Breviconoteuthis Rieber, 1973

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 : 12-15

Genus Breviconoteuthis Rieber, 1973

Type species: Atractites breviconus Reis, 1907 ; p. 148, pl. 3. fig. 3 by monotypy.

Diagnosis (after Fuchs & Donovan, 2018): Phragmocone very small to small, brevi- to slightly cyrtoconic, circular in cross section, apical angle 38°–40°; ratio of chamber length to diameter about 0.15; pro-ostracum three-lobed, longer than phragmocone, anterior median field rounded; siphuncle marginal; rostrum unknown.

Diagnosis (emended): Phragmocone very small to small sized, brevi- to slightly cyrtoconic, circular in cross section, apical angle 30–40°; ratio of chamber length to diameter between 0.15–0.25; pro-ostracum three-lobed, longer than phragmocone, anterior median field rounded; siphuncle marginal; rostrum unknown.

Stratigraphic and geographic occurrences: So far known only from the upper Anisian (Wettersteinkalk) of Austria (Tyrol), Switzerland ( Fuchs & Donovan, 2018) and Slovakia (Anisian—lower Illyrian; this paper).

Remarks: Breviconoteuthis and the slightly younger genus Phragmoteuthis Mojsisovics, 1882 (Carnian), the eponym of the order Phragmoteuthida , share a three-lobed proostracum morphology. Terefore, both genera can presently be distinguished only by phragmocone characters. Te phragmocone of Breviconoteuthis displays a ventral curvature that is so far unknown in Phragmoteuthis .

Te genus Zugmontites Reis, 1907 (upper Anisian) is based on a single specimen whose phragmocone parameters are close to those of Breviconoteuthis . Fuchs and Donovan (2018) interpreted Zugmontites as a putative phragmoteuthid owing to the absence of a proostracum. Due to the lack of available specimens, it can be presently not excluded that Zugmontites mojsisovicsi Reis, 1907 , the type spieces of Zugmontites , is identical to Breviconoteuthis breviconus . One feature delimiting the two type species might be the ventral curvature that seems to be more distinct in Breviconoteuthis than in Zugmontites .

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 ). Te 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: Te 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. Te preserved part is up to 65 mm long and 45 mm wide and includes 11 chambers. Terefore, 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. Te ratio chamber length to chamber diameter varies from 0.19 to 0.23 (average 0.22). Te sutures are unusually inclined towards the venter (backwards inclined). Tey 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. Tis 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. Tere 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). Te 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 . Te 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).

Te 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: Te 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 .

Overall cephalopod diversity

Cephalopod diversity at locality Podhradie consists of: Coleoids—aulacoceratids (probably 1 taxon—too fragmentarily preserved), Breviconoteuthis aff. breviconus , 2 nautiloid species (indetermined), and 7 ammonoid species (see above). Taxonomically (at species levels), coleoids represent 18% of the cephalopod fauna.

Cephalopod diversity at locality Harmanecká Cave— Kozelník (same lithostratigraphical unit): Coleoids— Mojsisovicsteuthis boeckhi , 1 indetermined aulacoceratid specimen, 1 nautiloid species (indetermined), 4 ammonoid species (see above). Coleoids taxonomically (at species levels) represent 29% of the cephalopod fauna.

Rather scarce fossil record of coleoids, however, supports overall high Anisian cephalopod diversity including ammonoids, nautiloids and coleoids at equal time and space.

Palaeoenvironment

Te limestones of the Ráztoka Limestone Member are represented by filament, filament-crinoidal, crinoid-bivalve-gastropod to crinoidal microfacies. Part of the bioclasts was produced on a shallow-water carbonate platform, from where it was redeposited to the sedimentation area of these limestones at the platform periphery, probably situated on subsiding tectonic blocks ( Havrila et al., 2016). Relatively shallow-water neritic environment probably at the margin of neritic carbonate platform for the Ráztoka Limestone was also proposed in the type area of this member in Nízke Tatry Mts by Kochanová and Michalík (1986), however here the limestones bear a frequent distinct lamination possibly revealing cross and ripple mark (?)-bedding, the features unknown in the studied localities.

Te geochemical record unambigenously provided organic mater linked to a rich algae cover. Te samples contained about 0.005% of extractable matter that corresponded with the low total organic carbon contents (Additional file 1: Table S2). In the extracts, n -alkanes ranging from n-C 14 to n -C 19, isoprenoid coumpounds including pristane (Pr) and phytane (Ph), fatty acids and their esters were identified. n-Alkanes in sediments can generally come from multiple sources and are considered important biomarkers for terrestrial higher plants, algae and bacteria ( Peters & Moldowan, 1993). For shortchain n-alkanes in the C 15 –C 21 range, that were identified, aquatic algae and/or bacteria can be considered as primary input sources. However, they generally produce n -alkanes with an odd number of carbons, such as n -C 15, n -C 17, and n -C 19 ( Cranwell et al., 1987), and such obvious odd–even carbon predominance was not observed in the studied sediments. A likely explanation for this anomalous distribution could be diagenetic reduction of n -fatty acids under reducing conditions ( Simoneit, 1977) or a highly saline carbonate environment ( Pearson & Obaje, 1999).

Next to the n -alkanes, also the saturated (14:0, 16:0, and 18:0), monounsaturated (16:1 and 18:1), and the polyunsaturated (18:2) fatty acids were identified. Te shorterchain fatty acids are produced by all plants, but they are the dominant lipid components of algae and bacteria (Ervin, 1973; Simoneit et al., 1979; Wang & Liu, 2012).

Tese isoprenoids are used to estimate redox conditions ( Didyk et al., 1978), since pristane is believed to be generated by an oxidative pathway, while phytane is generated by reductive pathways. Te graph of the dependence of Ph/n-C 18 on Pr/n-C 17 is used to provide information on the depositional environment, relative maturity and possible diagenetic processes. For the studied samples, the graph shows that the starting material was seaweed, which was preserved in a reducing environment ( Fig. 9 ).

Te whole combination in the samples of identified compounds: n-alkanes, isoprenoids and fatty acids, along with their specific distribution, is indicative of organic matter coming from an algal source. No traces of any other source of organic material were found.

Based on palaeontological, sedimentological and geochemical records, we have reconstructed depositional environment and cephalopod diversity during the sedimentation of dark-grey organodetritic crinoidal limestones ( Figs. 10 , 11 ). Additional geochemical records showed the presence of organic matter linked to abundant algae. We suppose the algal cover played an important role on the former shallow carbonate platform and its subdiding peripheries, where the studied localities were situated in that time. Observed redeposits from the adjacent shallow-water carbonate platform document a continuous connection of the sedimentation area of Ráztoka Limestone with this high productivity environment. Te algae vegetation in the Anisian may, with question mark, resemble significantly shallower-water sea-grasses which occurred at the end of Cretaceous Period ( Forsey, 2019; van der Ham et al., 2007). Tese conditions were probably suitable spots of cephalopod diversity and disparity, as we can see in Carpathian localities.

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

Fig. 9 Plot of Pr/n-C17 versus Ph/n-C18 cross plot showing the source and depositional environments of the natural samples (from Beds 3, 6 and 7, locality Podhradie)

Fig. 10 A Reconstruction of cephalopod habitat within Western Carpathian Ráztoka Limestone, Illyrian Trinodosus—Reitzi Zones. Reconstruction: Petr Modlitba, with courtesy of author. B 1. Nautiloids. 2. Diverse ammonoids. 3. Aulacoceratids. 4. Mojsisovicsteuthis. 5. Breviconoteuthis. The benthic fauna is composed by abundant crinoids, echinoids, bivalves and brachiopods. Algae meadows are supposed based on geochemical data. C Fragment of partly tectonically deformed phragmocone of undetermined aulacoceratid; scale bar equals 1 cm

Fig. 11 Detailed reconstruction of the sea-bottom rich in algae, sponges and crinoid meadows, showing also the common presence of conodonts and a representative of coleoid cephalopod. Petr Modlitba, with courtesy of author