manado coelacanth and the geohistory of southeast asia

Part : ZOOGEOGRAPHY OF COELACANTH
MANADO COELACANTH AND THE GEOHISTORY OF
SOUTHEAST ASIA
Yasuhiko Taki
President, Japan Wildlife Research Center
If the discovery of Latimeria chalumnae can be referred
to as the zoological finding of the 20th century, that of
the second species, L. menadoensis, in Sulawesi is the
zoogeographical event of that century. he occurrence of L.
menadoensis in Sulawesi is considered to provide evidence
to the Gondwanan origin of a part of Southeast Asia as
well as Wallacia and Australia. However, we know almost
nothing about how the Coelacanth lineage including
these two living forms has survived the long period after
the disappearance of fossil crossopterygians in the late
Cretaceous. Also, it remains as an enigma that the two
living species are nearly similar in external morphology
and show rather close genetic relationships in spite of their
presumable long geographic isolation from each other.
1938
20
60
2
20
2
21
Gondwanan origin of Southeast Asia
In the conventional zoogeographical division of the
world, Southeast Asia is usually included in a region called
Oriental or Indian Region together with India and southern
China (e.g., Beaufort, 1951; Darlington, 1966). This region
is recognized as a part of the Old World owing to its
faunistic afinity with the Palearctic Region.
Southeast Asia consists of a continental section (major
part: Indochinese Peninsula) and an insular section (major
part: the Greater Sunda Islands). The faunistic similarity
of the two sections, most remarkably in freshwater fish
fauna, is usually attributed to the land connection of the
two sections by the sea regression during the Pleistocene.
However, I have suggested that the affinity between the
two sections should have been originated from a much
earlier period (Taki, 1978).
In the course of examination of the geographic
distribution of freshwater fish groups in Asia, I came to
believe the Gondwanan origin of Southeast Asia on the
basis of these affinities between the two sections and
between Southeast Asia as a whole and India and other
16
T h e C o e l a c a nt h , Fa t h o m t h e My s t e r y 2 0 0 7
areas once constituted Condwanaland, most notably the
common occurrence of the family Osteoglossidae in both
Southeast Asia and the Australian region, as well as in
Africa and South America (Fig. 1). No living form occurs
in India, but a fossil genus has been reported from this
subcontinent as well as from Sumatra in Southeast Asia.
All these areas excepting Southeast Asia have so far been
known to have constituted Gondwanaland together with
the Antarctic Continent.
My hypothesis of the Gondwanan origin of Southeast
Asia found a support from geological observations;
Ridd (1971) demonstrated that India, Southeast Asia and
Australia constituted a part of Gondwanaland before its
break-up (Fig. 2). More recently, it was reported that parts
of the northern edge of Gondwanaland rifted into several
land masses and migrated northward to form parts of
Southeast Asia (Nakazawa, 1985) (Fig.3).
Scleropages formosus
Scleropages jardini
Scleropages leichardti
Heterotis niloticus
Arapaima gigas
Osteoglossum bicirrhosum
Osteoglossum ferreirai
Fig. 1. Geographic distribution of the ishes of the family Osteoglassidae.
I
Fig. 2. Reconstruction of India, Southeast Asia and Australia
before break-up and continental drift (from Rigg, 1971; partly
modiied).
Fig. 3. Reconstruction of the paleogeography of the Tethys Sea
region (from Nakazawa, 1985; partially modified). Red part:
Indochina and Malay bocks.
17
Part : ZOOGEOGRAPHY OF COELACANTH
Speculation on the distributional history of
Latimeria chalumnae and L. menadoensis.
The discovery of Latimeria menadoensis in Sulawesi
has posed a puzzle as to the evolutionary history of this
species and its African counterpart, L. chalumnae, because
of their morphological similarity and genetic closeness
(divergence time of the two species: 1.22-1.42 million
years ago in Pouyaud et al., 1999 and 4.7-6.3 million years
ago in Holder et al., 1999), in spite of a 10,000 km gap
of their distribution (Fig. 4). However, a recent study has
suggested that the separation time would have dated
back to a much earlier period, some 35 million years ago
(Inoue, 2005), enabling us to examine the distributional
history of Latimeria from a zoogeographical standpoint.
Fig. 4. Geographic distribution of two living forms of coelacanth of the
genus Latimeria. Red circle: L. chalumnae; blue circle: L. menadoensis.
Based on the present-day geographic distribution of
Latimeria confined in the Gondwanan regions, it is likely
that the ancestral stock of the two Latimeria species has
originated in coastal waters along the Tethys Sea. Fig. 5
shows the present-day distribution of the two species
plotted on a map reconstructing the world some 65 million
years ago. Although the divergence of the two species
is estimated to have taken place in more recent periods
(Inoue et al. (2005)), this igure seems to underscore the
speculation that the two living forms of Latimeria originated
in Gondwanaland.
Fig. 5. Occurrence of living forms of Latimeria ploted on a map 65 million
years ago (Cretaceous period). (Map from Dietz and Holden, 1970).
18
T h e C o e l a c a nt h , Fa t h o m t h e My s t e r y 2 0 0 7
References
Beaufort, L. F. de. 1951. Zoogeography of the land and
inland waters.
Sidgwick and Jackson, London, vii+298 pp.
Darlington, P. J/ Jr/ Zoogeography: the geographical
distribution of animals. John Wiley & Sons, New York,
London, Sidney, xii;675 pp.
Dietz, R. S. and . C. Holden. 1970. The breakup of
Pangea. Sci. Am., 223(4): 30-41.
Holder, M. T., Erdmann, M. V., Wilcox, T. P., Caldwell, R. L.
and Hills, D. M.
1999. Two living species of coelacanths? Proc. Natn.
Acad. Sci., 96: 12616-12620.
Inoue, J. G., M. Miya, B. Venkatesh, M. Nishida. 2005.
The mitochondrial genome of Indonesian coelacanth
Latimeria menadoensis (Sarcopterygii: Coelacanthiformes)
and divergence time estimation bet ween the t wo
coelacanths. Gene, 349: 227-235.
Nakazawa, K. 1985. The Permian and Triassic systems in
the Thesys – their paleogeography. Pages 93-111 in
Nakazawa K. and M. Dickins, ed. The Thethys. Tokai
Univ. Press, v+317 pp.
P o u y a u d , L ., W i r j o a t m o d j o, S ., R a c h m a t i k a , I ,
Tjakrawidjaja, A., Hadiaty, R. and Hadie, W. 1999. Une
nouvelle espece de coelacanthe. Preuves genetiques
et Morphologiques. C. R. Acad. Sci. Paris, Siences de
la vie/Life sciences, 322: 261-267.
R i d d, M . F. 1971. S o u t h - E a s t A s i a a s a p a r t o f
Gondwanaland. Nature, 234: 531-533, ig. 1-2.
Taki, Y. 1978. An analytical study of the ish fauna of the
Mekong basin as a biological production system in
nature. Res. Inst. Evol. Biol., Spec. Publ. (1): 74 pp., 3
pls.