Title:
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Herbivory in Antarctic fossil forests and comparisons with modern analogues in Chile
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During the Tertiary (~ 50 million years ago) forests were present in Antarctica,
but fossil evidence of insect life in the forests is rare. Extensive fossil floras from
Antarctica contain evidence of insect herbivory on the leaves; these provide indirect
evidence of past insect life. Such preservation of the behaviour of insects (insect
trace fossil) can be used to examine the diversity of insects that lived in the forests
of Antarctica in the past.
Palaeogene (65 Ma - 35 Ma) fossil floras from two localities on the Antarctic
Peninsula (King George Island and Seymour Island) were examined for the presence
ofinsect trace fossils. Fossil leaves were preserved as impressions and
compressions within siltstones and sandstones and represent leaves that were
preserved within a quiet lake environment (King George Island) or shallow marine
setting (Seymour Island). The floras were dominated by leaf morphotypes that
resemble modem Nothofagaceae (Southern beeches), but leaves similar to other
Southern Hemisphere families were also present, including the Cunoniaceae,
Proteaceae and Lauraceae.
Over 2,000 fossil leaves were examined for traces of past insect activity. Over
150 fossil leaves (6.9%) contained evidence of feeding traces on the leaves (54 trace
types from King George Island and 19 from Seymour Island). The trace fossils were
grouped into four functional feeding types: general leaf chewing, skeleton feeding,
leaf mines and leaf galls. General leaf chewing was the most common trace type at
both localities and leaf mines the least common.
The nearest living analogues of the Antarctic Palaeogene forests are the
Valdivian and Magellanic forests of Chile and so insect activity in these forests was
studied in order to understand past insect activity in Antarctica. The diversity of
insect traces in the Chilean forests was investigated at six sites within National
Parks, covering alatitudinal range between 37°S and 55°S. Insects associated with
two deciduous species, Nothofagus pumilio and Nothofagus antarctica, were of
particular focus. The factors that affected the level of insect damage and the
proportion ofleafmines and galls included height within the tree,orientation ofleaf
within the tree, altitude, season, leaf age, latitude, plant species and insect species.
Insects which created similar general leaf chewing traces in the modem forests
in Chile siinilar to those on the fossil leaves were larvae of Lepidoptera
(Geometridae), Hymenoptera (Symphyta) and the larvae and adults of Coleoptera
(Chrysomelidae, Curculionidae, Cerambycidae). Leaf mines were created by
species of Coleoptera and Hymenoptera. Species of Diptera (Cecidomyiidae) and
Hymenoptera (Cynipidae) created leaf galls. Other invertebrates (Acari
(Eriophyidae) and Nematoda (Tylenchida)) also created leaf galls in Chile, similar to
fossil leaf galls from Antarctica.
Herbivory types on the fossil flora from King George Island were most similar
to modem types in Puyehue (a northern study site, Chile) and those from Seymour
Island were most similar to Torres in the south, indicating a possible climatic control
on their distribution. Based on this relationship, estimates of palaeoclimate of
Antarctica suggest that the climate of King George Island to the west of the
Peninsula was warmer and wetter (3.5°C - lO.4°C mean annual temperature, 3.5°C
24.3°C maximum and minimum mean monthly temperature and 1500 mm annual
precipitation) than the cooler and more stable environment at Seymour Island to the
east (3.5°C - 10AoC mean annual temperature, -O.4°C - 16°C maximum and
minimum mean monthly temperature, and 570 mm annual precipitation).
The studies of fossil and modern insect traces in Antarctica and Chile have
provided a unique opportunity to reconstruct past insect life of Antarctica during the
Palaeogene. This is the first documented evidence of insect life during the
Palaeogene on Antarctica and highlights the value of modern analogue comparisons
to obtain a greater insight into past insect ecology.
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