Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan 237
Fishes of the order Gonorynchiformes have the slender body, large dorsal fin and
large pectoral fin below the dorsal fin. Anal fin base is shorter than the dorsal fin
base. The dorsal fin is large and the length of the dorsal fin base is longer than the
anal fin base in the order Gonorynchiformes. The large pelvic fin is situated below
the dorsal origin in the families Gonorynchidae and Kneriidae (Nelson, 1984). The
number of branched caudal fin rays is 17 (1,9,8,1) and one epural is present in the
order Gonorynchiformes. (Fujita, 1990).
The character of the position of the fins and the caudal skeleton of this species
indicates the relationship to the order Gonorynchiformes.
Faunal comparison
Faunal comparison in the Wakino Subgroup.
The present author recognized three different paleoichthyofaunas in the fishes of
the Wakino Subgroup. The first fauna are found in the First Formation (Wj) which
correlates to the Sengoku Formation. This fauna is constituted of Lepidotes macropterus
of the order Semionotiformes, Nipponamia satoi of the Amiiformes, Chuhsiungichthys
yanagidai of the Ichthyodectiformes, and Aokiichthys toriyamai, A. changae, A. otai, A.
uyenoi, A. praedorsalis, and A. sp. of the Osteoglossiformes. Among them, fishes of the
genus Aokiichthys of the order Osteoglossiformes are most abundant in numbers of
species and individuals. The individuals of L. macropterus, N. satoi and C. yanagidai
are quite few in number. The present author proposes to designate this fish fauna as
the Nipponamia-Aokiichthys fauna.
The second fish fauna is found in the Third Formation (W3) which correlates to
the Lower Wakamiya Formation. This fauna is composed of Paraleptolepis kikuchii
and P. elegans of the order and family incertae sedis, Chuhsiungichthys sp. of the
Ichthyodectiformes, and Wakinoichthys aokii and W. robustus of the Osteoglossiformes.
Fishes of the genus Paraleptolepis and Wakinoichthys are abundant in numbers of species
and individuals. The osteoglossiform fishes, W. aokii and W. robustus are different
from the osteoglossiform fishes of the Nipponamia-Aokiichthys fauna. The present
author proposes to designate this fish fauna as the Paraleptolepis-Wakinoichthys fauna.
The third fauna is found in the Fourth Formation (W4) which correlates to the
Upper Wakamiya Formation. This fish fauna is composed of Chuhsiungichthys japon
icus of the order Ichthyodectiformes, Yungkangichthys macrodon and Wakinoichthys aokii of
the Osteoglossiformes, and Diplomystus primotinus, D. kokuraensis, D. altisomus and D.
sp. of the Clupeiformes. Fishes of the genus Diplomystus are most abundant in
number of species and individuals. Individuals of Chuhsiungichthys and Yungkangich
thys are few in number. Wakinoichthys aokii is the second most abundant in this fauna.
The present author proposes to designate this fish fauna as the Diplomystus-
Wakinoichthys fauna.
Fish faunas of the Wakino Subgroup are composed of the primitive halecostome