Altaspiratella elongatoidea ( Aldrich, 1887 )

Janssen, Arie, Sessa, Jocelyn & Thomas, Ellen, 2016, Pteropoda (Mollusca, Gastropoda, Thecosomata) from the Paleocene-Eocene Thermal Maximum (United States Atlantic Coastal Plain), Palaeontologia Electronica (Athens, Greece) 19 (3), pp. 1-26 : 6-10

Altaspiratella elongatoidea ( Aldrich, 1887)

Figures 3.1-4, 4

v*1887 Physa elongatoidea Aldrich , p. 83.

v. 1895 Spiralis elongatoidea (Aldrich) ; Aldrich, p. 5, pl. 2, fig. 9.

v. 1899 Spiralis elongatoidea (Aldrich) ; Harris, p. 103, pl. 12, fig. 25.

v. 1934 Limacina elongatoides [sic] (Aldrich); Collins, p. 177, pl. 7, fig. 1.

v. 1965 Limacina elongatoidea (Aldrich) ; Palmer and Brann, p. 358.

v. 1966 Spiratella (Altaspiratella) elongatoides [sic] (Aldrich); Korobkov, p. 74.

v.? 1982 Plotophysops bearnensis Curry , p. 40, pl. 1, fig. 9a-c.

?[1986] Spiratella tutelina Curr. ; Merle, p. 43 (non Curry).

v.?1990 Altaspiratella bearnensis (Curry, 1981 [sic]); Janssen, p. 68.

? 1992 Altaspiratella bearnensis (Curry) ; Hodgkinson, Garvie and Bé, p. 13, pl. 1, figs. 1, 2.

v. 1992 Altaspiratella elongatoidea (Aldrich) ; Hodgkinson, Garvie and Bé, p. 14, pl. 1, fig. 3.

? [1996] Altaspiratella bearnensis (Curry, 1981) ; Kunz, p. 164, pl. 30, figs. 1-3.

v.? 2010 Altaspiratella bearnensis ( Curry, 1982) ; Cahuzac and Janssen, p. 24, pl. 2, figs. 1- 4; pl. 3, fig. 1.

Type material. To date exclusively known by the holotype, USNM 638862 .

Type locality. Choctaw Corner , Clarke Co., Alabama, USA (Eocene, early Ypresian, NP 10) .

Material examined. Wilson Lake section, NP 9 and NP 10a ( Table 1); Bass River section, NP 10a ( Table 2); Clayton section, NP 9b, 10a ( Table 3); Cambridge-Dorchester section ( Table 4).

Description. Shell sinistral, conical, oblong, about twice as high as wide, with up to six slightly convex, comparatively high whorls that gradually increase in diameter, separated by an incised, oblique suture. Apical angle c. 35-40°. The whorls attach below the periphery of the preceding whorl, where the shell may be slightly angular, especially in immature individuals. All specimens are preserved as pyritic internal molds, frequently compressed or otherwise crumpled, and no adult shell parts with developed apertural features are preserved.

Discussion. Two very similar species in this genus are Altaspiratella elongatoidea ( Aldrich, 1887) and A. bearnensis ( Curry, 1982) . The former was introduced from the Ypresian of Alabama (Bashi Member of the Hatchetigbee Formation, NP 10; the marine portion of the Bashi was constrained by Sluijs et al. (2014) to lie above the CIE, and is thus younger than our samples, which are in the peak PETM interval) and was with certainty only known by its holotype. Altaspiratella bearnensis was first described from the Marnes de Gan, at Gan (Pyrénées-Atlantiques, France; Ypresian, NP 12/ 13), from where extensive material of this species is available in the Naturalis collection. Holo- and paratypes are in the Natural History Museum, London, UK (nr BMNH CG. 21255).

Hodgkinson et al. (1992, p. 13) discussed these two forms, together with another Ypresian, relatively high-spired species, Limacina tutelina ( Curry, 1965) , but decided to maintain them as separate taxa, stating that there is little resemblance between complete specimens, as neither of these two species has the well-developed anterior indenture so prominent in A. bearnensis . However, the single specimen of A. elongatoidea is incomplete, lacking its apertural parts, so a comparison of these structures with those in A. bearnensis is impossible.

Cahuzac and Janssen (2010, p. 24, pl. 2, figures 3c and 5a) also discussed both Altaspiratella species and found a small difference between the type specimens. In the holotype of A. elongatoidea the first apical whorl is markedly wider than in the type of A. bearnensis , as well as in all additional specimens of that species. It was not decided whether these two taxa are synonyms, because of A. elongatoidea , only the holotype specimen was available. Comparison of figures 2 and 3 on plate 1 of Hodgkinson et al. (1992), respectively, identified as Altaspiratella bearnensisi and A. elongatoidea (holotype), however, demonstrates hardly any differences.

Similarly, all specimens recorded herein are incomplete and do not preserve adult apertural features. The small difference noted by Cahuzac and Janssen (2010), however, seems to be present in a single sufficiently well preserved immature specimen ( Figure 3.4 ), which makes a synonymy of these two taxa less likely. Therefore, and in the absence of completely developed specimens of A. elongatoidea , we hesitate to consider these species identical, even if their stratigraphical ranges overlap (see below).

Distribution. Altaspiratella elongatoidea to date was only known from its type locality (NP 10). The material recorded herein demonstrates it presence immediately above the Paleocene/Eocene boundary (NP 9), continuing into zone NP 10a.

Apart from its type locality as specified above, Altaspiratella bearnensis was subsequently recorded from the ‘Middle Blue Marls Formation’ of Pradelle-en-Val ( France, Aude department; Ypresian NP 10; Pirkenseer et al., 2013). From the North Sea Basin, the species is known from Ypresian localities in Belgium (Mont Panisel Formation, Knokke borehole), and several localities in the London and Hampshire basins ( England, London Clay Formation, divisions D and E, NP 10-11; King, 2016). Additional, more remote occurrences are in Egypt (Thebe Formation, Luxor, Valley of the Kings; probably NP 13; Naturalis collections) and Kazakhstan (Aktulagay; NP 12; King et al., 2013). Hodgkinson et al. (1992, text-figure 3) recorded Altaspiratella bearnensis from the Weches Formation of Texas (zone NP 15, mid-Lutetian).

Figures

FIGURE 3. Altaspiratella elongatoidea (Aldrich, 1887). 1, Wilson Lake section, sample 31, depth 100.89-100.95 m, RGM 777 230; apertural view. 2, Clayton section, sample 9, depth 91.44-91.4 m; RGM 777 308a; apertural view. 3-4, Wilson Lake section, sample 42, depth 104.24-104.30 m; RGM 777 251a, 3: apertural view, 4: apical view.

FIGURE 4. Altaspiratella elongatoidea (Aldrich, 1887). Computed tomography (CT) scan of the specimen pictured in Figure 3.3-4, resolution 1.6 micrometer/voxel, 165 kV, detector exposure timing 750 ms. For animated version, see online at palaeo-electronica.org/content/ 2016/1662-pteropoda-from-the-usa-petm. By clicking on the image, the interactive 3D model is activated, and the reader can use the mouse to rotate the specimen and change magnification.