Liostracina cf. kaulbacki Shergold, Laurie & Shergold, 2007

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 : 44-45

Liostracina cf. kaulbacki Shergold, Laurie & Shergold, 2007

Fig. 21

Material. Four cranidia figured, CPC42352–CPC42355. 138 poorly preserved cranidia not figured (mostly fragments).

Description. Cranidium up to 4 mm long (sag.), outline transversely subelliptical, maximum width across posterolateral projections of fixigenae, narrowest point at anterior tip of palpebral lobes (γ–γ); slightly convex (sag., tr.). Anterior margin strongly rounded. Posterior margin slightly bowed forward. Anterior branches of facial suture (γ-β section) appear to diverge from one another, then curve abruptly towards the midline from β. Glabella anteriorly truncate, parallel-sided, oblong in outline; moderately convex, with maximum convexity across midwidth, lateral slopes gently convex; width:length ratio of 70%, occupying approximately 70% of the cranidial length; axial furrow narrow (sag., exsag., tr.) and deep; all lateral glabellar furrow, except SO, effaced. Occipital ring short (sag.), becoming slightly narrower abaxially, posterior margin bowed strongly backwards. Shallow, narrow (sag.) SO, directed transversely. Anterior cranidial border incompletely known. Anterior border furrow slightly wide (sag., exsag.) and shallow. Preocular field moderately convex, strongly downsloping toward the anterior border furrow. Preglabellar field with a shallow, almost effaced preglabellar furrow. Preglabellar field approximately 19% of sagittal cranidial length. Palpebral lobes (tr.) incompletely preserved. Eye ridge faint to almost completely effaced. Palpebral area of fixigena transverse, maximum width (tr.) is 93% the adjacent glabellar width. Postocular field short (exsag.), and slightly downsloping toward the posterolateral projections; bacculae completely effaced. Posterolateral projections of fixigena narrow (exsag.), strongly downsloping towards lateral corners. Posterior border narrow (exsag.), separated from fixigenal field by deep, moderately narrow (exsag.) border furrow.

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

Discussion. Cranidia of this taxon were recovered in large numbers, often distorted, at the 85-3057 spot locality. Specimens are coarsely preserved as sandstone moulds with limited fine detail. They are remarkably similar to Liostracina kaulbacki Shergold, Laurie & Shergold, 2007 form the Mindyallan Skewthorpe Formation of Western Australia, possessing effaced median preglabellar and glabellar furrows, a shallow anterior border furrow, and lacking bacculae (cf. Shergold et al. 2007, fig. 13A–G). Liostracina kaulbacki also occurs in a sandy lithofacies and given that limited detail is preserved in the coarse moulds, the lack of features is likely taphonomic rather than representing true morphology. Lack of pygidial or other sclerite material from the Goyder Formation and the indifferent nature of preservation make precise taxonomic assignment difficult.

Occurrence. Only recovered from 85-3057 ( 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.

FIGURE21. Liostracinacf.kaulbacki Shergold, Laurie & Shergold, 2007.All specimenscome from spot locality 85-3057.A, CPC42352, partial cranidium. B, CPC42353, partial cranidium. C, CPC42354, partial cranidium. D, CPC42355, partial cranidium.All scale bars are 1 mm.