Biology Reference
In-Depth Information
being integrated into a searchable resource of immense value to taxonomists,
biogeographers, ecologists, foresters, economic botanists, biographers, his-
torians of science, conservationists, archeologists, and paleobotanists.
The underlying principle is that if a fossil leaf, fl ower, fruit, seed, or wood
anatomy matches a specimen in the reference collection of modern plants,
it is considered identifi ed. The key phrase is “if it matches.” In the early
days of paleobotany, the characters used for matching were relatively few,
comparisons were made using a hand lens or the low power of a light micro-
scope, and the size of collections in herbaria were considerably smaller and
biased toward northern temperate regions. For example, in the early 1900s,
the holdings in each of three major herbaria in the New World—the Mis-
souri Botanical Garden, the New York Botanical Gardens, and U.S. National
Herbarium—were less than 1 million, whereas now they are each approach-
ing or exceed 6 million specimens. SEM (scanning electron microscopy)
and TEM (transmission electron microscopy) are standardly used to study
fossils, and there are extensive collections of seeds in the U.S. Seed Her-
barium of the Department of Agriculture; woods at North Carolina State
University and the University of Wisconsin; and cleared leaves in the Paleo-
biology Division of the Smithsonian Institution, Peabody Museum of Yale
University, and the Museum of Paleontology of the University of Califor-
nia, Berkeley. Leaf clearings (fi g. 4.4) are supplemented by x-ray photomi-
crographs (Wing 1992), and together they reveal cellular details, venation,
stomata morphology, arrangement, and density (Passalia 2009), epiphytes,
parasites, and inclusions. The minute dark structures in fi gure 4.4, for
example, are raphid crystals. Many of these features preserve in fossil
leaves, and with more complete collections, modern techniques, standard-
ized terminology, electronic imaging, databasing, and the wide array of an-
cillary and context information now available, plant fossils are providing an
increasingly reliable inventory of ancient lineages, past vegetation, and, by
extrapolation, paleoenvironments.
The interpretation of paleoenvironments and the reconstruction of veg-
etation history from the identifi ed material is based on two independent
approaches. One is the modern analog or NLR (nearest living relative)
method. The assumption is that most Cenozoic plants (e.g.,
Larrea
, creo-
sote bush;
Opuntia
, cactus;
Nymphaea
, water lily;
Rhizophora
, mangrove)
had about the same ecological requirements and occupied similar habitats
as the extant plant. When this assumption is assessed against evidence such
as the associates of the fossil in the assemblage, presence of morphologi-
cal adaptations refl ecting a particular environment, habitat diversity as re-
vealed by the geology of the region, and established trends in climate—for
