Bruce H. Tiffney

The Use of Geological and Paleontological Evidence in Evaluating Plant Phylogeographic Hypotheses in the Northern Hemisphere Tertiary

Phylogeography posits that the sequence of speciation events within a clade should parallel the geographic migration and isolation of members of the clade through time. The primary historical features that govern migration and allopatry in land plants are changes in physical geography (e.g., oceans, mountains, and deserts) and in climate (e.g., moisture, temperature, and day length), features that are often interrelated. If we assume that living genera retain physiological stability through time, much as they retain the morphological features that allow their identification, then these environmental features of the geologic past may be used to test phylogeographic hypotheses of living genera based on phylogenetic analysis. The history of the climatic and geographic features of the Tertiary of the Northern Hemisphere agrees with many phylogenetically based phylogeographic hypotheses of living angiosperm genera but indicates that some hypotheses require reanalysis. While the parallel comparison of phylogenetic hypotheses and historical biogeographic evidence is in its infancy, the reciprocal illumination of the two approaches shows great promise for future application.

Similarity of Mammalian Body Size across the Taxonomic Hierarchy and across Space and Time

Although it is commonly assumed that closely related animals are similar in body size, the degree of similarity has not been examined across the taxonomic hierarchy. Moreover, little is known about the variation or consistency of body size patterns across geographic space or evolutionary time. Here, we draw from a data set of terrestrial, nonvolant mammals to quantify and compare patterns across the body size spectrum, the taxonomic hierarchy, continental space, and evolutionary time. We employ a variety of statistical techniques including “sib‐sib” regression, phylogenetic autocorrelation, and nested ANOVA. We find an extremely high resemblance (heritability) of size among congeneric species for mammals over ∼18 g; the result is consistent across the size spectrum. However, there is no significant relationship among the body sizes of congeneric species for mammals under ∼18 g. We suspect that life‐history and ecological parameters are so tightly constrained by allometry at diminutive size that animals can only adapt to novel ecological conditions by modifying body size. The overall distributions of size for each continental fauna and for the most diverse orders are quantitatively similar for North America, South America, and Africa, despite virtually no overlap in species composition. Differences in ordinal composition appear to account for quantitative differences between continents. For most mammalian orders, body size is highly conserved, although there is extensive overlap at all levels of the taxonomic hierarchy. The body size distribution for terrestrial mammals apparently was established early in the Tertiary, and it has remained remarkably constant over the past 50 Ma and across the major continents. Lineages have diversified in size to exploit environmental opportunities but only within limits set by allometric, ecological, and evolutionary constraints.

THE RECIPROCAL INTERACTION OF ANGIOSPERM EVOLUTION AND TETRAPOD HERBIVORY

Wing, S.L. and Tiffney, B.H., 1987. The reciprocal interaction of angiosperm evolution and tetrapod herbivory. Rev. Palaeobot. Palynol., 50: 179-210. We have interpreted the history of angiosperm herbivorous tetrapod interactions based on the fossil record of the two groups. This history can be divided conveniently into four stages. Stage 1, lasting ~40 Ma (Barremian Campanian), was characterized by diverse large herbivores, few species of small herbivores, and r-selected angiosperms. The dominant interaction between herbivores and angiosperms during this stage was generalized herbivory. During Stage 2 (~ 10 Ma, Campanian Maestrichtian), small herbivores increased in diversity; larger angiosperms and larger angiosperm diaspores became more common. Generalized herbivory was still the dominant interaction in this stage, but frugivory/dispersal of angiosperm diaspores by small herbivores became more important. In Stage 3 (~ 25 Ma, Paleocene mid-Eocene) large angiosperms and large angiosperm diaspores were diverse; large herbivores were initially absent, later low in diversity. Frugivory/dispersal was common during this stage, generalized herbivory much less so. During Stage 4 (~ 30 Ma, Oligocene Recent), the relative importance of large vs. small herbivores and large vs. small angiosperms has varied by community, as has the relative importance of generalized herbivory vs. frugivory/dispersal. We infer the following evolutionary effects of angiosperms and tetrapods on each other. During Stage 1 generalized herbivory/disturbance by dinosaurs favored angiosperms that remained relatively small and r-selected. Increasing abundance and geographic spread of these r-selected angiosperms fueled the Late Cretaceous diversification of lowbrowsing ornithopod dinosaurs. The rarity of angiosperms with large diaspores provided little resource for a radiation of small herbivores. The low diversity of small herbivores created few opportunities for the evolution of small herbivore dispersal syndromes among angiosperms. The stability of angiosperm-vertebrate herbivore interactions during Stage 1 suggests this system of ecological relationships had internally self-reinforcing properties. The modest radiation of small herbivores during Stage 2 may indicate increased frugivory/dispersal. More common large angiosperm axes and diaspores show some angiosperm lines were becoming more K-selected. These imply a modification of the stable system formed during Stage 1. Extinction of all large herbivores at the K/T boundary destroyed Stage 1 ecological interactions and changed selective pressures on angiosperms. In the early Paleocene, generalized herbivory/herbivore disturbance was absent or uncommon. Denser vegetation, increased competition between plants, and increased seed dispersal/predation by small animals resulted in selection for larger seeds, diaspores and sporophytes. The distribution of resources in closed angiosperm vegetation permitted the radiation of small, arboreal, frugivorous birds and mammals, which in turn were important to the success of angiosperms with large, animal-dispersed seeds. Spread of arborescent angiosperm vegetation reduced resources and evolutionary opportunities available to larger mammalian herbivores, retarding their diversification, and in turn perpetuating low levels of generalized herbivory/disturbance. Stage 3 was another period during which angiosperm vertebrate herbivore interactions were stabilized by self-reinforcing behavior of the system. During Stage 4 increased seasonality began to favor shorter life cycles among angiosperms; herbaceous plants diversified and spread. Open, high-productivity vegetation was better exploited by large herbivores, which diversified, increasing generalized herbivory/disturbance that in turn created more habitat for r-selected angiosperms.

The Fayum Primate Forest Revisited

In Oligocene times, the Fayum area of northern Egypt was a subtropical to tropical lowland coastal plain with damp soils and seasonal rainfall that supported an abundance and variety of vegetation, including lianes (large vines), tall trees, and possibly mangroves, and a large and varied vertebrate fauna. The Oligocene marine strandline was close by and principal Jebel Qatrani Formation streams were probably brackish several kilometers inland due to tidal incursions. Sediments of the Jebel Qatrani Formation were deposited by several large meandering streams, associated with minor but sometimes extensive floodbasin ponds. These rocks provide no evidence for the former existence, in early Tertiary time, of a “Proto-Nile” River. Large accumulations of silicified fossil logs in the Jebel Qatrani Formation are autochthonous and the logs were transported only a short distance before burial. The Oligocene higher primates Aegyptopithecus, Propliopithecus, Parapithecus , and Apidium lived in this paleoenvironment and postcranial remains of Aegyptopithecus and Apidium demonstrate that these animals were arboreal. This scenario for the paleoenvironment of the Fayum area in Oligocene times differs greatly from the nearly treeless, sparsely vegetated, semiarid sahelien Oligocene Fayum paleoenvironment populated by terrestrial primates that was recently proposed by Kortlandt (1980) .

Angiosperm growth habit, dispersal and diversification reconsidered

SummaryPrevious studies have sought to elucidate the relationship between dispersal mode (biotic versus abiotic) and the taxonomic diversification of angiosperm families, but with ambiguous results. In this study, we propose the hypothesis that the combination of (1) the large seed size required of plants germinating in closed, light-poor environments and (2) the necessity to move disseminules away from the maternal plant in order to avoid intraspecific competition, predation and pathogens should favour biotically-dispersed relative to abiotically-dispersed woody arborescent angiosperms, resulting in higher diversification of the former. In this paper, we seek patterns of diversification that support this hypothesis. We examine the association between dispersal mode, growth habit and taxonomic richness of monocotyledon and dicotyledon families using (1) contingency table analyses to detect the effect of dispersal mode on the relative abundances and diversification of woody versus herbaceous taxa and (2) non-parametric analyses of variance to detect the statistical effect of dispersal mode on taxonomic diversification (mean number of species per genus, genera per family and species per family) in monocot and dicot families dominated by biotic or abiotic dispersal. We found a clear statistical effect of dispersal mode on diversification. Among families of woody dicots, dispersal by vertebrates is associated with significantly higher levels of species per genus, genera per family and species per family than is abiotic dispersal. The same pattern is observed among woody monocots, but is not significant at the 0.05 level. Among families of herbaceous monocots and dicots, the situation is reversed, with abiotically-dispersed families exhibiting higher levels of diversification than vertebrate-dispersed families. When woody and herbaceous families are pooled, there is no association between dispersal mode and diversification. These data coincide with evidence from the fossil record to suggest vertebrate dispersal has positively contributed to the diversification of woody angiosperms. We suggest that vertebrate dispersal may have promoted the diversity of extant taxa by reducing the probability of extinction over evolutionary time, rather than by elevating speciation rates. Our results suggest vertebrate dispersal has contributed to, but does not explainin toto, the diversity of living angiosperms.

Character diversification and patterns of evolution in early vascular plants

Available data on the stratigraphic ranges of latest Silurian and Devonian vascular plant macro-fossils (sporophytes) and spores provide insights into the tempo and mode of early tracheophyte evolution. Patterns of diversification, origination, and extinction conform in general to the predictions of Sepkoskis kinetic model of diversification. Rates of generic origination and extinction vary not only through time but also between organ systems for a single time interval. This fact, coupled with data on longevity and turnover and comparative morphological observations, can be used to document mosaic evolution in early vascular plant history. Mosaic evolution is an important theme in plant evolution; indeed, what we recognize as macroevolutionary events often correlate with brief periods of pronounced mosaicism. Such evolutionary patterns reflect the developmental biology of tracheophytes in which individual organs often have life spans that are considerably shorter than the life of the whole plant. Under these conditions, individual organs or organ systems can respond to different sets of evolutionary pressures. The major period of early vascular plant diversification occurred during the late Early and early Middle Devonian Period, 30 Myr or more after the origin of the group. Such lags in diversification are not uncommon in the fossil record. Sometimes they reflect extrinsic controls on diversification, but in other cases they appear to be a consequence of intrinsic rates of origination and extinction.

Phanerozoic Land-Plant Diversity in North America

A strong correlation exists between the outcrop area of nonmarine rocks deposited during a given geologic period and the observed vascular plant diversity for the same period; however, diversity residuals characteristic of certain periods may have underlying biological causes. Within-flora diversity changes through time indicate that stepwise increases in community species packing have accompanied major tracheophyte evolutionary innovations. Total and within-flora data suggest that the track of North American land-plant diversity has been similar in nature, but not in timing, to that inferred for marine invertebrates.

Phylogeography, Fossils, and Northern Hemisphere Biogeography: The Role of Physiological Uniformitarianism1

Abstract Biogeography is one of the most synthetic of biological undertakings; it requires placing a substantiated phylogenetic model in a geological, climatological, and ecological context, all of which shift through time. In the past two decades, the application of cladistic and molecular techniques has diversified our grasp on phylogeny. This has allowed the formulation of hypotheses of past distribution patterns based on samples from available living material and algorithms for their interpretation. Fossils contribute to these cladistic approaches by adding morphological checkpoints to character associations in time and by providing a basis for estimates of rates of divergence. However, fossils also check these hypotheses by direct occurrence (does a fossil of the taxon occur where predicted?) and by ecological suitability (is it reasonable that the taxon could occur in the predicted environment?). The first test is straightforward if difficult, requiring the finding of a specific fossil in a specific place and time. The second is based on the assumption of physiological uniformitarianism—that fossil and modern taxa united by a common morphology possess similar physiologies. If correct, then hypotheses of past distribution must accord with the predicted physiological tolerances of the taxon in question. Application of physiological uniformitarianism to phylogeographic hypotheses, together with new paleontological data, suggest (a) the validity of many established phylogeographic hypotheses; (b) the need to reevaluate others; and (c) the recognition that the North Atlantic land bridge likely functioned as a link between the Old and New Worlds into the Later Tertiary, contrary to this authors earlier papers.

Integration of Paleobotanical and Neobotanical Data in the Assessment of Phytogeographic History of Holarctic Angiosperm Clades

Attempts to reconstruct phytogeographic history based exclusively on either modern or fossil distribution patterns may give misleading results. Local extinction within a widespread clade can undermine phylogeographic hypotheses based on modern‐day distribution patterns; e.g., within the Aceroideae, Dipteronia is the sister group to Acer and is presently known only from Asia; the discovery of Dipteronia in the North American Tertiary requires a rethinking of hypotheses based solely on the modern distribution of the two genera. Conversely, the fossil record alone cannot provide a well‐resolved phytogeographic history because the availability of well‐preserved fossils for a particular time interval differs among regions. The most informative method for deducing the phytogeographic history of a given clade is to conduct phylogenetic analyses that include both fossil and extant representatives to deduce the sequence of dispersal and/or vicariance events indicated by the most parsimonious trees. The choice of taxa for such investigations should be at least partially based on the richness and quality of paleontological data. The Ulmaceae sensu stricto are cited as an example to illustrate the effect of including versus excluding an extinct genus from morphological phylogenetic analyses. Cedrelospermum (Tertiary of southern Mexico through midlatitude North America and Europe) is resolved as a link, both phylogenetically and geographically, between the Central and South American taxa Ampelocera and Phyllostylon and the genera of North America, Europe, and Asia. Inclusion of the extinct taxon in the data matrix along with the extant taxa significantly alters the resulting phylogeographic model.

Late Tertiary floral assemblage from upland gravel deposits of the southern Maryland Coastal Plain

A diverse flora has been discovered in a dark clay lens in upland gravel in southern Maryland near Brandywine. More than 49 taxa have been identified in the assemblage, which includes leaves, seeds, fruits, pollen, and a Taxodium (bald cypress) trunk. The vegetation is dominated by deciduous trees and vines. Four taxa are now absent from North America but survive elsewhere; one is extinct. A late Miocene age and warm-temperate climate are inferred from the flora. The clay lens probably represents a cutoff distributary in the extensive braided stream system that covered the area and is unique in Maryland. Similar dark clays have been described from Miocene sands and gravels in New Jersey. The Brandywine flora is the first direct evidence of the Miocene age of part of the fluvial upland deposits of Maryland. On the basis of the age inferred from the flora, the Brandywine deposit is correlated with the St. Marys Formation or the Eastover Formation, which are upper Miocene shelly marine units south and southeast of Brandywine.