Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

238 Yoshitaka Yabumoto
orders Semionotiformes and Amiiformes, and the primitive teleostean orders
Ichthyodectiformes, Osteoglossiformes and Clupeiformes. The osteoglossiform fish
and clupeiform fish are most abundant in numbers of species and individuals.
There are nine species belonging to 3 genera and 2 families of the order Osteoglossi
formes, and 4 species belonging to the Clupeiformes. The present author proposes
to designate the entire fish fauna of the Wakino Subgroup as the Wakino fish fauna
(Tab. 7).
The Nipponamia-Aokiichthys fauna is entirely different from other fish faunas of the
Wakino Subgroup and it does not have any species in common with other faunas.
Only genus Chuhsiungichthys of the order Ichthyodectiformes is common to other
faunas, but the species is different (Fig. 96, Tab. 8).
The Paraleptolepis-Wakinoichthys fauna has a species, Wakinoichthys aokii, in com
mon with the Diplomystus-Wakinoichthys fauna. The Diplomystus-Wakinoichthys fauna is
similar to the Paraleptolepis-Wakinoichthys fauna except for Diplomystus and Paraleptolepis.
There is a possibility that Diplomystus originally came from the sea, for Diplomystus has
primitive characters in the predorsal scute, rounded anterior and posterior ends and
an unremarkable median crest of the predorsal scute, which suggest their origin in
the sea.
Comparison with Cretaceous freshwater fish faunas in China.
Chang and Chow (1986) roughly grouped fossil fishes from the Late Mesozoic
and Cenozoic in China into seven assemblages according to their composition and
distribution.
Among them, the fish fauna of the Wakino Subgroup resembles the Mesoclupea
assemblage (assemblage 2) from the Zhejiang, Anhui, Jiangxi, Fujian and other
provinces in southeastern China. There are several families and genera common to
both faunas. Four families, Semionotidae, Amiidae, Chuhsiungichthiidae and
Lycopteridae, and two genera, Lepidotes and Yungkangichthys are common to both
faunas. But the Hiodontidae, Ellimmichthiidae and Huashiidae of the Mesoclupea
assemblage are absent in the Wakino fish faunas. Two families, Wakinoichthiidae
and Clupeidae, of the Wakino Subgroup are not found in the Mesoclupea assemblage.
Among the Wakino fish faunas, the Nipponamia-Aokiichthys fauna is closest to the
Mesoclupea assemblage in the existence of fishes of the families Semionotidae and
Amiidae. Lepidotes macropterus is close to Neolepidotes yungkangensis and Sinolepidotus
chekiangensis Wei, 1976. Aokiichthys is close to Paralycoptera except for the number of
vertebrae. Nipponamia is related to Sinamia and Ikechaoamia. But the three families,
Hiodontidae, Ellimmichthiidae and Huashiidae, are absent in Nipponamia-Aokiichthys
fauna.
Ma and Sun (1988) separated the Early Cretaceous fish fauna in the Jiling and
Zhejiang Provinces of China into four faunas on the basis of their stage, composition
and distribution. These are the Lycoptera-Asiatolepis-Huashia fauna in the Jiling