Trachoparia, Chang, 1963

Betts, Marissa J., Claybourn, Thomas M., Brock, Glenn A., Jago, James B., Skovsted, Christian B. & Paterson, John R., 2019, Shelly fossils from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia, Acta Palaeontologica Polonica 64 (3), pp. 489-522 : 494-495

Trachoparia ? sp.

Figs. 3 , 4 .

Material.—Eight partial cranidia, six figured (SAM P57221– 57226). All from limestone clasts in the WPC, Kangaroo Island, South Australia; Dailyatia odyssei Zone.

Remarks.—The cranidia from the limestone clasts of the WPC, while fragmentary, preserve enough features to confidently assign them to the Solenopleuridae . Of the many genera erected within this family ( Jell and Adrain 2003), the WPC taxon is most similar to species of Trachoparia from the Miaolingian of North China ( Chang 1963; Zhang and Jell 1987; Yuan et al. 2012). Shared cranidial characters include: a prosopon exhibiting pustules of differing sizes; wide axial, anterior border, and posterior border furrows; short (sagittal) anterior border; and the absence of a preglabellar field.

Obvious differences in the specimens documented here relate to the shape of the glabella and the occipital ring. The WPC taxon possesses a rather pointed glabellar anterior ( Figs. 3A 1 , 4E ), compared to the more rounded frontal glabellar lobes of Trachoparia species from North China ( Chang 1963; Zhang and Jell 1987; Yuan et al. 2012). In this regard, the WPC specimens more closely resemble a fragmentary cranidium from the Changhia Formation in Shandong, North China ( Zhang and Jell 1987: pl. 42: 5) that was questionably assigned to the solenopleurid Eilura . The WPC taxon also has a subquadrate occipital ring, the lateral extremities of which appear to terminate at the axial furrows ( Fig. 4D, E ). In contrast, specimens of Trachoparia from North China (e.g., Chang 1963: pl. 1: 12; Zhang and Jell 1987: pl. 42: 11; Yuan et al. 2012: pl. 87: 1–3, pl. 88: 4, 7, 10, 12a, pl. 107: 18) show an occipital ring that tapers abaxially and extends onto the proximal posterolateral corners of the fixigenae. Based on cranidial material alone, it is difficult to ascertain if these differences are interspecific within the concept of Trachoparia (sensu Yuan et al. 2012) , or whether the WPC taxon warrants placement in another (possibly new) genus, hence the tentative assignment here.

Figures

Fig. 3. The solenopleurid trilobite Trachoparia? sp. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Latex cast of partial cranidium (SAM P57221) showing pustulose ornament and strongly tapered glabella in dorsal (A1), anterior (A3), and oblique anterolateral (A4) views; testate cranidium in dorsal view (A2).

Fig. 4. The solenopleurid trilobite Trachoparia? sp. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Partial testate cranidia in dorsal views. A. SAM P57222 showing short (sag., exsag.) anterior border. B. SAM P57223 showing faint eye ridge and palpebral lobe. C. SAM P57224 showing wide axial and posterior border furrows. D. SAM P57225 showing deep occipital furrow and subquadrate occipital ring. E. SAM P57226 showing strongly tapered glabella and subquadrate occipital ring.

Fig. 1. Map showing study area on northern Kangaroo Island, Australia. Dashed line indicates Stansbury Basin extent.