Hintzeia parafirmimarginis, Mcadams, Neo E. B. & Adrain, Jonathan M., 2011

Mcadams, Neo E. B. & Adrain, Jonathan M., 2011, Systematics of the Lower Ordovician pliomerid trilobite Hintzeia, with species from the Great Basin, western USA, Zootaxa 2910, pp. 1-45 : 11-12

Hintzeia parafirmimarginis n. sp.

Plates 5–9

2003 Hintzeia cf. aemula ; Hintze and Davis, fig. 88.

2009 Hintzeia sp. nov. 1; Adrain et al., p. 557, fig. 8C, F.

Material. Holotype, SUI 115122, and assigned specimens SUI 115121, 125533-125558, from Section HC6 165.2, Garden City Formation (Tulean; Psalikilus spinosum Zone ), Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho; UU 10051.90, exact locality uncertain, Fillmore Formation (presumably Tulean, Psalikilus spinosum Zone , but exact horizon unknown), Ibex area, Millard County, western Utah.

Etymology. Latin para, against, and the specific epithet firmimarginis .

Diagnosis. Glabella nearly square; hypostome with fine tubercles and granules on anterior half to two-thirds of anterior lobe of middle body; pygidial spines conical, strongly tapered, and moderately splayed.

Description. Hintzeia parafirmimarginis n. sp. is morphologically very similar to H. firmimarginis ( Hintze, 1953) and is treated via differential discussion. Ratios are given to facilitate comparison with the other species.

Cranidia of H. parafirmimarginis are only subtly different from those of H. firmimarginis , with sagittal length 46.4% (41.3–51.1%) maximum width across genal angles and maximum glabellar width across L1 97.6% (91.1– 105.9%) sagittal length; with shorter frontal areas (anterior view); a weakly developed rostral suture arc on the median anteroventral rim of the anterior border; a shorter anterior border furrow more overhung by the anterior border; narrower LF; anterior of LF also more obscured by border; slightly more straight-sided glabella ; slightly wider interocular fixigenae; more inflated and prominent eye ridges and palpebral lobes; wider posterior fixigenae; and with slightly coarser granulose sculpture and deeper, denser fixigenal pitting.

The hypostomes are also very similar, but that of H. parafirmimarginis is slightly shorter, with width across shoulders 68.9% (67.0, 70.7%) sagittal length; anterior wings slightly shorter and narrower; middle body more strongly inflated, more densely granulose, without posteromedian effacement; lateral branches of middle body furrow less posteriorly convergent, shallower, extend only to about half length of middle body; posterior border shorter, more strongly posteromedially tapered; and with spines on lateral and posterior borders very small points rather than larger rounded nubs.

Hintzeia parafirmimarginis is the only species of the genus for which a rostral plate has been found. It is attached to the articulated specimen (Pl. 8, fig. 4), so only the anterior face is exposed. Rostral plate sub-equilaterally triangular, with dorsal edge slightly longer than lateral edges, wider than long, densely granulose.

Librigenae of H. parafirmimarginis are narrower than those of H. firmimarginis , with width of librigenal field measured at midpoint of eye 34.9% (32.0–37.0%) length along lateral border furrow; field shorter, more strongly posteriorly tapered, less densely and less deeply pitted; lateral border wider, especially near anterior edge of field, and posteriorly tapered along length of field; and with slightly shorter anterior and posterior projections of border.

The thoracic segments are virtually identical. The axial width is 38.4% (35.8–39.9%) width across anterior pleural band.

The pygidia differ most significantly (cf. Pl. 3, fig. 28, Pl. 7, fig. 13). Those of H. parafirmimarginis are shorter and narrower, with sagittal length from articulating furrow 60.9% (58.7–64.0%) width across anterior pleural band of first segment; axis less strongly vaulted; inner pleurae narrower (anterior views); posterior pleural bands shorter, more roundly inflated, not flattened; interpleural furrows shorter; pleurae more strongly posteriorly directed; spines longer, narrower, more strongly tapered, more inflated, not recurved, less widely separated; sculpture slightly coarser; doublure slightly longer medially.

Ontogeny. As in H. firmimarginis , the anterior border of H. parafirmimarginis lengthens, the lateral sections widen, and the median posterior arcuate curve develops; the glabella becomes shorter and wider; the median LO tubercle lessens in prominence; the axial furrows broaden; the eye ridges become more distinct from the arc of the palpebral lobe; the posterior fixigenae broaden; the genal spine is reduced in size, although a small spine remains even on very large cranidia (Pl. 8, fig. 5); and the coarseness of the granulose sculpture is slightly decreased (cf. Pl. 5, figs 1, 31, Pl. 9, fig. 1). The hypostomes (Pl. 7, figs 1, 3, 4) are very close in size, but it is possible to observe the anterior wings becoming broader; the lateral border widening, especially at the posterolateral corners; and the posterior border lengthening, especially medially. The librigenal field widens and elongates slightly; the pits deepen; the eye decreases in size relative to the field; and the lateral border also widens, but the anterior and posterior projections become relatively shorter as the field increases in length (cf. Pl. 6, figs 9, 11 with Pl. 6, fig. 1 and Pl. 9, fig. 2). Thoracic morphology varies by the position of the segment, but the axis and axial furrows widen; the furrows for the posterior articulating tongue become more incised; the flange of the spines lengthens; and the granulose sculpture decreases in coarseness (cf. segments of Pl. 6 with thorax of articulated individual, Pl. 8). Pygidia widen; the inter-ring, axial, and interpleural furrows lengthen or widen; the terminal piece elongates; the anterior pleural band develops on the second segment (Pl. 7, fig. 12, best seen on left side); the pleural spines lengthen and splay further apart; and the granulose sculpture decreases in coarseness (cf. Pl. 7, fig. 23, Pl. 9, fig. 5).

Discussion. There is little intraspecific variation in H. parafirmimarginis . Cranidia of the same sizes (Pl. 5, figs 3, 15; 18, 19; and 26, 31) are essentially identical, although the amount of LF covered anteriorly by the anterior border varies slightly. The slope of the posterior branch of the facial suture along the librigenal field, and the point of the change in slope are also slightly different. The pygidium of Pl. 7, fig. 14 has a smaller terminal piece relative to its axis. The splay of the pygidial spines differs slightly among the specimens, but that could also be due partly to preservation, as those of Pl. 7, figs 12, 13 are slightly crushed. The hypostomes are not comparable in size, and the thoracic segments require a larger sample for comparison.

Compared to Hintzeia plicamarginis Simpson et al., 2005 , H. parafirmimarginis has a shorter, wider, less strongly anteriorly bowed anterior border with a wider, shorter median anteriorly arcuate curve in the posterior margin, the border is much less depressed medially over the curve in anterior view, and it also seems to develop the median curve in relatively larger cranidia (cf. Pl. 5, fig. 15 with fig. 12.10 of Simpson et al. [2005]); the anterior bor- der furrow is shorter, especially medially and laterally in the apodemal pits; L1 is slightly wider and larger relative to the other lateral glabellar lobes; the median node on LO is less distinct; the interocular and posterior fixigenae are slightly wider; and the granulose sculpture overall is slightly denser and finer. The hypostome (cf. Pl. 7, fig. 1 with fig. 14.9 of Simpson et al. [2005]) is relatively shorter and broader; with wider anterior wings; a shorter, wider middle body with a much longer (medially) posterior lobe, closely spaced granules anteriorly, and without distinct pits; narrower shoulders with the widest part located much further anteriorly; and with smaller spines spaced further apart on the lateral border; and a longer, more granulose posterior border. Librigenae of H. parafirmimarginis are very similar, but the librigenal field is narrower, especially posteriorly, and much less pitted; the lateral border furrow is more strongly curved; the lateral border is also more strongly curved, especially along the posterior projection; and less doublure is visible in external view. The pygidium is shorter, with a broader axis; shorter, relatively wider terminal piece; much shorter (measured obliquely), more conical pleurae that curve strongly posteroventrally and lack a lengthy recurved tip; and the ventral pygidial border is shorter, without a raised anterior rim.

Cranidia of H. parafirmimarginis differ from those of H. celsaora in possessing a more strongly anteriorly bowed anterior border with a median anteriorly arcuate curve in the posterior margin and with a shallow, ill-defined rostral suture arc on the edge of the doublure only of larger specimens (anterior view); a longer, narrower glabella with a longer or more anteriorly exposed LF; a slightly shorter, deeper SO; and a more prominent median node on LO. Hypostomes are very similar, but that of H. parafirmimarginis is more elongate; the middle body has fine granules on only the anterior portion of the anterior lobe; the lateral border is wider, and the spines are only small nubs; and the posterior border is slightly longer and more finely granulose. Librigenae are wider in both the librigenal field and lateral border; the field is much wider anteriorly and less deeply pitted; the lateral border is wider, more so anteriorly, and slightly more finely granulose. Thoracic segments of the two species are nearly identical, except that some of those belonging to H. celsaora (Pl. 14, figs 4, 12) display a slight notch near the ventrolateral tip of the spine, and no segments of H. parafirmimarginis show this feature. Pygidia are also very similar, but that of H. parafirmimarginis is wider, with a narrower axis; the terminal piece is shorter; the pleurae are longer (oblique), less strongly posteriorly directed, more anterolaterally bowed, and splayed more, with much more space between the tips of the spines; the ventral pygidial border is slightly longer and wider; the doublure is much shorter and more strongly medially pointed; and the sculpture is much denser.