Breviconoteuthis aff. breviconus ( Reis, 1907 )

Košťák, Martin, Schlögl, Ján, Fuchs, Dirk, Havrila, Milan, Kolar-Jurkovšek, Tea, Vörös, Attila, Havelcová, Martina, Šurka, Juraj, Havrila, Jakub & Holcová, Katarína, 2024, Rare Middle Triassic coleoids from the Alpine-Carpathian system: new records from Slovakia and their significance, Swiss Journal of Palaeontology (19) 143 (1), pp. 1-19 : 12-13

Breviconoteuthis aff. breviconus ( Reis, 1907)

( Fig. 7E–L ).

Studied material: A single specimen from the locality Podhradie ( Slovakia, No. KGP-PO-001; stored at Comenius University in Bratislava ). The specimen was compared to the type material—e.g. B. breviconus (No. PIMUZ M12 ; Fig. 7M ) stored in the Paläontologisches Institut und Museum der Universität Zürich, Switzerland ; and Zugmontites mojsisovicsi Reis, 1907 (No. 1901-II- 508; Fig. 7N–O ) stored in the Bayerische Staatssammlung für Paläontologie und Historische Geologie München , Germany .

Locality: Podhradie ( GPS 48° 39 ′ 27.2 ″ N 18° 03 ′ 11.2 ″ E), eastern part of the Považský Inovec Mts.

Description: The specimen represents a steinkern of a brevi- to slightly endogastric cyrtoconic phragmocone. Its apical angle measures 34° in dorsoventral and 32° in lateral views. Neither mineralized (e.g., conotheca, septa, sheath) nor nonmineralized shell material (e.g., proostracum) is preserved. Also, the ontogenetically oldest chambers are missing. The preserved part is up to 65 mm long and 45 mm wide and includes 11 chambers. Therefore, the phragmocones diameter seems to be dorsoventrally flattened; at least in the ontogentically youngest chambers. Annular constrictions on the outer surface, which correspond to former mural ridges, suggest a septal distance that gradually increases from 4 mm (apical part) to 8 mm at the anterior part. The ratio chamber length to chamber diameter varies from 0.19 to 0.23 (average 0.22). The sutures are unusually inclined towards the venter (backwards inclined). They appear to be simple without lobes or saddles. In ventral view, one can recognize a longitudinal depression that likely correlates with the former position of the siphuncle. This observation implicates that the septal necks were in contact with the inner surface of the conotheca, which in turn suggests a marginal rather than a submarginal siphuncle. There is no evidence of a longitudinal keel along the dorsum.

Comparisons: In having a brevi- to slightly cyrtoconic phragmocone ( Fig. 7M herein), the here reported Breviconoteuthis aff. breviconus is similar especially to the holotype of Breviconoteuthis breviconus Rieber, 1973 . Taking into consideration that our specimen might have suffered a faint compaction, their apical angles do not differ significantly. Major differences between our Breviconoteuthis aff. breviconus and Breviconoteuthis breviconus concern the chamber distance (longer in our specimen ~ 4–8 mm vs. 2–3 mm in the holotype) and in the siphuncle characteristics (its wider cross-section in our specimen). The inclination of the septa, which is backward in our specimen, might represent the main difference, but this character is unfortunately poorly known in the type specimens.

Mojsisovics (1871, tab 2, fig. 9) described a similar taxon Aulacoceras ellipticum . The figured specimen resembles Breviconoteuthis aff. breviconus in the septal and cameral arrangement (cf. Fig. 7E, F ). However, the chamber distances are visibly larger in B. aff. breviconus . Furthermore, A. ellipticum is laterally compressed (in this respect, it more resembles genus Mosisovicsteuthis , see above), whereas B. aff. breviconus is dorsolaterally flattened. Regarding this aspect, A. ellipticum may represent another and younger Breviconoteuthis species (Austriacum Zone, Carnian; Mojsisovics, 1871), although the lateral compression also links this specimen to Zugmontites ( Fig. 7N, O , herein).

The slight phragmocone compaction may have resulted in different compressions of phragmocones in several phragmoteuthid taxa. We assume our specimen might be slightly dorso-ventrally flattened, therefore, the original cross-section should actually be more circular. However, the compression is very slight as it is seen in septal shapes, showing no significant deformation ( Fig. 7 K, L ).

Stratigraphy and palaeogeography: The species is known from the Middle Triassic (upper Anisian) of Switzerland, Austria ( Fuchs & Donovan, 2018) and Slovakia (this report). Here, it comes from dark-grey to black biodetritic limestones of the Ráztoka Limestone Member of Zámostie Limestone Formation, dated to lower Illyrian (upper Anisian), uppermost part of the Trinodosus Zone (Pseudohungaricum Subzone) —lowermost part of the Reitzi Zone.

Palaeobiogeographic distribution of recorded coleoids is shown on the Fig. 8 .

Figures

Fig. 7 A–D, Mojsisovicsteuthis boeckhi (StÜrzenbaum, 1875), Bakony (Hungary), Anisian, Reitzi Zone. A Specimen No.T.3206 with preserved final chamber in lateral view. B Specimen No.T.81 with preserved final chamber in lateral view.The constriction of the last septum prior the final chamber is well seen in both specimens.C–D Specimen No.T.255. C lateral view; D detail of the septum attachment to the phragmocone wall. E–L Breviconoteuthis aff. breviconus, upper Anisian, lower Illyrian, Podhradie,Slovakia.E Ventral view; F, G lateral views demonstrating backwards inclined septa; H dorsal view; I, J cross section at the apical part; J position of the siphuncle; K, L micro-CT imaginations; K longitudinal section in lateral view; L longitudinal section in dorso-ventral view. Specimen No. KGP-PO-001. M Breviconoteuthis breviconus (Reis, 1907), original of Rieber (1974: Fig. 3), upper Anisian,Besano Formation, Monte San Giorgio, Switzerland. N, O. Zugmontites mojsisovicsi Reis, 1907, holotype, No. 1901-II-508, upper Anisian,Wettersteinkalk, Austria. N Lateral view; O dorso-ventral view. Scale bar equals 1 cm

Fig. 8 Palaeobiogeographic distribution of genera Mojsisovicsteuthis and Breviconoteuthis (Anisian–Carnian).While Mojsisovicsteuthis (larger straight phragmocone) shows large geographic distribution, the genus Breviconoteuthis (smaller phragmocone) is known only from few sites in the Alpine-Carpathian system