Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

Early Cretaceous Freshwater Fisli Fauna in Kyushu, Japan 127
exposed dorsal surface of the head region. The premaxilla is attached to the
neurocranium having 4 large canine like teeth.
The lower jaw is narrow at the anterior half and the depth rapidly increase at
the posterior one third. Three canine like teeth are visible on the anterior part of the
dentary. The premaxillary teeth arc larger than the dentary teeth. A boundary
line between the dentary, anglo-articular and supraangular is indistinct. A suture of
each bone on the neurocranium is obscure. The interorbital space is narrow.
About half of the gular plate is preserved and the whole shape can be restored. The
gular plate is nearly rhombic in ventral view (Fig. 8).
The right hyomandibular is preserved. The part between the condyle of
hyomandibular for the neurocranium and the opercular process is narrow and deeply
concave in V-shapc. The ventral end of the hyomandibular is divided into two
parts. The metapterygoid is thin and rounded at the lower part. The upper part of
the metapterygoid is not visible, because it is under the neurocranium. The
quadrate is thick. The second extrascapular is long with the cephalic division of
main lateral line. The ecratohyal is long and cylindrical with 8 or more branchiostegals.
The shoulder girdle is obscure. A pair of pectoral fins are preserved
and have 11 or 12 fin rays respectively.
Most part of the dorsal fin is missing, but the anterior and the posterior end is
definable (Fig. 10). The dorsal fin base is long. The dorsal origin is above the 16th
vertebra and the end of dorsal fin base is above the 45th vertebra (Fig. 10). The
caudal fm is rounded. The total number of the centrum (include ural centrum) is
75. The neural and haemal spines of the caudal vertebrae are alternately present.
The length of vertebral centra is shorter than the depth. The ural centra arc slightly
curved upward (Fig. 9).
Fig. 12. A lateral view of the head of Sinamia zdanskyi Stensio, 1937. From Stensio, 1937.