Hintzeia celsaora ( Ross, 1951 )

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 : 12-17

Hintzeia celsaora ( Ross, 1951)

Plates 10–14

1951 Protopliomerops celsaora Ross , p. 135, pl. 31, figs 1–5, 8–15 (non pl. 31, figs 6–8), pl. 34, figs 9–12, 20, pl. 35,

fig. 29?

= 1953 Protopliomerops aemula Hintze , p. 206, pl. 22, figs 13–17 (non pl. 22, fig. 9 = Hintzeia firmimarginis [ Hintze]).? 1953 Protopliomerops aff. P. celsaora Ross ; Hintze, p. 207, pl. 22, fig. 10.

1957 Hintzeia aemula (Hintze) ; Harrington, p. 811.

1957 Hintzeia celsaora (Ross) ; Harrington, p. 811.

1961 Hintzeia aemula (Hintze) ; Whittington, p. 917.

? 1973 Hintzeia celsaora (Ross) ; Demeter, pp. 56, 58, pl. 3, figs 11–13 (only).? 1973 Genus and species undetermined; Demeter, pl. 5, fig. 17 (only).

1973 Hintzeia aemula (Hintze) ; Hintze, p. 17.

1986 Hintzeia aemula (Hintze) ; Ingham et al., p. 503.

1987 Hintzeia aemula (Hintze) ; Edgecombe and Chatterton, p. 345.

1989 Hintzeia celsaora (Ross) ; Dean, pp. 13, 20.

1997 Hintzeia celsaora (Ross) ; Lee and Chatterton, p. 691.

1997 Hintzeia celsaora (Ross) ; Ross et al., p. 19

1998 Hintzeia celsaora (Ross) ; White and Lieberman, pp. 61, 106.

1999 Hintzeia celsaroa [sic] (Ross); Hoel, p. 276.

2003 Hintzeia celsaora (Ross) ; Hintze and Davis, p. 73.

2003 Hintzeia celsora [sic] (Ross); Hintze and Davis, p. 301 (Correlation Chart 3).

2003 Hintzeia aemula (Hintze) ; Jell and Adrain, p. 384.

2005 Protopliomerops celsaora Ross ; Simpson et al., p. 538.

2005 Hintzeia aemula (Hintze) ; Simpson et al., p. 541.

2009 Hintzeia celsaora (Ross) ; Adrain et al., p. 559, fig. 9A, E.

Material. Assigned specimens SUI 125559-125567, from Sections HC5 186.5 m and HC6 171.0 m, Garden City Formation (Tulean; Hintzeia celsaora Zone ), Hillyard Canyon, Bear River Range, Franklin County, southeastern Idaho; SUI 125568, 125569 from Section D 59T m, Fillmore Formation (Tulean; Hintzeia celsaora Zone ), southern House Range, Ibex area, Millard County, western Utah; SUI 115142, 115143, 125570-125595 from Section G 118.6 m, Fillmore Formation (Tulean; Hintzeia celsaora Zone ), southern Confusion Range, Ibex area, Millard County, western Utah.

Diagnosis. Anterior border without median curve in posterior margin and with shallow rostral suture arc in anteroventral rim (anterior view); glabella wider than long; librigenae narrow, with narrow field and abrupt change in slope of posterior branch of facial suture midway along field; hypostome teardrop-shaped, with densely, finely tuberculate anterior lobe and effaced posterior lobe; thoracic segments with long articulating furrow, and some with notch in pleural spine; pygidium subquadrate, with short, slightly splayed spines.

Description. Cranidium moderately short, wide, subtrapezoidal in outline, with sagittal length 47.8% (44.7– 50.0%) maximum width across genal angles, highly vaulted (sag., tr.) axially and fixigenally, with dense, finely granulose sculpture on all areas; anterior border highly inflated, wide, long medially and abruptly tapered at lateral margins, very gently anteriorly bowed; doublure expressed mainly as anterior face of border, exposing ventral half of anterior face of posterior wall of border, doublure only a rim ventrally, rim with broad, shallow median arc formed by course of rostral suture (anterior view); anterior border furrow short, longer laterally and in apodemal pits at junctions with axial furrows, very deep, very gently anteriorly bowed, slightly overhung by border medially; glabella fairly short and wide, nearly square, with width across L1 108.9% (101.5–117.3%) sagittal length, parallel sided to slightly anteriorly tapered, moderately vaulted (sag., tr.), with independently inflated lateral lobes; lateral lobes roughly equal in length and width, but L1 more subtriangular in shape rather than rectangular, lobes each about 1/3 total glabella width, frontal lobe short, narrow, subtriangular; glabellar sulci short (S1 longer), deep, incised, producing strong ventral apodemes, with slightly posteriorly elongate inner ends, anterolaterally directed at about 30–50° from transverse; SO short medially, flared laterally into apodemal pits located level with about half width of L1, moderately deep medially, very deep in pits, confluent with axial furrows; LO long medially, abruptly tapered to about half median length at and lateral from apodemal pits, moderately inflated, with small median tubercle located at half length; doublure reaches not quite to SO, elliptical, laterally tapered, smooth except for very fine transverse ridge at midlength (Pl. 10, fig. 20, Pl. 12, fig. 17); axial furrows narrow, deep, incised, subparallel (e.g., Pl. 10, fig. 1, Pl. 12, fig. 13) or gradually anteriorly convergent (e.g., Pl. 10, fig. 13, Pl. 12, fig. 1) and slightly laterally bowed, intersect all other cranidial furrows except palpebrals; frontal areas very short, narrow, small, triangular (best seen on Pl. 10, figs 6, 8, 9, 16), set off from eye ridges by line of small pits; eye ridges mildly inflated, arcuate, short (oblique) and narrow; palpebral furrows long (oblique), narrow, incised, with arcuate to shallowly sigmoid course, define posterior edge of eye ridges and palpebral lobes; palpebral lobes located level with S2, short, arcuate, with narrow anteriorly recurved posterior section, slightly dorsolaterally raised, but lower than curvature of fixigena (anterior view); interocular fixigena short, wide, triangular, nearly horizontal between axial furrows and fulcrum; posterior fixigena slightly longer than interocular, more than twice as wide, rectangular, with rounded anterolateral margin, strongly downturned from fulcrum (anterior view), entire fixigena with dense scatter of small pits on top of very fine granules, and with slightly raised, unpitted border along axial and posterior border furrows; posterior border furrow mostly transverse, with strong, rounded forward curvature at genal angle, short adaxially, slightly longer along middle section of course, then rapidly tapered anterolaterally at genal angle, mostly deep, but shallower along anterolateral section; posterior border short adaxially, expanded laterally to maximum length of about double adaxial length at genal angle, then sharply tapered to a point, genal angle rounded, with very small stubby spine; doublure of short rim adaxially, rotated outward and partially expressed dorsally as extremely short articulating tongue set off anteriorly by extremely short, incised furrow (Pl. 10, fig. 20), expanded laterally to maximum length just before genal angle, and shallowly cut by facial suture just adaxial from genal angle (Pl. 10, fig. 20).

Hypostome long and narrow, posteriorly tapered, widest across anterior wings, with width across shoulders 74.6% (70.1–78.0%) sagittal length; anterior border extremely short medially, flared laterally into small, roughly equilaterally triangular anterior wings with small, deep wing process pits; anterior border furrow extremely short, deep, incised medially, shallower laterally toward meeting with lateral branches of middle body furrow, strongly anteriorly bowed, nearly semicircular in course on most specimens (narrower on specimens of Pl. 10); middle body elliptical, long, narrow, only slightly tapered, nearly same width posteriorly as anteriorly; anterior lobe strongly ventrally inflated, ovoid, roughly three times longer than posterior lobe, with dense, coarse sculpture of small tubercles; middle body furrow strongly impressed only on short, narrow, anteriorly divergent lateral branches, effaced medially; posterior lobe of middle body mainly defined by effacement, U-shaped, wider than anterior lobe, longer medially than laterally, with long lateral branches wrapping about halfway up sides of anterior lobe, weakly ventrally inflated; lateral border furrows narrow, deep, incised, shallower anteriorly at intersection with anterolateral end of middle body furrow and posteriorly toward posterior border furrow; posterior border furrow narrow, short, shallow, weakly posteriorly convex; lateral border moderately inflated, narrowest at long, shallow lateral notch, posteriorly expanded to shoulders, narrowed, then expanded again to maximum width at pair of spines anterior to posterolateral corners, slightly tapered adaxially to posterolateral corners, with small, pointed spines at shoulders, posterolateral corners, and point slightly posterior from halfway in between, densely granulose, with slightly finer granules than on middle body; posterior border moderately long, slightly longer than maximum width of lateral border, narrow, posteriorly tapered, strongly downturned (lateral view), with same granulose sculpture as lateral border, and slightly larger pointed median spine; doublure short, reaches about half length of posterior bor- der and nearly entire width of lateral borders, strongly dorsomedially upturned, smooth.

Rostral plate unknown.

Librigena long and narrow, very roughly subtriangular in outline; anterior branch of facial suture very short along field, almost three times longer along anterior projection of lateral border, with junction angle of about 90°; posterior branch of facial suture very long, steep and gently posteriorly bowed from eye to about midlength, then less steeply angled at about 30° to lateral border, then posterodorsally curved along posterior projection of lateral border, all three segments of approximately equal length; eye not well known, but small, elliptical (Pl. 13, fig. 5), located on steeply raised platform (Pl. 13, figs 1, 3); librigenal field irregularly triangular, narrow, long, with width of field under midpoint of eye 27.2% (25.1–31.0%) length along lateral border, gently laterally convex (ventrolateral views), densely granulose and pitted like fixigenae; lateral border furrow moderatly narrow, deep, gently laterally bowed; lateral border long, with long anterior and posterior projections, anterior projection somewhat posteromedially rotated, creating triangular flange (ventrolateral views), border very wide anteriorly, widest level with anterior edge of field, increasingly tapered posteriorly to blunt point, strongly inflated, with inflation highest anteriorly and decreasing posteriorly, densely granulose with coarser granules matching those of anterior border; doublure effaced, wide, not quite as long as librigena, bluntly terminated anteriorly at about half length of anterior projection, gradually tapered posteriorly, with small portion of inner face visible in external view at posterior end.

Thorax of 15 segments, widest anteriorly, with sides subparallel to about segment seven, then increasingly strongly tapered posteriorly, with each segment highly vaulted pleurally and axially (sag., tr.), with fulcral angle of approximately 115–120° separating steep distal portions of pleurae from horizontal proximal parts, and with very fine granulose sculpture; articulating half ring short, approximately equal to length of axial ring medially, tapered laterally, semilunate; articulating furrow long medially, sharply anterolaterally tapered into very deep apodemal pits located just adaxial from axial furrows, shallow medially, deep laterally; axial ring short, subrectangular with rounded lateral margins and slightly anterolaterally directed ventrolateral sections, 39.3% (36.6–42.6%) width across anterior band of segment, moderately inflated; doublure short, laterally tapered, elliptical, effaced but for fine transverse median ridge (Pl. 14, fig 7); axial furrows narrow except widened triangularly at junction with pleural furrows, deep, incised, subparallel along axial ring, then strongly anteriorly convergent; anterior pleural band slightly inflated, very short, about half length of posterior band, wide, with about 1/3 width distal to fulcrum, with extremely short, wide articulating tongue set off from anterior edge by extremely short, incised furrow, and with small, anterodorsally directed articulating hook structure at ventral tip (Pl. 14, fig. 12); pleural furrow short, very deep, incised, very slightly shallowed and anteriorly directed at tips; posterior pleural band wide, short, lengthened ventrolaterally into long, gently anteromedially rotated facet and spine base (lateral and anterior views), moderately inflated, with long, strongly tapered spine projecting ventrolaterally from base, with very shallow notch on some specimens (Pl. 14, figs 4, 12); doublure short adaxially until spine base, posterodorsally rotated to form very short articulating tongue separated from inflated band by short (longer adaxially; posterior view), deep furrow, doublure very rapidly expanded to long, wide inner face of spine.

Pygidium of five segments and terminal piece, short, moderately wide, subrectangular, with sagittal length from articulating furrow 72.6% (69.0–74.9%) width across anterior pleural band of first segment, highly vaulted axially and pleurally (sag., tr.); articulating half ring short, semilunate, laterally tapered; articulating furrow long, fairly shallow medially, deeper laterally into apodemal pits; axis highly vaulted anteriorly, progressively less vaulted posteriorly to gently inflated terminal piece, with each axial ring strongly independently inflated, short, wide anteriorly, strongly posteriorly narrowed, with fifth ring a little less than half width of first ring, more coarsely tuberculate than pleurae; terminal piece triangular, narrow, elongate, enclosed by fifth pair of pleurae; inter-ring furrows long (first furrow slightly laterally shortened; subsequent furrows shorter overall), deep, but shallower medially, with deep apodemal pits just adaxial from axial furrows; axial furrows strongly anteriorly divergent from tip of terminal piece, narrow, wider at intersections with interpleural furrows, deep anteriorly, shallower posteriorly over fourth and fifth pleurae and along terminal piece; anterior pleural band well expressed only on first segment, gently inflated, short, a little more than 1/3 length of posterior pleural band, wide, reaching to level with base of spines, strongly posteriorly directed, with very short transverse articulating flange on anterior edge separated from posterior portion of band by very short, incised furrow (Pl. 14, fig. 23), and with small anterodorsally curved hook structure at tip (Pl. 10, fig. 23) like that of thoracic segments, expressed as short raised stripe on second segment of large pygidia only (Pl. 14, fig. 19) and pinched out just past fulcrum; pleural furrow short, deep, shallower ventrolaterally, strongly anterolaterally bowed in course; posterior pleural band long, highly inflated, with rounded inner margin, strongly posteriorly directed, with each pair increasingly so, third and fourth pair subparallel, fifth pair posteriorly convergent, posterior pairs decreasing in length (exsag.), each band gently laterally flattened, with spines more strongly compressed into buttress shape (lateral view), spines long, moderately wide, tapered to bluntly pointed tips, narrowly but well separated, gently anteroventrally curved, segments with coarser granules lining edges (dorsal view) and on ventral edge of spine (lateral view); interpleural furrows short (first furrow longer), deep, increasingly shallower posteriorly, posteriorly directed to follow pleural curvature; pygidial border expressed ventrally (Pl. 10, fig. 28, Pl. 14, figs 25, 30), short, broadly U-shaped, coarsely granulose on small specimens (Pl. 10, fig. 28) or smooth (Pl. 14, figs 25, 30); pygidial doublure (anterior views; Pl. 10, fig. 29, Pl. 14, fig. 26) very long medially, broadly rounded and strongly anterolaterally tapered, effaced.

Ontogeny. The ontogeny of Hintzeia celsaora is the best known of the Great Basin species, and the material includes an articulated M13 meraspid individual (Pl. 11, figs 1–8) missing only the librigenae, rostral plate, hypostome, and the pleurae of the 12th thoracic segment. This specimen is likely also the best known example of a pliomerid meraspid (but see also Ross [1951], pl. 33, figs 3, 6–8, 12). Compared to H. plicamarginis Simpson et al., 2005 , the cranidium is very close in size to that of their fig. 12.2, and the transitory pygidium is equivalent to their stage G (fig. 5.3). The cranidia show most of the differences present in larger specimens. The immature cranidium of H. celsaora is shorter and wider overall; the anterior border is much less anteriorly curved, although that of H. plicamarginis has not begun to develop the median posterior arcuate curve; the glabella is shorter and wider, with wider lateral lobes and median region, and LF is narrower; and the fixigenae are longer. Likewise, the pygidia show the same differences as in more mature specimens; that of H. celsaora is shorter and narrower, with a relatively wider axis; the pleurae are shorter, more inflated, and more strongly posteriorly directed; and the pleural spines are shorter, narrower, and strongly downturned. The pygidium of H. celsaora also appears to be more densely tuberculate, but the SEM image of Simpson et al. is also figured at a size too small to show the sculpture.

The H. parafirmimarginis cranidium of Pl. 5, fig. 26 is slightly smaller. It has not yet developed the indentation in the posterior margin of the anterior border, but the glabella is longer and narrower; the fixigenae are shorter; and LO is shorter. The latter may be an ontogenetic difference; the H. parafirmimarginis cranidium of Pl. 5, fig. 22 is closer in size to that of the H. celsaora meraspid and its LO is much longer. However, the cranidium is crushed and unsuitable for general comparison. Cranidia of H. firmimarginis are too large for suitable comparison, as are pygidia of both it and H. parafirmimarginis .

Ontogenetic changes are well exemplified in the specimens of H. celsaora . As in other species of Hintzeia , the anterior border lengthens and widens, but it does not develop the median posterior indentation; the glabella shortens, narrows anteriorly, and the lateral lobes increase in width as the median lobe narrows; the axial furrows widen; the fixigenae widen slightly; and the granulose sculpture becomes less well developed (cf. Pl. 10, figs 1, 15, Pl. 12, fig. 1 and articulated individual of Pl. 11). The hypostome elongates; the anterior wings grow longer and wider; the middle body elongates and the sculpture on the anterior lobe decreases in density; the middle body furrow deepens; the lateral border widens slightly and its spines become blunter; and the posterior border lengthens slightly (cf. Pl. 10, fig. 14, hypostomes of Pl. 13). Librigenae are all of nearly the same size and therefore uninformative. The granulose sculpture of the thoracic segments becomes finer and sparser, especially on the pleurae. The pleurae may also develop a small notch in the anterior margin of the posterior pleural band, near the tip of the spine. The notch is visible on two of the larger segments (Pl. 14, figs 4, 12), but is not apparent on any segments of the articulated individual (Pl. 11), although it may simply be hidden by spines of other segments. Pygidia widen, especially anteriorly; inter-ring furrows and interpleural furrows lengthen; the anterior pleural band of the second segment develops; axial furrows widen slightly; the axis increases in width and its posterior taper is stronger; spines splay slightly and the tips become very slightly more pointed; and sculpture becomes finer, especially in the reduction of the coarse granules on the axial rings (cf. Pl. 14, figs 19, 24).

Discussion. Demeter (1973) suggested that Protopliomerops aemula Hintze, 1953 , is a junior synonym of H. celsaora ( Ross, 1951) . Simpson et al. (2005, p. 538), on the other hand, not only rejected this synonymy but excluded Protopliomerops celsaora from the genus Hintzeia . We have recovered large samples of both species and these indicate that they are certainly synonyms. Confusion probably stems from small original sample sizes, misassociated sclerites, and differing photographic orientations. Comparison of similarly sized sclerites from Ibex illustrated on Plates 12–14 with those from the Garden City Formation illustrated on Plates 10 and 11 reveals no obvious morphological differences. They occur together with multiple other species also shared between all of the horizons (see Adrain et al., 2009, pp. 557–559 for a summary).

Hintze assigned a small cranidium (1953, pl. 22, fig. 9) from Section G-8/306' (99.3 m) to " H. aemula ", but this is the type horizon of H. firmimarginis , and that is the identity of the cranidium. All of the material figured by Ross (1951) comes from a single horizon, limiting the possibility of incorrect association. However, his pygidium ( Ross, 1951, pl. 31, figs 6–8) is incorrectly associated, though its affinity is uncertain. Most notably, it is longer (sag.) than our figured H. celsaora pygidia, but retains distinct tuberculate sculpture whereas there is a clear ontogenetic process of effacement illustrated in our specimens. We recovered several pygidia from Section HC6 171.0 (likely Ross' type horizon) which are direct matches for those from Section G 118.6 m at Ibex.

Intraspecific variation in H. celsaora is low. In the cranidia, the glabella varies slightly in length (cf. Pl. 10, figs 13, 15), although it also shortens as the overall size of the cranidium increases (cf. Pl. 12, figs 1, 3). The lengths and widths of cranidial furrows also vary slightly (cf. Pl. 11, fig. 12, Pl. 12, fig. 1). The hypostome in Pl. 13, fig. 18 is narrower and more elongate than the others, and has shorter spines. Among librigenae, the slopes of the posterior branch of the facial suture vary slightly, as does the position of the change in slope relative to the length of the field. The thickness of the pygidial spines varies slightly, as does the splay between spines (posterior view; cf. Pl. 14, figs 21, 22).

Hintzeia celsaora was compared to H. parafirmimarginis in the discussion of the latter taxon. It differs in much the same way from H. firmimarginis : the anterior border is not strongly anteriorly bowed nor is the posterior margin medially curved, and it has a rostral suture arc in the anteroventral rim; the anterior border furrow is shorter and nearly transverse in dorsal view; the glabella is shorter and wider; the median LO node is less prominent; the interocular fixigenae are wider, but the posterior fixigenae are narrower and longer; and the sculpture overall is slightly coarser, with larger fixigenal pits. The hypostome is shorter, with smaller anterior wings; the middle body is less strongly posteriorly tapered, the posterior lobe is slightly shorter, and the anterior lobe has much coarser sculpture extending further posteriorly; the middle body furrows are less incised, but the lateral border furrows are deeper; the lateral border is narrower, especially at the shoulders and toward the posterolateral corners, and its spines are longer and more sharply pointed; and the posterior border is much shorter, with a longer, more sharply pointed median spine. The librigena has a much shorter anterior branch of the facial suture; an abrupt change in slope midway along the posterior facial suture; a much narrower field; and a relatively wider lateral border, with a longer posterior projection and shorter anterior projection, and coarser sculpture. Thoracic segments are very similar, but those of H. celsaora have a longer articulating furrow, and on some segments the posterior band is notched near the base of the spine. Pygidia are very different: they are much narrower, with a wider axis; a slightly longer and narrower terminal piece; shorter, narrower, and more conical pleurae; much shorter, blunter, more closely spaced, and more ventrally directed pleural spines; a much shorter and narrower, smooth ventral pygidial border; and a much longer doublure.

The morphology of H. plicamarginis is much more similar to that of H. firmimarginis and H. parafirmimarginis than to that of H. celsaora . Hintzeia celsaora has a wider, much less anteriorly bowed anterior border without an indentation in the posterior margin and with a rostral suture arc in the anteroventral rim; a shorter, nearly transverse anterior border furrow; a shorter, wider glabella with a narrower LF; a less prominent LO node; and wider interocular fixigenae and longer posterior fixigenae. The hypostome is shorter and wider, as is the middle body; the anterior lobe of the middle body is shorter; the middle furrow is much shallower; the posterior lobe is longer; the anterior lobe is tuberculate, and both lobes are less pitted; the anterior wings are wider and larger; the shoulders are located more anteriorly; the lateral border is slightly wider, with more pointed spines which are spaced further apart near the posterolateral corners; and the posterior border has a more distinct median spine. The librigena is much narrower, particularly the librigenal field; the anterior branch of the facial suture is much shorter and the posterior branch has a change in slope at mid-length; the lateral border is slightly narrower, more curved, and has a longer posterior projection and shorter anterior projection. The pygidium is much shorter and slightly narrower; the axis is wider; the pleurae are much shorter, narrower, more conical, and strongly posteriorly directed; the spines are much shorter, slightly closer set, strongly downturned, and lack a lengthened recurved tip; and the ventral pygidial border is much shorter and narrower, without an inflated inner rim.

Hintze (1953) reported Hintzeia aff. H. celsaora (Ross) from a talus block at Section G 462', and figured a single partial cranidium (pl. 22, fig. 10). We have recently collected talus from this interval and the range of Hintzeia celsaora may be extended upward. It is also possible that Hintze's specimen is a new species of Hintzeia very similar to H. celsaora , as it is not very well preserved, and the other sclerites are unknown.

Demeter (1973, p. 53) claimed that H. celsaora ranged through 488 feet of the Fillmore Formation, but this is largely based on misidentification of specimens. He also figured a number of specimens from Section G and Mesa ( Demeter, 1973, pl. 3, figs 9–14) as H. celsaora . The pygidia of his figures 11–13 are from Mesa, but are stratigraphically approximately equivalent to G 112–116 m, morphologically similar to H. celsaora , and are likely conspecific. The other sclerites represent a new species of Protopliomerella Harrington, 1957 (unpublished work in progress). An unidentified transitory pygidium from the same equivalent range at Mesa ( Demeter, 1973, pl. 5, fig. 17) may also belong to H. celsaora , but it is very small and figured at low magnification. It could also belong to any other pliomerid from the H. celsaora Zone.