Nepeidae, Whitehouse, 1939

Smith, Patrick M., Paterson, John R. & Brock, Glenn A., 2018, Trilobites and agnostids from the Goyder Formation (Cambrian Series 3, Guzhangian; Mindyallan), Amadeus Basin, central Australia, Zootaxa 4396 (1), pp. 1-67 : 53

Nepeidae gen. et sp. indet.

Fig. 26D–F

Material. A single partial cranidium figured, CPC42400.

Description. Largest cranidium 4 mm long (sag.). Cranidium trapeziform, length:width ratio 70%, maximum width across posterolateral projections of fixigena; narrowest point of cranidium forward of the palpebral lobes (γ– γ), where it is about 64% of maximum cranidial width (tr.). Anterior margin strongly rounded; posterior margin incompletely preserved. Anterior branches of facial suture subparallel, then convergent to anterior margin; posterior branches strongly divergent, curved to distal end of posterolateral projection. Glabella narrow (tr.) and moderately convex, with maximum convexity at about midwidth, width:length ratio of 67%, occupying about 58% cranidial length; slightly tapering forward, width (tr.) across anterior 60% maximum width of glabella; anterior glabellar margin truncate. Axial furrow broad and indistinct. Bacculae poorly developed. Lateral glabellar furrows narrow (exsag.) and deep. S1 directed posteromedially; S2 shorter (tr.) than S1, only being a small indentation in the lateral glabellar surface; S3 poorly developed or absent. Occipital ring of moderate width; SO moderately wide (sag.), bowed slightly forward medially, shallow medially and deepening abaxially. Anterior border downsloping to anterior margin; length (sag.) 7% total cranidial length. Anterior border furrow shallow and poorly defined. Preglabellar field possesses an inflated preglabellar boss, triangular in outline, with the anterior border furrow bowed around its anterior margin, maximum width (tr.) of boss approximately equal to anterior glabellar width. Preocular field strongly convex and strongly downsloping adaxially towards preglabellar boss. Palpebral lobe small, less than 4% cranidial length (sag.), not clearly defined. Eye ridges faint, thin (exsag.), extending from the anterolateral corners of the axial furrow in a straight line towards the anterior tip of palpebral lobes. Palpebral area of fixigena flat to slightly convex, gently downsloping towards axial furrow. Postocular field flat anteriorly and downsloping near the posterior border furrow. Posterolateral projections of fixigena with a steep downturn at the lateral extremities, directed posterolaterally and widening (exsag.) posteriorly. Posterior border incompletely preserved. Posterior border furrow shallow, wide (exsag.), widening (exsag.) strongly near posterolateral extremities.

Prosopon incompletely known from exfoliated specimen.

Hypostome, rostral plate, librigena, thorax and pygidium unknown.

Discussion. This single, poorly preserved cranidium was recovered from the lowest exposed horizon of the Goyder Formation in the GOY section (GOY 49.4 m). A cranidium with a trapeziform outline, moderately tapered glabella with two pairs of lateral glabellar furrows, preglabellar boss with a triangular outline, and strongly downsloping posterolateral projections suggests an affinity with the nepeids. The presence of a triangular preglabellar boss would support placement in Penarosa Öpik, 1970. However, the Goyder Formation specimen has small palpebral lobes and lacks the S3 furrow, placing it outside the concept of the genus (Paterson 2005). The combination of small palpebral lobes and a faint anterior border in the Goyder Formation specimen also resembles the holotype of Ascionepea janitrix Öpik, 1967, which Paterson (2005) interpreted as a juvenile specimen (and thus junior synonym) of Ferenepea hispida Öpik, 1967. Given the paucity of material of this taxon, it is placed under open nomenclature.

Occurrence. GOY section horizon 49.4 m ( Fig. 3 ).

Figures

FIGURE 3. Generalised lithostratigraphy and taxon ranges through the Goyder Formation at the GOY section. Sampled horizons are indicated on the right side of the section, with sample numbers representing tape meterage along the section line (see Fig.2). Measurements on the left side of the section are in meters (true thickness) from the base of the Goyder Formation. SF = Shannon Formation, PSS = Pacoota Sandstone. Solid black circles represent the occurrences of taxa present in the GOY section. Hollow circles represent the approximate stratigraphic occurrences of taxa found at nearby spot localities. Ranges of taxa found only atspot localities approximate, and has been inferred using lithological, faunal and geographical information.

FIGURE 26. A–C, Biaverta sp., CPC42399, partial cranidium; sample GOY/97; A, dorsal view; B, anterior view; C, oblique anterolateral view. D–F, Nepeidae gen. et sp. indet., CPC42400, partial cranidium; sample GOY/67; D, lateral view; E, dorsal view; F, oblique anterolateral view.All scale bars are 1 mm.