Exceptionally large quantities of outstandingly well-preserved, free specimens of larger foraminifera from late Miocene sediments of the Dominican Republic invite an analysis of their structure in detail. The structures of the porcelaneous larger foraminifera reveal that most of them are not candidates for a direct ancestry of the species living today in the Caribbean. Although the late Miocene period has produced Caribbean endemists, in particular within the agglutinated group of the textulariellids and the lamellar-perforate group of the amphisteginids, the porcelaneous archaiasines and soritines are more closely related to the early Miocene forms of the Neotethys than to the Recent Caribbean endemists. These relationships are derived from their relative structural similarity and call for the proposition of appropriate additional taxa on the generic and specific levels. Miocene Miarchaias new genus develops several centimeters large, cyclical agamonts with meandropsinid structures covering the lateral surface of the disc (M. meander new species) whereas species of smaller shell size do not have cyclical generations (M. modestus new species). On the other hand, populations of cyclical schizonts and/or gamonts exhibit structures similar to the Recent, spiral Androsina: Androsinopsis radians new genus and species. The other new taxa erected here, Annulosorites spiralis new genus and species and Cyclorbiculina miocaenica new species, reflect differences in the apertural face and the respective arrangement of radial partitions as used to differentiate Recent Sorites from Amphisorus. Specimens to be attributed to the genera Cycloputeolina and Parasorites are present in the late Miocene of the Dominican Republic. They exhibit an exoskeleton in contrast to true soritids, and will need an eventual worldwide revision on the species level.

Caribbean coral reef communities were restructured by episodes of accelerated biotic change during the late Oligocene/early Miocene and the late Pliocene/early Pleistocene. However, rigorous description of the effects of rapid biotic change is problematic because preservation and exposure of coral-bearing deposits is not consistent in all stratigraphic intervals. In the Caribbean, early and middle Miocene exposures are more rare than late Miocene and Pliocene exposures. One exception is the late early to early middle Miocene Tamana Formation of Trinidad, and old and new collections from this unit were studied to determine the timing of recovery after the Oligocene/Miocene transition. A total of 41 species of zooxanthellate corals were recovered from the unit, including 21 new records. Within these assemblages, species first occurrences outnumber species last occurrences by a factor of four (31 first occurrences and eight last occurrences). The extension of the stratigraphic ranges of species previously first recorded in Pliocene sediments has reduced an apparent Pliocene pulse of origination, indicating that the Pliocene/Pleistocene transition was largely a result of accelerated extinction against a background of near-constant origination. The fact that few species last occur in the Tamana fauna indicates that the Oligocene/Miocene transition was complete by the end of the early Miocene.

This study represents the first in a series tracing the early evolution of a dominant Caribbean reef coral, the Montastraea “annularis” species complex, using a combination of morphometric and phylogenetic approaches. It focuses on Costa Rica and Panama; additional geographic locations and reef environments will be treated in subsequent work. To distinguish species, new landmark methods are developed by comparisons with genetically characterized modern colonies from Panama. The fossil material consists of transverse thin-sections of 94 well-preserved specimens of M. annularis-like corals collected in Plio-Pleistocene reef sequences in the Limón basin of Costa Rica and the Bocas del Toro basin of Panama. The landmarks comprise 27 spatially homologous points, which define the thickness and structure of the corallite wall and associated costosepta. Bookstein size and shape coordinates are analyzed using cluster analysis and canonical discriminant analysis, and a total of 10 morphotypes are distinguished. Cladistic analyses are performed using characters derived partially from morphometric data. A matrix consisting of 16 taxa and eight characters is analyzed using global parsimony and a sister group of two species as the outgroup. The results reveal two distinct evolutionary groups, which are distinguished by the new corallite wall characters. One group contains one modern species, and the other contains a second; the relationships of the third are poorly resolved.

Despite the low number of equally parsimonious trees, high numbers of plesiomorphic taxa, long range extensions, and lack of agreement with genetic data indicate that the new characters alone are inadequate for completely interpreting evolutionary relationships, and more samples and characters are needed. Nevertheless, these preliminary results do show that three modern species of the M. “annularis” complex arose prior to accelerated extinction at the end of late Pliocene to early Pleistocene faunal turnover of Caribbean reef corals, and two may have originated younger than 4 Ma. Six or more new species may be represented in upper Pliocene to lower Pleistocene sequences in Costa Rica and Panama. Coexistence of predominantly pre- and post-turnover clades may have been responsible for the high diversity observed within the species complex in these two sequences.

I investigated the degree to which the interpretation of reef coral distribution data is influenced by the numerical and taxonomic scale of analysis in Pleistocene coral communities from the Caribbean Sea. Patterns of community differentiation analyzed at both species and genus levels showed only small differences using different numerical scales (relative abundance, rank abundance and species presence and absence). Whereas some differences were observed between species and genus level patterns, they had little effect on paleoecological interpretations. The greatest differences occurred when presence and absence analyses of assemblages sampled along 40-m transects were compared with those sampled along 40-m transects augmented by a one-hour search for rare taxa. These results suggest that paleoecological interpretations of Quaternary coral communities are robust to numerical scale of analysis at the species and genus level, and to taxonomic scale between the species and genus level. However, interpretations of community structure are sensitive to sampling intensity, geographic scale, and sample size.

Three new Miocene-Pliocene species of the cheilostome bryozoan Metrarabdotos from Venezuela are atypical in showing significant evidence that as many as half the colonies originated asexually (clonally) by “regeneration” from previously existing colonies, rather than almost exclusively from ancestrular zooids (products of metamorphosis of sexually produced larvae), as is characteristic of the genus. The extremely low proportion of zooids (less than two percent) recognizably committed to producing larvae (ovicelled) in these Venezuelan species agrees with that reported in a variety of Danian (Paleocene) genera in which clonal propagation has been reported to predominate. However, all but two of 17 other living and fossil species of Metrarabdotos also have fewer than two percent of their zooids ovicelled, even though all but one of more than 250 colony bases examined originated from ancestrulae. The lack of significant correlation in Metrarabdotos between frequencies of ovicelled zooids and of ancestrular colonies suggests that clonal propagation may not have diverted resources from sexual reproduction. This inference is supported by the retention in these species of a level of heritable morphologic variation (estimated by partitioning among-colonies and within-colonies variance in zooid characters) that is commensurate with that estimated for species of Metrarabdotos in which propagation was apparently entirely by sexual means. Thus, sexual reproduction throughout the genus was apparently sufficient to maintain the genetic diversity from which speciation could proceed at normal rates. As estimated by both cladistic and nearest-neighbor morphologic-stratigraphic methods, the three Venezuelan species occupy quite different positions in the inferred phylogeny of Metrarabdotos. Thus, the elevated level of clonal propagation in these species appears to be a response to local conditions, most probably high productivity associated with upwelling, that promoted more rapid vegetative growth while leaving the level of sexual reproduction unchanged.

Cyclostome bryozoans are present in 83 samples collected as part of the Panama Paleontology Project (PPP) and representing sediments deposited during the Miocene-Pleistocene in several basins on the Caribbean and Pacific sides of the Central American Isthmus. Preliminary study has resulted in the identification of 23 species. Most of these are left in open nomenclature and assigned questionably to genera, pending detailed study and comparison with cyclostomes previously described from this region and elsewhere. Maximum sample diversity is 13 species and median diversity two species. An equal number of species is present in the Caribbean and Pacific basins. The cumulative collection curve for the PPP cyclostome samples shows a flattening, implying that further sampling will not increase diversity substantially. About 11 percent of calcareous species in the PPP bryozoan fauna are cyclostomes, the remainder being cheilostomes. This relatively small value is consistent with anecdotal data for Recent bryozoans which suggest a decrease in the proportion of cyclostomes within bryozoan faunas from high to low latitudes. Species with erect colonies dominate among the cyclostomes, in contrast with the PPP cheilostomes in which encrusting species greatly outnumber erect species.

Geminate species are morphologically similar sister-species found on either side of the Isthmus of Panama. The existence of all geminates in the tropical Eastern Pacific ocean and the Caribbean Sea is most often explained by vicariance: closure of the Central American Seaway 3.1 to 3.5 Ma simultaneously isolated populations of species with amphi-American distributions. In this paper, we test the potential of morphological measurements for discriminating between Recent geminate species pairs from three genera (Arca, Arcopsis, and Barbatia) in the bivalve family Arcidae and examine the prospects for distinguishing nominal species in the fossil record. Fourteen morphological variables were used to characterize shell shape and multivariate methods were used to discriminate between five Recent species pairs. Collection sites were also used as a priori groups for discrimination to describe patterns of intraspecific morphological variation and to evaluate differences among samples from different geographic regions.

On average, 84 percent of specimens within geminate pairs are classified correctly following five separate discriminant analyses with nominal species as the grouping variable. Although all but one arcid species pair are discriminated with high statistical significance, some collection sites within species are highly morphologically distinct. Overall, a large proportion of specimens from each collection locality (79 percent on average) can be classified correctly to site although no single site possessed a multivariate centroid that was significantly different from all other conspecific centroids. The distinctiveness of some collection sites, however, raises the possibility that some nominal species may harbor cryptic species, indicating the need for wider geographic surveys of both molecular and morphological variation within geminate species pairs.

The eigenvalue coefficients derived from the Recent samples of one geminate pair (Arca mutabilis and A. imbricata) were used to assess the potential for identifying arcid species in the fossil record. Discriminant analyses of fossil Arca indicate that the forms that characterize Recent A. mutabilis and A. imbricata are present in the fossil record as far back as the Late Early Miocene, in the Cantaure Formation of Venezuela. Because a deep water connection between the Eastern Pacific and Western Atlantic existed until the Middle Miocene, the morphological differences associated with Recent A. mutabilis and A. imbricata likely existed well before the rising Isthmus affected ocean circulation patterns in tropical America. Therefore, despite great overall morphological similarity, these putative geminate species likely have a time of divergence that is at least four times older than final seaway closure. The geographic distribution of fossils also suggests that morphological forms associated with each Recent species had amphi-American distributions both before and after isthmus formation but are now geographically restricted to either side of the isthmus in the Recent fauna.

The shell microstructure of Carboniferous and Triassic permophorids; Triassic and Recent carditids; Devonian, Carboniferous, and Triassic crassatelloideans; and Jurassic through Recent cardioideans is examined in a phylogenetic context, using separate microstructural and morphologic data sets, as well as a combined data set. The microstructural and morphologic data sets are significantly incongruent, but the combined data set suggests that modiomorphoideans (modiomorphids and permophorids) are basal to crassatelloideans; crassatelloideans are basal to carditids (including Septocardia), and carditids are basal to cardiids. On the other hand, the possibility of direct permophorid ancestry for the carditid-cardiid clade cannot be excluded, as suggested by the retention of permophorid-like matted (transitional nacreous-porcelaneous) structure in some early carditids and cardiids. In the absence of stratigraphic data and other evidence for phylogenetic relationships, shell microstructure offers limited potential for assessing subfamily-level phylogenetic relationships within the Cardioidea. This is because of microstructural convergences reflecting biomechanical adaptations for fracture control and abrasion resistance, and possibly also selection for metabolic economy of secretion in tropical, oligotrophic habitats. General evolutionary trends in cardiid shell microstructure are nevertheless apparent: Cretaceous cardiids completely replaced an ancestral laminar, matted structure in their inner shell layer with non-laminar porcelaneous structures; evolved better defined CL structure, stronger reflection of the shell margins, and increased thickness or secondary loss of the ancestral prismatic outer shell layer; and, in Protocardia (Pachycardium) stantoni, added inductural deposition. Some Cenozoic cardiids then evolved wider first-order crossed lamellae, non-denticular composite prisms, composite fibrous prisms, ontogenetic submergence of a juvenile non-denticular composite prismatic outer shell layer into the CL middle shell layer, or ontogenetic submergence of the inner part of a juvenile fibrous prismatic outer shell layer into the CL middle shell layer.

The shell microstructure of Hemidonax donaciformis is unusual for a cardioidean, and suggests closer affinities with the superfamily Tellinoidea than with the superfamily Cardioidea.

Extensive inductural deposits in Protocardia (Pachycardium) stantoni raise the possibility that photosymbiosis evolved among some Mesozoic members of the Protocardiinae, thereby increasing the likelihood that this feature has evolved several times independently in the Cardiidae.

Cemented, calcareous periostracal granules or spines are known to occur in modiolopsoideans, mytiloideans, modiomorphids, permophorids, trigonioids, astartids, cardiids, myoids, pholadomyoids, and septibranchoids. Consequently, the presence of these structures is not necessarily indicative of close anomalodesmatan affinities.

Phylogenetic reconstructions of two tropical American venerid genera, Chione and Chionopsis (subfamily Chioninae) were attempted at the species-level. The purposes of the analyses were to provide historical reconstructions of origination and extinction events in the two clades, as well as patterns of invasion and diversification. The analyses were based entirely on conchological characters to facilitate the inclusion of a substantial number of fossil taxa, but difficulties were encountered due to the quality of preservation and availability of material. Nevertheless the two genera were established as monophyletic clades, and the reconstructions yielded considerable insight into their histories in tropical America. The analyses suggest that both genera originated in the tropical western Atlantic, Chionopsis by at least the early Oligocene, and Chione in the early Miocene. Various branches of both genera subsequently invaded the tropical eastern Pacific several times prior to Seaway closure, with only one possible reciprocal invasion of the western Atlantic. Pliocene extinction affected both genera more significantly in the western Atlantic relative to the eastern Pacific, and diversity is higher today in the latter region. These conclusions are not entirely consistent with the fossil records of the genera, but this incongruency highlights the need for much more extensive sampling of the eastern Pacific Cenozoic record.

Previous descriptions of Tucetona lack a consistent system using diagnostic characters and only two recent Caribbean ‘species' are recognized. In this study, textural and structural features of the Tucetona shell are examined and used as the basis for comparison to other glycymerids and in the recognition of morphospecies. Standard diagnostic characters based mainly on the cross-sectional shape of ribs and on hinge teeth ontogeny are presented and used to distinguish six recent Caribbean morphospecies. The shell texture has been examined by light and scanning electron microscopy, showing the interior of glycymerid hinge teeth structured by two bundles of crossed lamellar texture. Whereas European Glycymeris examined for comparison correspond in their hinge plate textures to the one found in Tucetona, differences from a Caribbean Glycymeris sp. are described. Simple lamellar, crossed-lamellar and cone complex crossed-lamellar textures showed the same basic crystallite subunits.

Collectively, studies of the structure of Neogene diversity change in tropical American mollusks have lacked 1) species-level analyses within well-established clades; 2) consideration of abundance and sample size on diversity estimates and comparisons; and 3) geographic comparisons within temporal intervals. This study takes all three factors into consideration and compares Miocene to Recent species richness patterns in tropical American marginellid gastropod species within the clade Prunum Volvarina. Rarefaction analyses of more than 16,000 specimens from more than 500 samples are used to standardize comparisons of species richness through time and space. Species richness in Prunum Volvarina from the Miocene to the Recent of the Tropical Western Atlantic (TWA) is compared along a latitudinal gradient from north to south (Florida, the Dominican Republic, and Venezuela). Additionally, temporal patterns of diversity change are compared between the TWA and the Tropical Eastern Pacific (TEP: Peru, Ecuador, Colombia, Panama, and Costa Rica).

As is the case with most Neogene lineages, the number of marginellid specimens and samples differ significantly through both time and space. Rarefaction analyses of both specimens and samples indicate that: 1) significant geographic differences in species richness were detected between the Miocene, Pliocene, Pleistocene, and Recent of the TWA; 2) temporal patterns of species richness were similar in the northern and southern TWA; 3) from the Miocene to the Recent, marginellid species richness in the TEP has always been significantly less than TWA diversity; and 4) from the Miocene to the Recent, TWA diversity decreased significantly, whereas TEP diversity was stable and low. Separate rarefaction analyses using the numbers of specimens and samples did not always produce concordant results and indicate that the unit of analysis influences estimates of species richness. Discordant specimen/sample rarefaction results may be a product of sample size. Intrinsic ecological and evolutionary differences do not appear to be primary contributors to differences in marginellid species richness between the TEP and TWA.

The earliest known members of the Thais clade of rapanine muricid neogastropods comprise four species from the Cantaure Formation (early Miocene: Burdigalian) of Venezuela; three of these species are new. Neorapana rotundata Gibson-Smith et al., 1997, is most closely related to the Recent Pacific Mexican N. tuberculata (Sowerby, 1835), and represents the only known Atlantic occurrence of the genus. Thais brevicula new species is closest to T. callaoensis (Gray, 1828) from the Recent of northern Peru and the Galápagos. A review of the genus Thais indicates that the typical members of this group occur in the South Atlantic, West Africa, and eastern Pacific, but not in the Recent fauna of the southern Caribbean. Stramonita bifida new species is a large species related to the Recent S. haemastoma floridana (Conrad, 1837), which occurs throughout the Caribbean. A review of American species of Stramonita indicates that the taxon S. biserialis (de Blainville, 1832) from the Recent fauna of the eastern Pacific, and the taxon S. h. haemastoma (Linnaeus, 1767), may each be composed of more than one species despite the teleplanic dispersal of their larvae. Stramonita semiplicata new species is closely related to the Recent S. bicarinata (de Blainville, 1832) from the South Atlantic, and represents a lineage that occurred in the Caribbean region until at least the late Miocene. It may have given rise to the eastern Pacific genus Acanthais. The higher diversity and greater antipredatory specialization of eastern Pacific as compared to western Atlantic members of the Thais clade may have resulted from higher post-Miocene rates of speciation and lower extinction rates in the eastern Pacific.

Tonnoidean gastropods have planktotrophic larval lives of up to a year and are widely dispersed in ocean currents; the larvae maintain genetic exchange between adult populations. They therefore are expected to respond rapidly to new geographic barriers by either extinction or speciation. Fossil tonnoideans on the opposite coast of the Americas from their present-day range demonstrate that larval transport still was possible through Central America at the time of deposition of the fossils. Early Miocene occurrences of Cypraecassis tenuis (now eastern Pacific) in the Caribbean probably indicate that constriction of the Central American seaway had commenced by Middle Miocene time. Pliocene larval transport through the seaway is demonstrated by Bursa rugosa (now eastern Pacific) in Caribbean Miocene-latest Pliocene/Early Pleistocene rocks; Crossata ventricosa (eastern Pacific) in late Pliocene rocks of Atlantic Panama; Distorsio clathrata (western Atlantic) in middle Pliocene rocks of Ecuador; Cymatium wiegmanni (eastern Pacific) in middle Pliocene rocks of Atlantic Costa Rica; Sconsia sublaevigata (western Atlantic) in Pliocene rocks of Darien, Pacific Panama; and Distorsio constricta (eastern Pacific) in latest Pliocene-Early Pleistocene rocks of Atlantic Costa Rica. Continued Early or middle Pleistocene connections are demonstrated by Cymatium cingulatum (now Atlantic) in the Armuelles Formation of Pacific Panama. Tonnoideans indicate that the Central American seaway began to be constricted after early Miocene time, and some larval transport through the seaway was possible throughout Pliocene time. Intermittent marine connections were maintained at least during late Pliocene to early Pleistocene interglacial periods of high sea-level, and alternated with a land bridge during glacial periods of low sea-level.

Fossil crinoids are described from the Lesser Antilles for the first time. Crinoids are now known to occur in the Miocene of Carriacou, the Grenadines (four species), and in the Eocene and Miocene of Barbados (three species). Taxa include: isocrinid sp. indet., hyocrinid sp. indet. (both Eocene); the isocrinids Neocrinus decorus (Wyville Thomson, 1864) and Isocrinus sp., the bourgueticrinid Democrinus? sp., and the comatulid Horaeometra sp. (all Miocene). Despite the preponderance of taxa in open nomenclature, these are among the very few records of fossil crinoids from the Antillean region. Faunas are dominated by the columnals of isocrinids; bourgueticrinid and millericrinid columnals, and comatulid centrodorsals, are very rare, despite comatulids being both the most diverse crinoids in the modern fauna and the only group that occurs in shallow-water environments. Post-Eocene crinoid faunas in the Antillean region include taxa that are similar, at least at the generic level, to those of the present day. Democrinus? sp. from Carriacou is the first pre-Quaternary bourgueticrinid from the Antilles. Horaeometra sp. is the first fossil comatulid from the Antilles to be classified to generic level.

The extant crinoid fauna of the tropical western Atlantic includes 23 genera/34 species of “stalkless” comatulid crinoids and eight genera/ten species of stalked crinoids. This is far greater than the known diversity of fossil crinoids from the Antillean region, which spans circa 120 Ma. The apparent rarity of fossil crinoids is probably part artefact, produced by collection bias, taphonomic effects, and the relative rarity of exposures of sedimentary units deposited in 150 m, i.e., the environment of extant stalked crinoids.

We report the discovery of an extremely rich, previously undescribed Caribbean late Miocene to early Pliocene ichthyofauna represented by one hundred forty species of elasmobranchs and teleosteans from the Cubagua Formation, northeastern Venezuela. The fauna exhibits significant ecological differences compared with common neritic Caribbean Neogene assemblages. The bathymetric distributions of taxa, based on living counterparts, ranges from 0 to 100 m depth. The exceptional co-occurrence of deep water (epipelagic, mesopelagic and benthopelagic), and shallow water (neritic) taxa is best interpreted as the consequence of ocean upwelling in the proximity to the deep-water Cariaco Trench. Patterns of predator and prey are established and corroborate upwelling. Special remarks are made regarding previously unknown late Miocene to early Pliocene Caribbean ichthyofaunas, the absence or rarity of reported fossil taxa in the Recent Caribbean fauna, and a paleo- upwelling indicator (Lampadena jacksoni new species).

The reliability of any survey of biodiversity through geologic time depends on the rigor and consistency by which taxa are recognized and samples are identified. The main goal of the Neogene Marine Biota of Tropical America (‘NMITA’) project is to create an online biotic database ( http://nmita.geology.uiowa.edu) containing images and synoptic taxonomic information that are essential to collecting and disseminating high-quality taxic data. The database consists of an inventory of taxa collected as part of several large multi-taxa fossil sampling programs designed to assess marine biodiversity in tropical America over the past 25 m.y. In the first phase of the project, data for ∼1,300 taxa and ∼3,800 images are currently being entered into a relational database management system on an IBM RS6000 at the University of Iowa. Eleven taxonomic groups are represented: bivalves, gastropods (muricids, marginellids, strombinids), bryozoans (cheilostome, cyclostome), corals (azooxanthellate, zooxanthellate), benthic foraminifers, ostracodes, fish. The lowest taxonomic rank is species (genera/subgenera in mollusks) and the highest is family. Data that are collected and displayed on taxon pages include: (1) taxonomic authorship, synonyms, type specimens, and diagnostic morphologic characters; (2) images of representative specimens and associated museum catalog and measurement data; (3) distributional information including geologic ages, stratigraphic units, and spatial locations; and (4) higher level classification (genera and families) and bibliographic information. Illustrated glossaries of morphologic terms, character matrices, and identification tools are being developed for corals and mollusks. Interactive geographic maps and stratigraphic columns have been designed to provide information about taxa collected at different locations.