Beu: Evolution of Janthina and Recluzia 
157 
Age 
m.yr. 
Epoch 
Internat. 
Stages 
Blow 
zones 
Miyazaki 
Pref. 
Kochi 
Pref. 
Shizuoka 
Pref. 
Yamanashi 
Pref. 
Chiba 
Pref. 
Ibaraki 
Pref. 
0 . 77 - 
1 - 
1.81 
2 - 
2 . 6 - 
3- 
3 . 6 - 
4- 
5- 
5 . 33 - 
6H 
TARANTIAN 
IONIAN 
O 
o 
H 
CO 
LU 
_I 
CL 
o 
o 
LU 
o 
o 
N23 
N22 
N21 
N20 
N19 
N18 
N17B 
N17 
Takanabe 
Formation 
MIYAZAKI 
GROUP 
Tsuma 
Formation • 
Tano 
Formation 
Ananai 
Formation 
TONOHAMA 
GROUP 
Hijikata Fm. ▲ 
Dainichi ▲ 
Formation ^ 
KAKEGAWA 
GROUP 
Tamari 
Formation 
SAKARA 
GROUP 
Akebono 
Formation 
SHIZUOKA 
GROUP 
(Osozawa • 
Member) 
SHIZUOKA 
GROUP 
MIURA 
GROUP 
Senhata 
Formation * 
Hitachi 
Formation 
HATSUZAKI 
GROUP 
Figure 21. Stratigraphical position of Janthina fossil localities in Japan. Symbols: A Janthina chavani', • Janthina typica. Grey tone = 
stratigraphical hiatus; not all stratigraphical units are identified. 
seem to be no records of Janthina from early Piacenzian 
rocks in Japan. Apart from this, the Japanese succession helps 
to confirm the origination of J. chavani during Piacenzian 
time, at around 3.0 Ma. As in New Zealand, many thick, 
well studied, younger Japanese successions record complex 
glacial-interglacial sequences over quite large areas in 
Japan (e.g., Ito, 1998), but very few Janthina fossils have 
been recorded from them. Possibly both successions lay 
within water too cool to be inhabited by Janthina at that 
time. Nevertheless, the thick Japanese Pleistocene marine 
successions potentially provide one of few locations where 
the later evolution of Janthina might be revealed. 
An interesting interpretation of the Japanese succession 
was provided by Tomida et al. (2013: 62): “The Late 
Neogene eustatic curves of Malmgren and Berggren ... 
show major rises in global sea level at c. 6.8 Ma (N17a), 
5.7 Ma (N17b), 5-3.8 Ma (N18-19), 3-2.6 Ma (N20-lower 
21), and 2.0-1.8 Ma (upper N21). Our field studies of Late 
Neogene molluscan faunas in Japan have shown the clear 
correspondence between stratigraphic levels with warm- 
water faunas and the times of major eustatic sea level rises 
... Additional study has shown that Janthina occurs in all 
major Neogene transgressions. All these facts support the 
idea that vigorous, warm currents flowed along the Pacific 
coast of Kyushu in the earliest Pliocene (N18), and in the 
latest Pliocene (lower N21)” Occurrences of Janthina in 
Japan are interpreted as related to incursions of the tropical 
Kuroshio Current rather than with periods of onshore winds, 
although both likely occurred simultaneously to record the 
occurrence of Janthina. 
Overview of time ranges. None of the successions described 
above establishes the full evolutionary history of Janthina , 
for the following reasons: 
1 No succession is known that records the extinction of 
Janthina chavani or its replacement by a later species such 
as J. janthina ; 
2 No succession records the evolution of a living Janthina 
species, although isolated Piacenzian or Gelasian sites in 
Jamaica and the Philippine Islands indicate that J. globosa 
had evolved before J. chavani became extinct; 
3 Only the succession at Santa Maria Island includes Janthina 
krejcii ,; 
4 The writer is not aware of any other successions that would 
clarify this evolutionary history further, with the possible 
exception of Bridgewater Limestone in south-eastern 
South Australia and south-western Victoria. Bridgewater 
Limestone extends both much older (well back into the 
Pliocene) and much younger (up to MIS 3) than the fossils 
recorded here from Naracoorte (Sprigg, 1952; Murray- 
Wallace et al., 2001; Blakemore et al, 2015) and potentially 
could reveal the full evolutionary history of Janthina. 
The gently uplifted successions around southern Australia 
include beautifully preserved, abundant fossil material of 
Janthina. Bridgewater Limestone, Point Ellen Formation 
and Roe Calcarenite record the gentle lapping of the sea 
onto a tectonically passive margin, where the neustonic 
fauna was cast ashore in abundance, and preserved during 
late Pliocene-Pleistocene sea-level high-stands. Little else 
has happened since, other than gradual slight uplift, and 
cementation of calcareous beds through pedogenic processes 
in the case of Bridgewater Limestone. Unlike tectonically 
active areas such as Japan and New Zealand, almost no 
younger rock has ever been deposited on these units, and 
their fossils are well-preserved and undeformed. In contrast, 
tectonically active margin sequences in New Zealand and 
Japan have longer but much less well-preserved Janthina 
