Panisaspis, Neo & Adrain, 2011

Neo, Usa & Adrain, Jonathan M., 2011, 2969, Zootaxa 2969, pp. 1-68 : 6-7

Panisaspis n. gen.

Type species. Panisaspis millardensis n. sp., from the lower Blackhillsian ( Strigigenalis plicolabeona Zone ) of western Utah, USA.

Other species. Panisapsis deltaensis n. sp. (Tulean; Heckethornia bowiei Zone ); Panisaspis loganensis n. sp. (Tulean; Hintzeia celsaora Zone ); Protopliomerops ? quattuor Hintze, 1953 (Tulean; Psalikilopsis cuspidicauda Zone and Psalikilus typicum Zone ); Panisaspis rancherensis n. sp. (Tulean; Psalikilus pikum Zone ); Panisaspis sevierensis n. sp. (Tulean; Psalikilus pikum Zone ); and Panisaspis topscityensis n. sp. (Tulean; Protopliomerella contracta Zone ).

Etymology. From the Latin noun panis, bread, and Greek noun aspis, shield, in reference to the long, slender pygidial spines that resemble breadsticks. Gender is feminine.

Diagnosis. Cranidium with anteriorly tapered glabella and short, wide anterior border (transformed to a subsemicircular anterior border and laterally bowed glabella in derived species). Hypostome sub-rectangular, with long posterior border, and spines at shoulders and posterolateral corners (transformed to long, broad, ovoid, with rounded margin in derived species). Pygidium with close, subparallel spines of roughly even length (transformed in most species to shorter fourth spine pair and longer third spine pair); terminal piece with a narrow gap exposing its posteromedian edge (or the median part of its enclosing furrow) between the fourth pair of pleurae.

Discussion. Ibexaspis Přibyl and Vaněk in Přibyl et al., 1985, is the likely sister taxon of Panisaspis . A forthcoming work will revise Ibexaspis , including abundant new material of the type species and multiple new species. It is a diverse clade with an origin contemporaneous with Panisaspis . Early members of either genus are phenetically quite similar, and both groups undergo significant within-group morphological change. As explained in the results of the phylogenetic analysis, a straight-sided, gently anteriorly tapered glabella, and a terminal piece with a narrow gap exposing its posteromedian edge (or the median part of its enclosing furrow) between the fourth pair of pleurae are the basal synapomorphies of Panisaspis . Revision of Ibexaspis and description of its diversity, together with a broader analysis of pliomerid relationships, will permit a more extended comparative treatment.

Hintze (1953) misassigned sclerites of two separate younger species of Ibexaspis to Panisaspis quattuor (see discussion of P. quattuor ). Based on new field data, the earliest species of Ibexaspis occurs in the Psalikilopsis cuspidicauda Zone , and the genus ranges upward into the " Pseudocybele nasuta Zone ". Ibexaspis shares potential synapomorphies with Panisaspis including a semicircular anterior border; large, semicircular LF; small L1; ovoid hypostome; short, wide librigenal field; and a kinked librigenal lateral border. The cranidia differ in that those of Ibexaspis are altogether more convex (sag., tr.), usually possess a highly vaulted glabella, and have small genal spines. Ibexaspis pygidia have four segments, like those of Panisaspis , but the spines are always short, of equal length, and splayed, and the pygidia have either a small, enclosed terminal piece or none at all. They also commonly have median axial nodes. Both pygidia and cranidia typically have coarser tuberculate sculpture than do those of Panisaspis .

Hintze (1953) originally assigned Panisaspis quattuor to Protopliomerops Kobayashi, 1934 . The type species of Protopliomerops , P. seisonensis Kobayashi, 1934 , is not well known; cranidia are small and irregularly oriented, no librigenae were figured, and only the ventral surface of the single pygidium was illustrated. The cranidia are somewhat similar to Panisaspis quattuor in overall shape (narrow, elongate glabella; broad triangular fixigenae; anteriorly postitioned palpebro-ocular ridge), but not in detail. Notably, the anterior border of P. seisonensis is much broader and extends over the inner portion of the palpebro-ocular ridges, the glabella is more elongate and straight-sided, and the fixigenae are much longer. The pygidium is very dissimilar; it is short and wide, with five axial rings and short, broad spines of even lengths. The broad similarity of the cranidia is likely plesiomorphic or convergent, and the two genera do not seem to be closely related.

Demeter (1973) figured a number of sclerites from Section G and the Mesa Section ( Hintze, 1973) that could belong to members of Panisaspis . However, the small photographs and lack of views to supplement the standard dorsal for most specimens hinders identification. Identifiable or tentatively identifiable sclerites are included in the species synonymies herein, but some remain enigmatic. The pygidium of Demeter's pl. 3, fig. 5a–c, from Mesa Section, which he called Protopliomerops sp. III, clearly belongs to a derived species of Panisaspis , but its coarse granulose sculpture and posteriorly widened third spines are unique. The same horizon yielded a small cranidium which Demeter figured (1973, pl. 2, fig. 10) as Protopliomerops aff. P. quattuor and incorrectly associated with a cranidium and pygidium belonging to Ibexaspis ; it may also represent this species. The Mesa horizon correlates roughly to Section H 131 m, so these sclerites may alternatively be specimens of Panisaspis sp. 1 (the cranidium and/or pygidium) or Panisaspis sp. 2 (the cranidium; possibly the pygidium if the third spines become less swollen through ontogeny). The range of these taxa would then be slightly extended. It is unlikely that the cranidium represents P. deltaensis , as it is coarsely sculptured. Demeter also figured a number of sclerites as "genus and species undetermined". The hypostomes of pl. 6, figs. 1, 4, 7 resemble those of P. quattuor , but diagnostic details cannot be seen in the photographs. They could also belong to other pliomerids with a similar plesiomorphic hypostome. The hypostome of pl. 6, fig. 2 is similar to that of P. topscityensis , but not enough detail is visible to confirm the association. Likewise, it is possible that the five-segmented pygidium of pl. 6, fig. 6 is a transitory pygidium of P. quattuor or another species, and that the damaged pygidium of pl. 6, fig. 11 may represent a derived species of Panisaspis with a posteriorly exposed terminal piece.