Aponileus ugolekae, Adrain, 2012

Adrain, Jonathan M., 2012, The Lower Ordovician (upper Floian) bathyurid trilobite Aponileus Hu, with species from Utah, Texas, and Greenland 3293, Zootaxa 3293 (1), pp. 1-67 : 21

Aponileus ugolekae n. sp.

Plate 12, figs 21, 25–36, Plates 13–15, Plate 16, figs 15–19

Material. Holotype, cranidium, SUI 131127 (Pl. 13, figs 1, 3, 5, 9), and assigned specimens SUI 131128–131150 , from Section J 46.3 m, assigned specimen SUI 129331 from Section J 40.0 m and assigned specimens SUI 129312–129215 from J 46.8 m, Wah Wah Formation ( upper Floian ; Blackhillsian ; " Pseudocybele nasuta Zone "), southern Confusion Range , Ibex area, Millard County, western Utah, USA.

Etymology. After Ugolëk.

Diagnosis. Cranidium entirely lacking tuberculate sculpture; cranidial fixigenae broader than in any other species; genal spine huge and scythe-like, very broad at base; librigenal field greatly reduced in area and narrow.

Description. Although Aponileus ugolekae has some striking autapomorphies, particularly on the librigena, it remains fundamentally similar to A. belkaae , and as with A. strelkaae description is best accomplished via an extended comparison with that species, cataloguing all differences. Cranidium with width across frontal areas relative to sagittal length approximately similar, but glabella relatively smaller, so that frontal areas and interocular fixigenae are considerably broader; axial furrows straight and oblique versus flared laterally anteriorly; glabella not waisted; glabella completely lacking tuberculate sculpture versus clearly retained sculpture on median and posterior areas; SO shallow and lacking any transverse ridge; LO narrower, longer, and lacking tubercles versus densely tuberculate; palpebral lobe somewhat larger, and much more anteriorly set.

Librigena with eye slightly narrower relative to length; field much narrower, both anteriorly and posteriorly; posterior border merged with genal spine in larger specimens versus clearly distinct; lateral border much more shallow anteriorly; genal spine huge, with base as wide as entire body of librigena, long, flattened, broad for most of length, and scythe-like, versus narrow, rapidly tapering, and only moderately long; anterior edge of genal spine base extended forward to connect with lateral border opposite midlength of eye versus behind rear of eye.

Pygidium of four versus three segments, though fourth only obvious in ventral view; raised line sculpture much finer and denser; tubercles completely absent from versus crowded on axis; pygidium wider relative to sagittal length; axis slightly longer and more V-shaped versus U-shaped posteriorly; axial furrows shallowed prior to posteromedian union, hint of a faint post-axial ridge in some specimens, versus confluent medially to fully circumscribe the axis posteriorly; axial rings poorly versus well expressed; pleural furrows shallow to obscure versus well expressed.

Discussion. The phylogenetic position of Aponileus ulgolekae was discussed under results of the analysis above. A key question is whether A.? veterokae, which is resolved as its sister species, is genuinely an ingroup Aponileus . This is dealt with under discussion of that species below.