygidia (cf. Pl. 18, fig. 1; Pl. 19, fig. 22) elongate slightly; the pleurae become more posteromedially directed and create a rounded lateral margin overall; the axis widens and deflates slightly; the axial rings shorten medially as the inter-ring furrows lengthen; the axial furrows become deeper and wider; the pleural tips separate slightly; and the fine granules and tiny pits on the axis and pleurae become more effaced.

Discussion. The left S3 of one cranidium (Pl. 14, fig. 1) does not reach the axial furrow. The posterior border of one hypostome (Pl. 16, fig. 14) is irregularly rounded and spineless; it may be a healed injury. One pygidium (Pl. 18, fig. 23) has a very small, irregularly shaped terminal piece. The axial furrow is impressed over the left side only of the sixth pleurae of one pygidium (Pl. 19, fig. 2).

Protopliomerella bowlesi most closely resembles P. seegeri , and they are compared in the differential discussion of the latter. The six-segmented pygidium differentiates this species from the older species P. stegneri and the younger species P. kerouaci , but other sclerites are more comparable. Protopliomerella bowlesi is also compared to P. stegneri in the discussion of that species.

Compared to Protopliomerella kerouaci , P. bowlesi has an overall narrower, less anteriorly tapered, more highly inflated (especially posteriorly) glabella with coarser granulose sculpture medially, fewer and smaller tubercles outlining the glabellar lobes, and shallower glabellar furrows, longer and narrower (especially anteriorly) palpebro-ocular ridges; a slightly wider hypostome (particularly across the lateral notch) with a longer posterior lobe of the middle body and narrower and shorter lateral and posterior borders; a wider librigena with a wider (anteriorly) and less pitted field; and a relatively wider six-segmented pygidium with a smaller terminal piece lacking a complex impression, shorter pleurae, and a shorter (anterior view) doublure.

Hintze figured specimens from Section G 158.1 m and G 238.3 m (1953, pl. 22, figs 11, 18–20) referred to as Protopliomerops aff. P. contracta . The two specimens from G 158.1 m are specimens of P. bowlesi . Hintze noted that the cranidium (fig. 19) differed from that of Protopliomerella contracta in its less anteriorly tapered glabella, and lower palpebro-ocular ridges. He also stated that the hypostome (fig. 11) had smaller lateral border spines. The two stratigraphically higher specimens represent P. okeeffeae (see discussion). Hintze figured a six-segmented pygidium from G 158.1 m as Protopliomerops sp. 6 (1953, pl. 22, fig. 12), and this also belongs to P. bowlesi .

A single badly damaged pygidium from G 155.6 m likely represents Protopliomerella bowlesi . It is broken anteriorly, but evidence from a count of pleurae and damaged axial rings indicates six segments, which rules out assignment to P. stegneri . Demeter (1973, pl. 6, figs 10, 12) figured pygidia from approximately G 150.1 m, which have seven segments and are likely Protopliomerella n. sp. B (see discussion of that taxon). However, in lateral view (Pl. 19, fig. 23) the pygidium from G 155.6 m appears to include the ventrolateral portion of the anterior pleural band, suggesting that the damage has not removed additional anterior segments, and that the pygidium is that of P. bowlesi .