Biology Reference
In-Depth Information
Metasequoia
,
Sequoia
,
Taxodium
), Cupressaceae (
Thuja
, arborvitae), and
Taxaceae (
Taxus
, yew) are only generally similar in morphology to their
modern-day representatives. In the pollen record, this complex of families
is identifi ed as t-c-t, and the macrofossils (cones and twigs) include such
extinct genera as
Drumhellera
. At the generic level, some present-day Asian
trees like
Glyptostrobus
, similar in ecology to the American
Taxodium
(bald
cypress) that grows in swampy habitats often in standing water, and
Ginkgo
,
growing in more mesic but still moist habitats, are often present. They are
preserved in fl oras such as the Eureka Sound Group on Ellesmere Island
of the Northwest Territories, and on Axel Heiberg Island in the Canadian
High Arctic. The plant formation is the polar broad-leaved deciduous for-
est, consisting of angiosperms such as platanoids (sycamore-like),
Populus
(poplar-like), and extinct members of the family Trochodendraceae (trees
or tall shrubs to 20 m, now represented by one species in southern Japan).
These are mixed with the deciduous gymnosperms noted above, and with
an understory of ferns,
Lycopodium
(ground “pines”), and horsetails (
Equi-
setum
). Plants of warmer habitats occur mostly along the coast, and those
of cooler habitats grow in the interior and in the uplands. Together they
constitute a generalized “boreotropical” fl ora from which the tropical part
will eventually disappear after the early Eocene, and from which part of
the temperate deciduous forest will later be derived. The polar broad-leaved
deciduous forest extends southward from the shores of the Arctic Ocean
from about 70°N to 60°N-50°N, where there is a transition to more meso-
thermal, evergreen vegetation.
Temperatures toward the south in the zone between about 50°N to
40°N are warmer than in the north during the Cretaceous, with an MAT
of 15°C-20°C. This is the region of the northern Rocky Mountains that at
100 Ma ranges from shallowly submerged to low-lying hills. Eastward of
the slopes, the land is mostly inundated, while to the west it descends into a
mosaic of down-faulted basins, uplifted ranges, and eastward-moving land
fragments being fused into the geologically complex landscape of western
North America. Dinosaurs are abundant, and their remains are preserved
at localities around present-day Edmonton and Calgary in Alberta, Canada,
and at the Utah-Colorado border in an area later to be designated as Dino-
saur National Monument. Other animals in the Lancian (Late Cretaceous)
North American Land Mammal Age are the multituberculates—the name
describes the multicusped teeth of rodentlike animals around the size of
squirrels that will be extinct before the end of the Eocene—marsupials be-
longing to extinct lineages, and other marsupials distantly related to modern
opossum, (all small, no larger than a rat, and insectivorous). They do not
