Thomasariidae Cooper and Dutro, 1982

Halamski, Adam T. & Baliński, Andrzej, 2019, Thomasaria vs. Pyramidalia conundrum in Devonian brachiopod systematics solved: An argument to formalize epitypification under the ICZN, Acta Palaeontologica Polonica 64 (2), pp. 399-408 : 401-404

Family Thomasariidae Cooper and Dutro, 1982

Stratigraphic and geographic range. —Middle to Late Devonian, Eifelian?, Givetian to Frasnian (corrected herein).

Genus Thomasaria Stainbrook, 1945

= Pyramidalia Nalivkin, 1947

Type species: Thomasaria altumbona Stainbrook, 1945 ; Iowa, USA; Independence Shale, upper Frasnian (after Day and Witzke 2017), Upper Devonian.

Remarks.— Pyramidalia Nalivkin, 1947 with type species Spirifera simplex Phillips, 1841 is a synonym of Thomasaria . As shown below, the shell of Spirifera simplex is impunctate ( Fig. 2E 6), Pyramidalia is thus a spiriferide, not a spiriferinide (contrary to, among others, Ivanova 1959; Pitrat in Boucot et al. 1965; Johnson 2006). Morphology and internal structures of Spirifera simplex and Thomasaria are very similar. More precisely, Spirifera simplex is in accordance with the diagnosis of Thomasaria given by Johnson (2006: 1864), except for the cardinal angles that may be either acute ( Fig. 2C 1 ) or rounded ( Fig. 2D 1 ). It should be noted, however, that the cardinal process was not observed due to preservational condition of the sectioned specimen of Spirifera simplex . Moreover, the internal morphology of the dorsal valve is known solely for Thomasaria warreni Cooper and Dutro, 1982 from the Frasnian of New Mexico ( Cooper and Dutro 1982: pl. 40: 26–27; pl. 43: 1–9) and for Thomasaria cf. altumbona from the Frasnian of Belgium ( Mottequin 2008: fig. 56). The dorsal valve of T. altumbona has been sectioned neither by Stainbrook (1945) nor by Pitrat (1965), Johnson 2006), or any subsequent author. Notwithstanding these minor issues, the most satisfying solution is clearly treating Pyramidalia as a junior subjective synonym of Thomasaria , following Baliński (1979), Brice (1985), Oleneva (2006), Halamski and Baliński (2013), and Alekseeva et al. (2018).

García-Alcalde (2010: 58) suggested the following differences between Pyramidalia and Thomasaria warrant distinction at genus level: (i) symphytium lacking in Thomasaria , present in Pyramidalia ; (ii) crural plates lacking in Thomasaria , present in Pyramidalia ; (iii) cardinal angles acute or right-angled in Thomasaria , rounded in Pyramidalia ; iv) dental plates in Thomasaria longer than in Pyramidalia .

As a matter of fact, the above-mentioned differences are either nonexistent or insufficient for distinction at genus level.

(i) A pair of conjunct apical plates fused with the bases of the dental plates umbonally and extending below the level of interarea is present in Thomasaria altumbona ( Johnson 2006) . Cooper and Dutro (1982: pl. 35: 2–3) showed that in T. altumbona there is also a pair of convex plates rising from lateral edges of the delthyrium. This strongly suggests that a convex pseudodeltidium (symphytium sensu García-Alcalde 2010) covering the delthyrial opening was present at least in adult-gerontic shells.

(ii) Inner socket ridges are present in both Thomasaria and Pyramidalia (see Fig. 3B for the former and Cooper and Dutro 1982: pl. 43: 6–7 for the latter). García-Alcalde (2010) misinterpreted the inner socket ridges in Pyramidalia palentina García-Alcade, 2010 from the Givetian of the Asturias as crural plates (crural plates are defined as being in contact with the valve floor, which is not the case in any of the referred brachiopods).

(iii) The position of the maximal width and, in consequence, the form of postero-lateral extremities are subject to ontogenetic (compare Halamski and Baliński 2013: fig. 36A, C, H) and intraspecific (compare Fig. 2A 1 –D 1 ) variability.

(iv) Such a difference is not significant for a distinction at genus level (compare Stainbrook 1945: fig. 2.14A–C; Fig. 3A ).

Brachiopods presumably belonging to Thomasaria were reported under various generic names (including Pyramidalia ) from Europe: south-western England ( Phillips 1841; Webby 1964); Eifel, Germany ( Schnur 1853 –1854); Montagne Noire, France ( Bergeron 1889; Brice 1985); Pyrenees, France ( Joseph et al. 1980); Ardennes, Belgium ( Mottequin 2008); Holy Cross Mountains and Dębnik Anticline, Poland ( Gürich 1896; Sobolew 1909; Biernat 1966; Baliński 1979, 2006); Cantabrian Mountains, Spain ( van Loevezijn 1986; García-Alcalde 2010); Asia: central Asia ( Nalivkin 1930); China ( Hou 1963); Urals ( Tschernyschew 1887; Skompski et al. 2001); Timan ( Oleneva 2006); Caucasus ( Alekseeva et al. 2018); Afghanistan ( Brice 1971); Iran ( Brock and Yazdi 2000); North America: Iowa, USA ( Stainbrook 1945); New Mexico, USA Cooper and Dutro 1982), Alaska, USA ( Nilsen et al. 1980); Alberta, Canada ( Warren and Stelck 1956; MacKenzie 1965); District of Mackenzie, Canada ( McLaren et al. 1962); and Africa: Anti-Atlas, Morocco ( Halamski and Baliński 2013).

Stratigraphic and geographic range. —Middle to Late Devonian (Eifelian?, Givetian to Frasnian). The presence of Thomasaria in the Eifelian stage of its type region is probable, but has not been proved conclusively. Data provided by Schnur 1851, 1853 –1854) are equivocal due to imprecise stratigraphy and uncertain taxonomy (the identification of Spirifer simplex given by Schnur 1851: 12 was considered doubtful by Schnur 1853 –1854: 208; Spirifer pyramidalis is from the Frasnian of Büdesheim, see e.g., Korn et al. 2013 for the age; the identification of Spirifer nudus is considered uncertain by Schnur 1853 –1854). The report from the upper Eifelian of Skały in the Holy Cross Mountains by Halamski and Zapalski (2006: 147) is based on a misquotation of Biernat’s material coming from the Givetian of Miłoszów and should be excluded. The age of Pyramidalia paoshanensis Hou, 1963 from South China is given as “Eifelian (?)” ( Hou 1963: 425).

Figures

Fig. 2. Spiriferide brachiopod Thomasaria simplex (Phillips, 1841) from the Middle Devonian of south-western England, UK (type region).A–C. Articulated shells (TCD 16991c, A; TCD 16991b, B; TCD 16991a, C) from Port Stephens, in dorsal (A1–C1), ventral (A2–C2), lateral (A3–C3), anterior (A4–C4), and posterior (A5–C5) views. D. Lectotype, articulated shell GSM 6915 from Wolborough, in dorsal (D1), ventral (D2), lateral (D3), anterior (D4), and posterior (D5) views. Reproduced with the permission of the British Geological Survey ©UKRI. All rights reserved. E. Topotype, articulated shell NHMUK PI B 2807 (specimen serially sectioned, see Fig. 3) from Wolborough, in dorsal (E1), ventral (E2), lateral (E3), anterior (E4), and posterior (E5) views, enlargement (SEM micrograph) of the secondary shell layer showing impunctate condition (E6). F. Articulated shell TCD 16991d from Port Stephens, fragmentary posterior view showing the delthyrium partially closed by a convex pseudodeltidium.

Fig. 1. A. Geographical location of the study area in north-western Europe. B. Geological map of eastern Cornwall and southern Devon (Devonian after House and Selwood 1966, otherwise simplified and modified after British Geological Survey 1957). Black asterisks show fossil localities mentioned in the text. The white asterisk shows the presumed position of “Port Stephens” (see text for further explanation).

Fig.3. Transverse serial sections of spiriferide brachiopod Thomasaria simplex (Phillips, 1841) through shell NHMUK PI B 2807 (topotype) from the Givetian of Wolborough, England, UK. Sections through ventral (A) and dorsal (B) valves. The schematic drawings on the left of each section describe the direction of sectioning (see text). Distances measured in millimetres from the tip of the ventral and dorsal umbos, respectively. Gray areas denote local silicification.