Kokuraichthys tokuriki n. gen. and sp., Early Cretaceous osteoglossomorph fish in Kyushu, Japan.

Abstract

Kokuraichthys tokuriki is described from the Early Cretaceous Dobaru Formation of the Wakino Subgroup, Kitakyushu in the northern part of Kyushu, Japan, as a new genus and species of Osteoglossomorpha. This new species is considered to be more closely related to Hiodontiformes or Lycopteriformes than Osteoglossiformes because it has a single epural and no neural spine on the first ural centrum. Although it has significantly fewer vertebrae (36 or 37), K. tokuriki is tentatively assigned to Hiodontiformes because of the long anal fin base, the anterior position of the dorsal fin and the reduced neural spine on the first preural centrum.

Full text

New osteoglossomorph sh from Early Cretaceous in Kyushu, Japan 67Bull. Kitakyushu Mus. Nat. Hist. Hum. Hist., Ser. A, 11: 67–72, March 31, 2013
Kokuraichthys tokuriki n. gen. and sp., Early Cretaceous osteoglossomorph fish in
Kyushu, Japan
Yoshitaka Yabumoto
Kitakyushu Museum of Natural History and Human History, 2-4-1 Higashida,
Yahatahigashi-ku, Kitakyushu 805-0071, Japan
e-mail: yabumoto@kmnh.jp
(Received December 7, 2013; accepted March 18, 2013)
ABSTRACT
— Kokuraichthys tokuriki is described from the Early Cretaceous Dobaru Formation of the Wakino
Subgroup, Kitakyushu in the northern part of Kyushu, Japan, as a new genus and species of Osteoglossomorpha.
This new species is considered to be more closely related to Hiodontiformes or Lycopteriformes than
Osteoglossiformes because it has a single epural and no neural spine on the first ural centrum. Although it has
signicantly fewer vertebrae (36 or 37), K. tokuriki is tentatively assigned to Hiodontiformes because of the long
anal n base, the anterior position of the dorsal n and the reduced neural spine on the rst preural centrum.
KEY WORDS
: Early Cretaceous, Hiodontiformes, Japan, Kyushu, Osteoglossomorpha, Wakino Subgroup
INTRODUCTION
The Early Cretaceous lacustrine beds forming the Wakino
Subgroup of the Kanmon Group are distributed in the northern
part of Kyushu, Japan (M
atsumoto, 1951). The type locality of
the Wakino Subgroup is Miyawaka, Wakamiya City, Fukuoka
Prefecture. The Wakino Subgroup consists of the Sengoku,
Nyoraida, Lower Wakamiya and Upper Wakamiya formations
in ascending order, from where many mollusks have been found
(O
ta 1953, 1960). The equivalent of the Wakino Subgroup
is distributed in Kitakyushu City (O
ta, 1955, 1957, 1959).
Nineteen species of freshwater fishes in eight genera and six
families have been described from the subgroup in Kitakyushu
(U
yeno, 1979, Yabumoto, 1994). In the present paper, a new
osteoglossomorph sh from the Wakino Subgroup is described.
LOCALITY AND HORIZON
The fossil described herein was found from the Dobaru
Formation of the Wakino Subgroup in Tokuriki, Kokuraminami
ward, Kitakyushu, Fukuoka Prefecture, Japan. The Dobaru
Formation is the lowest formation in the subgroup, which
consists of the Dobaru, Takatsuo, Gamo, and Kumagai for-
mations in ascending order (N
akae et al., 1988). The age of the
formations have been considered as the Early Cretaceous, Valan-
ginian to Barremian (O
ta, 1981, Matsumoto et al., 1982). The
fossil fish assemblage from the Dobaru Formation is recog-
nized as the Nipponamia - Aokiichthys fauna (Y
abumoto, 1994),
which consists of Lepidotes macropterus, Nipponamia satoi,
Chuhsiungichthys yanagidai, and ve species of the genus Aoki-
ichthys.
METHODS
Preparation. —Any bone was removed from the specimens
with a needle under a microscope. The bone impressions
of fossils were then coated with a very thin synthetic resin,
surrounded with a low clay wall. Latex was poured onto the
fossil impression in a vacuum. The latex was allowed to dry for
about an hour and then peeled from the fossil. The latex cast was
scanned and the caudal part was drawn on a personal computer.
Both the specimen and the latex peel were observed under a
microscope.
Counts and Measurements. —Standard length measurement
was made from the estimated tip of the snout to the posterior
end of the hypural along the midline of the body. Body depth
was measured from the origin of the dorsal n to the estimated
abdominal margin. Head length was measured from the esti-
mated tip of the snout to the estimated posterior end of the opercle
along the midline of the body. Fin ray and vertebral counts
were made according to H
ilton (2002).
Osteological Terminology. —Names of bones follow H
ilton
(2002; 2003).

Yoshitaka yabumoto68
20 mm
Fig. 1
A
B
Fig
.
1.
Kokuraichthys tokuriki
gen. et sp. nov.,
A.
holotype, KMNH VP 100,326,
B.
drawing of A.

New osteoglossomorph sh from Early Cretaceous in Kyushu, Japan 69
PALEONTOLOGICAL DESCRIPTION
Osteoglossomorpha Greenwood et al., 1966
Order Hiodontiformes
Taverne, 1979
Kokuraichthys gen. nov.
Type species. Kokuraichthys tokuriki sp. nov.
Etymology. Kokura, old name of the district of the locality,
ichthys, sh in Greek.
Diagnosis. As for type species; monotypic.
Kokuraichthys tokuriki sp. nov.
Figs. 1–3.
Holotype. KMNH VP 100,326, left side exposed, almost com-
plete, excepting the antero-ventral part of the head. This is the
only known specimen of this new species.
Diagnosis. This new species is distinguished from other species
of Hiodontiformes and Lycopteriformes by the following combi-
nation of characters: long anal-n base about 3.2 times dorsal-
n base, 31 proximal anal-n pterygiophores, 36 or 37 preural
vertebrae.
Etymology. tokuriki after the locality of the type specimens.
Description of the holotype
The dorsal line from the snout to the origin of the dorsal
fin is moderately convex. The ventral edge of the abdomen is
strongly convex; the depth between the centra to the abdominal
margin is about 1.4 times the depth between the dorsal margin
and the centra. The dorsal-n base is short and located slightly
posterior from the middle of the body and anterior to the anal
n. There are nine proximal radials of the dorsal n. The anal-
fin base is very long and its origin is under the anterior end
of the dorsal-n base; the anal n has 31 proximal radials. The
basipterygium of the pelvic n is short and located slightly an-
terior under the dorsal-n origin. The pelvic n is located at the
middle of the body (Figs. 1 and 2).
The ribs are moved downward apart from the abdominal
vertebrae. The anteriormost three ribs are preserved close to
the shoulder girdle apart from the others. All ribs are long,
moderately curved and reached near to the ventral margin of
the abdomen. Fourteen pairs of ribs can be counted. The total
number of preural vertebrae is 36 or 37, with16 abdominal
vertebrae (estimated based on association with the ribs) and the
20 or 21 caudal vertebrae. The length of the centrum is shorter
than the depth. There are 16 supraneurals. The rst and second
supraneurals are short, whereas the length of the third and
Fig. 2
Fig. 2.
Kokuraichthys tokuriki
gen. et sp. nov., restoration of the skeleton.

Yoshitaka yabumoto70
fourth is almost the same or only slightly shorter than those of
the posterior ones, which are equal in length (Figs. 1 and 2).
The neural arch and spine on the first preural centrum
are not observed. Two ural centra and at least six hypurals are
observed (probably more hypurals hidden by the base of fin
rays). The first ural centrum is articulated with the first and
second hypurals. The second ural centrum is articulated with the
third to sixth hypurals. There is a diastema between the second
and third hypurals. Four strap-like uroneurals are located above
the ural centra and the preural centra, and do not cover widely
the lateral side of these bones. There is the fth uroneural that
is a short angled bone located on the base of the third to sixth
hypurals. The anterior ends of uroneurals reach the third preural
centrum. There is a single long epural. The caudal n is forked
and has probably 16 n rays (Fig. 3).
Remarks
Several characters observed in the caudal skeleton of the
new genus and species, Kokuraichthys tokuriki are considered
to be plesiomorphic for osteoglossomorphs and basal teleostean
shes. These are: 16 branched caudal n rays as in Lycoptera,
hiodontids and mormyrids (see H
ilton, 2003; Hilton and Britz,
2010); absence of the neural spine on the first ural centrum;
five pairs of uroneurals, including four strap-like ones as seen
in Lycoptera, Hiodontiformes, Ostrariostoma, Kuntulunia, and
Singida within Osteoglossomorpha (H
ilton and Britz, 2010);
two hypurals supported by the rst ural centum; probably four
hypurals supported by the second ural centrum; and the dorsal
hypurals do not fused to the second ural centum (H
ilton and
B
ritz, 2010). The presence of a single epural suggests that
K. tokuriki gen. et sp. nov. belongs to Osteoglossomorpha,
because it is considered a synapomorphy of the group (H
ilton
and B
ritz, 2010; Wi ls on and Mur ray, 2008). Two orders,
Osteoglossiformes and Hiodontiformes, are generally recognized
in Osteoglossomorpha (e. g. H
ilton and Britz, 2010). Nelson
(2006) accepted the order Lycopteriformes Chang and Chou,
1977 for Lycopteridae and includes the order Ichthyodectiformes
in Osteoglossomorpha. However, N
elson (2006) was unique
in including Ichthydectiformes in Osteoglossomorpha, as
P
atterson and Rosen (1977), Taverne (1979) and virtually all
subsequent authors have found that Ichthyodectiformes is basal
to crown teleosts (including Osteoglossomorpha). One of the
characteristics of Ichthyodectiformes is having the lateral side of
the ural centra and the preural centra covered by the uroneurals.
Kokuraichthys tokuriki gen. et sp. nov. therefore does not belong
to Ichthyodectiformes because the uroneurals do not cover the
lateral side of the ural centra and the preural centra (Fig. 3).
Kokuraichthys tokuriki gen. et sp. nov. dose not belong
to Osteoglossidae + Notopteridae, because it lacks one of the
synapomorphies of this group, having the neural spine on the
first ural centrum fully developed (H
ilton, 2003; Hilton and
B
ritz, 2010). Furthermore, it does not belong to the order
C
A
B
U1
H3
H2
H1
H6
UN5
UN1-4
EP
U2
PH
PU1
H1
H6
EP
UN5
U2
PH
U1
PU1
UN1-4
Fig. 3
Fig. 3.
Kokuraichthys tokuriki
gen.
et sp. nov., caudal region of the holotype, KMNH
VP 100,326.
A.
peel of the caudal region,
B.
drawing of A,
C.
reconstructed drawing
from B. Abbreviations: EP, epural; H1, first hypural; H2, second hypural; H3, third
hypural; H6, sixth hypural; PH, parhypural; PU1, rst preural centrum; U1, rst ural
centrum; U2, second uroneural; UN1-4, rst to fourth uroneurals; UN5, fth uroneural.

New osteoglossomorph sh from Early Cretaceous in Kyushu, Japan 71
Osteoglossiformes, because the absence of epural is regarded as
a synapomorphy of Osteoglossiformes (N
elson, 1969, Hilton,
2003, W
ilson and Murray, 2008). The neural spine on the
first preural centrum is not observed and is probably reduced.
This condition is seen in most specimens of extant Hiodon
(H
ilton, 2003; Hilton and Britz, 2010) but not in Lycoptera,
fossil Hiodon and other hiodontiformes such as Yanbiania L
i
1987, which have a full neural spine of the rst preural centrum
(P
atterson and Rosen, 1977; Hilton and Britz, 2010; Hilton
and G
rande, 2008).
In summary, Kokuraichthys tokuriki gen. et sp. nov. is
considered to be a member of Osteoglossomorpha, and it is
closer to Hiodontiformes or Lycopteriformes than Osteo-
glossiformes, but it differs from all other genera of Hidonti-
formes and Lycopteriformes in having the combination of the
following characters: fewer vertebrae (36 to 37 in Kokura-
ichthys, 34 to 36 in Aokiichthys, and more than 40 in other
genera); a long anal-n base (3 times the dorsal-n base in Kokura-
ichthys, 2 to 3 times in Hiodon, and almost the same or slightly
larger than the dorsal-fin base in other genera); and having
the dorsal n anterior to the anal n (it is also seen in Hiodon
tergisus L
esueur, 1818, H. woodruf (Wilson, 1978) and H. consteni-
orum L
i and Wilson, 1994). Kokuraichthys tokuriki may have
some relationship to Aokiichthys, which is from the same
formation and locality (the Dobaru Formation at Tokuriki), due to
similarity in the number of vertebrae. In the present study, K. tokuriki
is tentatively assigned to Hiodontiformes because it has the
long anal-n base, the position of the dorsal n anterior to the
anal n and the reduced neural spine on the rst preural centrum.
ACKNOWLEDGMENTS
The author is very grateful to Dr. Teruya Uyeno of National
Museum of Nature and Science, Tokyo and Dr. Eric J. H
ilton
of Virginia Institute of Marine Science for their review and
valuable comments. The author thanks Mr. Tateyu A
oki for
donation of the holotype.
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