Panisaspis sevierensis, Neo & Adrain, 2011

Neo, Usa & Adrain, Jonathan M., 2011, 2969, Zootaxa 2969, pp. 1-68 : 10-11

Panisaspis sevierensis n. sp.

Figs. 12–16

2009 Pliomeridae gen. nov. sp. nov. A; Adrain et al., p. 570, fig. 16Q.

Material. Holotype, pygidium, SUI 125681 , from Section H 163.3 m and assigned specimens SUI 115310 , 125649–125680 , 125682–125695 , from Section H 163.3–182.6 m, Fillmore Formation (Tulean; Psalikilus pikum Zone ), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. From Sevier Lake, which lies to the east of the Ibex area.

Diagnosis. Librigena with very long posterior projection of lateral border; third pair of pygidial spines long and very widely splayed; terminal piece with single pair of indentations at about 1/3 length.

Description. Panisaspis sevierensis is morphologically similar enough to P. millardensis that it is treated via extended comparison. Ratios are given to aid comparison with other members of the genus.

Cranidia of P. sevierensis are extremely similar to those of P. millardensis . They differ mainly in having a slightly shorter and wider glabella, with width 97.5% (89.7–101.1%) length, slightly larger L1 relative to other lateral lobes, and possibly slightly larger palpebral lobes (cf. Figs. 6.1 and 6.2 with 12.3), although that comparison cannot be made with exactly equally sized specimens. The cranidial length/width ratio for P. sevierensis is 44.6%, based on the specimen of Fig. 12.10.

Hypostomes of P. sevierensis and P. millardensis are also very similar, but those of P. sevierensis are narrower (width 89.4% (87.1–91.0%) length), with narrower and less pronounced shoulders, narrower borders, and fewer pits on the middle body.

Librigenae of P. sevierensis are somewhat more elongate, with a slightly shorter field [width 43.6% (40.8– 48.5%) length along lateral border furrow and length of field 42.1% (40.5–43.1%) length of lateral border], with a longer posterior branch of the facial suture (measured along the lateral border), a slightly narrower lateral border with a larger amount of doublure visible externally, slightly smaller granulose sculpture on the border, and a much less pitted librigenal field.

Panisaspis sevierensis segments are not well known, but they are slightly more finely granulose than those of P. millardensis , and possibly have more small tubercles on the axis (cf. Figs. 9.1 with 13.26; two tubercles on a complete axial ring vs. three on a partially missing ring).

Pygidia of P. sevierensis are wider (length 71.9% (67.0–76.5%) width, using same measuring points) than those of P. millardensis , with a slightly narrower axis, slightly narrower and shallower axial furrows, wider pleurae, much longer and thicker third pleural spines which are also more strongly posterodorsally upturned, slightly thicker and more conical spines overall, a smaller terminal piece with only one pair of indentations at about 1/3 length and a more widely exposed posterior margin, more effaced sculpture overall, and a shorter, wider merged pleural wall.

Ontogeny. Panisaspis sevierensis cranidia are less well known, but ontogenetic changes seem to closely resemble those of P. millardensis . The smallest cranidium ( Fig. 12.19) is narrower across the fixigenae, with a shorter, broader genal spine than the larger cranidia. The most complete cranidium ( Fig. 12.10), compared to the largest cranidia ( Figs. 12.1, 12.3, 12.16; cranidia of Fig. 13) has a shorter anterior border; slightly narrower and less laterally convex glabella; and narrower LO; and the sculpture overall is coarser. Hypostomal and thoracic changes cannot be assessed with the material available. Librigenae (cf. Fig. 14.3, 14.4) increase in the length and height of the librigenal field, and the curve underneath and posterior from the anterior projection of the lateral border increases in steepness. The pygidium (cf. Fig. 15.1, 15.14, 16.3) elongates slightly compared to its width; the interrings furrows lengthen considerably; the axial furrows widen; the spines splay further away from each other and taper more rapidly; and the sculpture decreases in coarseness.

Discussion. Cranidia of Panisaspis sevierensis differ subtly from those of P. deltaensis . The anterior border is slightly narrower; L1 is slightly smaller relative to the other lateral glabellar lobes and less rounded in outline; the lateral fixigenae are shorter; and the genal spine is narrower. Hypostomes of P. sevierensis are ovoid and possess rounded borders, unlike the sub-rectangular and spinose-bordered hypostome of P. deltaensis . The pygidium of P. sevierensis can be distinguished by its more widely splayed spines, particularly the third pair; longer fourth pair of spines; and distinct pair of indentations at about 1/3 length of the terminal piece. Panisaspis sevierensis is compared with P. rancherensis in the discussion section of the latter.