|JAPAN'S NEW MIDDLE PALAEOLITHIC RESEARCH|
Japanese Pleistocene Landbridges
|Home | Index||
by Charles T. Keally|
March 20, 2005
last revised: October 9, 2010
Today, Japan consists of four main islands and two major chains of small islands. The main islands from north to south are Hokkaido, Honshu, Shikoku and Kyushu. The island chains are the Nampo Shoto (Izu-Ogasawara) chain, extending from the Tokyo Bay-Izu Peninsula area to the Mariannas, and the Nansei Shoto extending from the southern end of Kyushu to Taiwan. The Nansei Shoto has two parts: the Satsuma group of islands in the north, and the Ryukyu group of islands in the middle and south. The Satsuma group (Tanegashima, Akushima, Amami Oshima) is part of Kagoshima Prefecture at the southern end of Kyushu. The Ryukyu group is Okinawa Prefecture, and it has two parts: the main Okinawa group of islands (the middle of the Nansei Shoto chain) and the Sento group of islands (the Miyako, Ishigaki and Yaeyama island clusters, the southern end of the Nansei Shoto chain).
At times of lowered sea levels, the main islands of Honshu, Shikoku and Kyushu usually were connected in one landmass, called Hondo, mainland or main islands.
Japan is separated from the continent by the Sea of Japan (Hokkaido and Honshu), the Tsushima and Korean straits (western Honshu and Kyushu) and the East China Sea (Kyushu and the Ryukyuan chain). In the north, Hokkaido is separated from Sakhalin Island by the Soya Strait. The Kurile Island chain extends northeastward from the eastern tip of Hokkaido to the Kamchatka Peninsula in northeastern Russia. And the Pacific Ocean borders the whole eastern side of the Japanese islands.
The methodology for studying early evidence for watercraft presently relies primarily on evidence of humans on islands that never were connected to a continental landmass, or close cultural similarity across a strait that was a water connection throughout the Pliocene and Pleistocene.
(Note that the dates 500 ka [ka=1,000 years] and 300 ka are now generally thought to be 630 ka and 430 ka [Kawamura 2001: 40, citing Konishi & Yoshikawa 1999; Taruno 2010].)
In 1989, Kawamura et al. (1989: 317, 324) said that the number of species immigrating to Hondo from the continent in the late Middle Pleistocene (about 300 ka to about 120 ka) was few, but the recent literature appears to agree that in fact NO land animals immigrated to Hondo from the continent after about 430 ka. However, there remains a small possibility that very short-lived land bridges did appear during the Middle Pleistocene, roughly 100 ka to 800 ka (Taruno 2010), one about 130 ka (Takahashi 2007).
Honshu-Hokkaido: Hondo and Hokkaido were connected via a landbridge about 500 ka and about 300 ka [now given as 630 ka and 430 ka], seen in the immigration of land animals from Hokkaido to Hondo (Dobson & Kawamura 1998). During the time of the landbridge between Hondo and Hokkaido ca. 300 ka [now ca. 430 ka], Palaeoloxodon naumanni and Sinomegaceros yabei entered Hokkaido from the south (Kawamura 1998: 255). In fact, Palaeoloxodon naumann possibly migrated to Hokkaido twice from the south, the second time about 30 ka across the Tsugaru "ice bridge" or by swimming (Takahashi et al. 2004).
Hondo and Hokkaido were connected a third time during the last glacial period, with migration of only large land animals moving across the "ice bridge" that formed on the narrowed Tsugaru Strait. These animals included Alces alces, Bos primigenius, Bos priscus, Ursus arctos, Equus (Kawamura et al. 1989, Table 1, pp. 320-322, p. 323). Humans also crossed the Tsugaru Strait from Honshu to Hokkaido at least as early as 20-22 ka, and possibly as early as 30-35 ka, but there is no evidence to know whether they crossed the "ice bridge" like the large animals or whether they used watercraft.
Hokkaido-Continent: Hokkaido was connected to the continent via Sakhalin Island during most of the Late Pleistocene, about 100-10 ka, with land mammal migration moving from the continent to Hokkaido. During the late Late Pleistocene, Mammuthus primigenius entered Hokkaido from the north (Kawamura 1998: 255; Takahashi et al. 2004, Table 5, p. 175).
Ryukyuan Islands-Continent/Kyushu: There is disagreement about land connections between the Ryukyuan islands and the continent or Kyushu. Kawamura (1998: 255) says that the northern Ryukyu (Okinawa and north) fauna are all endemic species from pre-Pleistocene, suggesting there were no Pleistocene landbridges connecting these islands to the continent or Kyushu, but the southern Ryukyu islands (Miyako group) have endemic species plus immigrants that arrived via landbridges in the Middle and Late Pleistocene.
Ujiie (1998: 247, 249), on the other hand, claims there was a landbridge from Taiwan to Amami Oshima ca. 75-12 ka BP [Amami Oshima is at the northern end of the middle group of Ryukyuan islands], based on 18O quantities, planktonic foraminifer and AMS 14C dates, and analysis of salinity. This landbridge disappeared in the Late Glacial due to both sea level rise and tectonic uplift. The changes noted by Ujiie, however, could result from changes in the Black Current/Kuroshio resulting from shallower waters along the Ryukyun chain and the extension southward of the northern cold current, Oyashio.
Tsushima Strait: A major question concerning landbridges is the existence, or non-existence, of a landbridge between western Japan and Korea in the Late Pleistocene. This question focuses on the Tsushima and Korean Straits. According to Matsui et al. (1998: 231) the inflow of marine water into the Sea of Japan through the Tsushima Strait was greatly reduced at the LGM, 19-15 ka [the dates apparently are not calibrated]. The δ18O values in the Sea of Japan (Matsui et al. 1998, Fig. 4, p. 225) dropped from about 30 ka, reached a minimum ca. 19-16 ka, and then rose rapidly from ca. 16-15 ka; the salinity (o/oo) dropped from ca. 35-30 ka, reached a plateau ca. 25-22 ka and a minimum ca. 19-16 ka, and then rose rapidly from ca. 15 ka. The Tsushima Strait was only about 10 m deep at the LGM. (For more discussion of the Tsushima Strait during the Pleistocene, see: Tanimura 1981 and Mogi 1981.)
It is difficult to say there was no landbridge between Korea and Japan in the Late Pleistocene, but, if there was one, it was short-lived and it existed only at the peak of the last glaciation, at the LGM, long after humans had first arrived in the Japanese islands (Matsui et al. 1998: 231). Thus, any possible landbridge between western Japan and the continent in the Late Pleistocene has no bearing on the question of when humans first arrived in the islands.
There is possibly earlier evidence for humans crossing water. Stone artifacts found on the island of Flores in the Indonesian archipelago, and dated to about 840 ka, could have gotten into the Soa Basin on Flores at that time only if their human makers could travel across a body of water 25 km or more wide (Morwood et al. 2005: 6-7).
There is a need to explain why humans did not come to the Japanese islands before the Late Pleistocene. Without such an explanation, claims that the first humans did not arrive in the Japanese islands until 35-50 ka are based only on negative evidence, and given the present state of archaeological research that makes a weak argument.
During the Late Pleistocene, humans most likely would have had to use some kind of watercraft to get to the islands
NOTE: the bibliography search focused on the Japanese Daiyonki Kenkyu (The Quaternary Research) journal because it has numerous articles on coastal change, it is readily available, and it has English abstracts for all articles and many articles in English.
NOTE: the English translations are those given in the publication, when given, hence the odd English in some translations.
Back to Index