Diptocarps, Dipterocarpaceae, are the dominant trees of modern South
and Southeast Asian rainforests, and are also found in South America, Africa
and Madagascar. The group reach their maximum diversity today on the island of
Bornea, where there are over 280 described species of Diptocarp, but the
earliest fossil Diptocarps from Southeast Asia date back only as far as the
Oligocene, whereas fossil Diptocarps appear in western India in the Early
Eocene.
Modern Diptocarps are now found only in the south and east of India,
though they have a fossil record in the north and west of the country. This is
thought to be due to the relatively narrow climate tolerance of Diptocarps,
which strongly favour areas with high rainfall year round, while many areas of
modern India have a monsoonal climate, with a long dry season and a shorter wet
season. This monsoon climate is thought to have evolved as a result of uplift
in the Himalayas, which in turn has been driven be the collision between the
Indian and Eurasian continental plates. The narrow climatic tolerance of
Diptocarps makes them very useful in palaeoclimatic reconstructions, which is
particularly useful when trying to understand the evolution of the modern
monsoonal climate.
In a paper published in the Journal of Earth System Science in October
2013, Anumeha Shukla, RC Mehrotra and JS Gularia of the Birbal Sahni Institute ofPalaeobotany describe a series of Diptocarp wood specimens from the Oligocene
and Plio-Pleisctocene of northwest India.
The first specimen described is assigned to the species Dipterocarpoxylon jammuense, and comes
from the Plio-Pleistocene Raja Shumar Formation near Habur Village in the Jaisalmer
District of Rajasthan. Fossil woods of the genus Dipterocarpoxylon are thought to resemble woods of the extant genus
Dipterocarpus, which is currently
found in the Western Ghats of southern India and Assam in the northeast, as
well as in the Andaman Islands, and Southeast Asia as far east as the
Philippines, reaching its maximum diversity on the Malaysian Peninsula, Sumatra
and Borneo. The species Dipterocarpoxylon jammuense,
which has previously been recorded from Late Tertiary and Miocene deposits in
the Himalayan region, is thought to resemble the modern Dipterocarpus lowii, which is now found in the Malaysian region.
Dipterocarpoxylon jammuense (a), (b) transverse sections (T.S.) of the fossil showing
exclusively solitary vessels and scattered gum canals (marked by arrow), (c)
tangential longitudinal section(T.L.S.) of the fossil showing multiseriate rays
with long tails (marked by arrow), (d) T.L.S. showing sheath cells onthe flanks
of a multiseraite ray (marked by arrows) and (e) radial longitudinal section
(R.L.S.) showing heterogeneousray tissue. Shukla et al. (2014).
The second specimen described is assigned to the species Hopenium pondicherriense, and comes from
the Miocene Bhumbli Conglomerate at Lakhanka-Mithi-Viri on the east coast of
Bhavnagar District in Gujarat. Fossil woods of the genus Hopenium are thought to resemble those of members of the modern
genus Hopea, and Hopenium pondicherriense is thought to particularly resemble the
wood of Hopea glabra, a medium-sized
tree found today in southern India, and Hopea helferi,
a large tree found today in the Andaman Islands, Myanmar, Malaysia, Thailand
and Cambodia.
Hopenium pondicherriense (a) T.S. of the fossil showing solitary as well as grouping of
vessels, (b) T.S. showing tangentially arranged gum canals (marked by arrows),
(c) T.S. showing gum canals enclosed in parenchyma bands(marked by arrows),
(d), (e) T.L.S. of the fossil showing 3–4 seriate rays with crystalliferous
upright cells interspersed amongthe procumbent cells (marked by arrows), and (f)
R.L.S. of the fossil showing heterogeneous ray tissues with
crystalliferousupright cells (marked by arrows). Shukla et al. (2014).
The third specimen described is assigned to the species Shoreoxylon burmense, and comes from the
Early Miocene Kand Formation on the Ratanpurniriver bed at Ratanpor in
the Bharuch District of Gujarat. Fossil woods of the genus Shoreoxylon are thought to resemble those of the modern genus Shorea, which is largely confined to
rainforests today, and Shoreoxylon burmenseis
thought to particularly resemble the wood of the modern Shorea ovalis, which is found in Malaysia. Shoreoxylon burmense has previously been reported from Tertiary
deposits in Myanmar and northeast India.
Shoreoxylon burmense (a) T.S. of the fossil showing predominantly solitary vessels and
tangentiallyarranged gum canals (marked by arrows), (b) T.S. showing
paratracheal parenchyma around the vessels (marked by arrow),(c), (d) T.L.S. of
the fossil showing 2–3 seriate rays, (e) R.L.S. showing weakly heterogeneous
ray tissue, and (f) R.L.S.showing alternate intervessel pits. Shukla et al. (2014).
See also…
India separated from Africa about 130 million years ago, and was
effectively an island continent until its collision with Eurasia in the Middle
Cenozoic. Nevertheless the modern flora and fauna of India show strong
affinities with that of Africa, and while there was probably some...
Industrial scale timber extraction began on Borneo in the 1970s and during the period 1980 to 2000 more timber was harvested from Borneo than from Africa and the Amazon Basin combined. In addition much forest has been cleared to make way for monoculture plantations, for the palm oil, rubber and timber industries, as well as being burned in forest fires. For this reason the island is often assumed to be a hopeless case environmentally...
Kimberlite pipes are produced by rapid volcanic intrusions carrying magma from the Earth’s mantle rapidly to the surface, often resulting in explosive phreatomagmatic eruptions (explosions caused by hot magma coming into contact with water). These pipes are considered high value economic resources due to the common occurrence of diamonds within them. Surprisingly kimberlite pipes also often contain fossil...
Industrial scale timber extraction began on Borneo in the 1970s and during the period 1980 to 2000 more timber was harvested from Borneo than from Africa and the Amazon Basin combined. In addition much forest has been cleared to make way for monoculture plantations, for the palm oil, rubber and timber industries, as well as being burned in forest fires. For this reason the island is often assumed to be a hopeless case environmentally...
Kimberlite pipes are produced by rapid volcanic intrusions carrying magma from the Earth’s mantle rapidly to the surface, often resulting in explosive phreatomagmatic eruptions (explosions caused by hot magma coming into contact with water). These pipes are considered high value economic resources due to the common occurrence of diamonds within them. Surprisingly kimberlite pipes also often contain fossil...
Follow Sciency Thoughts on Facebook.
