Maurotarion periergum ( Haas, 1969 )

Adrain, Jonathan M., 2009, New and revised species of the aulacopleurid trilobite Maurotarion from the Lower Devonian (Pragian) of Nevada, Zootaxa 2215, pp. 1-23 : 5-11

Maurotarion periergum ( Haas, 1969)

(Figs 2–4)

1969 Otarion (Otarion) periergum Haas , p. 645, pl. 81, figs 4–10, [non fig. 11].?1969 Otarion (Otarion) sp.; Haas, p. 646, pl. 81, fig. 12.

1977 Otarion periergum Haas ; Campbell, p. 17.

1979 Otarion (Otarion) periergum Haas ; Chatterton et al., p. 811. 1981 Harpidella (Harpidella) perierga (Haas) ; Přibyl and Vanėk, p. 170. 1995a Maurotarion periergum (Haas) ; Adrain and Chatterton, p. 318. 1996 Maurotarion periergum (Haas) ; Adrain and Edgecombe, p. 420. 2008 Maurotarion periergum (Haas) ; Adrain et al., p. 657.

2008 Maurotarion periergum (Haas) ; Rustán, p. 348.

Type material. Holotype, cranidium, USNM 161165, and specimens USNM 161166 - 161171, all illustrated by Haas (1969, pl. 81, figs. 4–10), from USNM locality 17233.

Additional material. Illustrated specimens SUI 109012-109016, 109018-109029, 109031-109035 from locality CR-H, and SUI 109017, 109030 from locality CR-B.

Diagnosis. Cranidium with coarse tubercles on rear of glabella; genal spine inflated at base, with posterior border furrow continued along length and row of moderate sized tubercles adaxial to furrow; 13 thoracic segments, pleural regions lacking sculpture, rings with a very subdued transverse tubercle row; pygidium with four axial rings and transverse terminal piece, subdued transverse tubercle rows on posterior pleural bands and axial rings of first two segments, otherwise granulose dorsal sculpture.

FIGURE 2. Maurotarion periergum ( Haas, 1969) , from the Wenban Limestone (Pragian), Cortez Gold Mine haul road, southern Cortez Mountains, Eureka County, Nevada, USA. All specimens are from locality CR-H. 1, 4. Dorsal exoskeleton, SUI 109012, dorsal and right lateral views, x5. 2, 3, 6. Dorsal exoskeleton, SUI 109013, dorsal, ventral, and left lateral views, x4. 5. Dorsal exoskeleton, SUI 109014, dorsal view, x5. 7. Posterior part of thorax and pygidium, SUI 109015, dorsal view, x5. 8. Dorsal exoskeleton, SUI 109016, dorsal view, x6.

Description. Except where a range is indicated, cranidial measurements are based on the undistorted specimen of Figure 3.1. Cranidium with sagittal length 91% width across midlength of palpebral lobes; width across maximum divergence of anterior sections of facial sutures 91.7% (87.3–96.0) width across midlength of palpebral lobes; width across midlength of palpebral lobes 74.4% width across posterior fixigenae; cranidium with substantial dorsal convexity in sagittal profile; glabella independently inflated and describing sagittal arc distinct from that of LO or preglabellar field; preglabellar field with more sharply inflated area immediately in front of preglabellar furrow, anterior part descending steeply to anterior border furrow; SO with strong dorsal convexity in sagittal profile; anterior border with sagittal length 17.8% (16.7–18.8) cranidial sagittal length, long and dorsally flat on posterior ¾ of area; anterior aspect abruptly curved to form rounded forward-pointing rim with sculpture of fine, closely spaced raised lines, larger and more distinct near anterior/ventral margin; dorsal aspect of anterior border lacking sculpture; anterior margin of anterior border with nearly even and moderate anterior curvature in dorsal view; anterior border longest sagittally, slightly shortened exsagittally; anterior border furrow shallow and long (sag.; exsag.); with even anterior curvature in dorsal view, but less arcuate than anterior margin of anterior border, hence producing differential length of border sagittally vs exsagittally; anterior border furrow expressed not as a recessed area in the plane of the anterior border (in sagittal view) but set rearward and following the steeply declined slope of the preglabellar field; anterior border furrow of about the same length and depth along course, except distally near facial suture, where it is abruptly shallowed and much less distinct; preglabellar field with sagittal length in dorsal view 13.1% (12.8–13.4) that of cranidium, with background sculpture of very fine and faint caecal pitting; preglabellar field and frontal area with sparsely but evenly distributed small to medium tubercles; anterior sections of facial suture strongly anteriorly divergent immediately in front of β, curved more adaxially opposite anterior part of frontal area so as to be only moderately anteriorly divergent opposite anterior border; interocular fixigena quite broad, sloping downward in transverse profile from palpebral lobe toward axial furrow, with some dorsal inflation, sculpture smooth except for a very sparse smattering of very small tubercles in some specimens; anterior edge of interocular fixigena bounded by prominent eye ridge running obliquely from S3 slightly posteriorly to leading edge of palpebral lobe; eye ridge subquadrate in section, set off from frontal area by narrow, incised furrow and from interocular fixigena by much less prominent change in slope; palpebral lobe large, semilunate, adaxial ¾ of area sloped strongly downward toward interocular fixigena, abaxial ¼ of area sloped down toward lateral margin; sculpture of very fine granules, and faint pit set more or less centrally, and one or two small tubercles; glabella with sagittal length (excluding LO) 86.7% maximum width across rear of L1; axial furrows broad, relatively shallow, deflected in course laterally around L1 and wider opposite anterior half of L1 than opposite posterior half, deflected again around bulging L2, more anteriorly convergent in front of L2, and turned out once more at anterior edge of eye ridge near position of ventral fossulae, curving sharply into much narrower and more incised preglabellar furrow; preglabellar furrow describes flattened anterior arc, only moderately bowed anteriorly; SO about same breadth and depth as anterior part of axial furrow, deflected posteriorly around posterior bulge of L1, with slight posterior bow in median part; L1 teardrop shaped, anterior tip turned slightly abaxially, anterior edge set just posterior to midlength of palpebral lobe; L1 with dorsal inflation similar to that of main glabellar lobe, with sculpture of several small to moderate scattered tubercles; S1 deep along course, fully isolating L1, slightly deeper and wider distally near contact with axial furrow, of similar depth posteriorly to median part of SO; L2 developed as a small but distinct lateral bulge in front of S1; S2 discernible as a small notch or lateral depression set posterior to rear edge of eye ridge; L3 not independently inflated from main lobe of glabella; main lobe of glabella with sculpture of scattered tubercles of small to moderately large size, largest tubercles concentrated on posterior part and median mid-part, tubercles very sparse around anterior and anterolateral surfaces in front of L2; LO with sagittal length 13.6% (13.3–13.9) that of cranidium, shorter exsagittally behind L1, with sculpture of sparsely scattered small tubercles, somewhat less developed on anterior part in larger specimens, and small median node set slightly posterior to half sagittal length and slightly larger than other tubercles on ring; axial furrow deflected posterolaterally around chevron-shaped lateral margin of LO, confluent with posterior border furrow which is narrower than axial furrow; posterior part of fixigena inflated posterolateral to L1, smooth; posterior projection transverse to fulcrum, turned sharply posteriorly distal to fulcrum; posterior border short (exsag.) proximally, about doubled in length distal to fulcrum; posterior border furrow with slightly sinuous course, not turned posteriorly at fulcrum as much as posterior margin of projection; doublure beneath LO not completely preserved in any available specimen, but clearly broad and slightly concave; articulating groove developed beneath proximal part of posterior border; small but prominent fossulae set just abaxial to axial furrow in front of palpebral lobes.

Librigena with moderately large eye (smaller than in many congeneric species), visual surface not preserved in any available specimen; bilobate eye socle faintly expressed, nearly merged with field, best seen ventrally (Fig. 4.4); field moderately narrow and long, lacking in sculpture except for very fine background granulation and barely discernible caecal trunks and pitting (again best seen on internal surface); a few very small and very subdued tubercles developed on posterior part of field in some specimens near to posterior border furrow; lateral border furrow very shallow and broad, set subparallel to curve of lateral margin, mainly describing a change in slope from field to border rather than a depressed furrow; posterior border furrow narrow and incised; lateral and posterior border furrows meet at genal angle (lateral border furrow substantially shallower anterior to this junction) to run distally along dorsal aspect of genal spine; furrow on spine well expressed only proximally, very faint to indiscernible on distal parts of spine; lateral border broad and robustly inflated, of similar width anteriorly and posteriorly, lacking sculpture except fine subparallel raised lines on ventrolateral aspect; posterior border narrower than lateral border, but strongly inflated; genal notch oblique and arcuate; genal spine very broad at base and long, tapering evenly along length; row of moderately sized tubercles developed in most specimens on posterior border and along adaxial dorsal aspect of genal spine, in some specimens with a few very small accessory tubercles scattered proximally; anterior projection not markedly long; ventral aspect of lateral border with distinct rim developed along sharp break in slope to doublure, raised lines closely spaced along this rim; doublure forming a smooth and broad surface turned up to underlie inner half of border; inner margin of doublure running along adaxial edge of border furrow, forming sharp angle, but no Panderian notch, in front of base of genal spines; rim of lateral border grades into flattened base of genal spine; genal spine with broad, slightly flattened ventral aspect with sculpture of very fine granules.

Rostral plate (Fig. 3.9) very wide and short, connective sutures set almost transversely; anterior margin with anterior curvature matching that of anterior border, posterior margin with narrow curved median portion; ventral aspect with sculpture of raised lines similar to, but not confluent with, those on adjacent librigenal doublure; ridge developed at contact with doublure, matching that on adjacent librigena, inturned doublural area very small and subtriangular.

Hypostome with sagittal length 92.6% maximum width across anterior wings; width across shoulders 72.8% width across anterior wings; anterior margin nearly transverse medially with only slight posterior median bow, deflected posteriorly distally to run toward anterior wings; anterior wings turned slightly anteriorly at tips, large and subtriangular, with small ventral pit marking base of dorsal process; lateral margin straight immediately behind anterior wing, flared laterally to form shoulder, straight and obliquely set between shoulder and contact with posterior margin; posterior margin nearly straight, posterolateral corner with prominent short spine, lost in larger specimens; lateral border independently inflated, of similar width along length, with sculpture of fine raised lines set subparallel to margins; posterior border shorter (sag., exsag.) than lateral border is wide, with similar raised line sculpture in smaller specimens; posterior part of lateral border and all of posterior border effaced and nearly merged into broad shelf in larger specimens (Fig. 3.20); lateral border furrow deep and incised anteriorly, much shallower opposite posterior lobe of middle body, running very slightly adaxially anteriorly, turned out toward shoulder opposite posterior lobe of middle body; posterior part of lateral border furrow and posterior border furrow merged into broad depression occupying area behind middle body; depression shallowed in larger specimens; middle furrow describing deep, smooth U shape, running without interruption from lateral border furrow, deep laterally, shallower but sharply defined medially; anterior lobe of middle body with moderate to strong ventral inflation, lacking sculpture; posterior lobe of middle body much more weakly inflated than anterior lobe, describing shallow V shape with three independent subtle inflations, two laterally and one medially; doublure underlying lateral and posterior borders, lacking sculpture, forming small sharp obliquely set ridge beneath shoulder.

Thorax of 13 segments. Maximum thoracic width across fifth or sixth segment; axis occupying about 40% of segment width on first segment, about 32.5% on fifth, and about 30% on 13th; typical segment with very shallow W-shaped ring, longer (exsag.) near axial furrow than sagittally, with sculpture of a transverse row of very faint small tubercles; distinct but small median tubercle visible on anterior 4–5 segments, not discernible on posterior segments; ring set off from broad articulating half ring by short, transverse, and incised ring furrow; axial furrow shallow and set slightly obliquely so as to run very slightly posterolaterally; fulcrum set close to axis, proximal part of pleura narrower than distal part, accounting for about 35% of pleural width; pleural furrow deepest across fulcrum, set obliquely to run posterolaterally, with slight deflection in course around fulcrum, shallowed almost completely immediately at contact with axial furrow, narrowing to fine lineation distally and running toward posterior part of pleural tip behind articulating facet; anterior pleural band slightly shorter (exsag.) than posterior band; anterior band lacking sculpture; posterior band of some segments and in some specimens with transverse row of very small tubercles similar to that developed on axial ring; both pleural bands offset at fulcrum by strong, subtriangular articulating process developed FIGURE 3. Maurotarion periergum ( Haas, 1969) , from the Wenban Limestone (Pragian), Cortez Gold Mine haul road, southern Cortez Mountains, Eureka County, Nevada, USA. Specimens are from locality CR-H except where noted. 1, 4, 7, 10, 15. Cranidium, SUI 109017, dorsal, right lateral, oblique, anterior, and ventral views, x7.5 (CR-B). 2, 5, 8. Cranidium, SUI 109018, dorsal, left lateral, and anterior views, x7.5. 3, 6, 9. Cephalon lacking right librigena, SUI 109019, dorsal, left lateral, and ventral views, x10. 11. Hypostome, SUI 109020, ventral view, x10. 12 –14. Cranidium, SUI 109021, anterior, left lateral, and dorsal views, x10. 16 –19. Hypostome, SUI 109022, ventral, posterior, left lateral, and dorsal views, x10. 20. Hypostome, SUI 109023, ventral view, x10.

FIGURE 4. Maurotarion periergum ( Haas, 1969) , from the Wenban Limestone (Pragian), Cortez Gold Mine haul road, southern Cortez Mountains, Eureka County, Nevada, USA. Specimens are from locality CR-H except where noted. 1, 2, 4. Right librigena, SUI 109024, ventrolateral, external, and internal views, x7.5. 3. Cranidium, SUI 109025, dorsal view, x6. 5. Left librigena, SUI 109026, external view, x7.5. 6, 9. Left librigena, SUI 109027, ventrolateral and external views, x7.5. 7. Right librigena, SUI 109028, external view, x7.5. 8, 12, 13, 21. Pygidium, SUI 109029, ventral, right lateral, dorsal, and posterior views, x10. 10, 11, 14. Pygidium, SUI 109030, dorsal, left lateral, and posterior views, x10 (CR-B). 15, 16, 20. Pygidium, SUI 109031, dorsal, right lateral, and posterior views, x10. 17, 18, 22. Pygidium, SUI 109032, dorsal, right lateral, and posterior views, x10. 19, 24, 25. Pygidium, SUI 109033, right lateral, posterior, and dorsal views, x10. 23, 27, 28. Pygidium, SUI 109034, right lateral, dorsal, and posterior views, x10. 26, 29, 30. Pygidium, SUI 109035, dorsal, right lateral, and posterior views, x10.

forward from anterior band and received as notch in posterior band; pleural tips of first three segments short and developed into lateral point with small posterolaterally directed spine; pleural tips of segments 5–9 subquadrate; those of segments 10–13 more lobate and rounded; doublure underlying pleural tip with strong notch on posterior part for reception of leading edge of posterior segment during enrollment; doublure underlies posterior edge of posterior pleural band to fulcrum; proximal to fulcrum a transverse articulating groove is formed which receives a dorsal transverse ridge developed on the anterior edge of the anterior pleural band; strong knob-shaped apodeme projected ventrally and rear of axial furrow on each segment.

Pygidium with sagittal length 48.3% (43.7–51.4) maximum width; width across fulcra 62.1% (59.4–64.9) maximum width; axis with maximum anterior width 36.8% (34.9–38.4) maximum pygidial width and 92.5% (73.1–99.1) sagittal length of axis; sagittal length of axis 82.6% (79.3–85.5) sagittal length of pygidium; all dorsal pygidial surfaces with subdued, close-set granular sculpture; small, low tubercles developed most prominently on first axial ring and posterior pleural band of first segment; in some specimens very faint tubercles visible on second axial ring (Fig. 4.17); tubercles developed on posterior pleural band of second segment in most specimens, but fewer and more subdued than on first; tubercles in general more prominent on smaller specimens; largest specimen (Figs. 2.1, 4.10) lacking tubercles altogether; articulating half ring large; axis composed of four rings and a terminal piece; ring furrow incised, very short (sag., exsag.), bowed slightly anteriorly; first axial ring shorter sagittally than exsagittally, bulging abaxially near axial furrow; pseudoarticulating half ring very prominent on second segment, faint but expressed on all specimens on third; not discernible on fourth; axis with moderate transverse dorsal convexity; prominent muscle scars developed on anterolateral part of rings on all four segments in some specimens (e.g., Fig. 4.10); axial furrows with somewhat uneven course, deflected laterally around rings, posteriorly convergent, meeting posterior to fully circumscribe axis, though median part distinctly shallow in some specimens; pleural bands of first three segments clearly expressed, fourth indistinct; anterior and posterior pleural bands of approximately similar length (exsag.) except anterior band of first segment constricted distally behind articulating facet; pleural bands with granulose sculpture similar to that of rings; posterior pleural band of first and sometimes second segment of some specimens with transverse row of very small, subdued tubercles; broad border with granulose sculpture, longer/wider abaxially than sagittally, pleural and interpleural furrows running onto border at first segment, terminating at inner edge of border on posterior segments; posterior margin describing nearly even posterior arc in dorsal view, with only slight median indentation; pygidium flexed medially in posterior view; doublure with faint sculpture of raised lines, exactly underlying dorsal expression of border.

Discussion. Members of the Malvinokaffric Maurotarion dereimsi group remain the closest morphological comparison for M. periergum , and Adrain and Edgecombe (1996, p. 422) contrasted the taxa at length. Of the other species present in the Wenban Limestone, M. periergum is most similar to M. chrysion , with which it is compared under discussion of that species below.

Small holaspid hypostomes have a conventional aulacopleurid morphology (Fig. 3.16) with two small posteriorly directed spines at the posterolateral corners. Larger specimens (Fig. 3.20) have the posterior portion substantially altered, with the posterior and lateral borders partly effaced to form a broad shelf and the posterolateral spines reduced or lost.