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Methods
These research examples show the use of disparate data sources and tools. Data include sedimentary (PGAP database), fossil plant (Paleobiology Database), and dinosaur (The Dinosauria datasets). Paleogeographic coordinates and maps were derived from David Rowley (PGAP) and Chris Scotese (PALEOMAP Project). Making these databases interoperable and developing paleomapping tools will enable the geoscience community to undertake similar broad-scale research.
Research Examples
- Late Jurassic climates, vegetation and dinosaur distributions.
- Rees, P.M., Noto, C.R., Parrish, J.M. & Parrish, J.T. (2004). Journal of Geology, 112: 643-653.
ABSTRACT.
The Jurassic and Cretaceous are considered to have been warmer than today on the basis of various climate data and
model studies. Here, we use the available global record of climate-sensitive sediments, plants, and dinosaurs to infer
broadscale geographic patterns for the Late Jurassic. These provide a context for our more detailed accounts of the
Morrison and Tendaguru Formations in North America and East Africa. At the global scale, evaporites predominated
in low latitudes and coals in mid- to high latitudes. We ascribe these variations to a transition from drier to wetter
conditions between the equator and poles. Plant diversity was lowest in equatorial regions, increasing to a maximum
in midlatitudes and then decreasing toward the poles. Most dinosaur remains are known from low-latitude to marginally
midlatitude regions where plant fossils are generally sparse and evaporites common. Conversely, few dinosaur
remains are known from mid- to high latitudes, which have higher floral diversities and abundant coals. Hence, there
is an obvious geographic mismatch between known dinosaur distributions and their primary food source. This may
be due to taphonomic bias, indicating that most dinosaur discoveries provide only a small window on the diversity
and lifestyles of this group. On the basis of our global- and local-scale studies, we suggest that dinosaur preservation
was favored in environments toward the drier end of the climate spectrum, where savannas rather than forests
predominated. A holistic approach, incorporating climate and vegetation as well as geography, is required to better
understand patterns of dinosaur ecology and evolution.
Figure 1. Late Jurassic (150 Ma) paleogeographic maps (Mollweide projection with 30 degree latitude and longitude lines).
A, Plant localities, scaled according to the number of constituent genera. B, Evaporite and coal deposits. C, Dinosaur
localities, scaled according to the number of constituent taxa and showing the location of the Morrison (M) and
Tendaguru (T) Formations.
Figure 2. Distributions of dinosaur taxa (A) and plant genera (B) in 10 degree paleolatitudinal bins.
- Land-plant diversity and the end-Permian mass extinction
- Rees, P.M. (2002). Geology, 30: 827-830.
ABSTRACT. The Permian and Triassic represent a time of major global climate change from
icehouse to hothouse conditions and significant (ca 25 degrees) northward motion of landmasses
amalgamated in essentially one supercontinent, Pangea. The greatest of all mass extinctions
occurred around the Permian-Triassic boundary (251 Ma), although there is no
consensus regarding the cause(s). Recent studies have suggested a meteor impact and
worldwide die-off of vegetation, on the basis of sparse local observations. However, new
analyses of global Permian and Triassic plant data in a paleogeographic context show
that the scale and timing of effects varied markedly between regions. The patterns are
best explained by differences in geography, climate, and fossil preservation, not by catastrophic
events. Caution should be exercised when extrapolating local observations to
global-scale interpretations. At the other extreme, global compilations of biotic change
through time can be misleading if the effects of geography, climate, and preservation bias
are not considered.
Figure 1. Global paleogeographic maps (modified from Ziegler
et al., 1997; Rees et al., 2000). A: Late Permian (ca. 255 Ma);
major geographic regions are highlighted. B: Early Permian (ca.
285 Ma). C: Early Jurassic (ca. 190 Ma).
Figure 2. Global compilations of plant genera for 16 Permian and
Triassic stages. A: Temporal patterns of diversity and plant localities.
B: Spatial-diversity patterns, scaled in six size categories
within 10 degree latitudinal bins (largest squares, >75 genera; smallest,
1-15 genera).
Figure 3. Correlation of genus diversity and plant localities for
each Permian (P) and Triassic (T) stage (from data shown in
Fig. 2A).
Figure 4. A-E: Regional stage-level compilations of plant genera. F: Remaining data for terranes unassignable to five regions (geographic
units were delimited using tectonic and paleomagnetic evidence). Sequence and explanation of plots for each region as in Figure 2, except
that paleolatitudinal plots show locality distributions instead of within-bin diversity. Additional plot shows relative occurrences of genera
in each region, grouped into four categories: paleophytic (black: cordaites, gigantopterids, glossopterids, lycopsids, pteridosperms), mesophytic
(dark gray: cycadophytes, ferns, ginkgophytes, peltasperms, pinales), sphenopsids (light gray), and unassigned (white; stages
that are completely white [in B, E, F] have no plant record).
- Tracing the tropics across land and sea: Permian to present
- Ziegler, A.M., Eshel, G., Rees, P.M., Rothfus, T.A., Rowley, D.B. & Sunderlin, D. (2003). Lethaia, 36: 227-254.
ABSTRACT. The continuity through the past 300 million years of key tropical sediment types, namely coals, evaporites, reefs and carbonates, is examined. Physical controls for their geographical distributions are related to the Hadley cell circulation, and its effects on rainfall and ocean circulation. Climate modelling studies are reviewed in this context, as are biogeographical studies of key fossil groups. Low-latitude peats and coals represent everwet climates related to the Intertropical Convergence Zone near the Equator, as well as coastal diurnal rainfall systems elsewhere in the tropics and subtropics. The incidence of tropical coals and rain forests through time is variable, being least common during the interval of Pangean monsoonal climates. Evaporites represent the descending limbs of the Hadley cells and are centered at 10 degrees to 40 degrees north and south in latitudes that today show an excess of evaporation over precipitation. These deposits coincide with the deserts as well as seasonally rainy climates, and their latitudinal ranges seem have been relatively constant through time. Reefs also can be related to the Hadley circulation. They thrive within the regions of clear water associated with broad areas of downwelling which are displaced toward the western portions of tropical oceans. These dynamic features are ultimately driven by the subtropical high-pressure cells which are the surface signatures of the subsiding branches of the Hadley circulation. Carbonates occupy the same areas, but extend into higher latitudes in regions where terrestrial surface gradients are low and clastic runoff from the land is minimal. We argue that the palaeo-latitudinal record of all these climate-sensitive sediment types is broadly similar to their environments and latitudes of formation today, implying that the dynamic effects of atmospheric and oceanic circulation control their distribution, rather than temperature gradients that would expand or contract through time.
Fig. 11. Latitudinal frequency of coals (or peats) as summed by geological period from the Permian to the present. The data counts have been limited to one site per 5 degrees latitude and longitude quadrangle to minimize sampling bias and an adjustment has been made to account for the change in area of the quadrangles over the latitudinal range.
Fig. 12. Latitudinal frequency of evaporites as summed by geological period from the Permian to the present. The data counts have been limited to one site per 5 degrees latitude and longitude quadrangle to minimize sampling bias and an adjustment has been made to account for the change in area of the quadrangles over the latitudinal range.
Fig. 13. Latitudinal frequency of reefs as summed by geological period from the Permian to the present. The data counts have been limited to one site per 5 degrees latitude and longitude quadrangle to minimize sampling bias and an adjustment has been made to account for the change in area of the quadrangles over the latitudinal range.
Fig. 14. Latitudinal frequency of carbonates as summed by geological period from the Permian to the present. The data counts have been limited to one site per 5 degrees latitude and longitude quadrangle to minimize sampling bias and an adjustment has been made to account for the change in area of the quadrangles over the latitudinal range.
- Patterns of land-plant diversity, climate and geography in the Paleozoic and Mesozoic
- Rees, P.M. (2003). In: Evolutionary and Ecological Links Between Terrestrial and Marine Ecosystems in the Phanerozoic (Session 188). GSA abstracts, Seattle.
ABSTRACT. It is tempting to link broad-scale patterns of vegetation change observed through the Phanerozoic to concomitant changes in the marine realm, and to then invoke globally catastrophic events. However, such changes are typically subtle and can often be better understood by analyzing them in the context of gradual climatic and geographic changes. To illustrate this, 'raw' patterns of land-plant diversity (i.e. without considering climate and geography) are shown for the Paleozoic and Mesozoic of Europe and North America. Next, climate-sensitive sediments (e.g. coals, eolian sands and evaporites) introduce a somewhat independent means of determining broad scale patterns of climate change in terms of the precipitation/evaporation ratio. Finally, these patterns are assessed in the context of changing paleogeography and latitudinal motion, and reveal a more complex scenario of vegetation and climate change. Results are derived from analyses of data in the NCEAS Paleobiology and Paleogeographic Atlas Project (University of Chicago) databases, and the Paleomap Project. The available evidence shows that precipitation and plant diversity were highest in the low latitude 'tropical' regions during the Carboniferous and Early Permian, but were highest in the mid latitude 'temperate' regions during the Late Permian and Mesozoic. This change corresponds to the well-documented icehouse-hothouse transition, and raises the question of whether it also affected distribution patterns of shallow marine organisms. Such broad geoscience questions can be addressed by ensuring the interoperability of databases, an approach advocated by GEON (The Geosciences Network).
(Figures to come)
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