Geoscience Reference
In-Depth Information
The extinct genus
Florissantia
is known
from its beautiful flowers. The tough, five-
pointed calyx apparently persisted until
the fruits matured and then possibly acted
as a small parachute to aid dispersal. The
leaf of
Florissantia
is unknown. Elms
(Ulmaceae) are known not only from the
modern genera
Ulmus
(elm) and
Celtis
(nettle-tree, hackberry) but also from the
extinct genus
Cedrelospermum
. Leaves
and fruits have been found in association,
and
Cedrelospermum
was probably an
abundant tree around the lake shores,
because its leaves and winged fruits are
extremely common as fossils. It occurs
throughout Eocene and Oligocene floras
of North America and Eocene to Miocene
European floras. The hickory,
Carya
, has a
similar distribution, and the two genera
provide evidence for their emergence on
the American continent followed by
radiation across a land bridge that still
existed at that time, to the Eurasian
continent.
Climbing plants are evidenced by fossils
of
Humulus
, the hop (an ingredient of
beer) and
Vitis
, the grape, used to make
wine, of course, and
Smilax
(greenbrier,
cat's claw). The Sapindaceae is a family
of subtropical to tropical vines (e.g.
Cardiospermum
, the balloon vine) and
trees (e.g.
Koelreuteria
, the golden-rain
tree) that occur at Florissant and provide
evidence for a warmer climate than the
Rocky Mountains experience today.
Anacardiaceae are common; they include
the sumacs (
Rhus
,
231
) and poison ivy.
Their leaves characteristically turn red in
the autumn. Legumes (Fabaceae) are
recognized by their pods (
232
). Many plants
found at Florissant are known from just a
little further south today, in Mexico and
Central America; for example,
Cedrela
, the
West Indies cedar (not a true cedar),
Bursera
, the elephant tree, and
Oreopanax
,
the mano de león.
Grasslands as we know them today,
forming large swathes of continental
North America, had not yet evolved, but in
Florissant some of the earliest members of
the grass family, Poaceae, can be found.
Other monocotyledonous families in evi-
dence in Florissant include the Typhaceae
(cat-tail, reed-mace), common denizens of
swamps, and Arecaceae (palms), the rare
examples of the latter suggesting affinity
with the temperate fan-palms.
Insects
Florissant is justly famed for its insect
life, and our knowledge of Eocene
terrestrial and freshwater invertebrates
would be much poorer without
information from this important locality.
Among the more primitive true insects
are the familiar mayflies, whose nymphs
are aquatic and adults (imagines)
emerge in swarms. The imagines do not
feed; they mate and then shortly die,
hence the name for the order:
Ephemeroptera. They are surprisingly
rare at Florissant, given their attachment
to aquatic habitats. Another relatively
primitive order of insects is the
231
231 Compound leaves of Rhus stellariafolia
Anacardiaceae NHM. Longest leaf is
120 mm 4.7 in long.
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