Tumulduria incomperta Missarzhevsky

Skovsted, Christian B., Kouchinsky, Artem, Bengtson, Stefan & Holmer, Lars E., 2014, The problematic early Cambrian fossil Tumulduria incomperta represents the detached ventral interarea of a paterinid brachiopod, Acta Palaeontologica Polonica 59 (2), pp. 359-365 : 363-364

Tumulduria incomperta Missarzhevsky in Rozanov et al., 1969

Figs. 1–3 .

1969 Tumulduria incomperta sp. nov. Missarzhevsky; Rozanov et al. 1969: 175, pl. 6: 5, 6.

1974 Skeletal Problematica 1; Meshkova 1974: 193, pl. 26: 1–3, 6–7.

1987 Tumulduria incomperta Missarzhevsky ; Bengtson et al. 1987: 364, figs 1–6. (cum. syn.).

1987 Aldanotreta sunnaginensis Pelman ; Bengtson et al. 1987: fig. 7.

1989 Tumulduria incomperta Missarzhevsky ; Missarzhevsky 1989: 215, pl. 28: 6, 9.

1992 Tumulduria incomperta Missarzhevsky ; Rozanov and Zhuravlev in Lipps and Signor 1992: 257, fig. 9, panel 78.

1998 Tumulduria incomperta Missarzhaevsky ; Vasil’eva 1998: 115, pl. 44: 3, 7.

2008 Tumulduria incomperta Missarzhevsky ; Varlamov et al. 2008; pl. 13: 12, 13.

2010 Tumulduria incomperta Missarzhevsky ; Rozanov et al. 2010: 86, pl. 59: 5, 6.

Holotype: GIN 3593/138. Partial ventral interarea with narrow central pseudodeltidium and broken lateral margins. From Aldanocyathus sunnaginicus – Tiksitheca licis Zone, Aldan River.

Type locality: Aldan River, left bank, 7 km west of settlement Ugino section M 402 in Rozanov et al. 1969).

Type horizon: Tommotian Stage, Nochoroicyathus sunnaginicus Zone ,

Cambrian.

Diagnosis.—As for genus.

Material.—The available material consists of 34 partially complete ventral interareas, 15 dorsal valves and possible shell fragments collected from the Aldan and Uchur River regions (Pestrotsvet Formation, Nochoroicyathus sunnaginicus Zone, Tommotian Stage , southeastern Siberian Platform).

Description.—The morphology of both isolated Tumulduria interareas and associated ventral valve fragments ( Figs. 1 , 2 ) is described above. The dorsal valves are flat or very gently convex with a straight posterior margin and a weakly developed anterior sulcus ( Fig. 3 ). Growth is hemiperipheral. Dorsal interarea is absent or vestigial in smaller specimens Fig. 3B, C ), but larger specimens exhibit a low, catacline interarea ( Fig. 3A ). Under the slightly elevated umbo the dorsal interarea is divided by a small, triangular notothyrium lined on both sides by weakly defined ribs ( Fig. 3A 4). The internal morphology is poorly preserved, but one large specimen shows a weakly defined pair of ridges radiating from the umbonal region ( Fig. 3A 5).

The surface sculpture of the shell consists of fine concentric fila and variable, often slightly uneven, low ribs and furrows (transverse furrows on ventral interarea; Fig. 2A 3 ). On some shell fragments from larger shells, the concentric ornament is complemented by fine transverse furrows and nick points ( Fig. 2C ).

Discussion.—As discussed above, no complete ventral valves of Tumulduria are known, but based on comparison with Cryptotreta and Salanygolina the ventral valve is assumed to have been strongly convex with an orthocline triangular interarea with a narrow pseudodeltidium. Anterior to the umbo the shells are assumed to have had a large foramen, possibly with a colleplax, and as in Cryptotreta and Salanygolina where complete ventral valves are very rarely preserved) the structural weakness introduced by the umbonal foramen could account for the lack of preserved ventral valves.

The ornament, particularly on the ventral interarea, is generally more chaotic than in other cryptotretid brachiopods, including the other Siberian taxa Aldanotreta and Cryptotreta , and there is no trace of a pustulose micro-ornament such as in Salanygolina .

Stratigraphic and geographic range.—Same as for genus by monotypy.

Figures

Fig. 1. Paterinid brachiopod Tumulduria incomperta Missarzhevsky in Rozanov et al, 1969. Typical Tumulduria plates with pseudodeltidium and partially preserved lateral flanks representing ventral interarea. Aldan and Uchur River area, Nochoroicyathus sunnaginicus Zone, Siberia. A. NRM Br141128, sample 1825; A 1, view from above; A 2, oblique posterior view. B. NRM Br141129, sample 1825; B 1, view from above; B 2, oblique posterior view. C.NRM Br141130, sample 1825; C 1, view from above; C 2, oblique posterior view. D. NRM Br141131, sample 1825; D 1, view from above; D 2, oblique lateral view. E. NRM Br141132, sample JSP 1990 27/1; E 1, view from above; E 2, oblique posterior view. F. NRM Br141133, sample JSP 1990 27/1; F 1, view from above; F 2, oblique posterior view. G. NRM Br141134, sample JSP 1990 27/1; G 1, view from above; G 2, oblique posterior view. H. NRM Br141135, sample 1825; H , internal view; H , detail of internal surface with botryoidal structures.

Fig. 2. Paterinid brachiopod Tumulduria incomperta Missarzhevsky in Rozanov et al, 1969. Fragmentary valves. Aldan and Uchur River area, Nochoroicyathus sunnaginicus Zone, Siberia. A. NRM Br141136, sample 449, left lateral half of ventral interarea; A1, view from above; A2, oblique posterior view; A3, detail of pseudodeltidium in oblique view. B. NRM Br141137, sample 1832, fragment preserving junction of ventral interarea and ventral shell surface; B1, view from posterior; B2, oblique posterolateral view. C. NRM Br141138, sample 525, fragment of shell surface with fila and nick points.

Fig. 3. Paterinid brachiopod Tumulduria incomperta Missarzhevsky in Rozanov et al, 1969. Dorsal valves. Aldan and Uchur River area, Nochoroicyathus sunnaginicus Zone, Siberia. A. NRM Br141139, sample 1793; A 1, dorsal view; A 2, oblique anterior view; A 3, oblique posterior view; A 4, detail of cardinal area in oblique posterior view; A 5, oblique anterolateral view of internal surface. B. NRM Br141140, sample 1825; B 1, dorsal view; B 2, oblique posterior view. C. NRM Br141141, sample 1832; C 1, dorsal view; C 2, oblique posterior view; C 3, oblique anterior view of internal surface. D. NRM Br141142, sample 1832; D , internal view; D , detail of internal surface with botryoidal structures.