Trephina ranfordi, Smith & Paterson & Brock, 2018

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 : 17-20

Trephina ranfordi sp. nov.

Figs 7 , 8

Etymology. In honour of L.C. Ranford, for his work on the geology of the Amadeus Basin.

Holotype. CPC 42225, cranidium from the Goyder Formation at spot locality AS 178 ( Fig. 7B, N, O, Q ).

Paratypes. One cranidium: CPC42224 ( Fig. 7A ); one pygidium: CPC42380 ( Fig. 8E ) from sample GOY/67.0, 49.4 m above the base of the formation. Seven cranidia: CPC42226 ( Fig. 7C, L, M ); CPC42227 ( Fig. 7D ); CPC42228 ( Fig. 7E ); CPC42229 ( Fig. 7F ); CPC42230 ( Fig. 7G ); CPC42231 ( Fig. 7H ); and CPC42232 ( Fig. 7I ); three librigenae: CPC42233 ( Fig. 7J ); CPC42234 ( Fig. 7K ); and CPC42235 ( Fig. 7P ); ten pygidia: CPC42376 ( Fig. 8A, L ); CPC42377 ( Fig. 8B ); CPC42378 ( Fig.8C ); CPC42379 ( Fig. 8D ); CPC42381 ( Fig. 8F ); CPC42382 ( Fig. 8G ); CPC42383 ( Fig. 8H ); CPC42384 ( Fig. 8I ); CPC42385 ( Fig. 8J ); and CPC42386 ( Fig. 8K ), from sample GOY/97.0, 73.2 m above the base of the formation.

Other material. 49 cranidia, 27 librigenae and 39 pygidia not figured (mostly fragments).

Diagnosis. As for genus.

Description. Cephalon semicircular, up to 9 mm long (sag.). Cranidium subtrapezoidal in outline, length:width ratio of 60%, maximum width across posterolateral projections of fixigenae, narrowest point of cranidium at the anterior margin; strongly convex (sag., tr.). Anterior margin rounded. Posterior margin straight to slightly bowed anteriorly. Anterior branches of facial suture (γ–β) diverge slightly from one another at 24°, then curve abruptly towards the midline from β, slightly behind the border furrow, before they reach the anterior margin. Glabella anteriorly truncate, subquadrate in outline often with nearly parallel sides; glabellar anterior merges with anterior border; wide (tr.) and strongly convex, with maximum convexity across midwidth, lateral slopes gently convex; width:length ratio of 60% to 68% (mean 65%; n = 3), occupying entire cranidial length (sag.). Preglabellar furrow effaced, axial furrow narrow (tr.) and deep. S1 moderately well defined, intersecting axial furrow approximately level with δ, directed posteromedially for a short distance, before bifurcating with the anterior branch directed anteromedially and the posterior branch continuing posteromedially. S2 faintly developed, intersecting axial furrow just anterior to γ, directed transverly for a short distance, before bifurcating with the anterior branch directed slightly anteromedially and the posterior branch slightly posteromedially. S3 faint, directed anteromedially for a short distance before becoming indistinct. S4 variably developed, but when present is directed anteromedially (more so than S3) for half the distance (tr.) of S2 and S3. Short (sag.) occipital ring, becoming slightly narrower abaxially, posterior margin strongly bowed backwards. SO bowed backwards, moderately deep (sag.) and deepening abaxially. Anterior cranidial border narrow (sag., exsag.) and convex, obscured medially by fusion with glabella. Anterior border furrow deep and narrow (exsag.), except where obscured by glabella. Preocular field slightly convex, moderately downsloping toward the anterior border furrow, length (exag.) between anterior border and γ is 28% cranidial length (sag.). Palpebral lobes wide (tr.), long (exsag.), approximately 33% cranidial length, reniform in outline, defined by a narrow (tr.) palpebral furrow, anterior tip situated opposite the mid-point of L2, posterior tip situated slightly anterior to SO in smaller specimens and slightly posterior to SO in larger specimens. Eye ridge weakly defined on external surface, better defined on exfoliated surfaces, extending posterolaterally from axial furrow opposite L 3 in an almost straight line towards the anterior tip of palpebral lobe. Palpebral area of fixigena slightly convex, maximum width (tr.) is 60% adjacent glabellar width. Postocular field short (exsag.) and strongly downsloping toward the posterior border furrow. Posterolateral projections of fixigena strongly downsloping, maximum length (exsag.) at posterior of palpebral lobe 13% total cranidial length (sag.). Posterior border narrow (exsag.), separated from fixigenal field by deep, moderately narrow (exsag.) border furrow.

Librigena up to 9 mm in length excluding spine. Lateral margin, including that of genal spine, evenly curved. Genal field subtrapeziform, 76% of librigenal width (tr.) along posterior border, moderately convex. Lateral border well defined, gradually becoming wider (tr.) towards genal angle. Lateral and posterior border furrows narrow and deep. Distinct, low eye socle present, separated from genal field by wide eye socle furrow. Genal spine blade-like, length approximately 41% librigenal length. Doublure approximately the same width (tr.) as the lateral border.

Complete pygidia up to 8 mm long, fragments up to 11 mm (sag.); subtriangular in outline excluding spines, slightly convex, sagittal length:width ratio of 64% to 69% (mean 67%; n = 6) excluding spines. Anterior margin slightly curved, with articulating half-ring being slightly convex. Posterior margin evenly curved posteriorly and straight to weakly curved posterolaterally. Axis prominent, moderately narrow (tr.), strongly tapered posteriorly, width:length ratio of 75% to 81% (mean 78%; n = 3), short, occupying about 65% of sagittal length of pygidium. Narrow (sag.) articulating half-ring, faintly defined by a shallow, narrow (sag.) articulating furrow. Three well defined axial rings and a faint fourth present. Two anteriormost axial rings separated by shallow, narrow (sag., exsag.) inter-ring furrows, third and fourth axial rings separated by faint inter-ring furrow. Terminal piece ovate, small; short (sag.), faint, postaxial ridge present. Axial furrow moderately deep and narrow (exsag.), becoming shallower and broader posteriorly until fading out completely around terminal piece. Pleural regions only slightly convex, with three narrow (exsag.), moderately deep pleural furrows; a fourth much shorter (exsag.), shallower furrow is present in some individuals. First pleural furrow directed slightly posterolaterally, encroaching somewhat onto pygidial spine before terminating. Second and third pleural furrows directed posterolaterally, terminating halfway to the margins; fourth pleural furrow directed strongly posterolaterally and terminates behind the axial furrow. Border not well defined, only distinguishable by slight change in convexity. Pair of broad-based spines situated at anterolateral corners; spines are broad (tr.) and blade-like, curved posteriorly.

Prosopon comprising closely spaced granules over most of the cephalon, except the posterolateral corners of the glabella, palpebral lobes and librigenal borders that are covered by small, closely spaced pits. Glabellar furrows are smooth. Anterior cranidial border and the librigenal border also covered by well-defined horizontal terrace ridges. Pygidium covered by small, closely spaced pits over pygidial axis; pleural field with moderately sized pustules on pleural ribs. Spines and posterior margin covered with fine horizontal terrace ridges and evenly spaced pustules near the spine bases.

Hypostome, rostral plate and thorax unknown.

Discussion. Association of the different sclerites (cranidia, librigenae and pygidia) is based on their similarity in ornamentation, size, and stratigraphic co-occurrence. The cranidia from the Goyder Formation show considerable size variation, with specimens ranging from approximately 2–10 mm in length (sag.). Smaller specimens show a faint vestigial anterior border furrow of the glabella ( Fig. 7A ), whilst in larger specimens this furrow is almost completely effaced ( Fig. 7C, L ). Individuals with a vestigial anterior border furrow also show fainter glabellar furrows and smaller palpebral lobes than those that lack the anterior border furrow.

Occurrence. GOY section horizons 49.4, 64.9, 73.2 and 83.9 m ( Fig. 3 ). Specimens also occur at AS 168 , AS 178 and GOY WEST .

Distribution. Goyder Formation, Amadeus Basin, Northern Territory. Cambrian Series 3, Guzhangian (Mindyallan) in age.

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 8. Trephina ranfordi gen. et sp. nov. A–D, F–L come from sample GOY/97; E comes from sample GOY/67. A, L, paratype, CPC42376, partial pygidium; A, dorsal view; L, lateral view. B, paratype, CPC42377, partial pygidium.C, paratype, CPC42378, partial pygidium, latex cast. D, paratype, CPC42379, partial pygidium. E, paratype, CPC42380, partial pygidium. F, paratype, CPC42381, partial pygidium.G,paratype, CPC42382,partial pygidium.H, paratype,CPC42383,partial pygidium. I, paratype, CPC42384, partial pygidium.J, paratype, CPC42385, partial pygidium. K, paratype, CPC42386, partial pygidium. All scale bars are 2 mm, except A, B, H, K = 4 mm, and E, F = 1 mm.

FIGURE7. Trephinaranfordi gen.et sp. nov. A comes from sample GOY/67; C–M, P come from sample GOY/97; and B, N, O, Q come from spot locality AS178. A, paratype, CPC42224, partial cranidium. B, N, O, Q, holotype, CPC42225, partial cranidium; B, dorsal view; N, lateral view; O, oblique anterolateral view; Q, anterior view. C, L, M, paratype, CPC42226, partial cranidium; C, dorsal view; L, close up on fused anterior border; M, close up on ornament. D, paratype, CPC42227, partial cranidium. E, paratype, CPC42228, partial cranidium. F, paratype, CPC42229, partial cranidium. G, paratype, CPC42230, partial cranidium. H, paratype, CPC42231, partial cranidium. I, paratype, CPC42232, partial cranidium. J, paratype, CPC42233, partial librigena.K, paratype, CPC42234, partiallibrigena.P paratype, CPC42235, lateral view of partial librigena.All scale bars are 1 mm, except B, J, K, N, Q = 2 mm, and L, M = 0.5 mm.