We report a new discovery of Heterodontiformes shark teeth from the Upper Cretaceous of Kashima Formation（Santonian）of Hokkaido. They are identified as the anterior teeth of Heterodontus cf. carerens and Heterodontus sp. This discovery is the first record of anterior tooth of the genus Heterodontus from the Upper Cretaceous in the northwestern Pacific region. Species belonging to the genus Heterodontus are roughly classified into morphotype 1 and morphotype 2, with H. cf. carerens included in morphotype 2 and H. sp. included in morphotype 1.

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 Four elephantid fossil bones including the first lumber vertebra and two ribs, one fossil shell and one fossil wood fragment were investigated. These fossils have been stored in Akita Prefectural Museum since 2017. According to the fossil finder, they were collected from the waste soil in the construction site prior to the official excavation of the “Hamacho specimen” of Palaeoloxodon naumanni (Elephantinae), which was conducted in 1976 at a subway construction site 22 m below ground level near Hamacho 2-chome, Nihonbashi, Chuo-ku, Tokyo.  Comparing with the “Hamacho specimen” which has been stored in Hachioji City, the size and the state of preservation was equal, and also the first lumbar vertebra were well articulated with the 20th thoracic and the 2nd lumbar vertebrae of the “Hamacho specimen”. These results indicated that these fossil bones were parts of a skeleton of “Hamacho specimen”.  The pollen analysis of the sediment left inside the fossil shell (Saxidomus purpurata), even though the amount of extracted pollen was low, showed that the environment at the time was estimated to be an intermediate-temperate forests, in which deciduous broad-leaved trees with temperate coniferous trees such as Abies and Tsuga grow around wetlands and rivers. The fossil wood was identified as genus Celtis (Family Cannabaceae) based on the microscopic structure. This vegetation is consistent with the habitat of the P. naumanni, which has been reported previously.  On the other hand, the horizon of the “Hamacho specimen” has been considered to be the Upper Tokyo Formation, since the underlying continuous sand and gravel layer with a thickness of more than 5m was regarded as the Tokyo gravel Formation, and the alluviums were deposited immediately above it. However, recent studies reported that the gravel beds also exist under the Upper Tokyo Formation, not only at the bottom of that. This suggests that the horizon of the “Hamacho specimen” should be re-examined in the future.

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 Although many restoration figures of Basilosaurus have been drawn, the body shape is various and there is no study indicating the theoretical basis for restoration. The flukes in previous works are crescent-shaped same as those of living whales, not suitable for the body shape of Basilosaurus. The main subject of the present study is a suggestion of new life restoration with a different-shaped fluke based on new method for restoration. Life restoration is more difficult than skeletal reconstruction, because soft tissues like skin, subcutaneous tissues, and sense organs are not preserved as fossils. But aquatic body outline is correlated with the swimming pattern, so this correlation can be utilized. The fluke shape cannot be restored directly from skeletal characteristics, so a swimming pattern which matches the body shape was presumed, and then the fluke shape most suitable for the swimming pattern was considered. As a result, it is concluded that Basilosaurus, which had anguilliform body shape and anguilliform swimming pattern, had a rhombic fluke long along the sides of the body.

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