The Paleozoic and post-Paleozoic radiations of crinoids present an opportunity to explore genomic and ecological explanations for patterns of morphologic diversification. Analysis of discrete-character data that cover the principal features of the crinoid skeleton shows that both Paleozoic and post-Paleozoic increases in morphological disparity were abrupt; this is consistent with rapid exploitation of open ecological opportunities in both cases. For the post-Paleozoic, this result is sensitive to some aspects of data analysis and sampling, so it cannot be regarded as unequivocal. The deceleration in morphological diversification within each radiation is consistent with an observed decline in rates of taxonomic origination as well as with the attainment of functional or structural limits. Despite these similarities in the two radiations, Paleozoic crinoids exploited a wider range of morphological designs than did their post-Paleozoic successors. Post-Paleozoic crinoids exploited a wide range of ecological strategies despite being stereotyped in many aspects of form. This difference between the radiations is consistent with an increase in the rigidity of genetic and developmental systems. The range of post-Paleozoic designs is not in essence a subset of the Paleozoic spectrum. The two radiations resulted in morphological distributions that are largely nonoverlapping, perhaps reflecting a different range of ecological strategies.

“It's not all heterochrony.” Raff (1996)

“Heterochrony … explains everything.” McNamara (1997)

Few evolutionary topics have generated more confusion and controversy than heterochrony. Commonly defined as “evolution via change in rate or timing of development,” heterchrony has historically become associated with genocidal ideologies, simple-minded theories of evolution, and a bloated, baroque jargon describing patterns produced by largely unknown mechanisms. With a track record like that, perhaps the most surprising aspect of heterochrony is its continued, even rapid, growth as an area of productive scientific inquiry. For example, the number of papers devoted to heterochronic topics continues to increase in many evolutionary journals and books (reviews in Reilly et al. 1997; Klingenberg 1998), including those devoted to human development (Bogin 1997) and evolution (Vrba 1998; McKinney 1998; Parker and McKinney 1999).

The stratigraphic distribution of graptoloid species within the upper Middle Ordovician strata of New York State represents a complex pattern of origination, extinction, faunal migration, and fluctuating relative abundances. In particular, the observed patterns of species turnover at graptolite biozone boundaries are apparently strongly correlated with lithofacies, sampling strategies, and the depositional effects of relative sea-level change.

Vertical facies changes that occur within third-order depositional sequences and fourth- or fifth-order parasequences are mirrored by changes in the graptoloid faunal composition. Large-scale faunal turnovers at biozone boundaries tend to occur either at sequence boundaries or at flooding surfaces within sequences (e.g., the base of Highstand System Tracts). The base of the Corynoides americanus and Climacograptus (D.) spiniferus Zones coincide with major onlap events, and the Orthograptus ruedemanni Zone fauna appears just below a Lowstand Systems Tract. Within individual biozones, smaller-scale changes such as the fluctuating relative abundances of graptoloid species coincide with higher-order parasequence cyclicity. These distribution patterns resemble recent computer-generated models for the sequence stratigraphic distribution of hypothetical taxa.

By combining good biogeographic control with a detailed sampling program, we are able to see through the patterns attributable to depositional cyclicity and identify the different components of faunal turnover (migration, speciation, and extinction).

The Cretaceous angiosperm radiation offers an opportunity to examine patterns of morphological evolution in terrestrial plants and to compare them with patterns previously observed during radiations of marine animals. Focusing on evolution among angiosperm pollen types, I used average pairwise dissimilarity and total variance to describe changing morphological varieties (disparity) through the Cretaceous and Paleocene in North America. Angiosperm species diversity shows an approximately tenfold increase through this interval, but this taxonomic diversification is not matched by a comparable change in morphological disparity. Partitioning of morphological disparity among major pollen groups shows that most of the variance is contributed by eudicots from the Albian onwards. Constant disparity across the Cretaceous/Tertiary boundary despite decreased taxonomic diversity suggests that the Cretaceous/Tertiary extinction was not selective with respect to the pollen morphological characters analyzed here. The two measures of disparity show similar patterns. The overall pattern is robust to changes in character weighting, indicating that no one set of characters or weighting scheme is driving the pattern. Analyses of older data indicate that the initial burst of disparity in the Aptian could be due in part to analytical time-averaging. The observed incongruence between taxonomic diversity and morphological disparity suggests that morphological evolution in pollen was characterized by larger jumps early and smaller jumps later on, and is similar to that found in several groups of marine invertebrates.

Knowing the structure and branching order of the evolutionary tree is essential to many studies of the evolutionary process and the history of life. Most attempts to reconstruct evolutionary trees are based on rectangular matrices, in which coded states are assigned for each character and each taxon under study. Everyone who has tried to infer the pattern of evolution from such character-taxon matrices is confronted with a great deal of “noise” and uncertainty. Often, there are multiple “most parsimonious trees” (those requiring the fewest evolutionary steps), which often differ significantly in topology; and many nodes in such trees are poorly supported; that is, there are contradictions and inconsistencies in the data. Some of this noise arises for reasons well known to phylogeneticists. Character states may arise multiple times, evolve in parallel, or reverse (homoplasy); taxa vary insufficiently among themselves; and diversification may be so rapid that data are insufficient to detect the order of branching. Polytomies are regarded as a nuisance rather than as real information. Characters may be coded inappropriately, so that there are too many redundancies, inapplicable character states, and multistate characters, as well as dependence among characters. Moreover, it is highly debatable whether evolution is parsimonious, and there are conflicts about how to establish the polarity of characters (primitive vs. derived). (For reviews and discussion see Sober 1988; Huelsenbeck and Crandall 1997.)

The Cretaceous/Tertiary boundary event exerted a deep influence on the life of the benthic invertebrates in the Danish Basin. The density and taxonomic diversity of most groups fell abruptly and the lowermost Danian strata are almost barren of invertebrates. The echinoderms, and among them in particular crinoids of the family Bourgueticrinidae, are the only group that deviates form this general pattern and show an increase in the strata immediately above the boundary. This exceptional development is accompanied by a heterochronic change in which the largest element of the bourgueticrinid theca, the proximale, is lost by paedomorphosis (neoteny). In the Late Cretaceous bourgueticrinids the proximale is formed during early ontogeny by the incorporation of a columnal element into the theca, and the addition of new columnals stops once the proximale is formed. The paedomorphic change and the elimination of the proximale allow, in principle, columnals to be added throughout life. This new development is probably the result of a selection for longer stems. It is successful from the very beginning and Democrinus maximus, the earliest bourgueticrinid species in the Danish Basin without a proximale, makes up about 90% of the crinoid fauna in the lowermost Danian deposits.

Twelve different bones from the skeleton of the holotype specimen of the hadrosaurian dinosaur Hypacrosaurus stebingeri were thin-sectioned to evaluate the significance of lines of arrested growth (LAGs) in age assessments. The presence of an external fundamental system (EFS) at the external surface of the cortex and mature epiphyses indicate that the Hypacrosaurus specimen had reached adulthood and growth had slowed considerably from earlier stages. The number of LAGs varied from none in the pedal phalanx to as many as eight in the tibia and femur. Most elements had experienced considerable Haversian reconstruction that had most likely obliterated many LAGs. The tibia was found to have experienced the least amount of reconstruction, but was still not optimal for skeletochronology because the LAGs were difficult to count near the periosteal surface. Additionally, the numbers of LAGs within the EFS vary considerably around the circumference of a single element and among elements. Counting LAGs from a single bone to assess skeletochronology appears to be unreliable, particularly when a fundamental system exists.

Because LAGs are plesiomorphic for tetrapods, and because they are present in over a dozen orders of mammals, they have no particular physiological meaning that can be generalized to particular amniote groups without independent physiological evidence. Descriptions of dinosaur physiology as “intermediate” between the physiology of living reptiles and that of living birds and mammals may or may not be valid, but cannot be based reliably on the presence of LAGs.

We show that the decline in the extinction rate during the Phanerozoic can be accurately described by a logarithmic fit to the cumulative total extinction. This implies that extinction intensity is falling off approximately as the reciprocal of time. We demonstrate that this observation alone is sufficient to explain the existence of the proposed power-law forms in the distribution of the sizes of extinction events and in the power spectrum of Phanerozoic extinction, results that previously have been explained by appealing to self-organized critical theories of evolutionary dynamics.

Insects are the most diverse macroorganismic group to ever inhabit the planet, constituting a major share of the animal biomass in terrestrial and freshwater ecosystems. Since their first appearance in the fossil record some 400 million years ago, they have expanded ecologically into almost every niche except the ocean below the photic zone. When fossilized, their chitinous exoskeletons typically are well preserved, as evidenced by a respectable fossil record. They are found notably in lacustrine shales and amber but also occur in siderite nodules, lithographic limestone, sinter deposits, asphalt, and various glacial deposits. Insect fossils are major subjects in phylogenetic studies but are used to a lesser extent in understanding past ecological associations and reconstruction of ancient environments.

Paleotectonic reconstructions for the late Proterozoic have differed over the timing of the Cordilleran rifting between Laurentia and the East Gondwana cratons. Parsimony Analysis of Endemism (PAE) and phenetic clustering of the “Ediacara biota” were carried out, for comparison with competing paleotectonic hypotheses. All analyses show a common pattern of similarities among biotas. The biotas of Charnwood Forest and Newfoundland consistently group together, while the south Australian biota is closest to those of Baltica, northern Laurentia, and Siberia. The biota of southwest North America, though still poorly known, strikingly resembles that of Namibia—not that of northwestern Canada. This pattern is not obviously due to facies-related or preservational bias and is very different from Cambrian biogeographic patterns. The overall pattern is most consistent with the hypothesis that the western margin of Laurentia was in close contact with East Gondwana, with rifting taking place either during or just before the Vendian. This arrangement has been previously proposed as a paleotectonic hypothesis; however, most recent paleomagnetic and structural studies support the alternate hypothesis that this rifting took place more than 100 million years before the Vendian. Resolving this contradiction will require much more data on both organismal distribution and cratonal position.

Previous studies have suggested that unbiased random walks may serve as appropriate null hypotheses for the detection of pattern in stratophenetic series. While numerous processes that influence the perceived temporal morphological evolution of a species may yield stratophenetic patterns that conform to the model of a random walk, use of the model as a null hypothesis raises several concerns. First, unbiased random walks are only a subset of a much larger set of random motions, including biased and fractional random walks. Some of these motions could also serve as appropriate null models for stratophenetic patterns. Second, due in part to the fractal nature of random walks, many types of time series begin to resemble random walks statistically as sampling resolution decreases. Therefore, indiscriminate support for unbiased random walks as null hypotheses of stratophenetic pattern leads inevitably to the commitment of Type II errors (incorrect failure to reject a null hypothesis). In this paper we simulate different hypothetical patterns of microevolution using various random walk models and apply the test of the null hypothesis. The frequency of Type II errors increases as stratigraphic completeness decreases, but at a currently unknown rate. Moreover, the test is insensitive to nongradual patterns of anagenesis.

We also demonstrate that a previously published approach is closely related to a standard method of fractal time series analysis and represents a good qualitative test of evolutionary pattern. The statistical variation underlying this method, however, is currently unknown, and further work is required to make it a robust quantitative test.

The Cretaceous radiation of angiosperms initiated a major reorganization of terrestrial plant communities as dominance by pteridophytic and gymnospermic groups eventually gave way to dominance by angiosperms. Previously, patterns of biotic replacement have been assessed using measures based on taxonomic diversity data. However, using measures of both abundance and diversity to investigate replacement patterns provides more information about macroecological change in the fossil record than either can provide alone. Analyses of an updated and expanded database of North American palynological samples from Cretaceous sediments document a rapid increase in angiosperm diversity and abundance within individual fossil palynofloras (representing local/subregional vegetation). New analyses of floristic diversity patterns support previous results and indicate that the decline of free-sporing plants is more pronounced than the decline of gymnosperms. In contrast, analyses of abundance data appear to show that the decline of gymnosperms is far more pronounced than the decline of free-sporing plants. Detailed examination of both data sets segregated by paleolatitude shows that this apparent contradiction reflects biogeographical differences in the patterns of vegetational change (e.g., free-sporing plants declined in abundance at lower latitudes) as well as sampling bias (e.g., greater sampling in the northern region in the Late Cretaceous). Analyses accounting for these biases support the conclusion that as angiosperms radiated, free-sporing plants rather than gymnosperms (in this case, mainly conifers) experienced the most pronounced decline. A thorough understanding of the Cretaceous radiation of angiosperms will require both abundance and diversity data. It also will require expanding the analyses presented here into other geographic regions as well as sampling more completely at all spatial scales.

We have known since Trueman's classic work of 1922 that the Lower Jurassic Gryphaea of Britain exhibit phyletic size increase and heterochronic change in shape. Since Hallam's revisionary work in the 1960s, we have recognized that pronounced and generalized juvenilization of form accompanied this increasing size. This extensive literature provides invertebrate paleontology's most famous example of a biometrically documented, continuous anagenetic trend within a discrete lineage. But Gryphaea has also provoked great frustration because a key datum, required for a full solution, had been theoretically recognized but practically unavailable. We could identify the evolution of shape as paedomorphic, but could not specify the mode of heterochrony for this paedomorphic result because we could not standardize samples by common age or developmental stage.

In this paper, we provide sclerochronological data on sizes and shapes at specified ages marked by annual growth bands in two Jurassic sequences of Gryphaea: the classic Lower Jurassic series showing phyletic size increase with paedomorphosis, and an independent Middle–Upper Jurassic series illustrating neither size increase nor heterochrony. We prove that size increase in the classic series occurs entirely by faster growth (larger descendant sizes at the same ages as ancestors), and not by extended age (for descendants lived no longer than ancestors). The well-marked paedomorphosis of form probably arose as a correlated consequence of growing larger by extending and maintaining rapid juvenile growth rates—thus marking the heterochronic mode as a case of neoteny. The independent upper sequence, acting as a different replicate in a natural experiment, shows neither size increase nor heterochrony but does exhibit (in contrast with the classic sequence) evolution toward greater longevity.

Hallam's flow tank experiments indicated a strong adaptive advantage in shell stability for both larger size and paedomorphic form. Neotenous development provides an evolutionary pathway to the simultaneous acquisition of both favored traits—thus showing that “constraints” due to “correlations of growth” (Darwin's own phrase for the phenomenon) may be positive in promoting joint evolutionary advantages, and not only neutral (in carrying spandrels along with primary adaptations), or negative (by imposing inadaptive “baggage” upon trends in form through developmental correlation with selected traits).

A physical, model-based approach to body temperatures in dinosaurs allows us to predict what ranges of body temperatures and what thermoregulatory strategies were available to those dinosaurs. We argue that

1. 1. The huge range of body sizes in the dinosaurs likely resulted in very different thermal problems and strategies for animals at either end of this size continuum.

2. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in the absence of insulation. The smallest animals in which metabolic heating resulted in predicted body temperatures ≥ 2°C above operative temperatures (Te) weigh 10 kg. Body temperature would respond rapidly enough to changes in Te to make behavioral thermoregulation possible.

3. 3. Body temperatures of large dinosaurs (>1000 kg) likely were sensitive to both metabolic rate and the delivery of heat to the body surface by blood flow. Our model suggests that they could adjust body temperature by adjusting metabolic rate and blood flow. Behavioral thermoregulation by changing microhabitat selection would likely have been of limited utility because body temperatures would have responded only slowly to changes in Te.

4. 4. Endothermic metabolic rates may have put large dinosaurs at risk for overheating unless they had adaptations to shed the heat as necessary. This would have been particularly true for dinosaurs with masses > 10,000 kg, but simulations suggest that for animals as small as 1000 kg in the Tropics and in temperate latitudes during the summer, steady-state body temperatures would have exceeded 40°C. Slow response of body temperatures to changes in Te suggests that use of day-night thermal differences would have buffered dinosaurs from diel warming but would not have lowered body temperatures sufficiently for animals experiencing high mean daily Te.

5. 5. Endothermic metabolism and metabolic heating might have been useful for intermediate and large-sized (100–3000 kg) dinosaurs but often in situations that demanded marked seasonal adjustment of metabolic rates and/or precise control of metabolism (and heat-loss mechanisms) as typically seen in endotherms.

The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.

Conodont element function and feeding mechanisms are of considerable paleobiological importance, yet many details remain poorly understood and speculative. Analysis based on morphology, physical juxtaposition, and patterns of surface damage and microwear on pairs of Pa elements from individuals of Idiognathodus indicates that these elements crushed food by rotational closure, which brought the oral surfaces into complex interpenetrative occlusion. Other molariform conodont elements also functioned in this manner. Occlusion of this complexity is unique among nonmammalian vertebrates, and is all the more surprising given that conodonts lacked jaws. In addition to enhanced understanding of food processing in conodonts, our analysis suggests that many details of conodont Pa element morphology, which underpin taxonomy and biostratigraphy, can now be interpreted in a paleobiological, functional context.

Statistical analyses of occurrence data derived from new collections through scattered Caribbean sections indicate that increased speciation preceded a pulse of extinction during regional turnover of the Caribbean reef coral fauna in Plio-Pleistocene time. The data are based on samples that were newly collected and identified to species using standardized procedures. Age-dates were assigned using high-resolution chronostratigraphic methods. The results show that coral species with a wide range of ecological traits originated and were added to the species pool as much as 1–2 million years before extinction peaked at the end of the turnover interval. Local assemblages consisted of a mix of extinct and living species, which varied in composition but not in richness. Extinction was selective and resulted in a faunal shift to the large, fast-growing species that dominate Caribbean reefs today. The unusual relationship between origination and extinction may have been caused by changes in oceanic circulation associated with emergence of the Central American Isthmus, followed by the onset of Northern Hemisphere glaciation. The pattern of origination preceding extinction may have been responsible for the stability of reef ecosystems during the intense climatic fluctuations of the late Pleistocene, and for the composition and structure of modern Caribbean reef ecosystems.

The North African murine rodent Paraethomys evolved as an anagenetic lineage from the late Miocene until its extinction in the late—middle Pleistocene. A Fourier analysis of the outlines of the first upper and lower molars of this rodent was used to quantify the evolutionary patterns of this lineage and to compare evolutionary patterns to the climatic record. Morphological evolution and long-term environmental variations are strongly correlated. A change in molar shape, which may be related to the development of a more grass-eating diet, corresponds to the global cooling beginning around 3 Ma and the subsequent increase in aridity in North Africa. Concurrently, size increased, which may be related to increased masticatory efficiency or to metabolic adaptation to the cooler environmental conditions according to Bergmann's rule. This adaptive response to changing environmental conditions corresponds to an acceleration of evolutionary rates in the lineage. The modalities of the evolutionary response in size and shape are probably controlled by intrinsic factors such as different genetic determinisms for both characters.