Niche conservatism is increasingly recognized in diverse modern ecological settings, and it influences many aspects of modern ecosystems, including speciation mechanisms, community structure, and response to climate change. Here, we investigate the stability of niches with benthic marine invertebrates along a Late Ordovician onshore-offshore gradient on the Cincinnati Arch in the eastern United States. Using a Gaussian niche model characterized by peak abundance, preferred environment, and environmental tolerance, with these parameters estimated through weighted averaging and logistic regression, we find evidence of strong niche conservatism in peak abundance and preferred environment, particularly for abundant taxa. This conservatism is maintained in successive depositional sequences and through the nearly 9–10 Myr study interval. Environmental tolerance shows no evidence of conservatism, although numerical simulations suggest that the error rates in estimates of this parameter are so high that they could overwhelm evidence of conservatism. These numerical simulations also indicate that both weighted averaging and logistic regression produce useful estimates of peak abundance and preferred environment, with slightly better results for weighted averaging. This evidence for niche conservatism suggests that long-term shifts of higher taxa of marine invertebrates into deeper water are primarily the result of differential rates of origination and extinction. These results also add to the evidence of long periods of relatively stable ecosystems despite regional environmental perturbations, and they constrain the causes of peaked patterns in occupancy.

The geographic distribution of 293 Modern bivalve genera has been analyzed and found to be statistically correlated with distance. In particular, a least-squares regression analysis of the data indicates that the distance between faunal realms (D) in kilometers can be estimated using the equation D = (ln(d) + 0.4233)/−0.00013, where d is the Dice coefficient of faunal similarity. Analysis of 59 genera of Late Ordovician bivalves indicates that the above equation also describes their biogeographic distribution.

Using this formula, the distance between Laurentia and Scotland/Northwest Ireland was estimated to be 5500 kilometers. This is consistent with the reconstruction of a connection among these areas during the Late Ordovician based on brachiopod and graptolite biogeographic data.

Paleomagnetic and paleoclimatic data also suggest that Avalonia, Baltica, and Laurentia were at tropical latitudes. Distances between these paleocontinents can therefore be used to estimate paleolongitudes. If the location of England on the eastern side of Avalonia is used as zero degrees paleolongitude for the Late Ordovician as it is today, the paleolongitude for South America, Laurentia, Scotland and northwest Ireland, and Baltica would be 125°W, 45°W, 10°W, and 15°E, respectively. Because of drifting of the Avalonia plate, these paleolongitudes probably do not coincide with the longitudinal grid used today. The paleolongitudes indicate only the relative spacing between continents in the past. The methodology in this study should be useful for improving the accuracy of paleogeographic reconstructions for the Late Ordovician throughout the Cenozoic, and especially the Paleozoic periods for which magnetic seafloor anomaly data are not available.

Ecological theory predicts an inverse association between population size and extinction risk, but most previous paleontological studies have failed to confirm this relationship. The reasons for this discrepancy between theory and observation remain poorly understood. In this study, we compiled a global database of gastropod occurrences and collection-level abundances spanning the Early Permian through Early Jurassic (Pliensbachian). Globally, the database contains 5469 occurrences of 496 genera and 2156 species from 839 localities. Within the database, 30 collections distributed across seven stages contain at least 75 specimens and ten genera—our minimum criteria for within-collection analysis of extinction selectivity. We use logistic regression analysis, based on global and local measures of population size and stage-level extinction patterns in Early Permian through Early Jurassic marine gastropods, to assess the relationship between abundance and extinction risk. We find that global genus occurrence frequency is inversely associated with extinction risk (i.e., positively associated with survival) in 15 of 16 stages examined, statistically significantly so in five stages. Although correlation between geographic range and occurrence frequency may account for some of this association, results from multivariable regression analysis suggest that the association between occurrence frequency and extinction risk is largely independent of geographic range. Within local assemblages, abundance (number of individuals) is also inversely associated with extinction risk. The strength of association is consistent across time and modes of fossil preservation. Effect strength is poorly constrained, particularly in analyses of local collections. In addition to limited power due to small sample size, this poor constraint may result from confounding by ecological variables not controlled for in the analyses, by taphonomic or collection biases, or from non-monotonic relationships between abundance and extinction risk. Two factors are likely to account for the difference between our results and those of most previous studies. First, many previous studies focused on the end-Cretaceous mass extinction event; the extent to which these results can be generalized to other intervals remains unclear. Second, previous findings of nonselective extinction could result from insufficient statistical power rather than the absence of an underlying effect, because nonselective extinction is generally used as the null hypothesis for statistical convenience. Survivorship patterns in late Paleozoic and early Mesozoic gastropods suggest that abundance has been a more important influence on extinction risk through the Phanerozoic than previously appreciated.

We describe statistical methods to formulate and validate statements about survival rates given a small number of individuals. These methods allow one to estimate the age-specific survival rate and assess its uncertainty, to assess whether the survival rates during some age range differ from the survival rates during another age range, and to assess whether the survivorship curve has a particular shape. We illustrate these methods by applying them to a sample of 22 Albertosaurus sarcophagus individuals. We show that this sample is too small to provide any confidence in the claim that this species had a “convex” survivorship curve arising from age-specific survival rates that decreased monotonically with age. However, we show that a sample of 50 to 100 individuals has reasonable statistical power to support such a claim. There is evidence for the much weaker claim that average survival rates for ages 2 to 15 were higher than survival rates for later ages. Finally, we describe one way to account for size-dependent fossilization rates and show that a plausible positively-size-dependent fossilization rate results in a substantially non-convex survivorship curve for A. sarcophagus.

Colony-wide feeding currents are a common feature of many bryozoan colonies. These feeding currents are centered on excurrent macular chimneys that expel previously filtered water away from the colony surface. In some bryozoans these macular chimneys consist of a branching channel network that converges at a point in the center of the chimney. The bifurcating channels of the maculae are analogous to a stream channel network in a closed basin with centripetal drainage. The classical methods of stream channel network analysis from geomorphology are here used to quantitatively analyze the number and length of macular channels in bryozoans. This approach is applied to a giant branch of the trepostome bryozoan Tabulipora from the Early Permian Kim Fjelde Formation in North Greenland. Its large size allowed 18 serial tangential peels to be made through the 8-mm-thick exozone. The peels intersected two stellate maculae as defined by contiguous exilapores. The lengths of 1460 channels radiating from the maculae were measured and their Horton-Strahler stream order and Shreve magnitude scored.

We hypothesize that if fossil bryozoan maculae function as excurrent water chimneys, then they should conform to Horton's laws of stream networks and behave like closed basins with centripetal drainage. Results indicate that the stellate maculae in this bryozoan behaved liked stream channel networks exhibiting landscape maturation and stream capture. They conformed to the Law of Stream Number. They have a Bifurcation Ratio that falls within the range of natural stream channel networks. They showed a pattern opposite that expected by the Law of Stream Lengths in response to behavior characteristic of a centripetal drainage pattern in a closed basin. Thus, the stellate maculae in this bryozoan probably functioned as excurrent water chimneys with the radiating channels serving to efficiently collect the previously filtered water, conducting it to the central chimney for expulsion away from the colony surface.

A modern Lesser Flamingo (Phoeniconaias minor) assemblage was collected along the shoreline of Lake Emakat, a saline-alkaline lake in northern Tanzania. Taphonomic analysis found the assemblage to be heavily weathered. This is likely due to the bone's heightened exposure to solar radiation and corrosive soil and water chemistries, as is expected to occur in such depositional environments.

Analysis found that deep, wide, longitudinal cracks penetrate the medullar cavities of both weathered and unweathered long bones. The cause and taphonomic consequence of these cracks are addressed here, using data from Lake Emakat and from controlled studies. Results support repeated (episodic) submersion, followed by drying, as the causal mechanism behind these wet-dry cracks. Mineral salt uptake by bone may explain the early appearance and prevalence of these cracks in saline-alkaline lake settings, as compared to other depositional settings.

The rate of weathering and incidence of wet-dry cracking varies significantly across limb elements. This difference correlates to element specific resistance properties to external loading forces. Heavy weathering weakens the structural integrity of bone and can accelerate its fragmentation. This can lead to bird bone loss in nearshore and ephemeral wetland settings, which may then affect resulting skeletal part, diversity, and richness profiles. Heavy weathering can therefore obscure important taphonomic and paleoecological information.

The weathering data collected here are then applied to a fossil bird assemblage from the FLK Complex, (late Pliocene), Olduvai Gorge, in Tanzania. Results provide evidence for the effect of weathering on paleoecological and behavioral interpretations. Weathering should be considered when analyzing fossil bird assemblages.

The floral community along South Africa's southwest coast today is dominated by shrubby strandveld, renosterveld, and coastal fynbos vegetation. The grass family (Poaceae), represented primarily by C3 taxa, is scarce by comparison. Nevertheless, grass has a long history along this coast, as indicated by the presence of ∼5-million-year-old C3 grass pollen and phytoliths in sediments at the fossil locality of Langebaanweg E Quarry. Because the pollen and phytoliths of other plant families, including fynbos, have also been found, it has been difficult to determine whether grass was scarce or abundant in this environment. In order to shed light on this issue, I analyzed the dental mesowear of the E Quarry bovids. Results indicate that only one (Simatherium demissum) of seven analyzed species was a grazer. These compare well with the results of a microwear texture analysis, which indicate that none of the seven analyzed species were obligate grazers. These two studies point strongly toward a heavily wooded environment and not one that was dominated by grass. Although a conventional dental microwear analysis did identify three out of seven E Quarry bovid species as grazers (Bed3aN Damalacra, Kobus subdolus, and S. demissum), only S. demissum probably actually was a grazer. I suggest that the grazer signal exhibited by the other two bovid samples indicate that these species were taking advantage of a spike in grass abundance, probably during the winter growth season.

Incremental stages of major evolutionary transitions within a single animal lineage are rarely observed in the fossil record. However, the extraordinarily complete sequence of well preserved material spanning the 27-Myr existence of the marine squamate subfamily Mosasaurinae provides a unique exception. By comparison with extant and extinct analogs, the tail morphology of four mosasaurine genera is examined, revealing a pattern of evolution that begins with the generalized varanoid anatomy and culminates in a high-aspect-ratio fin, similar to that of sharks. However, unlike the epicercal caudal fluke of selachians in which the tail bends dorsocaudally, derived mosasaurs develop a hypocercal tail with a ventrocaudal bend. Progressive caudal regionalization, reduced intervertebral mobility, increased tail depth due to a marked downturn of the posterior caudal segment, and the development of finlike paired appendages reveal a pattern of adaptation toward an optimized marine existence. This change in morphology reflects a transition from anguilliform or sub-carangiform locomotion to carangiform locomotion, and indicates a progressive shift from nearshore dwellers to pelagic cruisers—a change in foraging habitat independently corroborated by paleobiogeographic, stable isotope, osteohistological, and paleopathological data. Evolutionary patterns similar to those observed in mosasaurine mosasaurs are seen in other secondarily aquatically adapted amniotes, notably metriorhynchid crocodyliforms, cetaceans, and ichthyosaurs, and may be explained by developmental modularity governing the observed phenotypic expression.

Phanerozoic trends in shell and life habit traits linked to postmortem durability were evaluated for the most common fossil brachiopod, gastropod, and bivalve genera in order to test for changes in taphonomic bias. Using the Paleobiology Database, we tabulated occurrence frequencies of genera for 48 intervals of ∼11 Myr duration. The most frequently occurring genera, cumulatively representing 40% of occurrences in each time bin, were scored for intrinsic durability on the basis of shell size, reinforcement (ribs, folds, and spines), life habit, and mineralogy.

Shell durability is positively correlated with the number of genera in a time bin, but durability traits exhibit different temporal patterns across higher taxa, with notable offsets in the timing of changes in these traits. We find no evidence for temporal decreases in durability that would indicate taphonomic bias at the Phanerozoic scale among commonly occurring genera. Also, all three groups show a remarkable stability in mean shell size through the Phanerozoic, an unlikely pattern if strong size-filtering taphonomic megabiases were affecting the fossil record of shelly faunas. Moreover, small shell sizes are attained in the early Paleozoic in brachiopods and in the latest Paleozoic in gastropods but are steady in bivalves; unreinforced shells are common to all groups across the entire Phanerozoic; organophosphatic and aragonitic shells dominate only the oldest and youngest time bins; and microstructures having high organic content are most common in the oldest time bins.

In most cases, the timing of changes in durability-related traits is inconsistent with a late Mesozoic Marine Revolution. The post-Paleozoic increase in mean gastropod reinforcement occurs in the early Triassic, suggesting either an earlier appearance and expansion of durophagous predators or other drivers. Increases in shell durability hypothesized to be the result of increased predation in the late Mesozoic are not evident in the common genera examined here. Infaunal life habit does increase in the late Mesozoic, but it does not become more common than levels already attained during the Paleozoic, and only among bivalves does the elevated late Mesozoic level persist through the Holocene.

These temporal patterns suggest control on the occurrence of durability-related traits by individual evolutionary histories rather than taphonomic megabiases. Our findings do not mean taphonomic biases are absent from the fossil record, but rather that their effects apparently have had little net effect on the relative occurrence of shell traits generally thought to confer higher preservation potential over long time scales.

Cases of convergent evolution, particularly within ecomorphological contexts, are instructive in identifying universally adaptive morphological features across clades. Tracing of evolutionary pathways by which ecomorphological convergence takes place can further reveal mechanisms of adaptation, which may be strongly influenced by phylogeny. Ecomorphologies of carnivorous mammals represent some of the most outstanding cases of convergent evolution in the Cenozoic radiation of mammals. This study examined patterns of cranial shape change in the dog (Canidae) and hyena (Hyaenidae) families, in order to compare the evolutionary pathways that led to the independent specialization of bone-cracking hypercarnivores within each clade. Geometric morphometrics analyses of cranial shape in fossil hyaenids and borophagine canids provided evidence for deep-time convergence in morphological pathways toward the independent evolution of derived bone-crackers. Both clades contained stem members with plesiomorphic generalist/omnivore cranial shapes, which evolved into doglike species along parallel pathways of shape change. The evolution of specialized bone-crackers from these doglike forms, however, continued under the constraint of a full cheek dentition and restriction on rostrum length reduction in canids, but not hyaenids. Functionally, phylogenetic constraint may have limited borophagine canids to crack bones principally with their carnassial instead of the third premolar as in hyaenids, but other cranial shape changes associated with durophagy nevertheless evolved in parallel in the two lineages. Size allometry was not a major factor in cranial shape evolution in either lineage, supporting the interpretation of functional demands as drivers for the observed convergence. The comparison between borophagines and hyaenids showed that differential effects of alternative functional “solutions” that arise during morphological evolution may be multiplied with processes of the “macroevolutionary ratchet” already in place to further limit the evolutionary pathways available to specialized lineages.

Fossil species of the family Hyaenidae represent a wide range of ecomorphological diversity not observed in living representatives of this carnivoran group. Among them, the cursorial meat-and-bone specialists are of particular interest not only because they were the most cursorial of the hyaenids, but also because they were the only members of this family to spread into the New World. Here we conduct a functional morphological analysis of the cranium of the cursorial meat-and-bone specialist Chasmaporthetes lunensis by using finite element modeling to compare it with the living Crocuta crocuta, a well-known bone-cracking carnivoran. As found with previous finite element studies on hyaenid crania, the cranium of C. lunensis is not differentially adapted for stress dissipation between the bone-cracking and meat-shearing teeth. A smaller occlusal surface on the more slender P3 cusp of C. lunensis allowed this species to use less bite force to crack a comparably-sized bone relative to C. crocuta, but higher muscle masses in the latter probably allow it to process larger food items. We use two indices, the stress slope and the bone-cracking index, to show that C. lunensis has a well-adapted cranium for stress dissipation given its size, but the main stresses placed on its cranium might have been more from subduing prey and less from cracking bones. Throughout the Cenozoic, other carnivores besides hyaenids convergently evolved similar morphologies, including domed frontal regions, suggesting an adaptive value for a repetitive mosaic of features. Our analyses add support to the hypothesis that bone-cracking adaptations are a complex model that has evolved convergently several times across different carnivoran families, and these predictable morphologies may evolve along a common gradient of functionality that is likely to be under strong adaptive control.

Dental morphology changes dramatically across the artiodactyl-cetacean transition, and it is generally assumed that this reflects the evolutionary change from herbivory and omnivory to carnivory. To test hypotheses regarding tooth function and diet, we studied size and position of wear facets on the lower molars and the stable isotopes of enamel samples. We found that nearly all investigated Eocene cetaceans had dental wear different from typical wear in ungulates and isotope values indicating that they hunted similar prey and processed it similarly. The only exception is the protocetid Babiacetus, which probably ate larger prey with harder skeletons. The closest relative of cetaceans, the raoellid artiodactyl Indohyus, had wear facets that resemble those of Eocene cetaceans more than they do facets of basal artiodactyls. This is in spite of Indohyus's tooth crown morphology, which is unlike that of cetaceans, and its herbivorous diet, as indicated by stable isotopes. This implies that the evolution of masticatory function preceded that of crown morphology and diet at the origin of cetaceans.

The evolutionary history of the Order Carnivora is marked by episodes of iterative evolution. Although this pattern is widely reported in different carnivoran families, the mechanisms driving the evolution of carnivoran skull morphology remain largely unexplored. In this study we use coordinate-point extended eigenshape analysis (CP-EES) to summarize aspects of skull shape in large fissiped carnivores. Results of these comparisons enable the evaluation of the role of different factors constraining the evolution of carnivoran skull design. Empirical morphospaces derived from mandible anatomy show that all hypercarnivores (i.e., those species with a diet that consists almost entirely of vertebrate flesh) share a set of traits involved in a functional compromise between bite force and gape angle, which is reflected in a strong pattern of morphological convergence. Although the paths followed by different taxa to reach this “hypercarnivore shape-space” differ because of phylogenetic constraints, the morphological signature of hypercarnivory in the mandible is remarkably narrow and well constrained. In contrast, CP-EES of cranial morphology does not reveal a similar pattern of shape convergence among hypercarnivores. This suggests a lesser degree of morphological plasticity in the cranium compared to the mandible, which probably results from a compromise between different functional demands in the cranium (e.g., feeding, vision, olfactory sense, and brain processing) whereas the mandible is only involved in food acquisition and processing. Combined analysis of theoretical and empirical morphospaces for these skull data also show the lower anatomical disparity of felids and hyaenids compared to canids and ursids. This indicates that increasing specialization within the hypercarnivorous niche may constrain subsequent morphological and ecological flexibility. During the Cenozoic, similar skull traits appeared in different carnivoran lineages, generated by similar selection pressures (e.g., toward hypercarnivory) and shared developmental pathways. These pathways were likely the proximate source of constraints on the degree of variation associated with carnivoran skull evolution and on its direction.

Diversity dynamics of the Permian–Triassic land plants in South China are studied by analyzing paleobotanical data. Our results indicate that the total diversity of land-plant megafossil genera and species across the Permian/Triassic boundary (PTB) of South China underwent a progressive decline from the early Late Permian (Wuchiapingian) to the Early-Middle Triassic. In contrast, the diversity of land-plant microfossil genera exhibited only a small fluctuation across the PTB of South China, showing an increase at the PTB. Overall, land plants across the PTB of South China show a greater stability in diversity dynamics than marine faunas. The highest extinction rate (90.91%) and the lowest origination rate (18.18%) of land-plant megafossil genera occurred at the early Early Triassic (Induan), but the temporal duration of the higher genus extinction rates (>60%) in land plants was about 23.4 Myr, from the Wuchiapingian to the early Middle Triassic (Anisian), which is longer than that of the coeval marine faunas (3–11 Myr). Moreover, the change of genus turnover rates in land-plant megafossils steadily fluctuated from the late Early Permian to the Late Triassic. More stable diversity and turnover rate as well as longer extinction duration suggest that land plants near the PTB of South China may have been involved in a gradual floral reorganization and evolutionary replacement rather than a mass extinction like those in the coeval marine faunas.

Quantifying the effects of taphonomic processes on species abundances in time-averaged death assemblages (DAs) is pivotal for paleoecological inference. However, fidelity estimates based on conventional “live-dead” comparisons are fundamentally ambiguous: (1) data on living assemblages (LAs) are based on a very short period of sampling and thus do not account for biological variability in the LA, (2) LAs are sampled at the same time as the DA and thus do not necessarily reflect past LAs that contributed to the DA, (3) compositions of LAs and DAs can be autocorrelated owing to shared cohorts, and (4) fidelity estimates are cross-scale estimates because DAs are time-averaged and LAs are not. Some portion of raw (total) live-dead (LD) variation in species composition thus arises from incomplete sampling of LAs and from biological temporal variation among LAs (together = premortem component of LD variation), as contrasted with new variation created by interspecific variation in population turnover and preservation rates and by the time-averaging of skeletal input (together = postmortem component of LD variation). To tackle these problems, we introduce a modified test for homogeneity of multivariate dispersions (HMD) in order to (1) account for temporal autocorrelation in composition between LAs and DAs and (2) decompose total LD compositional variation into premortem and postmortem components, and we use simulations to evaluate the contribution of within-habitat time-averaging on the postmortem component. Applying this approach to 31 marine molluscan data sets, each consisting of spatial replicates of LAs and DAs in a single habitat, we find that total LD variation is driven largely by variation among LAs. However, genuinely postmortem processes have significant effects on composition in 25–65% of data sets (depending on the metric) when the effects of temporal autocorrelation are taken into account using HMD. Had we ignored the effects of autocorrelation, the effects of postmortem processes would have been negligible, inflating the similarity between LAs and DAs. Simulations show that within-habitat time-averaging does not increase total LD variation to a large degree—it increases total LD variation mainly via increasing species richness, and decreases total LD variation by reducing dispersion among DAs. The postmortem component of LD variation thus arises from differential turnover and preservation and multi-habitat time-averaging. Moreover, postmortem processes have less effect on the compositions of DAs in habitats characterized by high variability among LAs than they have on DAs in temporally stable habitats, a previously unrecognized first-order factor in estimating postmortem sources of compositional variation in DAs.

Persistence in the structure of ecological communities can be predicted both by deterministic and by stochastic theory. Evaluating ecological patterns against the neutral theory of biodiversity provides an appropriate methodology for differentiating between these alternatives. We traced the history of benthic foraminiferal communities from the Huon Peninsula, Papua New Guinea. From the well-preserved uplifted reef terrace at Bonah River we reconstructed the benthic foraminiferal communities during a 2200-year period (9000–6800 yr B.P.) of reef building during the Holocene transgressive sea-level rise. We found that the similarity of foraminiferal communities was consistently above 60%, even when comparing communities on either side of a massive volcanic eruption that smothered the existing reef system with ash. Similarly, species diversity and rank dominance were unchanged through time. However, similarity dropped dramatically in the final stages of reef growth, when accommodation space was reduced as sea-level rise slowed. We compared the community inertia index (CII) computed from the observed species abundances with that predicted from neutral theory. Despite the differences in foraminiferal community composition in the younger part of the reef sequence, we found an overall greater degree of community inertia with less variance in observed communities than was predicted from neutral theory, regardless of foraminiferal community size or species migration rate. Thus, persistent species assemblages could not be ascribed to neutral predictions. Ecological incumbency of established foraminiferal species likely prevented stochastic increases in both migrant and rare taxa at the Bonah River site. Regardless of the structuring mechanisms, our reconstruction of Holocene foraminiferal assemblages provides historical context for the management and potential restoration of degraded species assemblages.

Theoretical morphology is the scientific field in which researchers model organism growth and form. The field is developed well in studies on skeletons, especially shells. Researchers have contributed echinoid skeleton models to the field, but these have yet to be recognized collectively. We present herein the first comprehensive review for echinoid skeleton models in theoretical morphology. We apply a phylogenetic systematic analysis to those models, use the resulting consensus cladogram to classify and interrelate the models in an analogy in which they are likened to fossil specimens in a biostratigraphic record, and utilize the biostratigraphic metaphor to define trends within theoretical morphology as it applies to echinoid skeleton models.

Taxonomic membership frequencies exhibit distributions in which groups with few numbers of subtaxa are much more common in a clade than those with more subtaxa. Here, a “broken plate” model is developed to describe such taxonomic memberships; some higher taxonomic group (the plate) is randomly subdivided into intermediate taxonomic units (plate fragments), whose sizes are dependent on the number of taxonomic subunits that they each contain. Theoretical distributions of membership frequencies produced by this model yield a superior fit to data from both modern and fossil groups, as illustrated by classifications for primarily fossil brachiopods and entirely modern mammals. The nature of these distributions is consistent with the contention that Linnaean membership frequencies result from the random partitioning of taxonomic/morphologic space. Moreover, numbers of taxa contained within hierarchically equivalent groups are unrelated, as are membership numbers at taxonomically higher and lower levels of consideration. Agreement between observed taxonomic memberships and those anticipated from the random partitioning of diversity as described by the “broken plate” model bears directly on a number of fundamental questions including the significance of extreme polytypy and inferred causes of adaptive radiation within many taxonomic groups.