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This is foliage of Papuacedrus
prechilensis (Berry) Wilf et al., comb. nov. (Cupressaceae),
from the middle Eocene Río Pichileufú flora of
Río Negro Province, Patagonia, Argentina. The monotypic
genus Papuacedrus...
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Fossil plants are windows to the past, providing us with clues
as to what our planet looked like millions of years ago. Not only
do fossils tell us which species were present before human-recorded
history, but they can provide information about the climate and how
and when lineages may have dispersed around the world. Identifying
fossil plants can be tricky, however, when plant organs fail to be
preserved or when only a few sparse parts can be found.
In the November issue of the American Journal of Botany
(http://www.amjbot.org/cgi/content/full/96/11/2031),
Peter Wilf (of Pennsylvania State University) and his U.S. and
Argentine colleagues published their recent discovery of abundant
fossilized specimens of a conifer previously known as "Libocedrus"
prechilensis found in Argentinean Patagonia. This plant was first
described in 1938 based on one fossil vegetative branch whose
characteristics were said to most closely match those of a living
South American dry, cold-climate conifer found in the study area:
Austrocedrus (Libocedrus) chilensis, the Cordilleran Cypress.
However, numerous characteristics of the leaves, including their
distinctive shape and stomatal arrangements, as well as seed cone
details of the newly discovered specimens entirely match those of
extant Papuacedrus, a closely related genus, currently found only
in tropical, montane New Guinea and the Moluccas.
Based on the newly discovered fossil specimens from 52 and 47
million years ago, Wilf and colleagues reassigned the fossil
species to Papuacedrus, under the new name combination Papuacedrus
prechilensis. One of the major implications of this reassignment is
that, because Papuacedrus is known from tropical montane habitats
and is physiologically limited to extremely wet climates, it adds
to the emerging evidence that Patagonia in the Eocene was a warm,
wet tropical place and not a cold, dry steppe as much of it is
today. It also adds a tropical West Pacific connection for
Papuacedrus, further establishing the interchange of flora with
Australia and neighboring areas via a warm and forested Antarctic
land connection during the Eocene. Indeed, less complete
Papuacedrus fossils have previously been found in Australia and
Antarctica.
"This is a wonderful example of how securely identifying
well-preserved and well-dated fossils can have many impacts," Wilf
noted. "These fossils contribute critical information about conifer
evolution as well as the biogeographic history of the Southern
Hemisphere. Combined with the robust site geology we have
generated, they also contribute to an important environmental
reinterpretation of a large area in the past. Papuacedrus
physiologically requires lots of moisture and cannot withstand
prolonged droughts."
Another important consequence of this find is how it relates to
the great diversity of other fossil plant as well as insect species
known from the Patagonian fossil sites. The lush, possibly montane,
rainforest environment indicated by Papuacedrus helps to explain
this stunning richness from the Eocene. "The revision [of this
species] not only forces a major shift in biogeographic affinity
(Patagonia to New Guinea), but also provides a decisive boost to
important hypotheses of rainforest climates during the Eocene in
Patagonia that had not been fully substantiated in previous work,"
Wilf said. "This in turn helps to explain the remarkable plant and
insect diversity found in Eocene Patagonia."
SOURCE
