Dailyatia decobruta Betts, 2019

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 : 513-518

Dailyatia decobruta Betts sp. nov.

Figs. 15–18 .

2015 Dailyatia sp. A ; Skovsted et al. 2015a: 64, fig. 51A–E.

ZooBank LSID: urn:lsid:zoobank.org:act:363F4F94-3687-4526-A0E1-347C028590D7

Etymology: From Latin deco, handsome or decorated, and bruta, beast; meaning “handsome beast”.

Holotype: C2a sclerite from Clast 5 ( SAM P57359 ; Figs. 17I and 18G ).

Type locality: Cape D’Estaing, Kangaroo Island , South Australia ( WGS84 coordinates: 35°34’53” S, 137°29’06” E) .

Type horizon: Lower Cambrian bioclastic limestone clasts, WPC.

Material.—Six A1 sclerites from Clast 1 and seven A1 sclerites from Clast 5, 11 figured (SAM P57329–57339); 13 C1 sclerites from Clast 1 and 12 C1 sclerites from Clast 5, 13 figured (SAM P57340–57351, 57358); three C2 sclerites from Clast 1 and nine C2 sclerties from Clast 5, 6 figured (SAM P57352–57357); seven C2a sclerites from Clast 1 and three C2a sclerites from Clast 5, 9 figured (SAM P57359– 57367).

Diagnosis. — Species of Dailyatia with strong ornament of raised pustules, often aligned to form strong pseudoplicae. A1 sclerite with strongly developed anterolateral plicae and strongly convex deltoid. Concave anterior field of A1 sclerite has closely spaced concentric wrinkles, rather than pustulose microornament. C1 and C2a sclerites are triangular, both generally with weak plication; both have strongly convex dorsal fields and strongly concave ventral fields resulting in a reduced internal cavity. C1 sclerites have a ventral field that is shorter than the dorsal field. C2a sclerites are elongate and curved, with slight torsion. Apex may be recurved over the ventral field. C2 sclerites are triangular, but are not as compressed as C1 and C2a sclerites, and are slightly torted.

Description. — Sclerites are united by their distinctive ornament, which consists of prominent concentric ribs with regularly spaced, often high, rounded pustules. Pustules can be aligned across the ribs forming strong pseudoplicae ( Fig. 17G–I ). Ribs are separated by a narrow, smooth, slit-like zone between inter-rib grooves ( Fig. 17G 2 , G 3 , H). Delicate reticulate microornament is well-developed on ribs and pustules, and weakly on the inter-rib grooves. Ornament generally smooths toward apex. No A2 or B sclerites have been recovered.

A1 sclerites are bilaterally symmetrical, with a V-shaped apertural outline ( Fig. 15 ). A1 sclerites have very strongly developed second anterolateral plicae that delimit a concave anterior field ( Fig. 15B 1 , C, D). The weak first anterolateral plicae and posterolateral plicae define narrow, elongate, triangular lateral troughs ( Fig. 15J ). Deltoid is strongly convex, and demarcated by weak postero-lateral creases. Field between posterolateral plication (delineating the lateral field at the posterior) and lateral crease (delineating the deltoid) slightly concave (for descriptive terminology for Dailyatia species see Skovsted et al. 2015a: fig. 5). Well-developed pustulose ornament and microreticulation occurs on ribs on the lateral and posterior fields, smoothing toward triangular apex. Pseudoplicae often formed by alignment of pustules. Pustules and microreticulation not developed on the anterior field, which exhibits fine, closely spaced, concentric wrinkles ( Fig. 15C, G 2 ).

C1 sclerites are triangular in apical outline with a deeply concave ventral field and convex dorsal field, resulting in a narrow internal cavity ( Fig. 16A–C ). Ventral field is significantly shorter than the dorsal field resulting in a wide apertural outline ( Fig. 16B, C, F, G 2 , L). Weakly developed radial plication on the dorsal field demarcates convex distal and slightly concave proximal fields. Apex with a single perforation. Pustulose ornament well developed on dorsal field, and weakly developed on ventral field. Triangular C2 sclerites exhibit strong torsion, and are not as compressed as C1 sclerites, with a relatively large internal cavity ( Fig. 17A–F ). Apertural outline is triangular. Broad dorsal field is defined by two strong radial plicae. Ventral field is concave, and is slightly shorter than the dorsal field.

C2a sclerites are elongate (high length:width ratio), with a triangular outline. Sclerites are strongly curved and highly compressed with convex ventral fields and concave dorsal fields ( Fig. 18 ). Sclerites are slightly torted, with the apex often twisting toward the concave ventral surface ( Fig. 18C, E ). Weakly developed central plication occurs on broad dorsal surface separating often slightly concave proximal field from convex distal field ( Fig. 18D 1 ). Pseudoplication is well developed through the alignment of pustules on concentric ribs on the dorsal and ventral surfaces. Ornament on dorsal surface generally more strongly developed than on ventral surface, particularly concentric ribs ( Fig. 18G, H ). Ornament smooths toward apex. Apex with single perforation.

Remarks. — Only two sclerites of D. decobruta Betts sp. nov. have been previously described; an A1 sclerite from the Mernmerna Formation ( Pararaia janeae Zone ) in the Donkey Bore Syncline, and a C1 sclerite from the North Boundary Creek section through the Mernmerna Formation in the Mt. Chambers area, eastern Flinders Ranges (likely P. janeae Zone ) ( Dailyatia sp. A in Skovsted et al. 2015a: fig. 51A–E; Betts et al. 2017b: figs. 4, 10). New material from the WPC conforms to the description of Dailyatia sp. A by Skovsted et al. (2015a). The A1 sclerites of this taxon from both the Flinders Ranges and the WPC have very narrow lateral fields, very broad anterior and posterior fields, and a very broad deltoid. The C1 sclerite from the Chambers Gorge area has a concave ventral field that is much shorter than the concave dorsal field, similar to that in the C1 sclerites from the WPC.

Sclerites from the Arrowie Basin and the WPC are united by their distinctive external ornament ( Fig. 17G–I ). Sclerites generally have weakly developed radial plication and strong concentric ribs. Well developed, rounded pustules on the concentric ribs align to create strong pseudoplication on all sclerites, particularly on dorsal surfaces. Ornament on ventral surfaces is less well developed, and pustules are not as closely spaced. Pustular ornament is not developed at all on the anterior field of the A1 sclerites ( Fig. 15C ). Abundant new material from the WPC clearly show well developed reticulate micro-ornament on the pustules along the commarginal ribs, with slightly weaker micro-ornament on the inter-rib grooves, and a smooth, narrow, slit-like groove between growth sets ( Fig. 17G 2 , G 3 ). Material from the Arrowie Basin exhibits elevated, rounded pustules, however Skovsted et al. (2015a) did not observe any reticulate micro-ornament on the specimens from the Donkey Bore Syncline or the Mt. Chambers area, though this is likely due to abrasion and the small sample size.

Dailyatia decobruta Betts sp. nov. is readily distinguished from D. ajax , which is characterised by numerous strong radial plicae on all sclerite morphs. In contrast, D. decobruta Betts sp. nov. sclerites have few radial plicae, with aligned pustules forming pseudoplicae on broad, convex dorsal and also occasionally on concave ventral surfaces. Dailyatia macroptera , while bearing fewer radial plicae than D. ajax , is still considerably more plicate than D. decobruta Betts sp. nov., particularly on the anterior field. This is unlike the anterior field in D. decobruta Betts sp. nov., which is convex and bears fine, concentric wrinkles rather than plicae or pseudoplicae.

Like D. decobruta Betts sp. nov., D. bacata also bears a pustulose ornament with microreticulations that can align to form pseudoplicae. However, this ornament differs from that in D. decobruta Betts sp. nov. as the pustules in D. bacata , while discrete, have relatively low relief. In D. decobruta Betts sp. nov., the pustules can have substantial relief from the surrounding surface of the comarginal rib, often rising to form dull points. Alignment of these pustules to form strong pseudoplicae is a characteristic feature of D. decobruta Betts sp. nov., and is often only weakly developed in other species.

The C1 sclerite of D. decobruta Betts sp. nov. has a similar triangular outline and pyramidal shape to C1 sclerites of Dailyatia odyssei . However, C1 sclerites of D. decobruta Betts sp. nov. differ in that they do not exhibit the same strong central plication on the dorsal field observed in D. odyssei ( Skovsted et al. 2015a) . In addition, the micro-ornament on the external surfaces of D. odyssei consists of fine, flattened pustules at regular intervals along the crests of the concentric ribs. This is unlike the relatively large, raised pustules in D. decobruta Betts sp. nov.

Dailyatia decobruta Betts sp. nov. A1 sclerites bear some similarities to those of Dailyatia helica as both have concave anterior fields that lack radial plicae or pseudoplicae. In both taxa, micro-ornament is instead better developed on the deltoid. In addition, both species have C2a sclerites. In D. helica , C2a sclerites are very strongly compressed and recurved, with the apex coiling over the ventral field in a tight whorl ( Skovsted et al. 2015a: fig. 40). The C2a sclerites of D. decobruta Betts sp. nov. are also compressed, with a reduced internal cavity, and while they are recurved, the apex does not coil over the ventral surfaces as in D. helica . Like the C1 sclerites in D. helica , C1 sclerites in D. decobruta Betts sp. nov. also appear compressed with a narrow internal cavity. However, C1 sclerites of D. helica have a complex pyramidial shape due to strong plication on the dorsal field, which is unlike C1 sclerites in D. decobruta Betts sp. nov.

Dailyatia decobruta Betts sp. nov. bears similarities to sclerites from the King George Island glacial erratics described as Dailyata ajax by Wrona (2004). These sclerites exhibit similar gross morphological characteristics, including compression and strong curvature, particularly in the C sclerites ( Wrona 2004: figs. 8A–E, 10A–C). In the King George Island material, micro-ornament can be developed as blade-like projections with fine reticulations ( Wrona 2004: fig. 11A 5, A 6), similar to that seen in some specimens from the WPC ( Fig. 17I ). However, the B sclerite illustrated by Wrona (2004: fig. 11D 6) bears a subdued, beaded micro-ornament unlike that in the WPC specimens, and the King George Island specimens do not feature the strong pseudoplication characteristic of D. decobruta Betts sp. nov. from the WPC. Skovsted et al. (2015a) noted the unique combination of characters in the Dailyatia specimens from the King George Island erratics and suggested that this assemblage may include more than one species.

B sclerites of D. decobruta Betts sp. nov. have not been recovered from the WPC. However, the distinctive morphologies of the A1, C1, C2, and C2a sclerites, coupled with the unique and easily identifiable external micro-ornament, is sufficient to distinguish this taxon from all previously described species of Dailyatia . Across most Dailyatia species, the A2 and B sclerites are relatively rare components of the scleritome, and it is anticipated that the as yet unknown B sclerites and perhaps A2 sclerites will be found when larger sample sizes are acquired.

Stratigraphic and geographic range.—Lower Cambrian of South Australia, Arrowie Basin ( D. odyssei Zone ): Donkey Bore Syncline, central Flinders Ranges and Mt. Chambers area eastern Flinders Ranges, Mernmerna Formation. Stansbury Basin ( D. odyssei Zone ): WPC, Kangaroo Island.

Figures

Fig. 15. The A1 sclerites of the camenellan tommotiid Dailyatia decobruta Betts sp. nov. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. A. SAM P57329 in apical view. B. SAM P57330 in apical view (B1); B2 shows the broad, convex deltoid. C. SAM P57331 in anterior view. D. SAM P57332 in apical view. E. SAM P57333 in apical view. F. SAM P57334 in apical view. G. SAM P57335 in apical view (G1); G2 shows the concentric, wrinkled ornament on the anterior field. H. SAM P57336 in apical view. I. SAM P57337 in apical view. J. SAM P57338 in oblique lateral view. K. SAM P57339 in oblique lateral view.

Fig. 16. C1 sclerites of the camenellan tommotiid Dailyatia decobruta Betts sp. nov. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. A. SAM P57340 in ventral view. B. SAM P57341 in ventral view. C. SAM P57342 in ventral view shows shortened ventral field (C1) and in oblique view (C2). D. SAM P57343 in dorsal view (D1); D2, apical view oriented to show overall convexity of sclerite. E. SAM P57344 in apical view. F. SAM P57345 in apical view. G. SAM P57346 in oblique view showing shortened ventral field (G1) and in ventral view (G2). H. SAM P57347 in dorsal view; H1–H3, show convex dorsal field with very weak plication. I. SAM P57348 in oblique dorsal view (I1); I2 shows convexity. J. SAM P57349 in oblique dorsal view; J1 shows curvature of sclerite in side view; J2 shows dorsal surface. K. SAM P57350 in dorsal view. L. SAM P57351 in oblique ventral view.

Fig. 17. C2 sclerites of the camenellan tommotiid Dailyatia decobruta Betts sp. nov. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. A. SAM P57352 in lateral view; A1, A2 show slightly different angles to capture three dimensionality of sclerite. B. SAM P57353 in lateral view. C. SAM P57354 in dorsal view; C1, C2 show slightly different angles to capture three dimensionality of sclerite. D. SAM P57355 in ventral view. E. SAM P57356 in ventral view. F. SAM P57357 in ventral view. G. SAM P57358, G1–G3, close ups of external ornament. H. SAM P57348, close up of external ornament. I. SAM P57359, holotype; I1, I2, close ups of external ornament.

Fig. 18. C2a sclerites of the camenellan tommotiid Dailyatia decobruta Betts sp. nov. from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. A. SAM P57360 in ventral view; A1–A3, multiple views showing strong convexity and compression of sclerite. B. SAM P57361 in lateral view. C. SAM P573762 in oblique ventral view (C1); C2, slightly rotated view showing extreme compression of sclerite. D. SAM P57363 in dorsal view; D1, D2, different views showing strong curvature of sclerite and weak plication on dorsal surface. E. SAM P57364 in dorsal view, E1, E2, multiple views showing strong curvature (including weak torsion). F. SAM P57365 in ventral view. G. SAM P57359, holotype in dorsal view. H. SAM P57366 in ventral view. I. SAM P57367 in oblique ventral view.

Fig. 2. Correlation chart showing shelly fossil biozones against the stratigraphic succession in the Flinders Ranges, Fleurieu Peninsula, and Kangaroo Island (adapted from Betts et al. 2018: fig. 27). Note: The succession in the NE Kangaroo Island is based on the Investigator-1 drill core in which the Mt. McDonnell Formation is not apparent (Gehling et al. 2011). Lower boundary of White Point Conglomerate (WPC) is likely faulted.Abundant and diverse shelly fauna (SSF) from the bioclastic limestone clasts in the WPC have an upper Dailyatia odyssei Zone age. Dashed lines indicate uncertain stratigraphic relationship. Abbreviations: K., Kulparina; P., Parabadiella; S., Sunnaginia.

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