BulL Kitakyushu Mus. Nat. Hist. Hum. Hist., Ser. A. 3: 135-143, March 31, 2005 Early Cretaceous freshwater fishes from the Tetori Group, central Japan Yoshitaka Yabumoto Kitakyushu Museum of Natural History and Human History, Yahatahigashiku, Kitakyushu, Fukuoka, 805-0071, Japan e-mail: yabumoto @kmnh.jp (Received September 10, 2004; accepted December I, 2004) ABSTRACT—Early Cretaceous freshwater fish fossils from the Kuwajima Formation of the Itoshiro Subgroup, Tetori Group described in detail for the first time are assigned to Lepidotes sp. (isolated scales), Sinamiidae (many isolated bones and scales), Pachycormidae (a dentary), Osteoglossiformes (a disarticulated skull with vertebrae and scales) and Teleostei (isolated scales). detail by Isaji et at. (2005). INTRODUCTION Two Early Cretaceous freshwater fish assemblages SYSTEMATIC DESCRIPTION have been found in Japan. These are the fossils from the Wakino Subgroup of the Kanmon Group of Kitakyushu Class Actinopterygii City in the northern part of Kyushu, and the Itoshiro Subclass Neopterygii Subgroup of the Tetori Group in Shiramine, Ishikawa Order Semionotiformes Prefectureand Shokawa, Gifu Prefecture in central Japan Family Semionotidae (Uyeno, 1979; Yabumoto, 1994; 2000). Genus Lepidotes Agassiz, 1839 Shokawa, Gifu Prefecture and Shiramine, Ishikawa Lepidotes sp. Prefecture (Figure 1) have yielded many fish fossil speci mens. The first fish fossil, a left lower jaw, was found in Figure 2 Kuwajima of Shiramine village in 1987, and was reported together with a few ganoid scales belonging to the Two scales (SBEI-818 and SBEI-1268) have been Semionotiformes, Holostei, Osteichthyes (Azuma and found. These scales have a thick cover layer of ganoin Hasegawa, 1989). Two sinamiid fishes recognized from that makes the exposed area of the scale smooth. The Shokawa were reported at the meeting of the exposed area is rectangular, and slightly deeper than long. Palaeontological Society of Japan (Yabumoto, 1997). The dorsal overlapped area exhibits a pointed process that Since 1997, many isolated fish scales and bones have been fit into the depression of similar shape at the ventral found in Kuwajima, Shiramine. In the present paper, the margin of the inner side of the scale dorsal to it, creating specimens from this locality are described in detail for the peg-and-socket articulation. The anterior overlapped first time. area shows two processes; the upper one extending antero- dorsally with a rounded end, and the lower one extending LOCALITY AND HORIZON anteriorly with an acute tip. There is a ridge on the inner surface from a point slightly below the middle of the All fish specimens described here have been found in anterior margin to the postero-ventral corner of the scale. Kuwajima, Shiramine, Ishikawa Prefecture, central Japan The thick ganoin covering and the dorsal and ante (Fig. I). The horizon is the Kuwajima Formation of the rior processes in the overlapped area of the scales are very Itoshiro Subgroup in the Tetori Group, and is from the similar to those of the genus Lepidotes, Semionotidae early Neocomian age. Depositional environments and (Woodward 1916-1919). Thus, the scalesare assignedto taphonomy ofthe Kuwajima Formation were described in the genus Lepidotes. This paper is one of those given at the Symposium of Early Cretaceous Terrestrial Biota held in the Kitakyushu Museum of Natural History and Human History on the 1st and 2nd of September in 2003. 136 Yoshitaka Yabumoto •igure 2. Scales of the genus Lepidotes from the Kuwajima Forma tion in Kuwajima. Ishikawa Prefecture. Japan, a. SBIZI-SIS: b. SBEI-1268. Scales indicate 5mm. anterior margin. This specimen is almost the same as the anterior part of SBEI-295. SBEI-014 is a left dentary. and the first fish fossil from the Tetori Group found in 1987. It has a deep coronoid process at the posterior portion, and its low. thick anterior part bears canine-like teeth curved inward. A series of pores opening from the mandibular canal run along the ventral margin of the dentary (Figure 3b). SBEI-1951 is a right dentary. Its anterior tip is missing. Posteriorly, the coronoid process is broken at the base, and bent inward. Anteriorly, there are canine like teeth curving inward. The estimated total number of Figure I. The locality of the Early Cretaceous freshwater fish fossils. teeth is 22 (14 preserved teeth and 18 sockets for missing teeth). The anterior tooth-bearing portion is moderately Order Amiiformes curved towards the symphysis (Figure 3c. d). Family Sinamiidae Two gular plates (SBEI-300 and SBEI-1208) have Genus Sinamia Stensio, 1935 been found. SBEI-1208 is almost complete only with its Sinamia sp. anterior tip missing. Its ventral surface is exposed, the anterior portion being narrower than its posterior portion. Figures 3 and 4 There is a very narrow groove in the middle of its anterior portion. The posterior portion is triangular with convex Most fish remains from Kuwajima can be referred to lateral margins, and a slightly concave, almost straight this taxon. There are all together 18 specimens of skull posterior margin (Figure 31*). SBEI-300 is less complete bones and 277 of detached scales. than SBEI-1208. lacking part of the posterolateral portion. Three specimens of maxilla (SBEI-295. SBEI-1860 It differs from SBEI-1208 in its wider anterior portion and and SBEI-2017) have been found. SBEI-295 is an almost shorter groove on the anterior portion, not reaching the complete left maxilla with only its posterior end missing; middle of the bone. There are many pits on the inner the bone gradually deepening posteriorly. The external surface of the bone of the latter (Figure 3e). surface is exposed. It has a relatively long and stout SBEI-817 is a right hyomandibular (Figure 3g) anterior articular process for the premaxilla. The large exposed in its lateral side. It is a hatchet-shaped bone canine-like teeth along the oral margin are strongly curved with a posterior process for articulation with the opcrcle. inward. Ornamentations on its lateral surface are in the The dorsal arm is slightly longer than the ventral arm. form of pits in the anterior and grooves in the posterior The foramen for the hyomandibular trunk (containing portions (Figure 3a). fibers from the facial and lateral line nerves) opens at the In SBEI-2017 only the middle portion of a left middle of the anterior margin of the dorsal arm. and the maxilla without teeth is preserved and looks the same as groove behind the foramen is located at the middle of the the middle part of SBEI-295. anterior margin of the bone. There is a nearly right angle SBEI-1860 is the anterior portion of a right maxilla. between the posterior margin of the ventral arm and the There are two pores on its inner face along the dorso- ventral margin of the process for articulation with the Cretaceous Fishes from Tetori Group. Japan 137 Figure 3. Fossils of the genus Sinamia from the Kuwajima Formation in Kuwajima. Ishikawa Prefecture. Japan, a. left maxilla. SBEI-295: b. left dentary. SBEI-014: c. dorsal view of left dentary. SBEI-295: d. outer view ofdentary. SBEI-I95I: e. gular plate. SBEI-1208: f. gular plate. SBEI-300; g. right hyomandibular. SBEl-817: h, right frontal, SBEI-823; i. cast of the left infraorbital, SBEI-1207; j. lea infraorbital, SBEI-1257. Scales of i and j indicate 2 mm. Other scales indicate 5 mm. 138 Yoshitaka Yabumoto opercle. The angle between the posterior margin of the margins of the ventral part are convex (Figure 4e). dorsal arm and the dorsal margin of the process for SBEI-317 is a left supracleithrum with only a small articulation with the opercle is slightly acute, but the axes dorsal portion of the bone preserved; most of the ventral of the dorsal arm and the process form an obtuse angle. portion being preserved as the impression of its inner face. The dorsal margin of the dorsal arm is convex. The proportion and shape are almost the same as those of SBEI-823 is a right frontal. Its dorsal surface is SBEI-315. A lateral line canal runs through the bone covered by an enamel layer. A series of pores opening from the dorsoanterior process to the pore opening on the from the supraorbital sensory canal are found on the inner surface at the point slightly above the middle of the dorsal surface of the bone. The suture for the dermo- posterior portion (Figure 4h). sphenotic is located just behind the shallow concavity of SBEI-301 is a left supracleithrum with its outer sur the orbit. The posterior margin of the frontal indicates face exposed. The enamel layer remains on the posterior that this species has a single parietal. The width of the and ventral portions of the outer surface. Its proportions anterior and posterior portions are almost the same. The are quite different from those of SBEI-315, -317. The suture with the left frontal is slightly undulate (Figure 3h). posterior margin is almost straight, and the anterior Two infraorbital (SBEI-I207 and SBEI-1257) bones margin, rather convex. The ventral margin is thin, and have been found. Specimen SBEI-1207 is an impression almost straight (Figure 4i). of a left infraorbital (probably the last one because of the SBEI-1192 is a left supracleithrum missing the ventral short length) (Figure 3i). Its dorsal portion bends slight part. The enamel layer remains on the postero-ventral ly inward. There are pits and grooves radiating from the part of the bone. Its posterior margin is almost straight point which is slightly above the middle of the anterior (Figure 4d). This specimen is similar to SBEI-301. margin of the bone. SBEI-1257 is a left infraorbital with a Many rhombic scales with a ganoin layer have been small posterior part missing (Figure 3j).