Catillicephalidae, Raymond, 1937

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 : 55

Catillicephalidae gen. et sp. indet.

Fig. 27D–F

Material. A single partial cranidium figured, CPC42402.

Description. Cranidium outline semicircular, incomplete specimen 3 mm long (sag.), maximum width across posterolateral projections of fixigenae, narrowest point at anterior tip of palpebral lobes (γ–γ); strongly convex (sag., tr.). Anterior strongly rounded. Posterior margin incompletely preserved, appears to have been bowed forward strongly. Anterior branches of facial suture (γ–α) converge anteriorly in a broad arc. Glabellar anterior strongly rounded, gently expanding anteriorly, obpyriform in outline; strongly convex (sag., tr.), with maximum convexity across midwidth, lateral slopes convex; width:length ratio of 75%, occupying 96% of the cranidial length; axial furrow narrow and deep. All lateral glabellar furrows except SO, effaced. Occipital ring of moderate length (sag.), becoming slightly narrower abaxially; posterior margin bowed backwards strongly; surmounted by a thin (tr.) spine near the posterior margin, spine is incompletely preserved. SO shallow, narrow (sag.), directed transversely. Anterior cranidial border lacking furrow. Preocular and preglabellar field moderately convex, downsloping toward the anterior border; short (sag.), 4% of sagittal cranidial length. Palpebral lobes small (exsag.), incompletely preserved. Eye ridge faint, extending posterolaterally from the axial furrow, just posterior of the anterior axial furrow, in a straight line towards the anterior tip of palpebral lobe. Palpebral area of fixigena slightly downsloping towards the lateral borders, maximum width (tr.) is 31% the adjacent glabellar width. Postocular field long (exsag.) and downsloping towards the posterolateral projections. Posterolateral projections of fixigena are slightly downsloping towards the lateral corners, with a steep downturn at the lateral extremities. Posterolateral corners with a small (exsag.) broad-based spine. Posterior border incompletely preserved.

Prosopon over entire cranidium is smooth.

Hypostome, rostral plate, thorax and pygidium unknown.

Discussion. This isolated cranidium closely resembles material described as “ Catillicephalidae , gen. nov. et sp. nov.” by Öpik (1967, p. 207, pl. 9, fig. 5) from the Mindyallan Georgina Limestone , later reassigned to Catillicephalina glasgowensis (Jago & Cooper, 2005) by Bentley et al. (2009). The Goyder Formation and Georgina Limestone material both possess an effaced obpyriform glabella, faintly developed eye ridges, anteriorly situated palpebral lobes, and posterolateral projections of the fixigena that steeply downturn at the lateral extremities (cf. Öpik 1967, pl. 9, fig. 5). However, the presence of a preglabellar field and occipital spine precludes assigning the Goyder Formation specimen to C. glasgowensis . The Goyder Formation cranidium also resembles a poorly preserved specimen identified as “ Avonina sp. nov. ”, also from the Mindyallan Georgina Limestone (Öpik 1967, p. 211, pl. 9, fig. 6); however, lack of detail on the GOY cranidium prevents further comparison.

Whilst the Goyder Formation cranidium possesses the typical morphology of a catillicephalid, it also closely resembles Interalia serena Öpik, 1967 from the Mungerebar Limestone of the Georgina Basin – a monotypic genus that Öpik (1967) assigned to the Lonchocephalidae Hupé, 1953 . The only obvious features that separate the Goyder Formation specimen ( Fig. 27D–F ) from I. serena (Öpik 1967, pl. 10, figs 6, 7) are the parallel-sided glabella with faint furrows in I. serena . It is possible that Interalia also belongs to the Catillicephalidae , but without an associated pygidium, this remains an open question. Given the paucity of sclerites from the Goyder Formation, this species cannot be confidently assigned to any known catillicephalid genus.

Occurrence. GOY section horizon 132.7 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 27. A–C, Paradistazeris sp., CPC42401, partial cranidium; sample GOY/173.6; A, dorsal view; B, oblique anterolateral view; C, lateral view. D–F, Catillicephalidae gen. et sp. indet., CPC42402, partial cranidium; sample GOY/173.6; D, dorsal view; E, oblique anterolateralview; F lateral view.All scale bars are 1mm.