For the part fifty years, the concept of evolutionary rates has been developed largely in an evolutionary or phenetic framework. Many authors discussed rates, but under previous systematic paradigms no standardized methods developed to provide a uniform and general framework in which temporal properties of different lineages could be objectively measured and compared.

We review recently developed methods for measuring rate-related properties of lineages that are based on phylogenetic analyses. Rate measurements are made directly from phylogenetic data matrices and cladograms. Because they benefit from the standardized procedures required to compile a data matrix, these methods are potentially exportable to a wide range of phylogenetic studies. Four potential factors relevant to the study of evolutionary rates in a cladistic framework have been analyzed with these methods: (1) morphological changes, (2) age and duration, (3) cladogenesis, and (4) species-diversity. We investigate interactions among these factors.

Underlying assumptions in using a cladogram to calculate rates of evolution are: (1) the tree reflects the history of the group, and (2) the distributions of character states on the tree reflects the true distribution of character states during the evolution of the group. The calculation of rates from a cladogram requires that: (1) the cladograms are derived from parsimony analysis (e.g., PAUP, HENNIG86) of species coded for discrete character states; (2) the phylogenetic pattern (or branching sequence) is superimposed on a geological time scale in which each species is mapped according to its geological age (temporal cladogram); (3) phylogenetic pathways (unidirectional series of consecutive cladogenetic events) are determined in such a manner that the selected origin is a hypothetical ancestor to the terminal taxa selected; and (4) rates are calculated along selected phylogenetic pathways.

Rates may be calculated as the number of changes—including autapomorphies, synapomorphies, and homoplasies—per unit of time. Alternatively, relative measures of rate may be obtained by comparing the average number of changes for an entire data matrix with changes in data subsets within the matrix. Five types of rates of morphological evolution can be determined and quantified along a phylogenetic pathway: (1) rate between two consecutive cladogenetic events, (2) rate during a geological period, (3) rate during a fixed period of time in millions of years, (4) relative rates of change for different morphological data subsets, such as dentition versus skeleton, and (5) relative rate along a selected segment of the cladogram, compared to the average rate measured for the cladogram as a whole. Various methods for comparing rates are investigated, such as Spearman Rank correlation, Fourier analysis, time series, and homoplasy index.

Classic examples of rates of morphological evolution were previously taken from bivalves, echinoderms, lungfishes, coelacanths, and mammals. In the present study, rates of evolution within and/or between the Dipnoi (lungfishes), the Actinistia (coelacanths), and the Mammalia are calculated and compared.

The central evolutionary, ecological and paleoceanographic questions of the American tropical Neogene relate to how and during what time the Central American Isthmus formed. Geographically, closure was located between the southern edge of the Chortis Block in southern Nicaragua and the Atrato Valley in Colombia. In this region we describe, on the Caribbean side, five Neogene sedimentary basins. They are the Atrato, Chucunaque, Gatun, Bocas del Toro, and Limon Basins. On the Pacific side the Neogene sediments formed as part of the Central American Trench and are well exposed in a series of uplifted blocks on the Nicoya, Osa and Burica Peninsulas. Our analysis allows 1) a construction of the sequence of contrasting sedimentary environments which characterize the different basins, giving a composite geological history of the isthmus for the Late Neogene and 2) identifies the comparable biofacies from the different basins which allow and constrain the evolutionary and ecological questions to be posed concerning the effect of the isthmus as a biogeographic barrier. Temporally, from it's partial emergence in the Middle Miocene, the isthmus shallows by the Early Pliocene (3.5–3.4 Ma) to less than 50 m (Duque-Caro, 1990) when there is a marked differentiation of shelf marine macrobenthic species between the Caribbean and the Pacific. The evidence from reliably dated, large, diverse exchanges of North and South American vertebrates on land constrains the final closure date to not later than 2.8–2.5 Ma (Marshall, 1988). Given that no conclusive evidence for final closure can come exclusively from a study of sedimentary facies, when depths of less than 50 m are involved, the present window of almost 1 Ma, during which final closure must have occurred, will only be narrowed further by the detailed study of very shallow-water fossil clades and complementary molecular data. Present studies indicate that such clades are abundantly preserved.

Chemosymbiosis can be identified in fossil taxa and followed through the fossil record with some certainty if several independent criteria are met. No hard part morphology reliably reflects a chemosymbiotic lifestyle, but soft part morphology can be used to demonstrate that chemosymbiosis is primitive in some groups. Throughout the evolutionary history of a taxon, faunal and facies associations can provide support for a chemosymbiotic interpretation. Biogeochemical evidence from fossil organic matter may, in some cases, demonstrate the δ13C depletion recognized as being chemosymbiotic in origin.

Morphology of extant lucinacean bivalves indicates that the superfamily was primitively chemosymbiotic and suggests that the Ungulinidae and some of the Thyasiridae have secondarily lost their bacterial symbionts. This observation, along with facies and faunal data, suggests that the family Lucinidae has always been chemosymbiotic and that the Lucinidae are a reliable group to use in evaluating the paleobiological effects of chemosymbiosis.

Biogeochemical evidence does suggest that lucinid bivalves were chemosymbiotic in the past and stable isotope analyses remain the only direct method for evaluating chemosymbiosis in the fossil record. For taxa with no extant members but with interesting faunal or facies associations, δ13C of the organic matrix is still the best hope of evaluating this trophic strategy.

The scientific community is in great need of input from paleontologists today in two key areas of societal concern: the historical basis of global change and losses of biodiversity. Paleontologists, with their unique perspective on rates of change in biotic communities and their training in filtering signal from noise in the fossil record, are the best placed scientists in biology to approach these problems from an historical viewpoint. In the classroom we give lip service to the central role of paleontology in understanding these problems. Yet with the exclusion of Quaternary (and particularly Recent) paleoecology from the mainstream of our field, we have abrogated this responsibility to other disciplines. Paleontologists are in danger of losing the opportunity to provide guidance on the very issues in paleontology where political interest and funding will lie in the not too distant future. As opportunities for employment of paleontologists in the petroleum industry fade, it is critical that academic paleontologists define new directions for graduate education in our field.

The paleontological community needs to reincorporate Quaternary paleoecology into its mainstream, emphasizing the importance of a paleobiological perspective in environmental problem solving. As the developers of theory and methodology in the interpretation of the fossil record it is our responsibility to set the agenda as to how paleobiology should be utilized. Our professional societies should provide leadership as advocates for funding research and training in the new areas of applied paleobiology, lest paleobiology (as we define it) be marginalized and traditional paleontology programs be viewed by their home institutions as increasingly irrelevant. Employment opportunities in biostratigraphy are a thing of the past; applied paleontology must redefine itself for career opportunities at the top of the column, in such areas as recent climate change or the fossil record of human-induced ecological disturbances. The PIRLA Project (Paleoecological Investigation of Recent Lake Acidification) provides an excellent example of applying paleobiology to such problems, using the Recent diatoms, crustaceans, insects and pollen fossils to understand the chronology of the acid rain problem in eastern North America.

Academic departments bear a responsibility to bring the important new applications of paleobiology into the classroom, demonstrating its societal relevance and training students to avail themselves of potential opportunities for paleobiologists in global change and biodiversity research. Recent developments in taphonomy or stratigraphic ordering of fossils could be extremely powerful tools if applied to environmental change problem solving. We need to make our students marketable by spending more time in the classroom teaching them about Recent diatom paleoecology and less on brachiopod biostratigraphy. Otherwise paleobiology may go the way of Egyptology.

The climate of the Amazon during the last northern glaciation may be taken to represent the normal climate of the basin throughout the Quaternary, since boundary conditions for Amazon and neotropical environments had not otherwise changed since the Andean orogeny and emplacment of the Isthmus of Panama late in the Teritary.

The few radiocarbon dated data describing the climate of the ice age Amazon suggest that the principal climatic forcing was cooling in excess of 6 o C, associated with modest reductions in precipitation. Unlike Africa, the New World tropics were not noticeably arid. The evidence for cooling comes from paleoecological data at the foot of the Equatorial Andes, where temperature sensitive taxa had descended 1500 m into elevations that now support rain forest. Pollen data from all elevations of the Andes show that climates continued moist throughout glacial cycles, thus making appropriate the application of moist air lapse rates to substantial evidence for cooling in the high Andes also. Evidence that reductions in precipitation were modest in the lowlands come from new pollen records from 2-300 m elevation in the central Amazon of Brazil.

A long record of lake sediments from lowland Panama possibly represents a complete glacial cycle. Pollen, phytolith, and other paleoecological data show both cooling and modest reductions in precipitation, in parallel with the Amazon records.

At all stages in glacial cycles, neotropical forests have been subjected to intermediate disturbance tending to prevent competitive exclusion. But the forests have never been fragmented or displaced into “refugia”. Vicariance has always been provided by the scales of geography and local disturbance. The forests are dynamic systems of species whose adaptive norms are appropriate to climates of the ice age earth, but which are able to form temporary accomodations in response to climatic change.

The modern Amazon rain forest was formed as an ephemeral response to the short-lived warm episode of the Holocene. Local concentrations of species, like those noted on elevated regions surrounding the Amazon basin by refugial theorists, can best be explained because occupying regions of greatest environmental change, with the consequent pattern of invasion and reinvasion necessary with each climatic shift.

A hundred years ago, Anomalocaris canadensis Whiteaves, 1892, was described as the body of a Phyllopod Crustacean. At NAPC III in Montreal in 1982, Whittington and Briggs showed that Anomalocaris canadensis was a claw, one of a pair at the front of an extraordinary predatory animal, whose jaws had previously been described as a jellyfish (Peytoia). The search to understand Anomalocaris and its relatives continues. So does the mistaken allocation of separated parts.

In 1991, the first complete Anomalocaris canadensis was collected. It has a fan tail, much like the tail of another Burgess Shale conundrum, Opabinia. Another new specimen shows that its head and claws were more flexible than previously realized, and its eyes were on stalks.

The large feeding claw, Appendage F, was allocated first to the arthropod, Sidneyia, by Walcott, then to the other Anomalocaris species, A. nathorsti, by Whittington and Briggs. The small size and lack of strong cross spines on the claws of A. nathorsti suggest that Appendage F probably came from another anomalocarid. Another puzzling feature on A. nathorsti is the thin, segmented structure running across the abdomen, one per body segment, ending in a club-shaped extremity on each side.

A third anomalocarid is now recognized in the Burgess Shale. Its front half is composed of 3 or 4 carapace like parts previously named Hurdia and Proboscicaris. Two small sheathed claws on stalks are attached at the rear of the “carapaces”. Hanging below the rear of the “carapaces” is a grasping, feeding organ composed of a pair of claws and Peytoia jaws with an inner set of teeth. It is connected to the body which has 11 segments and a tail. The two “oblique compressions” and the Peytoia jaws with the extra group of “spines” within the mouth allocated by Whittington and Briggs (1985) to Anomalocaris nathorsti almost certainly belong to the Hurdia anomalocarid.

It is evident that attempting to allocate anomalocarid parts to a particular anomalocarid is much like a Pin-the-Tail-on-the-Donkey game. In both cases the players are operating in the dark. The differences are that there is an unknown number of anomalocarids in the Burgess Shale and not only do they disarticulate easily, but they often have similar parts. As a consequence, our understanding of the anomalocarids is almost completely dependent on finding articulated specimens with the parts in place. This in turn depends on the success of field excavation. It took 100 years and 12 seasons of excavation to get the first complete Anomalocaris canadensis.

The most significant change in Pliocene oceanic circulation resulted from closure of the Tropical American Seaway between the Caribbean Sea and Eastern Pacific Ocean around 3 Ma. Faunal changes in Caribbean shallow-water marine organisms such as mollusks and corals have been attributed to possible environmental changes associated with this event, including cyclical cooling, initiation of a carbonate regime in the southern Caribbean, and upwelling of deeper waters on the continental shelf, but their occurrences and timing have been unclear.

This study uses the ecological and evolutionary record of benthic foraminifera of the upper continental slope to inner continental shelf to investigate environmental change in Caribbean shallow waters with respect to final closure of the interoceanic seaway. Benthic foraminifera are useful as environmental indicators so periods of increased taxonomic turnover should correspond to times of environmental change. Over 100 species commonly occurring in deposits of Caribbean Panama and Costa Rica dated from 6.5 to 1.6 m.y. were taxonomically standardized with existing literature and collections to produce stratigraphic ranges within the Caribbean region.

Although an average common species has lived from Early Miocene times until today, an increase in first appearances suggests that an interval of ecological restructuring occurred on the continental shelf to upper slope in latest Miocene time. The last 15 m.y. includes about 45% of the first and last appearances, 70% of which are comparably dated in other Caribbean strata. For the period from 15 to 3 Ma, about 75% of first appearances occurred between 7 and 3 Ma, and more than twice as many occurred between 7 and 5 Ma as occurred before or after that interval. Comparable numbers of continental shelf and slope taxa have first occurrences between 7 and 5 Ma, indicating a general change on the continental shelf to upper slope in the latest Miocene which preceded closure of the interoceanic seaway by 2 to 4 m.y. Few extinctions occurred in the last 7 m.y.; 86% of the common taxa less than 7 m.y. old in Panama and Costa Rica have survived to the present. The appearance of carbonate-loving species in Panama to Costa Rica at 4.6–5.0 Ma and northern Colombia by 5.0 Ma indicates a well established carbonate regime in the southern Caribbean by earliest Pliocene time. Benthic foraminiferal assemblages show no evidence of upwelling in the Panama-Costa Rican region through the Pliocene.

The Late Miocene environmental changes in shallow Caribbean waters preceded isotopic changes in open-ocean surface waters that occurred 4 to 3 Ma. Ecological restructuring took place in the latest Miocene, several m.y. before the seaway closed, and any subsequent environmental changes had little effect on benthic foraminifera of the Caribbean continental shelf.

The marine vicariant event resulting from the Pliocene emergence of the Central American Isthmus presents a unique opportunity for calibrating rates of molecular evolution. The synchronous fragmentation of the ranges of previously widespread taxa into Western Atlantic and Eastern Pacific components (geminates) enables one to make comparisons of rates among higher taxa on the same time scale and to evaluate the regularity of rates of molecular evolution among all species sampled. Other advantages of this approach are that the time scale (approximately 3 Ma) is one of particular interest for evolutionary biologists concerned with speciation and one that minimizes the ambiguities associated with augmentation of divergence values to account for multiple hits at a site. The divergence values derived for geminate pairs are independent, allowing statistical evaluation of variance in rates.

The current popularity of the relative rates test as the final arbiter of questions regarding rates and rate variation is primarily a matter of convenience and not a reflection of methodological superiority. A review of the commonly used techniques for calibrating rates of molecular evolution shows that each approach has limitations. Temporally based calibrations of rates are necessary complements to time-independent comparisons.

Interpretation of transisthmian molecular comparisons in the literature have in many cases been unduly influenced and confused by molecular clock assumptions and the restriction of studies to single higher-level taxa. Analysis of the apparently contradictory published data as well as new results from sequence comparisons of fishes, urchins and snails suggests a synthesis: taxon specific rates of molecular evolution, with reduced variance within taxonomic groups and great variance among all groups sampled.

Ediacaran taxa are a characteristic element of latest Precambrian biotas, with an effectively global distribution. Their time range is not well understood, but with one possible exception from western Canada Ediacaran faunas appear always to post-date the late Precambrian glaciations. There is also growing evidence that many Ediacaran taxa disappeared before the Precambrian-Cambrian boundary. These disappearances traditionally have been ascribed to changes in taphonomic circumstances, but a series of extinctions is a plausible alternative. Ediacaran fossils pose two major problems: Notwithstanding the reasons for their disappearance shortly before the Precambrian-Cambrian boundary, was their demise total or did some forms persist into the Cambrian? Second, is the traditional view that Ediacaran taxa are metazoans, many of a cnidarian grade, correct? Recently Seilacher, Bergström and others have argued that the Ediacaran organisms have a distinctive bauplan, difficult to reconcile with known phyla and possibly different from any metazoan.

In the Cambrian, Burgess Shale-type faunas are the principal source of information on soft-bodied metazoans. The differences between them and Ediacaran assemblages are largely self-evident, but there is now unequivocal evidence for at least one Ediacaran survivor from the Middle Cambrian Burgess Shale of British Columbia. This is a sea-pen-like animal, known from three specimens (one adult about 20 cm in length, and two juveniles). The fossils consist of a broad frond, with branches arising from a central axis on one side, while the opposite side is smooth apart from longitudinal ridges. The frond extends into a blunt holdfast that presumably was embedded in the muddy silt of the sea floor. This fossil is strikingly similar to the Ediacaran taxon Charniodiscus, best known from South Australia. The Burgess Shale example shows two important features. The first are pustule-like structures, possibly zooids, both on the branches and adjacent to the axis. The second feature is evidence for connections between the branches and axis, possibly representing canals. These features both support a comparison with extant pennatulaceans, and suggest that at least some Ediacaran taxa are correctly assigned to the metazoans.

Also occurring in the Burgess Shale is an enigmatic bag-like organism Mackenzia costalis. Clear evidence exists for it being benthic, but its mode of feeding is uncertain. The interior appears to have consisted largely of a spacious cavity, probably sub-divided by longitudinal partitions. In addition, an elongate strand may represent a discrete organ, perhaps connected with digestion or reproduction. No exact equivalent to Mackenzia appears to occur in Ediacaran assemblages, but bag-like taxa are a common component. These include erniettids, best known from Namibia, and Platypholina, from the White Sea region of Russia.

Estimating rates of evolution, whether taxic, morphological, or molecular, entails numerous conceptual and methodological difficulties. Some of these may be ontological: (1) because assigning rank to supraspecific taxa, even within a cladistic framework, is never entirely objective, rates based on enumeration of taxa of a given rank are questionable because the entities being counted are not likely to be comparable in any theoretically meaningful sense, (2) rates of character-state change assume those changes can be enumerated unitarily, but in what sense is a character-state transformation of one character “equal” to that of another character? (3) rates of character change within a species, or among species, presupposes that “species” have been individuated correctly and comparably, yet in the paleontological record at least, only character-state information is available to individuate those taxa: different concepts of species imply rates may be measured differently.

Difficulties in estimating rates may also be methodological. Rates of character change are sometimes estimated by transforming intertaxon differences/similarities to distances and then fitting them to a tree topology. Such transformations have the potential for error if distances are not corrected for homoplasy. With molecular data, these corrections necessitate assumptions, or empirical estimates, of patterns of character-state change (such as variation in probabilities of transition versus transversion substitutions) yet those parameters are themselves generally dependent upon some assumptions of relationships. Moreover, the values of those parameters will often vary depending upon the divergence times of the taxa being studied because of the accumulation of homoplasy.

While rates of character change are seemingly best studied by optimizing those changes directly on a tree, many factors can influence estimates of relative rates along each branch: (1) for a given set of taxa, there may be multiple equally parsimonious trees, each with different topologies and with different patterns of character optimizations, (2) even if there is a single most parsimonious tree, characters can be optimized in different ways, thus changing measures of rates, (3) different outgroups can change optimizations (and relationships of the ingroup) and thus lead to differences in rate estimation, and (4) adding or subtracting taxa (the taxic sample) can often alter patterns of optimizations and thus estimates of relative rate; thus assumptions about the extent of extinction within the group being studied are directly relevant for any determination of rates of change along branches leading to the taxa included in the sample.

Estimation of absolute rates presents additional difficulties because patterns of change within or across taxa must be calibrated to time. Rates depend upon assigning ages to lineages and the taxa being counted. Outside a cladistic framework accurate assignment is questionable, but even within a cladistic framework it is not at all straightforward.

None of these difficulties are arguments against efforts to measure rates of change, but to one degree or another they will have effects on the accuracy of our estimates and thus may need to be considered in any given analysis.

With the recent rapid improvement in the quality of the fossil record in both polar regions it has become possible to examine critically the development of high-latitude faunas and floras through time. Within arctic regions, distinctive biotas have been present, at least intermittently, since the early Permian, and in antarctic regions they can be traced back to the early Middle Devonian. It would appear that, whenever continents (and continental shelves) moved into the high latitudes they were the sites of significant biotic differentiation.

To investigate the ways in which taxa may have accumulated in the high latitudes through time, three simple global models have been proposed. In the first of these it is envisaged that major groups of plants and animals arose in the low latitudes and disseminated subsequently into the polar regions. Here they would become relicts and the latter would be regarded as refugia. The second model is almost exactly the reverse of the first in that it proposes that certain taxa arose in the polar regions and then spread, through time, into the low latitudes. Such a process may at first sight seem less likely, but the Antarctic fossil record in particular is providing important evidence to suggest that certain major groups of both plants and animals had a high-latitude origin. The third model differs substantially from the previous two in that it makes no a priori assumptions about either centres of origin or the process of dispersal. It merely states that, at certain times in the past, widespread distribution patterns have been disrupted in the low latitudes to form disjunct populations in the northern and southern hemispheres. It results in the classic bipolar pattern, which can now be traced back to at least the Early Jurassic period.

A major phase of Jurassic - Cretaceous bipolarity can be attributed to tectonic vicariance as the Pangean supercontinent disintegrated, and a major late Paleogene - early Neogene one can be related to climatic vicariance. Such hypotheses are attractive as they are testable by cladistic analysis. Although data available so far are limited, both fossil and living benthic molluscs offer considerable scope for future work.

Inoceramidae (Bivalvia) was a diverse, cosmopolitan family of large Cretaceous bivalves which occupied a wide range of marine environments, and experienced high rates of speciation. For biological and taphonomic reasons inoceramid taxonomy has been based almost exclusively on only two characters: shape and ornament. These characters commonly display high degrees of intraspecific variability. Previous biometric studies, using linear and angular measurements (eg. shell length, umbonal angle), have successfully discriminated between closely related species, and have overturned earlier qualitative taxonomies. Even comprehensive linear and angular measurements suffer from several disadvantages. They are restricted by instrumental limitations, are time consuming to gather, and neglect much information inherent in outline shape. Hence, the present study attempts to quantify differences in inoceramid shape and ornament using outline shape analysis complemented by a few simple distance measures. A digitised outline can be exactly described by a set of elliptic Fourier coefficients, and sets of such coefficients are treated as variables in a multivariate analysis of shape.

These methods have been used to examine the cosmopolitan, morphologically highly plastic, and highly subdivided Albian species Birostrina concentrica (Parkinson) and related forms. Collections from New Zealand (southern high latitude), England (northern high latitude), and Switzerland (Tethyan) show significant differences in the shape and maximum size of individuals. Preliminary analyses, however, have shown that within any region it is difficult to identify distinct sub-groupings based on shape or ornament. Furthermore, the total volume of morphospace occupied by B. concentrica (s.l.) can be accounted for largely by changes in morphology through ontogeny. In other words, for example, the change in shape of an individual through ontogeny can exceed the morphological distance between described subspecies. Ongoing morphometric examination of populations from different stratigraphic horizons is helping to unravel evolutionary and biogeographic patterns which are otherwise difficult to demonstrate.

Shape analysis is a tool that is largely underexploited by macropalaeontologists, and is particularly useful for the description of taxa with few landmarks or easily defined characters.

The mid-Cretaceous (Aptian-Turonian) was a critical interval in the modernization of terrestrial ecosystems. In particular, the rapid transition from vegetation dominated by pteridophytes (ferns, lycopods and sphenopsids), cycadophytes (true cycads, Bennettitales, “pteridosperms” with pinnate foliage) and conifers, to one dominated by angiosperms marks a pivotal change in the evolution of terrestrial floras. Current knowledge of the paleoecological circumstances of this transition is still rudimentary and based almost entirely on macrofloras and palynofloras from mid-to high latitudes of the Northern Hemisphere. Information from low paleolatitude areas is especially sparse and based almost entirely on palynofloras. Ongoing syntheses of published palynological data document the similarity of mid-Cretaceous palynofloras in a broad equatorial zone ranging from Ecuador in the west to Papua-New Guinea in the east (Africa-South America Floristic Province of Hemgreen). Palynofloras from this area are characterized by a high diversity and abundance of elaterate and ephedroid pollen grains (both probably gnetalean), low diversity of saccate conifer pollen grains and a paucity of pteridophyte spores relative to contemporaneous mid- and high latitude regions. Frequently, these palynofloras also show high levels of Afropollis and Classopollis-pollen (produced by probable winteroid angiosperms and extinct cheirolepidiaceous conifers respectively). Macrofossil floras corresponding to this low paleolatitude floristic assemblage are sparse but the assemblage of macrofossils now available from the from the Santana Formation (probable Albian) of north-eastern Brazil shows conifer leafy shoots (Araucariaceae or Cheirolepidiaceae) interspersed with macrofossils of ferns, various “pteridosperms'” occasional angiosperms, and possible Gnetales. Many of the plant fossils show structural features consistent with growth in arid environments (e.g., small leaf size, thick leaf textures, well-developed indumentum). The fossil record of woods from low latitude areas is difficult to evaluate because of uncertainties in dating many of the specimens that have been described. Previous analyses have suggested that woods from Cretaceous low-latitudes show only faint growth rings, however, in recently collected specimens from the Albian of Niger growth rings are marked. Taken together, the weight of paleobotanical data are consistent with the distribution of climatically sensitive sediments (e.g., presence of evaporites and aeolian sands, absence of well-developed coals) which has been interpreted to reflect at least seasonal aridity. Although existing paleobotanical data are sparse they provide no evidence for rainforests in low latitude areas during the mid-Cretaceous.

Beginning at around the late Cenomanian palynofloras from low paleolatitudes undergo a substantial compositional change (the transition to the Palmae Floristic Province of Herngreen & Chlonova). Classpollis pollen becomes much less abundant, the diversity and abundance of putative gnetalean pollen declines, while the abundance and diversity of angiosperm pollen (particularly forms probably referable to the Palmae) increases. Fossil woods associated with Campanian and Maastrichtian palynofloras from low latitudes show only weak evidence of growth rings. These data may imply a more equable distribution of rainfall than during the mid-Cretaceous and perhaps the initial, local, development of tropical rainforest vegetation. A latest Cretaceous-Early Tertiary initiation of tropical rainforest environments has important implications for patterns of diversification, not only in angiosperms but also in several of the most diverse lineages of nonangiosperm land plants, particularly the leafy liverworts (Jungermanniales), homosporous lycopods of the genus Huperzia, heterosporous lycopods of the genus Selaginella, and the “higher” filicalean ferns. In all of these groups the majority of extant species are restricted to tropical, frequently rainforest environments. While the origin of these groups may substantially predate the Cretaceous, the bulk of their extant diversity may have arisen over the last 70–50 million years.

For most of the Twentieth Century the angiosperm archetypal flower has been viewed as relatively large, multiparted, with spirally arranged fleshy appendages, and as being probably beetle pollinated as in some extant Magnoliales. However, the preponderance of fossil evidence indicates that flowers with such characters do not appear until the mid-Cretaceous, well after smaller simpler fossil flowers such as platanoids and chloranthoids. Winteraceous and Chloranthaceous pollen appears more or less simultaneously in the Lower Cretaceous, but rapidly mounting evidence for mosaicism in Cretaceous taxa makes it unwise to extrapolate floral structure on the basis of dispersed pollen. Mid-Late Cretaceous fossils illustrate an increasing proportion of simple flowered Rosidae in the angiosperm flora. We report new fossil evidence of charcoalified flowers and fruits representing at least 20–30 diverse angiosperm taxa from the Cenomanian and Turonian deposits of the Atlantic Coastal Plain. These fossil flowers include representatives with hypanthia and floral cups, sympetaly, syncarpy, inferior ovaries, campylotropous ovules, nectaries of various forms, specialized anther dehiscence, epipetalous stamens, and connate filament tubes. Major taxonomic groups (as defined by Cronquist) represented by these fossils include Dilleniidae, Magnoliidae, Rosidae, monocots, and possibly Caryophyllidae. Thus, the early Late Cretaceous angiosperm flora had greater floral diversity than has previously been documented. This array of floral structures includes features that are now associated with bees and other specialized insect pollinators, thus providing a new perspective on the evolution of insect pollination.

The historical and prevailing view regarding the distribution of nautiloid cephalopods is one of cosmopolitanism. There are several objections to such a sweeping view of this major group of marine invertebrates, but only the most significant are addressed here. First, unlike endemism, there is no clear agreement on the meaning of the term cosmopolitanism as used in biogeography. It is thus extremely difficult to gain a historical perspective without access to original data. I have found the term used for as few as four occurrences on four modern landmasses without reference to the paleogeographic relationships of these landmasses. Second, while a few nautiloid groups did compile impressive dispersal statistics, the fossil record clearly reveals that such periods of dispersal were generally brief in geological terms and that the group or groups involved did not colonize all available landmasses. Third, nautiloids were incapable of developing cosmopolitan distributions unless climatic constraints were removed by changes in the global system or by positioning all landmasses within the sub-tropical to tropical latitudes. Since there is no convincing evidence that either event occurred during the 520 million years of nautiloid evolution, it is perhaps more appropriate to view the distribution of nautiloids in terms of the number of landmasses colonized relative to the number of landmasses available for colonization. For nautiloids, the number of landmasses available for colonization was always fewer than the number of landmasses comprising the global paleogeography during any one slice of geologic time. Nautiloid genera restricted to one landmass are considered endemic, a condition exhibited by 65% of the Ordovician and Silurian genera and 81% of the Devonian genera. The maximum number of landmasses colonized by any one nautiloid genus for any one particular period of time was four, two fewer than the six available landmasses.

The basic biogeographic unit for nautiloid cephalopods is the genus. This is so because the dispersive potential of nautiloids was low when compared with true pelagic groups such as conodonts. Thus for nautiloid groups capable of dispersal among landmasses, the time needed to effect dispersal and insure permanence in the stratigraphic record was something greater than the longevity of the typical nautiloid species but less than the longevity of most genera. It seems reasonable that the best chance for the occurrence of cosmopolitan nautiloid genera would be at or near the zenith of those groups with attributes most suitable for dispersal. However, the fossil record for nautiloids shows that such periods rarely coincide with the peak intervals of total nautiloid diversity for the Lower and Middle Paleozoic (Arenig, Wenlock and Eifelian) occurring instead during succeeding intervals of time. Such events are generally confined to periods of modal diversity within each group. The lowest percentages of endemic genera and the intervals in which they occurred for the major nautiloid groups are: Ellesmerocerida (57%) and Endocerida (60%) for the Llanvirn, Actinocerida (36%) and Tarphycerida (45%) in the Llandeilo, Orthocerida (52%, 47%, 55%) and Oncocerida (66%, 66%, 75%) for the Caradoc, Ludlow, and Givetian, Discosorida (67%) in the Wenlock and Nautilida (62%) for the Givetian. While the low percentage of endemics for the Actinocerida and Tarphycerida translate into the highest percentages of genera found on more than three separate landmasses (20%), similar percentages of endemics for the Orthocerida do not. Nonendemic members of the Orthocerida are more common to two or three of the available landmasses with approximately 20% occurring in either of these configurations. The fossil record also shows that Devonian nautiloids were the most restricted with the majority occurring on no more than two landmasses.

These and other criteria indicate that the distributions of nautiloid cephalopods do not conform to the general perception of cosmopolitanism. At the generic level the group is largely endemic with reasonably large numbers of genera occurring on two or three landmasses with no genus occurring on all available landmasses during a given interval of time. Because of the type and manner of biogeographic barriers imposed on nautiloids, their distributions or patterns tend to have well defined limits with considerable predictive powers.

Cambrian deep-sea sediments have yielded few trace fossils. The first moderately diverse suite is found in an Arenig flysch sequence in Eire. There followed a gradual increase in diversity and abundance of trace fossils in deep-sea niches in the Palaeozoic and early Mesozoic. A major burst of behaviourial evolution appears to have taken place during the Cretaceous and, from then through the Tertiary, high levels of trace fossil abundance and diversity were maintained. This is confirmed by recent work on Miocene deep-sea sequences and from a superbly preserved, diverse, ichnofauna recently discovered in strata of Oligocene and Miocene age in the Makran Range of Iran.

In the past, it has been inferred that there was a gradual improvement in behavioral programming in deep-sea traces, with a trend towards economy of effort and perfection. However, Lower Palaeozoic deep water traces show careful, complex, behavioral programming which was to change little through the rest of the Phanerozoic.

Within the deep-sea, there are, however, significant variations in the ichnospectrum in different niches. For example, the inner parts of seep-sea sand fans, particularly the channelled areas, have a mixture of “deep” and “shallow” water traces, whereas the outer fan normally has only deep water forms.

There was a dramatic increase in abundance and diversity of trace fossils in Upper Precambrian and Lower Cambrian shallow water seas. The trace-producing animals rapidly filled all the available niches and in low energy, muddy, environments they evolved winding, meandering and patterned habits. Traces such as Taphrhelminthopsis, Helminthoida, Nereites, Paleodictyon and Squamodictyon had all evolved in clastic shelf seas during the pre-trilobite Lower Cambrian.

Significant colonisation of the deep oceans seems to have mostly been delayed until the Ordovician. A recently described suite of trace fossils from a flysch sequence in Eire includes such deep water types as: Glockerichnus, Helminthopsis, Lorenzinia, Paleodictyon and Taphrhelminthopsis. This migration into the deep sea is accompanied by a virtual absence of such traces from shallow water sequences after the Cambrian.

Deep water trace fossils therefore seem to have evolved initially in shallow water clastic seas and then migrated in to the deep ocean, thereby providing an exciting example of an onshore-offshore pattern. This may be of particular significance in that it is presumably mimicked by body fossil migrations in these early seas.

Pliocene faunal events in tropical and subtropical regions of the Americas and the Caribbean have been causally linked to global climatic events, particularly, progressive cooling and increased amplitude of climatic cycles between 3.5 and 2.0 Ma. However, the rate and magnitude of Pliocene temperature changes has been determined in only a few climate proxy records. Our study contrasts paleoceanographic conditions at 3 Ma, an extremely warm period in many areas, with conditions 2.4 Ma, a much cooler interval, in equator-to-pole transects for the North Atlantic and the North Pacific Oceans. By using microfaunal data (ostracodes from ocean margin environments and planktic foraminifers from deep sea cores), quantitative factor analytic and modern analog dissimilarity coefficient analyses were carried out on faunas from the following sections.

Our studies lead to the following conclusions: (1) Equator-to-pole thermal gradients in the oceans at 3.0 Ma were not as steep as they are today, but thermal gradients at 2.4 Ma were steeper than those today; (2)At 3 Ma middle to high latitudes were substantially warmer than today, but tropical regions were about the same; (3)Substantial cooling occurred in middle and high latitudes in the western North Pacific Ocean and the western North Atlantic between 3 Ma and 2.4 Ma; (4)Ocean water temperatures off the southeastern U.S. remained the same or cooled only slightly between 3 Ma and 2.4 Ma. Our results support the hypothesis that ocean circulation changes, probably resulting from the closure of near surface water by the Isthmus of Panama, had significant impact on equator-to-pole heat transport and global climate between about 3 and 2.4 Ma. They also argue against the hypothesis that climatically induced ocean temperature changes were directly linked to a major marine extinction in the southwestern North Atlantic and Caribbean.

There are several important changes in Phanerozoic climates that may have influenced terrestrial biota. Prior to the time of the terrestrial invasion in the early Paleozoic, an unvegetated landscape would have been associated with a larger seasonal cycle and decreased precipitation. Albedo and transpiration changes associated with the first appearance of plants should have changed this pattern, reducing the seasonal cycle and increasing precipitation. Enhanced soil weathering associated with vegetation should also have lowered atmospheric CO2 levels. During Pangaea time the giant landmass should again have caused very large seasonal cycles and decreased precipitation. Climate models invariably simulate below-freezing temperatures in winter on the supercontinent, a result at variance with inferred “equable” climates of the Jurassic. The large landmass should also have had very large Milankovitch variations. Seasonal warming during precession half-cycles of 10,000 years duration may have been associated with intermittent occupation of high-latitude sites that could bias interpretation of warmth in high latitudes. During the later Mesozoic (140–80 Ma) CO2 levels may have been several times higher than present. High CO2 levels should have affected the cycles of temperature and precipitation on land and also affected plants through the CO2 fertilization pathway. Subsequent decreased CO2 levels and continued breakup of landmasses may have influenced location of tropical rainbelts and perhaps the distribution of tropical rainforests. Numerous studies indicate that these changes, combined with expanded ice cover in the later Cenozoic, resulted in increasingly drier conditions in higher latitude land areas. The situation in the tropics is more uncertain, because there are conflicting signals from the marine realm as to the Cenozoic history of tropical sea-surface temperatures (SSTs). If early Cenozoic SSTs were in fact low (as indicated by some δ18O records), then tropical temperature and moisture levels may not have been high enough to sustain tropical rainforests. This summary highlights some of the excellent opportunities for interactions between paleontologists and paleoclimatologists in assessing the effects of climate change on terrestrial biota.

Different data and ways of ordering nature are relevant to different questions, and thus there is no single classification of natural phenomena appropriate for all questions in macroevolution.

Consider two distinct, coexisting modes of causal explanation in paleontology. The historical mode takes the form of a narrative, a sequence of events or situations, each one “explaining” the following event as a natural or obvious outcome. Traditionally, the historian of human society usually seeks explanations in terms of transitions from one state to the next. It is thus natural for the paleontologist-historian to regard the primary problems of macroevolution as involving the transformation of character states and the sequence of branching lineages. The data summarized by a cladogram are thus of direct relevance to a vast number of macroevolutionary questions requiring historical-mode answers. However, taxa per se, as groupings of organisms based on specific criteria, are not sequences of events and thus are not particularly relevant to these kinds of questions. In contrast, a functional (or mechanistic, or process) mode of explanation characterizes most of the rest of natural science. One may define a mechanism as a specified set of causal interactions among entities, controlled by parameters. The essence of a mechanism is that given the parameter values, the result is inevitable and predictable, and the process continues to “completion.” The entities that are functioning parts within the mechanism, and among which causal relations are specified, must usually satisfy the criteria of historical contemporaneity, geographic propinquity, and capacity to interact in the ways specified. There is no requirement involving common descent The paleontologist seeking answers to questions about mechanism must therefore be interested primarily in functional (usually ecological) entities (organisms, populations, communities, biotas) and their environments rather than taxa per se or extended sequences of splitting events. Historical sequences involving ecological entities may often be more informative about ecologically based processes than sequences reflecting character transformations within lineages, because an ecological entity, by definition, occurs in a specific environment that may be shared by other ecologically interacting entities.

Higher taxa thus have little relevance to explanation in macroevolution, although scientifically useful groupings of species may sometimes correspond to taxa defined with regard to common descent or other criteria. Pre-Darwinian taxa were groupings of species thought to reflect ideal (usually Divine) ordering principles. The idea that the nested monophyletic groups extracted from a cladogram form the only “real” scientific groupings of species is a vestige of this pre-Darwinian idealism. This metaphysical issue is irrelevant. Entities have meaning, or not, only with regard to particular scientific questions or mechanisms. Paraphyletic taxa have no meaning in cladistic practice. Likewise, it is difficult, if not impossible, to define the general functional role of clades, or to give a general biological interpretation of their fates. The value of a cladogram is not that it defines monophyletic taxa (which seem largely irrelevant to macroevolution), but that it represents a hypothesized sequence of historical events (which is relevant).

Traditional, “synthetic” taxa that may be paraphyletic are, like all taxa based on common descent, usually inappropriate candidates for interactors in macroevolutionary mechanisms. An exception may be the way synthetic taxa are analyzed statistically in large-scale taxonomic diversity studies, where they can stand in for more appropriate species-level or populational data that are not readily available. Studying extinction of clades rather than synthetic taxa is not approaching the same question with “better” data, but constitutes asking a different question — and one whose answer may be even less easily causally interpretable. Before expunging synthetic taxa from our collective memory, we should use them to gain whatever perspective they can give on the causes of major events in life's history.