Dicerobairdia buseri Forel, 2020

Forel, Marie-Béatrice, Kolar-Jurkovšek, Tea & Jurkovšek, Bogdan, 2020, Ostracods from the ‘ Raibl Beds’ (Carnian, Late Triassic) of Belca section in Karavanke Mountains, northwestern Slovenia, Geodiversitas 42 (21), pp. 377-407 : 384-386

Dicerobairdia buseri Forel , n. sp.

( Fig. 4 O-U)

urn:lsid:zoobank.org:act:6B59784E-073E-4D76-8C70-B3706E500C8A

TYPE MATERIAL. — Holotype: left valve( Fig. 4O ), BE18 (GeoZS6146). — Paratype: right valve ( Fig. 4S ), BE18 (GeoZS6150).

EXAMINED MATERIAL. — One carapace, nine left valves, ten right valves and several fragments.

DERIVATION OF NAME. — In honour of Prof. Dr. Stanko Buser (University of Ljubljana, Slovenia) for his outstanding contribution to the knowledge of the Slovenian geology.

OCCURRENCE. — Nicoraella ? budaensis conodont zone, late Julian-?earliest Tuvalian,Carnian,Late Triassic, samples BE2, 17, 18, 21 ( Fig. 3 ), Belca section, ‘Raibl Beds’, Karavanke Mountains, Slovenia (this work).

DIAGNOSIS. — A new species with reticulate lateral surface and poorly expressed dorso-lateral ornaments.

DIMENSIONS. — Fig. 5C.

DESCRIPTION

A large and relatively thick-shelled species with subrectangular outline in lateral view; greatest height located at the anterodorsal angulation at both valves, greatest length below mid-height; dorsal margin tripartite at both valves with anterodorsal angulation c. 30° and posterodorsal angulation c. 55°; anterodorsal border straight and long (from c. 28% of maximum of length in adult forms, Fig. 4Q , to c. 32% in younger instars, Fig. 4T ); dorsal border long and straight to gently convex (from c. 49% of maximum of length in adult forms, Fig. 4Q , to c. 53% in younger instars, Fig. 4T ); posterodorsal border steep and relatively short (c. 20% of maximum of length in adult and younger forms), close to straight in the youngest form, with a terminal concavity that accentuates through ontogeny; ventral border long (from c. 57% of maximum of length in adults, Fig. 4Q , to c. 48% in younger instars, Fig. 4T ), with oral concavity located in anterior part; posteroventral border about 1/3rd of maximum of height, very convex and bordered with marginal denticles visible at well preserved specimens (e.g., Fig. 4Q, R, U ); anteroventral border longer than posteroventral border, gently convex and flanged by marginal denticles visible at well preserved specimens; anterior maximum of curvature large and located around to slightly below mid-height; posterior maximum of convexity narrower, located below 1/3rd of maximum of height; anterodorsal, dorsal, posterodorsal and posteroventral borders and upper part of anteroventral border laterally compressed; anterior margin bordered by a large and low ridge in lower 2/3 rd, which then runs perpendicular to it and parallel to ventral margin, ending at the laterally compressed posteroventral area; two small elongate and reduced horns are built parallel to anterodorsal and posterodorsal borders at both valves; lateral surface evenly reticulate, with preferential longitudinal organisation of the reticulation visible at some specimens.

DISCUSSION

Dicerobairdia buseri Forel , n. sp. occurs from samples BE17 to BE 21 in the Belca section, and it is relatively abundant in BE18 ( Fig. 3 ). Dicerobairdia buseri Forel , n. sp. differs from D. torulosa Kristan-Tollmann, 1970 from the late Ladinian, Middle Triassic, of Dolomites, Italy (Kristan-Tollmann 1970) by lacking the small ventrolateral ridges at both valves and by the stronger development of the sub-anterodorsal and subposterodorsal horns at adult stage. The new species also differs from D. acornuta Kristan-Tollmann, 1978 from the early Carnian, Late Triassic, of Dolomites, Italy (Kristan-Tollmann 1978) by its subdorsal ornamentation at the right valve, which consists of sub-anterodorsal and sub-posterodorsal reduced horns rather than a continuous subdorsal ridge.At the left valve, the dorsal ornamentation of D. buseri Forel , n. sp. differs in being sub-anterodorsal and sub-posterodorsal elongate horns rather than a continuous ridge as in D. acornuta. Dicerobairdia buseri Forel , n. sp. also shows secondary reticulation all over the lateral surface whereas D. acornuta is micromammillate.

The specimens of Dicerobairdia buseri Forel , n. sp. from Belca section are distributed into at least four ontogenetic stages, from A-3 to Adult in ascending order ( Fig. 5C ). Noteworthy, left valves only occur in A-1 and Adult stages, while A-3 and A-2 stages are only known by right valves. The ontogenetic development of D. buseri Forel , n. sp. is marked by an overall increase in the length of the ventral border. The development from A-3 to A-1 is dominated by the increase of the dimensions. The transition from A-1 to Adult records the enhancement of the ventral ridge and the terminal concavity at posterodorsal border.

Figures

FIG. 4. — Ostracods from the Belca section, Karavanke Mountains, northwestern Slovenia, Carnian, Late Triassic. All specimens are deposited in the micropalaeontology collections of the Geological Survey of Slovenia, under the numbers GeoZS6132 to GeoZS6239, preceded by sample number: A, B, Acratia cf. goemeryi Kozur, 1970 emend. Forel et al. (2019a); A, lateral view of a right valve, BE21 (GeoZS6132); B, lateral view of a left valve, BE18 (GeoZS6133); C, Acratia sp. 1, lateral view of a broken left valve, BE18 (GeoZS6134); D, Acratia sp. 2, lateral view of a left valve, BE18 (GeoZS6135); E, Bairdia balatonica Méhes, 1911, lateral view of a left valve, BE17 (GeoZS6136); F-H, Bairdia cassiana (Reuss, 1869); F, lateral view of a right valve, BE18 (GeoZS6137); G, lateral view of a right valve, BE18 (GeoZS6138); H, right lateral view of a complete carapace, BE23/1 (GeoZS6139); I, Bairdia cf. perpusilla sensu Forel et al. (2019a), lateral view of a left valve, BE17 (GeoZS6140); J, Bairdia sp. 1, right lateral view of a complete carapace, BE18 (GeoZS6141); K, Bairdia sp. 2, lateral view of a right valve, BE23/1 (GeoZS6142); L, M, Bairdia sp. 3; L, lateral view of a left valve, BE18 (GeoZS6143);M, lateral view of a left valve, BE18 (GeoZS6144); N, Bairdiacypris sp. 1, lateral

FIG. 3. — Distribution of ostracod species through the Belca section, Karavanke Mountains, northwestern Slovenia.

FIG. 5. — Height/Length scatter plots of species recovered from the Belca section, Karavanke Mountains, northwestern Slovenia, Carnian, Late Triassic. In all diagrams, the dimensions of right and left valves of complete carapaces are linked. A, Bairdia balatonica Méhes, 1911; B, Bairdia cassiana (Reuss, 1869); C, Dicerobairdia buseri Forel, n. sp., all specimens are from the Belca section (this work); D, Mirabairdia longispinosa Kristan-Tollmann, 1978; E, Pontocypris? karavankensis Forel, n. sp. all specimens are from the Belca section (this work). Scale bars: 100 μm.