Bulletin of the Mizunami Fossil Museum

Bulletin of the Mizunami Fossil Museum No. 4

Fish otoliths from the Dainichi sands are described and reported. Following genera are first reported in Japan; Neoscopelus, Hymenocephalus, ?Sciaena, Paralichthinae, Heteromycteris, Areliscus, Lophiida. In addition, Sardinops, Rhynchocymba, Uroconger, ?Conger, Diaphus, Lampanyctus, Coryphaenoididae, Sillago, ?Argyrosomus, Sciaenidae, ?Evynnis, Gobiidae, Soleidae.

It is presumed that the Kakegawa Sea at that time was subtropical, because most of shallow-sea fishes such as Sillago, Sciaena, live mainly in the subtropical regions.

From the lithofacies and the benthonic molluscan assemblage, the sedimentary environment of the Dainichi sands has been presumed to have been shallow sea. But various fish otoliths which indicate following environments co-occurred from it; deep-sea fishes at about 30%, shallow-sea 49%, shallow-sea–river-mouth 21%. These otoliths have been very well preserved, being little breakage. Moreover, above various otolitbs co-occurred from the same stratum, too.

Though there have been several reports of the co-occurrence of deep-sea and shallow-sea fish otoliths from Miocene series, this is first reported from Pliocene series in this paper.

The author presumes that it causes this co-occurrence that some fishes which live in the deep sea now lived in the shallow sea during Pliocene. However, it cannot ignore the fact that deep-sea fishes are occasionally driven into the shallow sea now. Judging from the pattem of growth lines preserved in fossil otoliths, it is presumed that some fishes, such as Diaphus, which live in the deep sea now lived in the somewhat shallower sea than recent during Pliocene, but that others, such as Hymenocephalus, did in the deep sea as recent. It needs further detailed geologic facts and more strict histological studies on fossil otoliths to clear up the cause of this co-occurrence.