Discoceras antiquissimum ( Eichwald, 1842 )

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 129-132

Discoceras antiquissimum ( Eichwald, 1842)

Fig. 47C–D , 48A , 49A , 50A

Clymenia antiquissima Eichwald, 1840: 15 (nomen nudum).

Clymenia antiquissima Eichwald, 1842: 33 , pl. 3 figs 16–17.

Lituites trapezoidalis Lossen, 1860: 25 , pl. 1 fig. 2.

Lituites (Trocholites) antiquissimus – Schmidt 1861: 62, pl. 6 fig. 2a–g.

Lituites antiquissimus – Roemer 1861: 62, pl. 6 fig. 2f–g (non pl. 6 fig. 2a–e = Discoceras roemeri Strand, 1934, see below); 1885: 68, pl. 4 fig. 12. ― Karsten 1869: 53, pl. 19 fig. 7a–c.

Discoceras antiquissimum – Foerste 1925: 17, 58, pl. 18 fig. 1. ― Strand 1934: 32, pl. 2 figs 4, 11, pl. 4 figs 2–3, pl. 13 fig. 9. ― Thorslund 1936: pl. 2 fig. 11. ― Balashov 1953b: 265, pl. 12 fig. 1a–b. ― Sweet 1958: 99, text-fig. 13q. ― Stumbur 1959: fig. d. ― Neben & Krueger 1973: pl. 77 figs 24–25. ― Dzik 1984: 42, text-figs 9c–d, 12.39, pl. 7 fig. 1.

Discoceras antiquissima ― Hucke & Voigt 1967: 58, pl. 15 fig. 1.

Diagnosis

Discoceras with adult conch diameters more than 130 mm, WER of ca 1.9, decreasing with increasing conch size; whorl cross section slightly depressed with WWI 1.2–1.5 becoming less depressed in maturity, broadly reniform in juvenile stages, rounded trapezoidal with venter wider than dorsum in later groth stages; free mature body chamber with constriction near aperture; ornamented with prominent ribs, distance between ribs is one to two times the distance between two septa; siphuncle close to dorsal conch margin, ca 0.15–0.17 of whorl height, septal necks orthochoanitic. (Adopted from Strand 1934.)

Material examined

ESTONIA • 1 spec.; sine loco; Pirgu Regional Stage; GIT 878-152 • 5 specs; Haapsalu holm ; Adila Formation , Pirgu Regional Stage; GIT 225-1005 , GIT 225-973 , GIT 225-974 , GIT 426-138 , GIT 426- 375 • 3 specs; same data as for preceding; TUG 107-43 , TUG 46-150 , TUG 47-882 152 • 1 spec.; Hiiumaa Island, east shore between Heltermaa and Vahtrepa ; Pirgu Regional Stage; TUG 66-288 • 6 specs; Vormsi Island, Hosholm shore ; Adila Formation , Pirgu Regional Stage; GIT 840-246 , GIT 840- 247 , GIT 840-257 , GIT 840-64 , GIT 840-90 , GIT 840-91 • 2 specs; same data as for preceding; TUG 1743-59 , TUG 39-814 • 10 specs; Vormsi Island, Hosholm shore (tower locality); Adila Formation , Pirgu Regional Stage; GIT 840-255 , GIT 878-140 , GIT 878-141 , GIT 878-208 to GIT 878-212 , GIT 878-214 , GIT 878-221 • 1 spec.; Inju-Meriküla quarry ; Ärina Formation , Porkuni Regional Stage; GIT 426-384 • 1 spec.; Kersleti quarry ; Kõrgessaare Formation , Vormsi Regional Stage; TUG 939-67 • 1 spec.; Kohila ; Kõrgessaare Formation , Vormsi Regional Stage; GIT 426-382 • 1 spec.; Küti, near ViruJaagupi ; Kõrgessaare Formation , Vormsi Regional Stage; TUG 1745-322 • 1 spec.; Lohu (Pontiaki) springs; Adila Formation , Pirgu Regional Stage; GIT 878-137 • 1 spec.; Mahtra ; Pirgu Regional Stage; GIT 426-1080 • 1 spec.; Piirsalu quarry ; Moe Formation , Pirgu Regional Stage; TAM G1 :170 • 1 spec.; Paluküla quarry ; Kõrgessaare Formation , Vormsi Regional Stage; GIT 225-1017 • 1 spec.; Piirsalu quarry ; Moe Formation , Pirgu Regional Stage; GIT 426-381 • 1 spec.; same data as for preceding; TUG 46-153 • 1 spec.; Pirgu river outcrops ; Adila Formation , Pirgu Regional Stage; GIT 426-383 • 1 spec,; same data as for preceding; TUG 1745-298 170 • 1 spec.; Rabivere quarry ; Moe Formation , Pirgu Regional Stage; TUG 56-113 • 2 specs; Uuemõisa; Adila Formation , Pirgu Regional Stage; TAM G432:504 , TAM G432:505 113 • 1 spec.; Vohilaid Island, Vohilaid outcrop 2 (2 and 3 after B. Stein); Adila Formation , Pirgu Regional Stage; GIT 878-145 • 1 spec.; same data as for preceding; TUG 66-287 • 15 specs; Vohilaid Island, Vohilaid shore (E); Adila Formation , Pirgu Regional Stage; GIT 878-147 , GIT 878-148 , GIT 878-197 , GIT 878-199 to GIT 878-201 , GIT 878-204 to GIT 878-206 , GIT 878-207 , GIT 878-225 , GIT 878-313 to GIT 878-316 .

Type locality and horizon

Kärdla, Hiiumaa Island, Estonia; Vormsi–Pirgu regional stages (“Lyckholm Stufe” of Teichert 1930).

Description

The species has been described in detail by Strand (1934). Additional measurements, described herein, contribute to an understanding of the variability of WER and WWI ( Figs 48A , 49A ; supplementary data 5). The relative whorl width (WWI) decreases with conch size from ca 1.5 at whorl heights of ca 10 mm to 1.0– 1.2 in nearly adult specimens (whorl heights 30–35 mm).

The whorl expansion rate (WER) is 1.5–2.0 in nearly adult specimen, but it is considerably higher during early growth stages (maximum 3.6 in specimen GIT 426-138 at a conch diameter of 19 mm).

The largest specimen in the collections is specimen TAM G1:170 (described also in Strand 1934), a complete, mature specimen from Piirsalu, Estonia, Pirgu Regional Stage, with a diameter of 145 mm, a whorl height of 31 mm and a conch width of 31 mm. Whorl heights of 33 mm, and 31 mm, and respective widths of 36 mm and 31 mm, are known from specimen GIT 225-1005, TUG 46-153 from Pirgu Regional Stage.

Remarks

This species is unique to Discoceras because of its prominent juvenile to adult annulation. However, the strength of annulation varies between specimens, it appears to be absent in earliest growth stages ( Fig. 50A ), as well as during latest growth stages ( Fig. 47D ). The possibility exists that some variants with stronger or weaker annulation represent different species. However, the available material does not permit differentiation between species with different annulation patterns.

Figures

Fig. 47. Annulated species of Discoceras Barrande, 1867 of the Vormsi–Pirgu regional stages, Estonia. A–B. Discoceras paopense sp. nov. from Vormsi Regional Stage. A. Paratype TUG 2-730, from unknown locality, Estonia. B. Holotype TUG 2-719, Paope limestone quarry, Vormsi Regional Stage. C–D. Discoceras antiquissimum (Eichwald, 1842) from Pirgu Regional Stage. C. Specimen GIT 878- 208, from Hosholm shore (tower), Vormsi Island. D. GIT 878-148, from Vohilaid (E), Vohilaid Island. Scale bar = 20 mm, same scale in all figures.

Fig. 48. Whorl expansion rate of species of Discoceras Barrande, 1867 of the Vormsi–Pirgu regional stages, Estonia. A. WER of D. antiquissimum (Eichwald, 1842) (= circles) and D. paopense sp. nov. (= black triangles). White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934). B. WER of D roemeri Strand, 1934. White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934), and in Balashov (1953b); black squares = specimens described as D. angulatum (Saemann, 1853) in Strand (1934); black triangles = specimens described as Schroederoceras balaschovi Stumbur, 1956 in Stumbur (1956). C. WER of D. saemanni (Hyatt, 1894). White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934); black squares = specimens described as D. hyatti Strand, 1934 in Strand (1934).

Fig. 49. Whorl width index species of Discoceras Barrande, 1867 of the Vormsi–Pirgu regional stages, Estonia. A. WWI of D. antiquissimum (Eichwald, 1842) (= circles) and D. paopense sp. nov. (= black triangles). White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934). B. WWI of D roemeri Strand, 1934. White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934), and in Balashov (1953b); black squares = specimens described as D. angulatum (Saemann, 1853) in Strand (1934); black triangles = specimens described as Schroederoceras balaschovi Stumbur, 1956 in Stumbur (1956). C. WWI of D. saemanni (Hyatt, 1894). White circles = Estonian specimens described herein; black circles = specimens described in Strand (1934); black squares = specimens described as D. hyatti Strand, 1934 in Strand (1934).

Fig. 50. Early growth stages of species of Discoceras Barrande, 1867 of the Pirgu–Porkuni regional stages, Estonia. A. D. antiquissimum (Eichwald, 1842), specimen GIT 425-375, from Haapsalu holm, Pirgu Regional Stage. B. D. saemanni (Hyatt, 1894), specimen GIT 426-425, from Röa-Jakobi quarry, Porkuni Regional Stage. Scale bars = 10 mm.