Dalmanella testudinaria ( Dalman, 1828 )

Hints, Linda & Harper, David A. T., 2015, The Hirnantian (Late Ordovician) brachiopod fauna of the East Baltic: Taxonomy of the key species, Acta Palaeontologica Polonica 60 (2), pp. 395-420 : 409-410

Dalmanella testudinaria ( Dalman, 1828)

Fig. 10.

1828 Orthis testudinaria Dalman ; Dalman 1828: 115–116; pl. 2: 4a–e.

1968 Dalmanella testudinaria ( Dalman, 1828) ; Bergström 1968: 8; pl. 2: 5.

2010 Dalmanella testudinaria ( Dalman, 1828) ; Jin and Bergström 2010: 20–23 (see synonyms therein); figs. 3–6.

Material.— 355 specimens (including 207 measured specimens), partly embedded in rock. Porkuni Regional Stage , Kuldiga Formation , Hirnantian ( Upper Ordovician ); western Latvia, southern Estonia. Drill core and depth (in meters) of sample intervals with brachiopods. Depth of fragmentary preserved specimens is marked by “?”. Collection GIT 542 : Adze-6, 837.8–?846.5; Aispute-41, 991.6–?1000.75; Engure, 882.15–882.3 m; Ikla,?532.8–533.6; Mežmaļi-16, 902.6–910.95; Piltene-30, 1017.1; Riekstini-15, 846.15–?860.2; Ruhnu-500, 610.7–?616.1; Stirnas-18, 898.8–906.8; Vilcini-19,?899–907.0; collections LDM G: Anši-12, 913.7–918.7; Blīdene-5, 815.75–819.3; Dizrungi-17, 881.6–?893.8; Dreimaņi-11, 952.8–955.45; Ēdole-60, 832.5–836.8; Kronauce-20, 1049.1–1050.9; Mežvagari-13, 869.5–?879.1; Pāvilosta, 1082.6; Pliekalni-14, 877.0–883.1; Priekule-23,?1386.5; Remte-3, 958.0–958.8 .

Discussion.—The Swedish type material of Dalmanella testudinaria was recently revised by Jin and Bergström (2010). The interpretation of D. testudinaria in the East Baltic ( Hints 1975) is not substantially different from the revised concept of the species. The East Baltic specimens have a consistent shell shape, illustrated by the ratios of different measurements (shell length, width, thickness, width of interarea, distance of the maximum width from the umbo; Hints 1975). The average shell length/width ratio (L/W) is 0.91. The extreme values of that ratio 0.69 and 1.10 occur accordingly in 2 and 5 cases of 203 measured specimens. The L/W ratio slightly less than 1, is characteristic of the topotype specimens from Östergötland ( Jin and Bergström 2010: fig. 6). The hinge line is on average 0.64 of the shell width (variation from 0.52 to 0.78), close to that for the type material of D. testudinaria ( Jin and Bergström 2010) . The maximum width of shell occurs slightly behind the shell mid-length (ratio of the distance of maximum width from the umbo and shell length is 0.43 based on 42 measurements). The shell thickness is on average 0.43 of the shell length. The larger shells can be variably compacted, which increase the variation of measurements of shell thickness. The largest specimens from Latvia slightly exceed the size of the largest specimens from Borenshult in Sweden.

The number of costae and costellae is the most variable feature. The shells with an average length of 10.4 mm have a combined total of 48 costae and costellae. Shells that are 3.3 to 17.2 mm long have 30 to 75 ribs. The variation in rib number is larger than that of the measured linear characters. There are some regional differences in D. testudinaria particularly in the number of ribs per 2 mm at 2 mm from the umbo: 6–9 on Latvian, 7–10 on Swedish and 8–12 on Polish specimens. Capillae occur between the costae and costellae, similar to those on the Swedish specimens. All the specimens have a median interspace on the dorsal valve and well-developed, large punctae which have often pyrite infillings (Fig. 10I, J).

However, there are two characteristics which were not- ed by Jisuo Jin (personal communication 2010), who studied some specimens from the Riekstini core (depth 851.0 m). These are the occurrences of aditicules and a prominent cardinal process. The Swedish specimens have a relatively small cardinal process with a shaft and bilobate myophore, which occupies half or one-third the width of the notothyrial cavity. The specimen from the Riekstini core prepared by Jisuo Jin has incipient trilobate cardinal process, which is similar to the shell on Fig. 10G. In their cardinal process and aditicules, therefore, the East Baltic specimens resemble the North American Cincinnetina Jin, 2012 (formerly known as “ Dalmanella ” of the Cincinnati type area), but they lack the dorsal medial costa that is diagnostic of Cincinnetina . Three other specimens from the same sample have a prominent cardinal process bilobate with weakly developed crenulations, but not trilobate. Most of the Baltic specimens have cardinal process with bilobate, more or less strongly crenulated myophore (Fig. 10C–F), which is more robust and extends more posteriorly over the interarea compared with that of Swedish specimens. Such a cardinal process is more typical of other species, for example, the cardinal process of Cincinnetina multisecta ( Meek, 1873) from Laurentia ( Jin and Bergström 2010; Jin 2012). However, the faint capillae interrupted by strong growth lines (“pitted” ornament between the ribs), which are characteristic of the latter and several other species of Onniella and Cincinnetina in North America ( Jin and Zhan 2008; Jin and Bergström 2010; Jin 2012) are not apparent on Baltic specimens of D. testudinaria . However, such ornament (reticulated growth lines of Jin 2012) is described on the Baltic species Onniella trigona from the Porkuni Stage and lowermost Silurian ( Hints 1975; Rubel 2011).

→ Fig. 10. Dalmanellid brachiopod Dalmanella testudinaria ( Dalman, 1828) from the Kuldiga Formation of the Porkuni Regional Stage , Hirnantian ( Upper Ordovician ), East Baltic , western Latvia (A, B, D–K) and southwestern Estonia (C). A. Ventral valves, GIT 542-63 /1–10, Adze, depth 842.6 m (A 1 –A 10), exterior views. B. Shell, GIT 542-41 /1, Stirnas- 18, 899.55 m, anterior (B 1), ventral (B 2), dorsal (B 3), posterior (B 4), and lateral (B 5) views. C. Shell interior, GIT 542-76 , Ikla, 533.6 m, antero-lateral (C 1) and anterior (C 2) views. D. Dorsal valve, LDM G328-121 , Ēdole, 835.6 m, interior view. E. Dorsal valve, GIT 207-17 , Engure, 882.15 m, views of cardinalia and interarea. F. Shell, GIT 542-111 , Stirnas- 18, 899.2 m, view of cardinal process. G. Shell, LDM G328-74 , Mežvagari- 17, 869.5 m, posterior view (G 1) and view of cardinal process (G 2). H. Ventral valve, GIT 542-69 , Mežmali- 16, 918.6 m, view of interarea and teeth. I. Pyritized pores on posterior and lateral parts of ventral valves, Stirnas- 18, 903.8 m, GIT 542-114 /1 (I 1) and 542-114/2 (I 2), exterior views. J. Ornament of the shell with few aditicules, LDM G328-97 ; Dizrungi- 17, 888.3 m. K. Punctae on the broken shell surface, LDM G328-68 ; Kronauce, 1049.1 m. Scale bars 2 mm, except I

1

1 mm.

The presence of aditicules separates at least some of the East Baltic specimens from the Swedish type material and thus should be rejected from D. testudinaria following Jin and Bergström (2010). The type of cardinal process and occurrence of additicules is currently difficult to establish in differently preserved specimens from different localities in the Central East Baltic. More detailed studies of the punctae and shell microstructures of D. testudinaria are needed to confirm the diagnostic value of the aditicules. Currently the differences noted between the East Baltic specimens and those from the type locality in Sweden is considered as intraspecific variation.

Stratigraphic and geographic range. —This near-cosmopolitan species is mainly restricted to the Hirnantian Stage, Upper Ordovician, although related forms occur in the underlying Katian Stage. The species is a common component of the Hirnantia brachiopod fauna ( Rong and Harper 1988), particularly in Europe, including England, Ireland and Wales, Austria, Czech Republic, France, Norway, Sweden, Estonia, Latvia (this paper), and Lithuania ( Paškevičius 1997). The species also occurs in China, Burma, North America ( Canada), South America ( Argentina), and Asia ( Kazakhstan).