Panisaspis millardensis, Neo & Adrain, 2011

Neo, Usa & Adrain, Jonathan M., 2011, 2969, Zootaxa 2969, pp. 1-68 : 7-10

Panisaspis millardensis n. sp.

Figs. 5–11

1953 Undetermined gen. and sp. Loc. H-20. Zone H. (not described); Hintze, pl. 21, figs. 6, 7.

Material. Holotype, pygidium, SUI 125637 , from Section H 187.4 m and assigned specimens SUI 125596– 125636 , 125638–125648 , from Section H 185.6 m and 187.4 m, Fillmore Formation (Blackhillsian; Strigigenalis plicolabeona Zone ), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. From Millard County, Utah.

Diagnosis. Hypostome with very wide and long ovoid border; thoracic segments with very long (dorsoventrally), strongly downturned pleural spines; with pair of tubercles straddling axis; and with dense granulose sculpture all over; pygidium with densely granulose axis; pleural spines effaced dorsally except for posterior half of third pair; terminal piece with pair of indentations near anterior margin and second pair at about 1/3 length.

Description. Cranidium somewhat triangular in outline, short, wide posteriorly, with sagittal length 46.4% width across posterior border, moderately vaulted (anterior view), mostly due to sloping fixigenae; anterior border short, fairly wide, sub-circular in shape, ends even with S3, strongly anteroventrally curved such that doublure is expressed mainly anteriorly with only a short ventral rim, and with dense granulose sculpture; anterior border furrow short, deep, incised, strongly anteriorly bowed, longest and deepest in lateral section forming apodemal pits even with S3; glabella ovoid, long, relatively narrow, widest at S2, with width 100.0% (91.1–106.6%) sagittal length excluding LO, moderately vaulted (sag., tr.), with well defined lateral lobes and furrows, and with very dense sculpture of tiny granules; L1 small, subtriangular, L2 and L3 large, subrectangular, roughly equal in area, frontal lobe very large, sub-semicircular, all lateral furrows very short, slightly longer near axial furrows and at adaxial ends, very deep, with strong projection ventrally, all directed posteromedially at about 30º, S3 with slight anterior projection near abaxial end on some cranidia (e.g., Fig. 5.2, 5.11); SO short, fairly shallow medially, but deepens laterally into apodemal pits, course very gently W-shaped, gently anteriorly bowed medially, and wrapped around base of L1 laterally; LO long medially and tapered laterally, slightly narrower than base of glabella, gently dorsally inflated, with dense granulose sculpture and small but prominent median tubercle, doublure long medially, tapered laterally, lens-shaped, effaced; axial furrows narrow and deep, wider and shallower at intersections with lateral glabellar furrows, SO, and lateral branch of anterior border furrow, gently anteriorly divergent until S2, then gently convergent; palpebro-ocular ridges long, moderately wide, arcuate in shape with widest curvature posteriorly, with anterior edge defined by line of pits running dorsolaterally from intersection of axial furrow and S3, and with dense granulose sculpture; palpebro-ocular furrows narrow, moderately shallow, shallower anteriorly, gently sigmoid in course; fixigenae with moderately dense sculpture of tiny granules, and small caecal pits except near axial and posterior border furrows, interocular fixigenae long, narrow, triangular, posterior fixigenae short, wide, subrectangular, moderately ventrolaterally sloped, with gently anteriorly bowed anterior margin; posterior border furrow short, deep, incised, roughly transverse along posterior border, pointed at genal angle with short, medially directed anterior branch; posterior border short adaxially, expanded laterally to maximum length (about double) at genal angle, then strongly anteromedially tapered, with moderately thick and long, conical, gently tapered spine at genal angle, and dense granulose sculpture, doublure along posterior portions very short and rimlike, expanded rapidly to maximum length just before genal spine, then cut by facial suture at genal spine.

Rostral plate unknown.

Hypostome long, wide, with maximum width across anterior wings only slightly greater than across shoulders, width 96.2% (91.4–101.1%) sagittal length; anterior suture very broad, moderately anteriorly bowed; anterior bor- der very short medially, laterally expanded into long, wide, triangular wings with deep apodemal pits; anterior bor- der furrow short, deep, incised; middle body very large, narrow, elongate, sub-ovoid and posteriorly tapered, with lobes ill-defined; anterior lobe sub-ovoid, strongly ventrally inflated, with dense granulose sculpture concentrated anteriorly and scattered caecal pits; middle body furrow not impressed except as narrow, deep, anterolateral branches anteriorly coincident with lateral furrows and as very slightly impressed median crescent on larger specimens ( Fig. 8.1, 8.2); posterior lobe of middle body short, narrow, U- to V-shaped, effaced; lateral furrows narrow and very shallow between junctions with anterior border and middle body furrows, impressed when coincident with middle body furrows, shallow across lateral extensions of posterior lobe of middle body, then deep and slightly widened along posterolateral reaches of posterior lobe; posterior border furrow about twice as long as anterior border furrow, moderately deep; lateral and posterior borders broad and long, forming ovoid margin, gently ventrally flexed toward rims, with dense granulose sculpture; lateral notch fairly short and shallow dorsoventrally, but deeply mediolaterally impressed; posterior wing not adequately preserved; lateral doublure very wide, strongly dorsomedially raised, and posterior doublure imperfectly preserved.

Librigena overall long and wide, with width of field 43.9% (36.7–50.2%) length along lateral border furrow and length of field 46.0% (42.3–49.4%) length of border; base of visual surface arcuate, strongly elevated from librigenal field (ventrolateral views); librigenal field wide, fairly short, weakly convex, with dense sculpture of tiny granules somewhat concentrated near eye and moderately densely overlain by large caecal pits; lateral border furrow moderately short, very deep, incised, slightly curved; lateral border long and wide, about 1/2 width of librigenal field and twice as long as field, moderately inflated, with broad, shallow indentation in middle of border along anterior half of librigenal field, with long, dog-legged anterior and long, straight posterior projections, and with dense granulose sculpture; anterior branch of facial suture roughly L-shaped, slightly shorter along field than along border projection; posterior branch long and sloped at about 60º above horizontal along field, then short (about 3/4 length along field) and nearly transverse along border; lateral border doublure wide, with effaced and roughly crescentic inner true doublure and more inflated, granulose inner faces of anterior and posterior projections also visible, and also shown as slight triangular projection above posterior branch of facial suture in external view.

Total number of thoracic segments unknown. Thoracic segments short, broad, with axis 44.3% pleural width excluding spine, highly vaulted axially and pleurally; articulating half ring moderately short medially, semilunate and strongly laterally tapered; articulating furrow long, shallow over most of course but with large, deep apodemal pits anterolaterally, and with granulose sculpture in some specimens ( Fig. 9.1); axial ring fairly short, only slightly longer and wider than articulating half ring, strongly dorsolaterally inflated, with dense granulose sculpture and pair of small tubercles straddling posterior midline; axial ring doublure long, semilunate, smooth; axial furrows wide and flared anteriorly and posteriorly, slightly constricted along posterior pleural band, moderately deep, confluent with articulating, pleural, and posterior articulating ridge furrows; inner pleurae narrow, with very steeply curved fulcrum close to distal ends; anterior pleural band very short, finely granulose, with extremely short anterior articulating ridge set off posteriorly by short, shallow furrow, and with distal tips curved dorsomedially (anterior view) into articulating device; pleural furrow moderately short, flared ventrolaterally (lateral view), moderately deep, deeper adaxially; posterior pleural band long, strongly inflated with semicircular cross-section, with long, gently tapered, strongly downturned, semi-flattened blade-like to conical spine produced from fulcrum, and with dense granulose sculpture, posterior margin of posterior pleural band forms very short articulating ridge set off from inflated band by very short, deep, incised furrow.

Pygidium of four segments each bearing long, thick spine on posterior pleurae, with medium-sized triangular terminal piece, moderately vaulted (mostly axially), moderately long and narrow with sagittal length from articulating furrow to posterior tip of terminal piece 75.9% (72.7–78.6%) width across anterior pleurae; articulating half ring short, slightly narrower than first axial ring, laterally tapered, semilunate; articulating furrow short, deep (somewhat shallower medially), incised, with deep apodemal pits at lateral limits somewhat set back into anterior margin of axial ring; axis long and wide (about half maximum pygidial width), highly vaulted anteriorly and progressively less vaulted toward nearly flat terminal piece, strongly posteriorly tapered; axial rings moderately short, decrease slightly in length posteriorly, anterior rings wide, fourth ring about 3/4 width of first ring, each ring independently inflated, with semicircular cross-section, and with dense sculpture of fine granules (also on terminal piece of some specimens); terminal piece subtriangular to slightly heart-shaped, long, narrow, strongly posteriorly tapered, with two pairs of indentations: one pair of small dimples close to anterior margin, and one pair of larger, more elongate impressions at about 1/3 length, impressions merged or partially merged on many specimens, e.g., Fig. 10.3, 10.12, specimens of Fig. 11, and with posteromedian margin exposed; inter-ring furrows moderately long (first one longer), somewhat shallow medially, shorter and very deep laterally, producing large apodemes ventrally; axial furrows moderately wide, strongly impressed over first three segments, lightly impressed over fourth, then merged with narrow, posteriorly shallowing furrows along sides of terminal piece; only first segment with anterior and posterior pleural bands, anterior band very short, slightly longer laterally, strongly downturned at fulcrum, with slight inward curvature at tips for articulation; pleural furrow short, slightly flared laterally, deep, incised; posterior band long (3–4 times length of anterior band), narrow (about half width of first axial ring), strongly inflated, with rounded adaxial margins, and with spine produced from outer pleurae, outer pleurae strongly downturned, with ventral tips merged into rim of doublure; spine long, thick, conical, gradually tapered, mostly effaced dorsally and ventrally, but densely granulose along sides and toward tips; first interpleural furrow moderately long, slightly flared exsagittally, deep, posterolaterally directed at about 45º below horizontal, with subsequent furrows shorter and more posteriorly directed, and with third furrows nearly subparallel; second through fourth posterior pleural bands like first, but more strongly posteriorly directed, and with spines lengthening to a maximum nearly equal to the sagittal length of the pygidium on the third segment (also slightly posterodorsally upturned), then roughly half that length and almost subparallel on the fourth segment; pygidial doublure fairly short, tapered anteriorly, with rounded and slightly posteromedially peaked inner margin (anterior view; Fig. 10.10), effaced, merged with tips of pleurae to form short (lower posteriorly) raised wall with granulose exterior.

Ontogeny. Cranidia of Panisaspis millardensis (cf. Figs. 5.1 and 6.16) become wider and more vaulted overall through ontogeny. The glabella expands laterally, changing from anteriorly expanded to laterally expanded in shape, and the lateral furrows become longer, deeper, and more defined. Cranidial furrows (anterior border, axial, posterior border, palpebo-ocular, SO) lengthen and widen. Granulose sculpture is coarser on juveniles than adults, but the fixigenal pitting is more defined on large specimens. The genal spine becomes proportionately thinner and slightly longer. The hypostome (cf. Fig. 8.1, 8.13) widens considerably through ontogeny, with the middle body becoming narrower relative to the lateral border. The middle body becomes less granulose, with finer granules remaining concentrated anteriorly, and the pits increase in size and visibility. The lateral branches of the middle body furrow deepen. The lateral and posterior borders increase in width and length, their granulose sculpture remains dense but grows finer, and the margin becomes smoother as the very tiny spines at the shoulders and posterolateral corners fade away. The librigena (cf. Figs. 6.3, 7.16) changes only subtly in the specimens available for study. The librigenal field increases slightly in height and overall area, and its pitting deepens slightly. The lateral border furrow is somewhat wider and deeper in larger specimens. The lateral border widens and inflates slightly, and the anterior curve (along the outer rim of the anterior projection and on toward the main part of the border) steepens. Not enough information is known about the thoracic segments to discuss their ontogenetic changes. Pygidial changes (cf. Figs. 10.1, 11.4) are also fairly subtle. The axis becomes broader, with more inflated rings and longer inter-ring furrows; the axial furrows widen; the terminal piece increases in size (length and width) and its indentations increase in complexity (one pair versus two); the degree of spinal splay increases; the spines lengthen compared to the sagittal length of the pygidium; and the ends of the third and fourth spines develop coarse granules.

Discussion. The pairs of terminal piece indentations (e.g., Fig. 10.14) may represent poorly developed interring furrows for unexpressed fifth and sixth axial rings that have been subsumed into the terminal piece. The right L1 of the cranidium of Fig. 5.2 is deformed; it is smaller than the left L1 and S1 is longer on that side in compensation.

Panisaspis millardensis is most similar to its sister taxon, P. sevierensis , and they are compared in the differential description of the latter species. It is also compared to P. rancherensis in the discussion section of the latter. Panisaspis millardensis differs substantially from P. deltaensis , the next most similar species. The cranidium of P. deltaensis is not as well known, but its frontal lobe is smaller, L1 is bigger relative to the other lobes, the fixigenae are slightly narrower and longer, and the genal spine is much wider at the base. Panisaspis deltaensis has a long, narrow, rectangular plesiomorphic hypostome, with a narrow lateral border and small spines along the borders. Its librigena is wider and more elongate than that of P. millardensis , without a pronounced curve near the anterior projection. Pygidia of P. millardensis are narrower and longer than those of P. deltaensis , with a larger, more strongly and complexly impressed terminal piece; much shorter third spines and somewhat longer fourth spines (relative to each other and to pygidial length); and possess coarse granules near the ends of the third and fourth spines.