TELEOSTEI Müller, 1845

Miyata, Shinya, Isaji, Shinji, Kashiwagi, Kenji & Asai, Hidehiko, 2023, The first record of Lower Cretaceous otoliths from the Kimigahama Formation (Barremian) of the Choshi Group, Chiba Prefecture, Japan, Palaeontologia Electronica (a 20) 27 (1), pp. 1-23 : 5-7

Subdivision TELEOSTEI Müller, 1845 Teleostei fam., gen. et sp. indet.

( Figure 3 A-B)

Reference material. CBM (Natural History Museum and Institute, Chiba)–PV 8203 ( Figure 3A ) and six other otoliths

Description. The otoliths are thick, large, and approximately 3–5 mm length. The shape is nearly elliptical, the dorsal rim is straight, and the ventral and posterior rims are rounded. The interior side is convex. The dorsal margin of the posterior part of the rostral region is ventrally concave and slightly angulated. The margin is smooth and has no sculpturing. The sulcus is closed at the posterior end, and the ostium is open. The cauda is medial, straight, tubular, and elongated toward the posterior part. The anterior part of the rostrum is absent. The crista superior is present along the dorsal margin of the cauda, but the crista inferior is not recognizable.

Remarks. The present specimen is somewhat similar in the large and elliptical outline of sagitta with an elongated sulcus to that of Pterothrissinae such as Pteralbula galtina (see Schwarzhans, 2018, fig. 7E-G) or Pteralbula todolellana (Nolf, 2004, plate 2 fig. 1-6). However, the present specimen from the Barremian strata of the Kimigahama Formation exhibits a developed rostrum and straighter cauda. These characteristics distinguish it from typical Pterothrissinae . On the other hand, the specimen has a sulcus morphology that is like that of Argentinidae but differs from that of typical Argentinidae due to its larger size, reaching up to 5 mm, and lack of a pentagonal outer line.

The presence of Argentinidae and Pterothrissinae in the Valanginian strata of the Wawal claypit in Poland (Pindakiewicz et al., 2022) is consistent with the fact that these taxa are also present in the Barremian deposits of the Kimigahama Formation. Therefore, we suggest that the specimen represents either an Argentinidae or a Pterothrissinae . However, the specimen exhibits wear, making it challenging to definitively distinguish between the two groups. As a result, we provisionally assign it to Teleostei fam., gen. et sp. indet.

Superorder ELOPOMORPHA Müller, 1846

Order ALBULIFORMES Greenwood et al., 1966

Family ALBULIDAE Bleeker, 1859

Subfamily PTEROTHRISSINAE Greenwood, 1977 Pterothrissinae gen. et sp. indet.

( Figure 3 C-E)

Reference material. CBM–PV 8205 ( Figure 3C ) and 82 other otoliths

Description. The otoliths are thick, small, and approximately 1 mm length. The shape is nearly elliptical, the dorsal rim is almost straight, and the ventral and posterior rims are rounded. The external surface is convex. The ostial region is funnel-shaped, and the rostrum is slightly peaked. The sulcus is closed at the posterior end, and the anterior opening is ostial. The cauda is medial, straight, and elongated toward the posterior part. The crista superior and crista inferior are developed along the dorsal and ventral margins of the cauda. The dorsal depression is present above the crista superior.

Remarks. The present specimens are characterized by their thickness, a slightly pointed trostrum, a rounded outline, and a cauda that does not extend to the posterior rim. It is like the small otolith of the Pteralbula galtina (Koken, 1891) of the Albian Folkstone Gault, England, which is an otolith-based species (Stinton, 1973; Schwarzhans, 2018). However, the present specimen is smaller (approximately 1 mm), and the external side is convex.

Otoliths of Pterothrissinae typically exceed 1 cm (e.g., Schwarzhans and Stringer, 2020; Schwarzhan and Jagt, 2021; Schwarzhans et al., 2022; Stringer and Sloan, 2023). Therefore, the otoliths of Pterothrissinae in the Kimigahama Formation may be juvenile fishes. The known Early Cretaceous Pterothrissinae species include Pteralbula galtina , P. cantina , P. todolellana , P. polonica , and Elopothrissus pawpawensis (Shepherd, 1916; Stinton, 1973; Nolf, 2004; Schwarzhans et al., 2022; Pindakiewicz et al., 2022; see Table 3). In the Early Cretaceous, Nolf (2004) described fossil otoliths of Pterothrissinae approximately 1 mm in length as the “genus Pterothrissidarum” sp. According to his study, it remains to be determined whether “genus Pterothrissidarum” sp. represents an individual variation of P. todolellana or a member of another species. Even in our otoliths of Pterothrissinae , it is challenging to determine whether these otoliths to a previously described species or a new species of Cretaceous Pterothrissinae . Therefore, in this study, otoliths of juvenile Pterothrissinae from the Kimigahama Formation were assigned to Pterothrissinae gen. et sp. indet.

Figures

FIGURE 3. Otoliths from the Kimigahama Formation (Barremian) in Chiba Prefecture, Japan. 3A-B: Teleostei fam., gen. et sp. indet. A. CBM (Natural History Museum and Institute, Chiba)–PV 8203. A1) Dorsal view. A2) Line drawing of A1. A3) Inside view. A4) Line drawing of A3. B. CBM–PV 8204. B1) Dorsal view. B2) Inside view. C-E: Pterothrissinae gen. et sp. indet. C. CBM–PV 8205. C1) Dorsal view. C2) Line drawing of C1. C3) Inside view. C4) Line drawing of C3. D. CBM–PV 8324. D1) Dorsal view. D2 Inside view. E. CBM–PV 8325. E1) Dorsal view. E2) Inside view.Scale bar = 1 mm