Biology Reference
In-Depth Information
If it is granted that some mental capaciousness is required for envision-
ing the origin and development of New World ecosystems over a hundred
million years of time, this leads to a fourth and related organizational
premise. Namely, that conclusions about ecosystem history must be tested
within a context of information derived from multiple, independent lines of
inquiry. For vegetation history, these contexts include faunal history, trends
in climate, geologic events such as orogeny (mountain building) and tec-
tonics (plate movement), the coming and going of land bridges, and geo-
morphological structures (e.g., sand dunes, glacial moraines, and ancient
arches that formerly subdivided the landscape and its biota). Sedimentol-
ogy is another important context because sediments such as coal, lignite,
and bauxite form under warm temperature and plentiful moisture, while
deeply oxidized red beds, cross-bedded sandstones, mud cracks, and evapo-
rites like halite (salt) and gypsum all tell of aridity. The amount of titanium,
a terrestrial element, in ocean basins refl ects the extent of water fl ow from
the land into the basin (i.e., precipitation); ophiolites mark the time and
place where plates collided; and a meteoritic rise in iridium marks the time
when Earth and unearthly fragments collided. These sedimentary clues to
the paleoenvironment are preserved in the same rocks that contain the fos-
sils, and they provide a valuable context for reading ecosystem history.
Another context is phylogeny—the study of evolutionary relationships
between organisms based on combined morphological, cytological, and
multigene molecular approaches. This fl ags for special attention identifi ca-
tions of fossils unusually old for the lineage, placing them in an unexpected
part of the world or in unlikely association. For this context to be of greatest
value, we must reduce uncertainties in the fossil record (e.g., misidentifi -
cations, incompleteness of the record) and in molecular-based approaches
(fl awed molecular clocks and the dating of nodes, proposed phylogenetic
relationships in confl ict with morphological and other evidence), along
with occasional claims for the overriding sanctity of cladistics (as cited by
Liede-Schumann and Hartmann 2009; Stuessy and König 2009). Progress
is being made, primarily by way of examples provided through the studies
of experienced investigators objectively incorporating a multiplicity of ap-
proaches (e.g., Manos et al. 2007). The interactions between fossils, mor-
phology, and molecules are currently in the inevitable “debate before the
resolution” phase.
The basis for many of these contexts is generally understood, and they
are incorporated into discussions throughout this work. Others require
some explanation, presented in separate sections or chapters. Among the
latter are paleotemperature curves derived from oxygen isotope analysis
