Friday 6 June 2014

A fossil Filefish from the Middle Miocene of Nagano Prefecture in central Japan.

Filefish (Monacanthidae) are  Tetraodontiform Fish related to Triggerfish, Pufferfish and Trunkfish. They are found throughout shallow tropical and temperate waters in the Atlantic, Pacific and Indian Oceans. They get their name from their rough skins which was supposedly once used for finishing surfaces by by boatmakers. Despite being a widely distributed and specious group, they have a relatively short fossil record, with the oldest known specimens coming from the Miocene of North America, with later specimens being known from the Pliocene of North America, Italy and Greece, and the Pleistocene of Italy.

In a paper published in the journal Zootaxa on 10 April 2014, Yusuke Miyajima of Department of Geology and Mineralogy at Kyoto University, Fumio Ohe of Harayamadai in Seto City, Hakuichi Koike of the Shinshushinmachi Fossil Museum and Hiroshige Matsouka, also of the Department of Geology and Mineralogy at Kyoto University, describe a fossil Filefish from the in an outcrop of the Tazawa black mudstone Member of the Bessho Formation in the riverbed of the Hofukuji River at Sorimachi in Matsumoto City, Nagano Prefecture, central Japan. This locality has previously produced a variety of Fish fossils, as well as Molluscs (Scallops and Argonauts), Goose Barnacles and a Sperm Whale.

The specimen is placed in the extant genus Aluterus, which contains four living species found in tropical and temperate waters at depths of as great as 150 m. These are widely distributed across the globe, including in the waters off Japan. It is given the specific name shigensis, meaning ‘from Shiga’ the specimen being found close to the village of Shiga-Mura. It is preserved as a partial axial skeleton, lacking the head or pelvic girdle, as part and counterpart on a split slab of black siltstone.

Aluterus shigensis from the Bessho Formation at Sorimachi, Matsumoto City, Nagano prefecture. Photograph (A) and drawing (B) of the part of the specimen. Abbreviations: 1DBP, basal pterygiophore of the spiny dorsal fin; 2DP, pterygiophore of the soft dorsal fin; 2DP1, first pterygiophore of the soft dorsal fin; AF, anal-fin ray; AV1-7, first-seventh abdominal vertebrae; CF, caudal fin; C–H, compound terminal centrum; CV1-13, first-thirteenth caudal vertebrae; DS I, first dorsal spine; DS II, second dorsal spine; HS, haemal spine; LAF, last anal-fin ray; NS, neural spine; PH, parhypural. l shows the length of skeleton from second abdominal vertebra to caudal-fin base. Dotted area anterior to caudal fin shows the preservation of scales. Scale bars are 50 mm. Miyajima et al. (2014).

Aluterus shigensis. Photograph (A) and drawing (B) of the counterpart of the specimen. Abbreviations: 2DF, soft dorsal-fin ray; 2DP2, second pterygiophore of the soft dorsal fin; 2DPX, pterygiophore of the soft dorsal fin between neural spines of the ninth and tenth caudal vertebrae; AP, pterygiophore of anal fin; AP1, first pterygiophore of anal fin; PP, parapophysis. Other abbreviations as in Figure 3. Dotted area shows the preservation of scales. Square shows the area observed using SEM in Figures 7A and 7B. Scale bars are 50 mm. Miyajima et al. (2014).

Aluterus shigensis closely resembles the extant Aluterus scriptus, which has a global distribution in tropical and subtropical waters, where it lives on reefs and in lagoons, and has been reported living in temperate waters in areas where warm current flows are present. The Bessho Formation is thought to have been laid down in temperate waters, but contains significant numbers of formaminifera from warmer zones, implying the input of warm currents. This suggests that Aluterus shigensis could have pursued a lifestyle essentially similar to that of the modern Aluterus scriptus, implying that Filefish were not only reasonably widely distributed by the Middle Miocene (Japan and North America), but that they were already living similar lives to the modern Fish.

Scanning electronic microscope images of scales of the fossil, Aluterus shigensis (A and B) and the modern Aluterus scriptus (C). Note the close resemblance of the shape and size of scales of the fossil to those of extant Aluterus species. Scale bars are 100 ╬╝m. Miyajima et al. (2014).

Soft radiograph of a dried specimen of Aluterus scriptus. Miyajima et al. (2014).

Reconstruction of Aluterus shigensis. Scale bar is 50 mm. Miyajima et al. (2014).

A living specimen of the extant Filefish Aluterus scriptus in Aquarium Paris. 

See also…

 A new species of Pufferfish form French Polynesia.

Pufferfish of the genus Canthigaster (Sharp Nosed Puffers or...

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