Molecular data are becoming an indispensable tool for the reconstruction of phylogenies. Fossil molecular data remain scarce, but have the potential to resolve patterns of deep branching and provide empirical tests of tree reconstruction techniques. A total evidence approach, combining and comparing complementary morphological, molecular and stratigraphical data from both recent and fossil taxa, is advocated as the most promising way forward because there are several well-established problems that can afflict the analysis of molecular sequence data sometimes resulting in spurious tree topologies. The integration of evidence allows us to: (1) choose suitable taxa for molecular phylogenetic analysis for the question at hand; (2) discriminate between conflicting hypotheses of taxonomic relationship and phylogeny; (3) evaluate procedures and assumptions underlying methods of building trees; and (4) estimate rates of molecular evolution in the geological past. Paleontology offers a set of independent data for comparison and corroboration of analyses and provides the only direct means of calibrating molecular trees, thus giving insight into rates of molecular evolution in the geological past.

The mid-Mesozoic time was characterized by massive reorganization of the ecological structure of benthic marine communities. Although the general pattern of this “Mesozoic Marine Revolution” has been extensively documented, little is known about how it affected the taxonomic and morphologic diversities of individual lineages of organisms. Here I document group-level dynamics of the Mesozoic change using the fossil record of aporrhaid gastropods, a diverse and widespread family during that time. Using data gathered through field and museum work and extensive literature search, I compare and contrast patterns of taxonomic and morphologic change during the Jurassic and Cretaceous within a geographic framework. I also examine how the changes were manifested at different ecological and geographic scales.

The Mesozoic history of the Aporrhaidae includes two major radiations separated by a period of overall stability. While both radiations increased the taxonomic diversity of the family, they had very different morphologic consequences, resulting in a striking discordance between morphologic and taxonomic diversity patterns. The initial radiation during Bajocian-Bathonian times established two large morphologic groups within the aporrhaids based mainly on differences in the shape of the apertural margin. The second, post-Albian, radiation saw higher origination rates and increased taxonomic and morphologic diversity among genera having simpler apertural margins, while genera with elaborate multidigitate apertures declined in taxonomic diversity but not in morphologic diversity. During post-Albian times the group with simpler apertural margins also tended to be more widespread compared to the group with multidigitate apertures. Comparison of regional and global taxonomic diversities reveals a discordance between regional and global taxonomic patterns: while diversities within certain geographic areas increased in concert with the global radiation, those for other areas decreased substantially, resulting in a remarkably constant average taxonomic diversity within geographic areas.

Modern marine plankton communities include a broad diversity of metazoans that are suspension-feeding or micropredatory as adults. Many benthic marine species have larval stages that reside, and often feed, in the plankton for brief to very long periods of time, and most marine benthic communities include large numbers of suspension-feeders. This has not always been the case. Cambrian benthic communities included relatively few suspension-feeders. Similarly, there were few metazoan clades represented in the plankton, either as adult suspension-feeders or as larvae. Review of the fossil record suggests that the diversification of the plankton and suspension-feeding marine animals began in the Late Cambrian and continued into the Ordovician. These changes were accompanied by, and probably influenced, concurrent major changes in the marine realm, including an increase in tiering within benthic communities, the replacement of the Cambrian fauna by the Paleozoic fauna, and a general taxonomic diversification. The ultimate cause of these changes is uncertain, but it appears likely that the plankton was and is a refuge from predation and bioturbation for adults and larvae alike. The expansion in plankton biomass thus provided increased ecological opportunities for suspension-feeders in the plankton and benthos.

It has been argued that many clades originating in the early Paleozoic filled their design space rapidly while still at low taxonomic diversity. Standardization of morphology for analytical purposes facilitates testing of this claim. Here I document evolutionary patterns of morphological disparity in Ordovician-Devonian crinoids, using a set of 75 discrete characters covering the principal features of the crinoid stem, cup, tegmen, and arms. Disparity is measured as the average dissimilarity among species, the range of morphospace occupied, and the number of realized character-state combinations. Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity. Despite subsequent taxonomic diversification, the variety of crinoid form did not expand appreciably; increased diversity was accommodated by the evolution of variations upon the spectrum of designs established earlier. The data discussed here do not definitively imply specific sources of constraint, but the effective stasis in disparity supports previous arguments that some morphological limits were reached early in crinoid history.

Macroevolutionary change from the Middle to the Late Paleozoic crinoid fauna was not the result of mass extinction. The presumption that the decline of the middle Paleozoic crinoid fauna was from a single mass extinction event was tested using seriation, multidimensional scaling (MDS), binomial analysis, and bootstrapping simulations on a data set which is a comprehensive revision of old faunal lists. The data for these analyses were based on temporal distributions of 214 species from 69 late Osagean and early Meramecian localities from the midcontinental United States. The time under consideration is subdivided into seven informal intervals using MDS in conjunction with biostratigraphy. Seriation of species ranges into these intervals results in a gradual pattern of faunal turnover, and sampling bias can be eliminated as a cause for this more gradual pattern. MDS analysis of the crinoid range data is similar to MDS simulations using data with continuous, monotonic species turnover and dissimilar to a simulated mass extinction. Binomial analysis and bootstrapping demonstrate that the observed number of extinctions at the putative extinction boundary were not unusually high. All methods agree that extinctions throughout this time were high but spanned several time intervals and that rapid, monotonic faunal turnover describes the data better than mass extinction. Macroevolutionary processes other than mass extinction and microevolutionary processes must have dictated the character and composition of this remarkable faunal transition among the Crinoidea.

Potential hybrid fossil crinoids, Eretmocrinus magnificus x Eretmocrinus praegravis, are identified from the Lower Mississippian Fort Payne Formation of south-central Kentucky. These are the first fossil hybrid crinoids identified, and one of very few examples of hybrids recognized in the fossil record. Eretmocrinus magnificus x E. praegravis specimens have shapes and calyx plate sculpturing that are morphologically intermediate between well-defined, distinct parent species. Suspected hybrids occur at localities where parent species co-occur and where the parent species are the most abundant; the hybrids occur at what may have been the distributional margins of the parent species; and the mixture of characters on suspected hybrids seems to be morphogenetically partitioned. Parent species are derived from separate lineages within Eretmocrinus, and hybridization is the most probable explanation for these morphologically intermediate specimens. This example highlights the need to consider hybridization as a potential interpretation of intermediate morphologies among fossils and raises questions concerning the impact of hybridization for our interpretation of the fossil record and the role of hybridization in the evolutionary process.

The Neogene species Petaloconchus sculpturatus presents a contradiction in terms, for it grows whorl “packages” of nearly perfect regularity, but ranks within the most geometrically irregular family of uncoiled gastropods, the Vermetidae. We perform a first biometric study of vermetids (only possible because sufficient regularity of growth permits us to number and identify whorls) to specify and characterize the factors on both sides of this “exquisite tension” between promotion and prevention of recoiling. Promoting factors include the older phyletic heritage of preserved dextral coiling, and the more immediate vermetid (or specifically petaloconchid) features of growth toward open spaces (where regular coiling might proceed in an unimpeded fashion); radular excision of discordant feeding tubes with shaping of the resulting scar so that growth may proceed in conformity with previous whorls; and locking of subsequent whorls upon a keel formed by longitudinal bead-rows of the previous whorl. Preventing factors include prominent phyletic heritage of all vermetids—maximal early irregularity enjoined by discordance between larval and subsequent growth (with teleoconch wrapping itself around the protoconch), thus precluding an ordered substrate to act as a foundation for regular whorl “packages” of intermediary growth—and a set of features specific to this lineage and acting as geometric constraints. In this category, we particularly document the exceedingly low rate of whorl expansion and the consequently wide umbilical space that produces a shell akin to winding a cylindrical coil of narrow-diameter rope around the periphery of a wide circular platform. This complex combination of promoting and preventing factors produces a shell that is tantalizingly close to fully regular, but cannot truly reattain this previous phyletic state—thus providing a fine example of Dollo's Law at the centenary of his formation of irreversibility.

Late Paleocene planktic foraminifera exhibit strong positive correlations between carbon isotopic values and test mass, but negative correlations between oxygen isotopic values and test mass. Based on analogy with modern taxa, these trends are probably ecotypic and may or may not apply to an ontogenetic series. Among Acarinina and Morozovella species, the magnitude and direction of these trends resemble those of modern planktic foraminifera with dinoflagellate photosymbionts. This is consistent with current models of photosymbiosis and calcification in planktic foraminifera and suggests that Acarinina and Morozovella relied heavily on photosymbionts for nutrition.

Acarinina and Morozovella species resemble modern, strongly photosymbiotic taxa in their association with low and mid latitude nearsurface water masses. However, their test morphologies differ greatly from those of extant taxa that bear obligate photosymbionts. Earliest Paleocene taxa that exhibit a similar paleohabitat association and similar size-related isotopic trends are characterized by still different test morphologies. These comparisons suggest that (1) throughout geologic time, strong reliance on photosymbiont activity has been closely linked to habitat, but not to test morphology; (2) photosymbiosis has been a common and convergently evolved strategy of planktic foraminifera over geologic time, and (3) modern relationships between planktic foraminiferal test morphology and photosymbiont dependence are largely an artifact of geologically recent phylogenetic relationships and shared ecologic strategies.

Intersite comparison suggests that the stable isotopic signals of narrowly constrained size fractions of a late Paleocene Acarinina or Morozovella species can be used to reconstruct the magnitude and direction of relative variation in equilibrium stable isotopic values throughout its geographic and temporal range. This is supported by analogy with extant photosymbiotic taxa. However, since photosynthetic depletion of 12C leaves 13C-enriched HCO3-for calcification, the carbon isotopic values of Acarinina and Morozovella tests may have been consistently greater than paleoseawater values. Failure to account for this effect could lead to overestimation of late Paleocene marine productivity.