Haploceras tithonium ( Oppel, 1865 )

Vašíček, Zdeněk & Skupien, Petr, 2025, Revision of haploceratid ammonoids from the Štramberk Limestone, Jurassic-Cretaceous boundary beds (Outer Western Carpathians), Acta Palaeontologica Polonica 70 (3), pp. 421-441 : 432

Haploceras tithonium ( Oppel, 1865)

Figs. 3C , 4C , 8E, F.

1865 Ammonites tithonius Opp. ; Oppel 1865: 549.

1868 Ammonites tithonius Opp. ; Zittel 1868: 82, pl. 14: 1a, b (lectotype), 2a–c, 3a, b.

1953 Haploceras tithonium Opp. ; Slavin 1953: 53, pl. 3: 11, 12, text-fig. 4

1978 Haploceras tithonium (Opp.) ; Olóriz Sáez 1978: 20, pl. 1: 4a, b, 5.

1988 Haploceras (Haploceras) tithonium (Oppel) ; Főzy 1988: 53, text-fig. 8.

2020 Haploceras tithonium (Zittel) ; Sarti 2020: 90, pl. 4: 2A, B.

2024 Haploceras tithonium (Zittel) ; Sarti 2024: 90, pl. 4: 2A, B.

Type material: Lectotype (established herein) SNSB-BSPG AS III 797

from Hohenegger collection in Munich, originally figured by Zittel

1868: pl. 14: 1) as Ammonites tithonius Oppel.

Type locality: Štramberk Limestone , Castle Hill in Štramberk, Czech

Republic.

Type horizon: Tithonian or lower Berriasian .

Material. — Three specimens present in the Hohenegger collection in Munich ( SNSB-BSPG AS III 797–799) and four favourably preserved specimens, partly preserved as steinkerns, partly as external moulds, or with a recrystallized original shell ( PL5061 , PL5113, PL5115, Z2761) .

Description. —Specimens of small- to medium-sized, semi-involute, with high, medium-broad whorls and with a narrow umbilicus. The flanks of the whorl are slightly arched. They reach the greatest breadth at approximately one-third of the whorl height. From this height, the flanks slope gradually to the umbilicus. Near the umbilicus, a rather sharp transition to the steeper part of the whorl declining to the line of coiling is observed. Near the venter, the flanks of the whorl are separated unclearly from the venter. The venter is slightly arched and medium-broad.

Our specimens appear to be smooth or, rarely, very thin indistinct ribbing is observed.

Remarks.—The remains of weak, dense ribbing are clear in the area around the line of coiling in Zittel’s (1868: pl. 14: 1a) specimen SNSB-BSPG AS III 797, desinated here as lectotype.

In the juvenile specimen PL5061, three lobes (E, A, U 2) are favourably preserved. In specimen PL5113, part of the outer suture line is preserved with the external lobe, adjacent saddle E/ A and part of the adventive lobe. The preserved part is essentially identical to the suture line of Ha. elimatum . A more completle external suture of Ha. tithonium is also illustrated by Slavin (1953: text-fig. 4).

Measurements. —The lectotype: D = 61.0 mm has H /D = 0.565, U /D = 0.13, B /D = 0.38. Eight specimens under study have sizes from 25 to 55 mm in diameter. The other six specimens under study range 21.6 to 54.2 mm in diameter. Their parameters are as follows: H /D = 0.51–0.56, U /D = 0.13–0.19, B /D = 0.35–0.38 ( SOM 4). In Z2761, the phragmocone ends at a diameter D = 42 mm.

Remarks.—The flanks of the whorl of the specimen illustrated by Zittel (1868: pl. 14: 2a, b) are not as flat in cross-section as illustrated in Zittel’s fig. 2a. Haploceras tithonium is characterised—in contrast to other species in this genus—by a narrower umbilicus and a high and relatively slender whorl. Vígh (1984: 176, pl. 1: 1a, b) described Haploceras tithonium perumbilicatum as a new morphologically similar subspecies that differs from Ha. tithonium in having a smaller whorl height ( H /D = 0.44), broader umbilicus ( U /D = 0.23) and narrower whorl ( B /D = 0.32). It could, under the name Haploceras perumbilicatum , represent a dimorphic counterpart of Ha. tithonium . With regard to the sizes of both taxa, however, it is not possible to determine which of them is a macroconch and which is a macroconch.

Stratigraphic and geographic range.—Data on the stratigraphic position of Ha. tithonium are relatively scarce. Enay and Cecca (1986) state the uppermost lower Tithonian from Spain, and Főzy (1988), the upper Tithonian from Hungary. According to Slavin (1953), Ha. tithonium occurs abundantly in the Upper Jurassic of the Ukrainian Carpathians.

Our dated collection from the Štramberk Limestone in the Kotouč Quarry on Level 6 corresponds to the basal upper part of the lower Tithonian. The specimens described by Zittel (1868) come from Štramberk Limestone of the currently abandoned quarry below Castle Hill in Štramberk.

Genus Hypolissoceras Breistroffer, 1947

Type species: Ammonites carachtheis Zejszner, 1846 (pl. 4: 1) by monotypy. Tatra Mountains in Poland, probably lower Tithonian .

Remarks. —The genus is characterised in particular by a series of short, small ribs (crenulations) limited to the venter of adult specimens.

Figures

Fig. 3. Whorl sections of haploceratid ammonoids from Štramberk, Czech Republic, Tithonian–lower Berriasian. A. Haploceras elimatum (Oppel, 1865), SNSB-BSPG AS III 800 (Zittel 1868: pl. 13: 1a) at H = 33 mm. B. Haploceras staszycii(Zejszner,1846),SNSB-BSPGASIII 805 (Zittel 1870: pl. 27: 3a) at H = 37 mm. C. Haploceras tithonium (Oppel, 1865), SNSB- BSPG AS III 798 (Zittel 1868: pl. 14: 2a) at H = 25 mm. D. Hypolissoceras carachtheis (Zejszner, 1846), SNSB-BSPG AS III 47 (Zittel 1868: pl. 15: 1c) at H = 17 mm. E. Hypolissoceras woehleri (Oppel, 1865), MM 06 at H = 27 mm.

Fig. 4. Suture lines of haploceratid ammonoids from Štramberk, Czech Republic, Tithonian–lower Berriasian. A. Haploceras elimatum (Oppel, 1865).Almostcomplete outersuture line ofZ4224at H = 11.5mm.B. Haploceras staszycii (Zejszner, 1846). Substantial part of outer suture line of PL5061 (6th level, middle) at H = 14 mm. C. Haploceras tithonium (Oppel, 1865). Outer and adventive lobes with accompanying saddles of PL5113 at H = 15 mm. D. Hypolissoceras woehleri (Oppel,1865).Adventive lobe with parts of accompanying saddles of MM08 at H = 15 mm.A, adventive lobe; E, external lobe; U2, umbilical lobe.