Deltapliomera humphriesi, 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 : 28-32

Deltapliomera humphriesi n. sp.

Plates 34–43

1953 Protopliomerops sp. 4; Hintze, p. 210, pl. 21, fig. 4 [only; pl. 21, fig. 8 = Panisaspis quattuor (Hintze) ]. 2009 Ibexaspis sp. nov. 7; Adrain et al., p. 573, fig. 18I, M.

2009 Ibexaspis sp. nov. 8; Adrain et al., p. 573, fig. 18J.

Material. Holotype, pygidium, SUI 129755 (Pl. 43, figs 1, 2, 5, 8, 11), and assigned specimens SUI 115358 , 129674–129704 , from Section H 208.2 m, and SUI 115357 , 129705–129752 , 129756–129761 , from Section H 222.1 m, Fillmore Formation (Blackhillsian, Carolinites nevadensis Zone ), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. After Barry Humphries.

Diagnosis. Cranidium with anterior border furrow and most or all of border overhung medially by glabella; long and narrow interocular fixigenae (including frontal area); strongly anteriorly expanded glabella; palpebral lobes located in a relatively posterior position on cranidium; inner margins of lobes/palpebral furrows almost parallel to sagittal axis (in large specimens); librigena with wide field relative to congeners; pygidium with axial sculpture concentrated on anterior half of rings; sculpture of large cranidia and pygidia generally finely granular and densely spaced to dorsally effaced (see discussion); pygidial pleural spines thicker, more rounded in cross section than those of congeners; terminal piece well expressed in most specimens.

Description. Cranidial measurements were made on the sufficiently complete large specimens of Plates 34, 35, 38–40. Measurements were doubled from the sagittal midline where necessary. Cranidium very strongly vaulted (sag., tr.), with anterior face subvertical (see sagittal profile), long and broad, increasingly wide posteriorly, with sagittal length 99.8% (93.4–105.6%) width across γ, 73.4% (68.8–78.8%) width across δ, 69.3% (66.0– 74.4%) width across ε, and 52.3% (50.7–56.3%) maximum width across posterior projections; anterior border very short, slightly longer (oblique) at exsagittal ends, a little wider than LO, strongly anteriorly bowed in dorsal view and nearly overhung medially by glabella on most specimens, lateral portions of border slightly downturned in anterior view, with densely spaced sculpture of very fine tubercles; doublure expressed as very short anterior face of border, just a rim ventrally; anterior border furrow short and deep, incised, strongly anteriorly bowed, with narrow transverse section anterior to frontal areas; glabella very large, long, very broad, anteriorly expanded, with sagittal length 111.3% (101.8–122.3%) maximum width across mid-length of L3, sagittal length 81.1% (77.0– 84.1%) cranidial length, maximum width 38.3% (35.4–42.8%) maximum cranidial width, strongly inflated, with three well-defined lateral lobes, sculpture of small densely spaced tubercles (some specimens more effaced medially), with small, low tubercles on lobes; all lateral lobes narrow (tr.), L1 smallest, short and slightly more anteriorly directed than L2 and L3; L2 and L3 similar in appearance, L3 a little longer and bigger, both lobes approximately transversely oriented, LF semilunate, broad and anteriorly convex; glabellar furrows all fairly short, expanded exsagittally toward axial furrows, deep, except innermost ends abruptly shallowed, S3 always shallower than S1 and S2, S1 gently posteromedially directed, S2 transverse, S3 gently anteromedially directed; SO moderately long, lengthened in all specimens behind mid-width of L1, deep (shallower when longer), course subtransverse; LO fairly long, 14.2% (11.9–16.6%) sagittal cranidial length, broad, with maximum width 32.7% (30.6–35.0%) cranidial width, independently well inflated, mostly effaced (in large specimens), with a few small tubercles near corners; doublure broad, long, pinched out laterally, effaced; axial furrows very deep except over LO, a little wider at intersections with other cranidial furrows, meet all but palpebral furrows, course gently anteriorly divergent, more laterally bowed from L3 anteriorly; frontal areas subequant, short and narrow, subvertical, effaced but for a few scattered fine tubercles; palpebral lobes a little independently inflated, long, about 1/3 sagittal cranidial length, downturned anteriorly and posteriorly, held horizontally at about half-length, lobes narrow, a little wider posteriorly, inner margin straight except curved around posterior end, lateral margin unevenly arcuate, with strongest curvature posteriorly, lobes generally semi-elliptical to half-teardrop shaped, with short, posteriorly tapered postaxial ridge, and with sculpture of fine granules to effaced; palpebral furrows narrow (exsag.), deeply incised except at anteriormost edge of palpebral lobe, course roughly J-shaped, anteromedially angled along main part of palpebral lobe, hooked around posterior end and postocular ridge; interocular fixigenae long, subtriangular, narrowed anteriorly, roughly horizontal at palpebral lobes, very strongly downturned anteriorly, with sculpture of densely spaced small tubercles overlying scattered small pits; posterior fixigenae wide and relatively short, subrectangular, very strongly ventrolaterally sloped from fulcrum, about 50° below horizontal, with rounded anterior margin from cut of facial suture, sculpture like that of interocular fixigenae; posterior border furrow deep, fairly short, course gently anterolaterally directed, with exsagittal ends a little anteromedially curved; posterior border well inflated, wide, adaxial ends short, border rapidly expanded to maximum length at genal angle, then tapered slightly toward cut of facial suture, effaced except for rim of fine tubercles on anterior edge extending into posterior border furrow; doublure forming a rim ventrally adaxial to fulcral angle, turned out posteriorly, rapidly expanded abaxial to fulcral angle to maximum length just adaxial to genal angle, cut by facial suture at genal angle, effaced.

Hypostomal measurements were made on the specimens of Plates 36, 41. Hypostome ovoid and oblong, with width across shoulders (approximately equal to width across anterior wings) 90.1% (84.1–96.6%) sagittal length, densely covered in very fine tubercles except for posterior lobe of middle body, sculpture a little coarser and slightly sparser on anterior lobe of middle body than on borders; anterior border vanishingly short medially, also mostly overhung by middle body, drawn out laterally into anterior wings; wings small, triangular, about as wide as long, directed posterolaterally, with very deep wing process pit just inside outer edge; middle body relatively narrow, elongate, width across anterior tips of posterior lobe (even with shoulders) 68.9% (62.1–74.3%) sagittal length of middle body, strongly ventrally vaulted (sag., tr.), decreasing over posterior lobe to posterior border furrow, body poorly differentiated into anterior and posterior lobes on most specimens by almost totally effaced middle body furrow; middle body furrow only apparent anterolaterally where it meets lateral border furrow as notch in margin of middle body, particularly in large specimens (Pl. 36), otherwise represented by effacement of sculpture; anterior lobe makes up most of body, oblong, subtriangularly posteriorly tapered, sculpture of coarse densely spaced granules; posterior lobe U- or V-shaped, short and curved around anterior lobe, lateral arms pinched out at lateral border furrow, effaced; lateral border furrow deep, narrow, overlies middle body furrow anteriorly, then slightly wider toward confluence with posterior border furrow; lateral border narrow anteriorly, rapidly widens toward shoulder, then gradually narrows a little toward posterior border, gently ventrolaterally downturned at edges, rim slightly inflated, very finely tuberculate like anterior lobe of middle body, but tubercles slightly smaller and more densely distributed; posterior border furrow moderately shallow and a little longer than width of lateral border furrows, gently posteriorly arcuate; posterior border similar to lateral border; doublure of a short and narrow rim around posterolateral margin (likely longer, but not well preserved), with long, shallow lateral notch between wings and shoulder, effaced.

Librigenal measurements were made on the large, intact specimens of Plate 41, and on Plate 36, figure 23. Librigena wedge-shaped, with width under midpoint of eye 42.4% (38.8–47.5%) length along lateral border, gently laterally bowed and convex; eye fairly large, strongly inflated, domed with subrounded outline; eye adjacent to (and poorly differentiated from) elevated smooth area on field; anterior branch of facial suture long, section along anterior projection of lateral border slightly longer than portion along field, sections form angle of about 110–120° at lateral border furrow, with posterior section subvertical along field and anterior section gently anteroventrally sloped along projection; posterior branch of facial suture long, very steeply sloped along field, a little less so than anterior branch, then gently posteroventrally curved along short posterior projection of border, cuts border so that small sliver of underside of doublure is exposed; librigenal field subtrapezoidal, moderately wide and long, wider posteriorly, with width under midpoint of eye 42.3% (39.3–57.3%) length along lateral border furrow, with sculpture of very fine granules overlain by scattered small tubercles, and with small pits concentrated along posterior part of field, effaced except for granules opposite lateral border furrow; lateral border furrow deep and moderately wide, slightly shallower and wider anteriorly (e.g., Pl. 41, figs 5, 14); lateral border wide, narrower anteriorly toward long, anteroventrally directed anterior projection, narrower and tapered posteriorly on short, bluntly terminated posterior projection, border well inflated, less so posteriorly and slightly compressed to form sharper edge ventrolaterally (Pl. 41, fig. 4), with dense sculpture of small tubercles, tubercles finer and more densely spaced ventrolaterally; doublure broad, reaches almost to lateral border furrow, tapered to sharp point posteriorly, smooth but for a fine ridge or two along exsagittal margin (Pl. 36, fig. 32), turned ventrally along anterior projection.

Thoracic measurements were made on the specimens of Plate 42. Thoracic segments highly vaulted in axis and pleurae, short, moderately wide to wide (narrower segments, e.g., Pl. 42, figs 1, 3, 22 positioned more posteriorly in thorax), with moderately wide axis, axial width 52.4% (50.0–54.8%) width across anterior pleural band, maximum segmental width occurs across or near tips of pleural spines; segments with dense sculpture of fine granules all over, overlain by small tubercles; articulating half ring semilunate (Pl. 42, fig. 4), longer medially and gradually laterally tapered, relatively long, with densely spaced rim of very fine tubercles or coarse granules on posterior margin (shown well on Pl. 42, fig. 25); articulating furrow deep, slightly shallower medially, deepest anterolaterally, long, with very shallowly U-shaped course, broad median section very slightly anteriorly bowed, lateral sections more strongly anterolaterally directed; axial ring moderately independently inflated, short and relatively wide, very shallowly U-shaped, with broad, roughly transverse median section and shorter anterolaterally curved lateral sections, with posteriorly convex (e.g., Pl. 42, figs 1, 3, 22) or slightly medially anteriorly bowed (e.g., Pl. 42, figs 4, 17, 19) posterior margin, with line of small tubercles on anterior rim (effaced medially and only present on lateral sections of some specimens, e.g., Pl. 42, figs 17, 19), and with 3–4 larger tubercles on posterolateral ends of some specimens (Pl. 42, figs 2, 14); doublure of similar shape and size as articulating half ring, semilunate, pinched out laterally, effaced, anterior edge reaches posterior edge of articulating furrow; axial furrows moderately wide, deep, subparallel along posterior pleural band, with wider anterior and posterior ends due to curvature of adaxial end of pleural band, course deflected anteromedially around lateral edge of axial ring, then subparallel along very short edges of articulating half ring; anterior pleural band very short, a little longer exsagittally, slightly inflated, more inflated exsagittally to form articulating structure set off posteriorly by extremely short furrow, band equal in width to posterior band (excluding pleural spine), horizontal, except exsagittal tips curled under into very narrow doublure, effaced or very finely granulose; pleural furrow short, deep, incised, transverse to gently posterolaterally directed; posterior pleural band long, strongly inflated, fairly narrow, sculpture densely granulose, with transverse line of many small tubercles on anterior edge; pleural spine long, very strongly downturned, thick, tip tapered to blunt point, with sculpture of dense granules, and small tubercles continuing along anterior edge from pleural band, tubercles bigger ventrally, also with tiny tubercles along anterior edge of spine tip, and with short, more effaced articulating facet on exsagittal anterior edge defined posteriorly by very short furrow; doublure extremely narrow, only a rim curled under end of inner pleurae, best visible in anterior and posterior views.

Pygidial measurements were made on the most complete specimens of Plates 37, 43. Pygidium of four segments and terminal piece with spinose pleurae, strongly vaulted (sag., tr.), mostly from convexity of axis and curvature of pleural spines, semi-elliptical in outline, with sagittal length excluding articulating half ring and pleural spines 57.2% (53.0–63.8%) maximum width across anterior pleural band of first segment, and with sculpture of small tubercles concentrated near edges of furrows; articulating half ring short and wide, semilunate (but anterior curvature often not well preserved), effaced but for granules along posterior edge; articulating furrow deep, slightly shallower medially, long medially and tapered toward axial furrows, granulose; axis very broad anteriorly, with maximum width 52.3% (50.1–54.6%) pygidial width across anterior pleural band of first segment, strongly posteriorly tapered, with width of fourth ring 50.0% (46.1–57.7%) width of first ring, long, equal in length to main body of pygidium, very strongly vaulted anteriorly, decreasingly convex posteriorly to flat terminal piece; axial rings each strongly independently inflated, short, progressively shorter posteriorly, relatively wide, rings effaced in some specimens (Pl. 37, figs 1, 3), or with closely spaced tubercles along anterior margin or anterior half on others (Pl. 43, figs 1, 4); inter-ring furrows deep, short in most specimens, long and shallower medially in large specimens, transverse; terminal piece triangular, short and narrow, moderately inflated, with very small tubercles at least along anterior margin; axial furrows strongly anteriorly divergent, slightly laterally bowed, deep, moderately narrow, narrower along terminal piece and shallower, almost effaced posteriorly in some specimens (Pl. 37, figs 3, 14), furrows meet (or almost meet) at tip of terminal piece; anterior pleural band present only on first segment, wide, very short, slightly expanded exsagittally, moderately inflated, with extremely short furrow near anterior edge of outer pleurae for articulation; pleural furrow also only present on first segment, short, deep, incised, gently posterolaterally directed; posterior pleural bands strongly independently inflated, long and wide, bands increasingly posteriorly directed, with fourth pair subparallel to sagittal axis, mostly effaced, with a few small tubercles along margins and adjacent to axial furrows; pleural spines very long (oblique), strongly inflated, posterolaterally to posteriorly directed like pleurae, widely splayed, very strongly ventrolaterally curved, tapered along ventral margin from about half-length to blunt point, with dense sculpture of small tubercles (larger than main body sculpture) on posterior face, slightly smaller tubercles on lateral faces and at tips, inner face granulose or effaced; interpleural furrows long and deep, posterior furrows shorter, directed like pleurae; border expressed ventrally just inside base of pleural spines, narrow, moderately inflated; doublure held subvertically, but fully visible only in anterior view, slightly peaked medially, gently tapered anterolaterally, effaced.

Ontogeny. The cranidium (cf. Pl. 34, fig. 1, Pl. 38, fig. 1, Pl. 40, figs 3, 15, 18) overall becomes broader (excluding genal spines), more elongate, and more strongly vaulted (sag., tr.), and the sculpture changes from fairly closely spaced medium-sized tubercles to either almost totally effaced (specimens from H 208.2 m) or to very densely spaced small tubercles (specimens from H 222.1 m); the anterior border shortens and becomes overhung medially by the glabella; the glabella widens posteriorly more than it expands anteriorly, creating a bulbous but less posteriorly tapered outline, it inflates to become more vaulted (sag., tr.), the lateral furrows lengthen and deepen, and the lobes become more strongly independently inflated; SO lengthens and deepens; LO widens, and the median node and the tubercles on the posterior margin become more effaced; the palpebral lobes become effaced and move further posteromedially and lengthen; the interocular fixigenae broaden; the posterior fixigenae become more strongly downturned; the posterior border furrow lengthens; the posterior border lengthens at the genal angle; and the genal spine becomes reduced to a short spine (H 222.1 m) or to a nub (H 208.2 m).

The hypostome (cf. Pl. 36, figs 2, 26) becomes narrower and more elongate overall; the middle body inflates further, the anterior lobe also elongates and narrows, and the sculpture spreads posteriorly; the middle body furrow deepens and widens, but does not extend as far medially, giving the outline of the middle body a less hourglass-like shape in large specimens; the lateral border furrows widen and deepen; the posterior border furrow lengthens and shallows considerably; and the lateral border develops less prominent shoulders by widening more anterior and posterior to them.

Librigenae (cf. Pl. 41, figs 1, 15) are fairly close in size, but it is apparent that they become broader overall; the librigenal field broadens, particularly anteriorly, and develops pits more anteriorly while the tuberculate sculpture becomes finer and less densely distributed; the lateral border furrow broadens considerably and deepens; and the lateral border sculpture becomes larger. Thoracic segments are either too close in size, or not comparable in thoracic position (Pl. 42, fig. 3), and therefore cannot be evaluated for ontogenetic change.

The pygidium (cf. Pl. 37, figs 1, 27, Pl. 43, fig. 1) becomes narrower and more elongate overall; less strongly vaulted (sag., tr.); and effaced except for tubercles near edges of furrows and on pleural spines, although specimens from H 222.1 m usually also retain tubercles along the anterior portion of the axial rings; the axis becomes more elongate and less strongly posteriorly tapered; the axial rings become more strongly individually inflated; the axial furrows widen and deepen; the articulating and inter-ring furrows and the furrows between pleurae lengthen and shallow (particularly median sections of the articulating and inter-ring furrows); the pleural spines lengthen and splay further apart, and the tips become slightly more pointed.

Discussion. Deltapliomera humphriesi is compared to D. inglei , D. heimbergi , and D. eppersoni in the differential descriptions of those taxa.

Specimens of D. humphriesi from H 208.2 m differ slightly from those from H 222.1 m in that comparably large specimens are more effaced (see especially pl. 34, figs 1, 8, 14). It is difficult to know whether this effacement is taphonomic or biological, but we have observed a similar situation in common sclerites of species of Dimeropygiella Ross, 1951 , from H 208.2 m, which suggests post-mortem abrasion may have acted on this sample. Given that some sclerites from H 208.2 are not effaced (e.g., Pl. 34, fig. 11) and occasional specimens from H 222.1 m are at least partially effaced (e.g., Pl. 38, fig. 10) and that the samples do not otherwise seem to differ morphologically, we are confident that they represent the same species.