Maurotarion fooi, Adrain, Jonathan M., 2009

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 : 19-21

Maurotarion fooi n. sp.

(Fig. 8)

Type material. Holotype, cranidium, SUI 109048 (Figure 8.1, 8.5, 8.9, 8.13), and assigned specimens SUI 109049-109056, all from locality CR-D, Wenban Limestone (Pragian), Cortez Gold Mine haul road, southern Cortez Mountains, Eureka County, Nevada, USA.

Etymology. After Stan Foo, who was Chief Geologist at Cortez Gold Mine at the time the collections were made.

Diagnosis. Glabella with main lobe lacking sculpture; L1 small but with dense dorsal tubercles; frontal area lacking sculpture; librigenal field narrow, with very low, subdued tubercles; eye socle expressed as inflated anterior lobe; lateral border wide and flattened; librigenal lateral and posterior border furrows merged to run along dorsal aspect of genal spine; genal spine long, narrow.

Description. Measurements based on largest three nearly intact cranidia (Fig. 8.1–8.3). Cranidium with maximum width across posterior projections, but not fully preserved on any available specimen; width across anterior border 90.0% (87.3–93.5) width across midlength of palpebral lobes; sagittal length 96.1% (95.3– 96.6) width across midlength of palpebral lobes; anterior border of similar length sagittally and exsagittally, rear half flat, anterior half with slight dorsal inflation, curved toward anterior margin; anterior border with sagittal length 15.6% (14.6–17.1) that of cranidium, lacking dorsal sculpture, with fine raised lines, more robust nearer margin, along anterior aspect; anterior margin of anterior border with gentle and nearly even anterior curvature; anterior border with slight dorsal flex in anterior view; anterior border furrow shallow and long, with distinct inverted V shape, posterior edge more sharply defined along preglabellar field than anterior edge, which grades into border; furrow set in same plane as anterior border; preglabellar field with sagittal length 14.8% (14.5–15.1) that of cranidium, with moderate dorsal inflation not strongly deviating in sagittal profile from curve of glabella, running downward from glabella to border at moderate angle, lacking sculpture; frontal area broad and subtriangular, with sculpture in some specimens of very subdued moderate sized tubercles laterally; anterior sections of facial sutures parentheses-shaped in front of palpebral lobes, turned more nearly anteriorly opposite anterior part of frontal area and anterior border; eye ridge visible but not strongly developed, nearly effaced in some specimens, most strongly defined by a faint furrow anteriorly near S3; interocular fixigena lacking dorsal sculpture, narrow, sloped down from palpebral lobe to axial furrow, with only slight independent dorsal inflation; palpebral furrow distinct as sharp break in slope anteriorly and posterior, partially or wholly effaced in middle part; palpebral lobes large, margins not describing even semi-circular arc, but maximum of curvature at mid-length or slightly posteriorly, lacking sculpture except for pit at midlength set slightly away from center toward lateral margin, lobes mostly held in horizontal plane, only slightly tilted toward glabella adaxially; axial furrows only slightly anteriorly convergent, mainly due to lateral bulge of L1, broad and moderately deep, of same width posteriorly and anteriorly, running without interruption into anteriorly arcuate preglabellar furrow of amostly exactly same breadth and depth; main glabellar lobe with sagittal length 97.3% (94.7–98.8) maximum width across rear of L1; S1 deep, similar in width and depth to axial furrow, complete from axial furrow to SO and of similar depth and dimensions along entire course, fully isolating L1; S1 and SO form wider triangular depressions at junction; L1 relatively small, teardrop shaped, strongly inflated, with sculpture of fairly densely distributed medium-sized low and subdued tubercles; main glabellar lobe with only weak dorsal inflation, generally lacking dorsal sculpture but with subdued tubercles similar to those on L1 developed on anterolateral aspects in some specimens (e.g., Fig. 8.1); S2 visible as a faint notch, L2 small and with little independent inflation; S3 and L3 not distinct; SO with transversely straight course, short (sag., exsag.) and incised, longer at triangular junction with S1 and especially in posteriorly deflected course behind L1; LO with sagittal length 15.0% (14.5–15.4) that of cranidium, longest sagittally, only slightly shorter on portion behind main glabellar lobe, significantly shorter behind L1, mostly lacking dorsal sculpture, very subdued medium sized tubercles developed behind L1 and along posterior margin in some specimens, median node not discernible; posterior border furrow not fully preserved on any specimen, short (exsag.) and incised, with transverse course proximal to fulcrum; posterior fixigena reduced to narrow strip, moderately inflated, with a few small subdued tubercles, extended along posterior projection as very narrow strip; posterior border not fully preserved on any specimen, about half as long as median part of LO proximally, apparently longer distal to FIGURE 8. Maurotarion fooi n. sp., from the Wenban Limestone (Pragian), Cortez Gold Mine haul road, southern Cortez Mountains, Eureka County, Nevada, USA. All specimens are from locality CR-D and all magnifications are x12. 1, 5, 9, 13. Cranidium, holotype, SUI 109048, dorsal, left lateral, anterior, and ventral views. 2, 6, 10. Cranidium, SUI 109049, dorsal, right lateral, and anterior views. 3, 7, 11, 15, 18. Cranidium, SUI 109050, dorsal, right lateral, anterior, ventral, and oblique views. 4, 8, 12. Cranidium, SUI 109051, dorsal, right lateral, and anterior views. 14, 17, 20. Cranidium, SUI 109052, dorsal, left lateral, and anterior views. 16, 19, 22. Cranidium, SUI 109053, dorsal, left lateral, and anterior views. 21, 24, 27. Left librigena, SUI 109054, external, internal, and ventrolateral views. 23, 25. Left librigena, SUI 109055, external and internal views. 26. Left librigena, SUI 109056, external view.

fulcrum, moderately inflated and lacking dorsal sculpture; doublure beneath LO with faint raised lines; ventral aspect of posterior border with transverse articulating groove; fossulae weakly developed, position obscure.

Librigenal field with width at half length of eye 30.6% (27.2–34.0) exsagittal length; eye large, exsagittal length 54.6% (52.9–56.3) that of field, of similar width anteriorly and posteriorly (Fig. 8.27); eye socle not obvious posteriorly, but ellipsoid anterior lobe developed as a prominent swelling; visual surface set directly on field posteriorly; field with sculpture of only a few very subdued small to medium sized tubercles; lateral border furrow narrow, deepest opposite eye, notably shallower anteriorly and posteriorly just in front of contact with posterior border furrow; lateral border about same width as eye, slightly narrower anteriorly, moderately to strongly inflated, inner/dorsal aspect lacking sculpture, outer/ventrolateral aspect with sculpture of raised lines subparallel with margin, progressively more fully expressed abaxially; posterior border furrow narrower and slightly deeper than lateral border furrow, bowed slightly around rear of eye but otherwise with obliquely straight course to angular contact with lateral border furrow; posterior border about same length (exsag.) as lateral border is wide posteriorly, lacking sculpture, with very faint concave depression down center; posterior section of facial suture forming angular shoulder at contact with posterior margin; rear margin of posterior border set obliquely, forming slightly arcuate but still angular contact with genal spine; genal spine very long (not complete in any specimen, but at least 110% exasagittal length of remainder of librigena including anterior projection), slightly curved adaxially, broad at base (about half again as wide as posterior width of lateral border) and tapered evenly along length, flattened in section, with broader dorsal and ventral faces and narrower lateral faces; furrow running posterior from junction of lateral and posterior border furrows onto proximal part of dorsal face of genal spine, discernible over about proximal half of spine length; adaxial and abaxial edges of spine with raised lines similar to those on lateral aspect of lateral border, central aspect lacking sculpture; margin of lateral border with weak lateral convexity, subtle but definite break in slope opposite margin to separate lateral convexity of genal spine margin; anterior projection large, with long, oblique connective suture; ventral aspect of genal spine and doublure beneath lateral border with large raised lines, largest beneath border; inner edge of doublure beneath border turned up and inward, forming a sharp ridge at inner edge of lined portion; inner upturned part of doublure completely lacking sculpture, inner margin underlying adaxial margin of lateral border furrow; no Panderian notch evident.

Rostral plate, hypostome, thorax, and pygidium not recovered.

Discussion. The pygidium of Maurotarion fooi has not been recovered. Nevertheless the species is well represented by cephalic material and is clearly new and distinctive, so is judged well enough known to formally name. It was compared with M. chrysion and M. wenbanense under discussion of those species above. It differs from M. periergum in the possession of a basally narrower glabella with much smaller L1, the lack of tubercles on the main glabellar lobe and frontal area, inflated versus weakly expressed (mostly ventrally, Fig. 4.4) anterior eye socle lobe, a narrower librigenal field with subdued versus absent tubercles, librigenal lateral and posterior borders that unite in front of the genal spine base, and a much narrower genal spine. Maurotarion fooi differs from M. axitiosum ( Campbell, 1977) , which it most closely resembles, in the presence of more dense tuberculation on L1, slightly larger L1, and smooth versus tuberculate frontal areas. The species are similar in their general glabellar dimensions, deeply impressed cephalic borders, narrow librigenal field, posterior and lateral librigenal borders that unite in front of the genal spine, and long, narrow genal spine.