Kawamura, Yoshinari

Taruno, Hiroyuki

Yoahikawa, Shusaku

Osaka City University Repository

Journal of Geosciences, Osaka City University
Vol. 50, Art. I, p. 1- 6, March, 2007
Land bridge formation and proboscidean immigration
into the Japanese Islands during the Quaternary
I~ 1~ flll ,~t ~~i
Shusaku YOSHIKAWAa, Yoshinari KAWAMURAb and Hiroyuki TARUNOc
rff~ ~1 ~~ '-1
a Department of Geosciences, Faculty of Science, Osaka City University, Osaka 558-8585, Japan.
b Department of Earth Sciences, Aichi University of Education, Kar'iya, Aichi Prefecture 448-8542,
Japan.
C Osaka Museum of Natural History, Osaka 546-0034, Japan.
Abstract
Two land bridge stages are inferred between the mainland of Japan and the adjacent continent
during the past one million years, on the basis of the detailed stratigraphy of the Quaternary sequence
in the mainland, its accurate correlation with the marine isotope stages (MIS) and with the ODP cores
in Japan Sea, and the proboscidean biostratigraphy in the sequence, The two land bridge stages are
placed at MIS 16 and MIS 12, which are indicated by the immigration of the proboscidean species
from the continent, Stegodon orientalis and Palaeoloxodon naumanni respectively. An additional land
bridge stage at MIS 36 is also suggested by the immigration of Mammuthus trogontherii.
Key-words: Land bridge, Immigration, Stegodon orientalis, Palaeoloxodon naumanni, Quaternary,
Japanese Islands
Introduction
The Japanese Islands are composed mainly of four
major islands (Hokkaido, Honshu, Shikoku, Kyushu) and
the Ryukyu Islands which are separ'ated from each other by
narrow straits with varying depths (Fig. 1). In the Japanese
Islands, three biogeographic regions have been recognized
since the latter part of the nineteenth century. They are
Hokkaido, the Honshu-Shikoku-Kyushu complex and the
Ryukyu Islands. The boundary between the first and
second regions runs through the Tsugaru Strait with the
maximum depth of ca. 130m (Blakiston's line). The
Tokara Strait, with the maximum depth of more than
500m, represents the boundary between the second and
third regions (Watase's line). Furthermore, the boundary
between the second region and the adjacent continent is
drawn through the Tsushima Strait with the maximum
depth of ca. 130m (Korean Strait line).
Since the dawn of the Japanese biogeography and
paleomammalogy, the questions as to when, where from
and how mammals migrated into the main part of Japan
(the Honshu-Shikoku-Kyushu complex in biogeographic
sense) have been of crucial interest. Recent advances in
stratigraphy and chronology, paleomammalogy and paleo-
oceanography throw a new light on these long-standing
questions.
Land bridge stages and proboscidean
immigrations
In the Honshu-Shikoku-Kyushu complex, fluvio-
lacustrine and marine sequences covering all the periods of
the Quaternary are accurately dated by tephrostratigraphic
and magnetostratigraphic methods as well as other
chronological techniques. The sequences are best
investigated in the Osaka Plain (Itihara et al., 1997; Fig. I).
Recent studies have revealed that the sequence can be
closely correlated with the marine isotope stages (MIS),
and thus each horizon of the sequence can be dated
precisely (Fig. 2a, b). The marine clay beds numbered
2 Land bridge formation and proboscidean immigration into tile Japanese Islands during the Quaternary
OinrrItn·1
.... <:/- g t11t
...... /0. OUn/a·
J ............. Ins
I
1100 E
: ODP Site
: Mamiya Strait
(maximum depth: 18 m)
SS : Soya Strait (55 m)
TGS : Tsugaru Strait
(Blakiston's Line: 130 m)
TSS : Tsushima Strait
(Korean Strait Line: 130 m)
TKS : Tokara Strait
(Watase's Line: 500 m +)
Fig. I Map of east Asia showing the locations of the places related to this paper. Bathymetric contours are in meters.
Mal to Mal 3 (Fig. 2b) yielding warmth-loving floras are
coincident with high stands of sea level, and therefore
denoted by odd-numbed MIS. The fluvio-Iacustrine mud,
sand and gravel interposed between the marine clay beds,
yielding cold-loving floras are coneJated with low stands
of sea level, and therefore denoted by even-numbered MIS
(Itihara et at., 1997; Yoshikawa and Mitamura, 1999).
On the other hand, proboscidean fossils are obtained
successi vely in the sequence, and the stratigraphic range of
each proboscidean form has been determined (Kamei et at.,
1988; Kawamura, 1998; Taruno, 1999 ) (Fig. 2b).
Furthermore, systematic studies of the fossi I proboscideans
have revealed whether each form was an immigrant from
the continent or arose locally in the region. The first
appearances in the Honshu-Shikoku-Kyushu complex of
the species conspecific or closely related to continental
species are indicative of their immigration from the
continent, and probably suggest the land bridge formation
which allowed their immigration (Kawamura, 1998;
Konishi and Yoshikawa, 1999).
Stegodon aurorae, a small specialized endemic
stegodontid, first appeared around 2.6 Ma (million years
ago) and persisted until 0.7 Ma in and around the Osaka
Plain. This species probably arose in this region from S.
miensis or S. shinshuensis, an early Pliocene large
stegodontid in Japan closely related to the Chinese species,
S. zdanskyi. Subsequently, the primitive mammoth
Mammuthus trogontherii appeared around 1.2 Ma (MIS
35). The remains of this species from Japan were called
Paretephas protomammonteus, P. proximus, Archidiskodon
paramammonteus, M. shigensis and so on, by previous
authors (see Kawamura et at., 2007; Taruno and
Kawamura, 2007). This species is also recorded in northern
China between 1.66 Ma and 1.1 Ma (Wei et at., 2006). Its
appearance in the Osaka Plain suggests its immigration
through a land bridge that formed between China and this
region. The timing of the land bridge formation is inferred
to be the even-numbered MIS just prior to MIS 35,
possibly MIS 36, but the paleontological and stratigraphic
data are relatively insufficient around this horizon.
Shusaku YOSHIKAWA, Yoshinari KAWAMURA and Hirayuki TARUNO 3
Oxygenation
level
An Ox
OOP Site 797
(d)
Eu: Euxinic condition
Ox: Oxic condition
An: Non-euxinic
anoxic condition
_ dark layer
_ faintly-dark layer
c=:=J light layer
Litho-
stratigraphy
I
..c
15.
(J)
Cl
(c)
base Jaramillo
Mls12-Land Bridge
MIS14-------....
MIS8_ Aso-1 tephra
(255 ka)
-MIS10-----__.
-MIS6--------...
- MIS36- (Land Bridge)
---'II~-'--I--MIS18-------1.._'
---::1--_+__+- top Jaramillo
-~-+--+--base Brunhes---tl""--r--l-~ "...----
Proboscidean
range
-
marine clay
c=:=J
fluvio-Iacustrine
mud, sand and gravel
t
(b)
1--.......-01.-------1--- Aso-4 tephra
(88 ka)
12 ~(I)
11 £
c::
0
0>
10 e ::
--(1)
~ ~
9 ~ ..c:: eC::--:5-:J
8
c:: E ctl
ctl E c::E_-
ctl - o:J "0
7 ~ ~ &
6 c:: ~0 ~ ~"05 o -~-.E!
o c::
4 O-.~(1) L:::
ctl 0
3 cu c::[;L 0
"0
0
0>
~
~
Osaka Plain
Litho-
stratigraphy
0 180 (%0)
5.0 4.0 3.0
-=::::::----==----I--I--r-- I~·.,-_..__-----I-MIS2-------t
39
41
43
45
47
49
co
E
~I--......-tf------=-~....:::..:.-............-t-
::J
ro
~
(a)
(/)
Q.)
.c
c
::J
05
0.5
1.5
1.0
Age
(Ma)
0.0
Fig. 2 Stratigraphic data sets. (a) 0 180 record (Imbrie et ai., 1984) for the SPECMAP stack for the interval 0-0.62
Ma(Schackleton et ai., 1990) and ODP Site 677 for the interval 0.62-2.0 Ma (Schackleton, 1995). Numbers show
odd-numbered MIS. (b) Quaternary stratigraphy of the Osaka Plain (Itihara et al., 1997; Yoshikawa and Mitamura,
1999). Correlations with the oxygen isotope record are based on a combination of litho-, bio-, magneto- and tephro-
stratigraphy (Itihal"a et al., 1997; Yoshikawa and Mitamura, 1999; Biswas et ai., 1999). Twenty marine clay beds
(numbers in the column represent principal marine clay beds), which are characterized by wal-m-temperate and high
ea-Ievel conditions, were deposited during interglacial periods from MIS 37 to MIS 1. In the range chart, black
circles indicate proboscidean fossil occurrence. (c) Important mal-ker horizons of oxygen i otope-, magneto- and
tephra-stratigraphy. Aso-l and Aso-4 tephras are well-dated widespread tephras in the Japanese Pleistocene
(Machida, 1999). (d) Lithostratigraphy and the bottom water oxygenation level of Quaternary ediment in Japan Sea
(Tada et ai., 1992). Bottom water oxygenation conditions are estimated from the sedimentary structures and the ratios
of organic carbon content to total sulfur content. Thick dal-k layers representing euxinic condition were deposited
during glacial low stand periods (Oba et ai., 1991; Tada et ai., 1992).
4 Land bridge formation and proboscidean immigration into the Japanese Islands during the Quaternary
J
~ Palaeoloxodon naumanni
~IS12; 0.43 Ma I
- ...~ Stegodon orientalis
. ,
MIS16; 0.63 Ma ,
400 N /
o Pa/ae%xodon naumanni
• Pa/ae%xodon spp.
(ancestral or related
forms to P naumanni)
• Stegodon orienta/is
and related forms
Fig. 3 Routes and ages of the proboscidean immigrations. The distribution of principal proboscidean fossil localities, are
also shown. Stipping indicates the inferred land area during the land bridge stages (MIS 16 and 12).
At MIS 15, the mammoth was replaced in the Osaka
Plain by Slegodon orientalis, a medium-sized stegodontid
species well known from the Middle and Late Pleistocene
of southern China. Its appearance at this time suggests the
land bridge formation between this region and China just
prior to MIS 15, namely MIS 16. This species was again
replaced by the Naumann's elephant, Palaeoloxodon
naumanni, which is regarded as an immigrant from
northern China. Its appearance in the Osaka Plain at MIS
II or somewhat later (Fig. 2b), is suggestive of a land
bridge existing between the region and China just prior to
MIS 11, namely MIS 12. Moreover, the land bridge was
possibly present at this time between the region and
Hokkaido, which was indicated by the occurrence of this
elephant from the Late Pleistocene of Hokkaido, and by its
absence from the continental areas adjacent to Hokkaido
(Kawamura, 1998; Konishi and Yoshikawa, 1999;
Kawamura and Taruno, 2000).
Among the land bridge stages inferred above, MIS 16
and 12 are considered to be the colder stages when their
continental glaciations were stronger than those during the
other even-numbered stages. Hence the sea levels at the
stages were significantly lower than those at the other
stages (Schackleton, 1987; Rohling el al., 1998). Recent
investigations of the ODP cores obtained in Japan Sea
(Tada et al., 1992; Tada and Irino, 1999) indicate that the
dark layers indicative of euxinic condition of deep sea
water are better developed at the horizons correlative with
MIS 16 and 12, which resulted from the closed conditions
of Japan Sea (Fig. 2d). Such euxinic conditions suggest a
land bridge formation between the Honshu-Shikoku-
Kyushu complex and the adjacent continent, which
Shusaku YOSHIKAWA, Yoshinari KAWAMURA and Hiroyuki TARUNO 5
blocked the influx of the Tsushima Current.
Conclusion
This paper deals with the estimation of the
immigration ages of such proboscidean species as
Mammuthus trogontherii, Stegodon orientalis and
Palaeoloxodon naumanni into the mainland of Japan, which
are conelative with the ages of the land bridge formation
between the mainland and the adjacent continent on the
basis of the stratigraphy of the Quaternary sequence in the
mainland and Japan Sea, and the proboscidean
biostratigraphy of the sequence. We concluded that S.
orientalis and P. naumanni immigrated into the mainland
Japan through the land bridges from the continent at MIS
16 (0.63 Ma) and MIS 12 (0.43 Ma), respectively (Fig. 3).
Acknowledgements
We thank Hisao Kumai (Department of Geosciences,
Faculty of Science, Osaka City University), and Jin
Changzhu (Institute of Vertebrate Paleontology and
Paleoanthropology, Chinese Academy of Sciences) for
many useful comments and discussions. This study has
been partly supported by the Grant-in-Aid from the Japan
Society of Promotion of Sciences (project nos. 1385400 J
and 14390027).
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