A diverse fauna of numerous, well-preserved polyplacophorans are present in the Mississippian (Osagean) Gilmore City Formation, Humboldt Member at Humboldt, Iowa. Specimens were collected from oolitic and skeletal packstones. New taxa include Gryphochiton demissus new species, Euleptochiton ellipticus new species Platychiton gerki new genus and species, Angulochiton humboldtensis new genus and species, and Systenochiton triangulus new genus and species.

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.

The functional morphology and autecology of leperditicopid arthropods (Ordovician-uppermost Devonian) are analyzed in the light of well-preserved specimens from the Devonian of China and detailed comparisons with recent ostracodes. Leperditicopids were large, bivalved arthropods (adults ranging from 5 to about 50 mm in length) typically with an asymmetric carapace (strong ventral overlap), a complex muscular system (powerful adductors, extrinsic muscles, tendinous structures) whose insertions are preserved as scars on the inner surface of the exoskeleton and steinkerns, and an extensive radiating network of integumental sinuses probably involved in gaseous and ionic exchanges (oxygen uptake and transport, osmoregulation). The conspicuous chevron scars adjacent to the adductor scars are interpreted as the anchoring spots of mandibular tendinous structures possibly involved in the opening mechanism of the valves. The ultrastructure of the carapace is comparable to that of thick-shelled recent myodocopid ostracodes. A review of leperditicopid occurences (depositional environment, associated faunas and floras) shows that the group preferentially occupied very shallow marginal habitats (tidal flats, reef-flats, lagoons, embayments, or estuarian complexes) that were subjected to environmental stress (salinity, temperature, moisture). This ecological range implies specific adaptations (osmoregulation, resistance to desiccation) supported by morphological evidence (e.g., circulatory system, carapace closing system, thick shell). Most leperditicopids had epibenthic lifestyles and were probably detritus feeders. They may have been adapted (powerful mandibles) to scrape food on algal/microbial mats. Their typical pattern of occurrence (monospecificity, large numerical abundance) displays some of the characteristics of opportunistic populations (e.g., recent ostracodes, branchiopods) living in variable environments. Morphological similarities with Ostracoda are important (e.g., muscular and tendinous features, circulatory system, valve overlap, carapace ultrastructure) but taxonomic relationships with that group remain inconclusive because of the lack of evidence from soft parts.

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.

Schimperella acanthocercus, a new species of lophogastrid crustacean, is described from the Triassic of southwest China. This species is very similar to modern forms as well as the rare fossil Lophogastrida, known to date only from the Jurassic and Triassic. The sister “mysidacean” group to the Lophogastrida, the Mysida, are also rare in the fossil record; they too demonstrate remarkable similarities to living forms, suggesting that the extant “mysidaceans” had achieved “stable body plans” relatively early in their history, certainly by the Jurassic and Triassic. The third “mysidacean” group, the Pygocephalomorpha, have a considerably more extensive fossil record and are thus better understood. While “mysidaceans” are relatively rare in the fossil record, enough is known to suggest some possible biogeographic and evolutionary relationships.

The oldest Jurassic marine pleurodire is reported from the Jagua Formation in western Cuba. These remains are from levels of middle and late Oxfordian age. This turtle represents a new genus and species, Caribemys oxfordiensis. A phylogenetic hypothesis is proposed, whereby Caribemys is considered to be the sister group of Notoemys Cattoi and Freiberg, 1961, plus the Eupleurodira Gaffney and Meylan, 1988. The occurrence of Caribemys oxfordiensis n. gen. and sp. in the Jagua Formation along with plesiosauroids, pliosauroids, ophthalmosaurian ichthyosaurs, and metriorhynchid crocodiles, strongly suggests that during the Oxfordian a marine seaway was present in the Caribbean, connecting the western Tethys with the Pacific Ocean.

Over the past 75 years, the higher-level taxonomy of bivalves has received less attention than that of their fellow molluscs, gastropods. The publication of the bivalve volumes of the Treatise on Invertebrate Paleontology in 1969 was not followed by an explosion of study into the evolution of bivalves; rather, with only one or two exceptions, bivalve workers were noticeably absent from the cladistic and molecular revolutions that were taking place during the 1970s and 1980s, even as gastropods received considerable attention. Over the past ten years, cladistics and molecular systematics have begun to be applied to solve problems of bivalve evolutionary biology. These studies, most of which have been undertaken by paleontologists, have halted the stagnation in bivalve systematics. Bivalve systematics looks to have an exciting future, as the excellent fossil record of the Bivalvia will be used in conjunction with cladistics and molecular systematics to solve problems in not just bivalve evolution but evolutionary biology in general.

A new, flattened, eocrinoid-grade, blastozoan echinoderm Haimacystis rozhnovi new genus and species is described from the uppermost Lower Ordovician Wah Wah Limestone of western Utah. Although apparently most similar in morphology to the rhipidocystids, Haimacystis differs in its plane of thecal flattening, lack of one-piece marginals, and ambulacral system development. A comparison of overall morphology and plane of thecal flattening is presented for flattened blastozoans. Haimacystis was a streamlined suspension feeder attached to the sea floor by a holdfast at the end of a relatively short stem and bent over in the water column in moderate currents.

Silurian ramphoprionid polychaete annelids, represented by their jaws (scolecodonts), are described from extensive collections from Gotland, Sweden. The family Ramphoprionidae, monotypic at its original description, is sub-divided into four genera; Protarabellites Stauffer, 1933; Ramphoprion Kielan-Jaworowska, 1962; “Pararamphoprion” Männil and Zaslavskaya, 1985; and Megaramphoprion new genus. Identified species include “P.” cf. nordicus Männil and Zaslavskaya, 1985; P. rectangularis new species; P. staufferi new species; P. triangularis new species; and two Protarabellites species left in open nomenclature. Ramphoprion is represented by one new highly plastic species, R. gotlandensis, housing five distinguishable morphotypes showing gradual evolution. Megaramphoprion, which is most closely related to Ramphoprion, is represented by M. magnus new genus and species, a rare but distinctive taxon. Most species have long stratigraphic ranges within which important morphological changes can nonetheless be observed. The stratigraphic range of ramphoprionids includes, at least, the Ordovician to the Silurian. They are fairly rare in the Silurian of Gotland and where present they generally form less than 10 percent of the polychaete faunas, although occasionally reaching as much as 20 to 30 percent. Evolution, paleoecology, and surface structures of the investigated species are briefly discussed.

Phylogenetic analysis was used to evaluate evolutionary relationships within the Cambrian suborder Olenellina Walcott, 1890; special emphasis was placed on those taxa outside of the Olenelloidea. Fifty-seven exoskeletal characters were coded for 24 taxa within the Olenellina and two outgroups referable to the “fallotaspidoid” grade. The Olenelloidea, along with the genus Gabriellus Fritz, 1992, are the sister group of the Judomioidea Repina, 1979. The “Nevadioidea” Hupé, 1953 are a paraphyletic grade group. Four new genera are recognized, Plesionevadia, Cambroinyoella, Callavalonia, and Sdzuyomia, and three new species are described, Nevadia fritzi, Cirquella nelsoni, and Cambroinyoella wallacei. Phylogenetic parsimony analysis is also used to make predictions about the ancestral morphology of the Olenellina. This morphology most resembles the morphology found in Plesionevadia and Pseudojudomia Egorova in Goryanskii and Egorova, 1964.

More than thirty complete specimens of Carcineretes planetarius Vega, Feldmann, Ocampo, and Pope, 1997, a member of the extinct decapod family Carcineretidae, have been collected from the upper part of the Ocozocuautla Formation in Chiapas, southeast Mexico. Stratigraphic occurrences of Carcineretes in the Caribbean Province suggest that this crab should be regarded as an index fossil for the early Maastrichtian. Six samples of this species may represent individuals that died during molting. The sudden disappearance of this family at the end of the Maastrichtian and its restricted paleobiogeographic distribution in the vicinity of the impact site suggest that the Carcineretidae may have been affected by the Chicxulub impact. Other decapod specimens collected from the same localities were assigned to the Xanthidae; Parazanthopsis meyapaquensis new genus and species, and Megaxantho zoque, new genus and species, are described. They constitute the second and third reports of Cretaceous xanthid crabs from Mexico. A lagoonal paleoenvironment is suggested, based on associated fauna and flora. Occurrences of index species of benthic and planktic foraminifera along with that of diagnostic rudist species confirm an early Maastrichtian age.

Twentieth century fossil gastropod systematics relied extensively on neontological paradigms. However, recent appreciation of the extant gastropod diversity suggests that those early paradigms provided very unsound models. This likely is a greater problem for Paleozoic taxa than for Meso-Cenozoic gastropods because Meso-Cenozoic taxa frequently have easily recognized extant relatives whereas Paleozoic taxa frequently do not. Also, many of the taxa that apparently diverged in the Paleozoic now are limpets and retain little information about the morphologies of their coiled ancestors.

Snails could be a model taxon for investigating macroevolutionary patterns because of the clade's dense fossil record. However, paleontologists usually study only adult shells (teleoconchs), and many malacologists maintain that teleoconch characters reflect phytogeny poorly if at all. This is important because many macroevolutionary hypotheses make their most specific predictions given phylogeny. Studies evaluating species- or genus-level relationships typically use more shell characters and states than do studies evaluating suprageneric relationships, as expected if shells evolve rapidly. Monte Carlo tests reject a null hypothesis that rates of homoplasy are equal among shell and soft-anatomy characters for two neogastropod clades, but suggest that these rates differ by less than an order of magnitude. Finally, teleoconch characters fail to unite bellerophontiform species with gastropod muscle scars but successfully unites clusters bellerophontiform species with tergomyan muscle scars. These results corroborate the conventional wisdom that teleoconch character distributions reflect abundant homoplasy, but the results also suggest that these distributions reflect phylogeny, too.

If we can control the effects of homoplasy, then gastropods are an excellent “model” group for testing macroevolutionary hypotheses such as changing rates of evolution. Two obvious candidates are rates of morphologic evolution among basal neogastropods, and rates of molecular evolution within clades radiating after the K/T mass extinction.

A freshwater interbed of the Yemen Volcanic Group in central western Yemen yielded impressions of numerous, articulated, mostly complete frog skeletons. Recent dating of the volcanics and the stratigraphic position of the fossil bearing bed in the sequence support a Late Oligocene age for the frogs. These frogs are described as a new species of Xenopus, a genus that is today mostly confined to subsaharan Africa, and they provide evidence of the former, wider distribution of this genus on the Afro-Arabian Plate. The new species, X. arabiensis, differs from other Xenopus in its long maxilla and maxillary tooth row. It resembles X. muelleri in its dentate, azygous vomer and prominent, cone-shaped, distally-pointed prehallux, but differs from X. muelleri in having an atlantal intercotylar notch and longer distal prehallux bone. Climatic changes during the Neogene probably led to the extinction of Xenopus on the Arabian Peninsula; however, the timing of this event is not certain.

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.

Fusulinacean foraminifera have been described from several localities and horizons within the Upper Pennsylvanian and Lower Permian of the North American midcontinent (Beede, 1916; Dunbar and Condra, 1927; Skinner, 1931; Newell, 1934; Newell and Keroher, 1937; Merchant and Keroher, 1939; Dunbar and Henbest, 1942; Burma, 1942; Thompson, 1954, 1957; Thompson et al., 1956; Douglass, 1962; King, 1988; Sanderson and Verville, 1988), but surprisingly, a comprehensive account of fusulinacean biostratigraphy of the stratotype of the Upper Pennsylvanian Virgilian Stage has never been published. This report summarizes fusulinacean biostratigraphic data from the Virgilian section in the stratotype region of southeastern Kansas. The publication of this dataset is particularly important because of the current efforts to standardize global Pennsylvanian chronostratigraphy (Metcalfe, 1997), and related efforts and debates concerning the definition and correlation of stages in the Upper Pennsylvanian and Lower Permian succession of North America.

Distinguishing among members of the Hexapodidae Miers, 1886, the Asthenognathinae Stimpson, 1858, and the Chasmocarcininae Serène, 1964, is difficult in fossil specimens that lack preserved pereiopods or sterna. Members of the Hexapodidae are easily identified if sterna and pereiopods are present, because possession of four pairs of pereiopods and seven exposed sternites is diagnostic for the family. Several features of the dorsal carapace are useful in differentiating among genera assigned to that family and other subfamilies belonging to the Goneplacidae and Pinnotheridae; however, dorsal carapace characters are less useful in assigning taxa at the family or subfamily level. A key to the taxa discussed herein permits generic differentiation based upon the relative dimensions of the carapace, the shape and size of the orbits, the shape and size of the rostrum, carapace ornamentation, and the degree of fusion of abdominal somites in males.

A new species of Palaeopinnixa Via, 1966, Palaeopinnixa rotundus, is described from the Eocene Coaledo Formation of Oregon, USA. A new hexapodid genus and species, Globihexapus paxillus, is recognized from the Miocene Astoria Formation of Washington, USA. Prepaeduma decapoda Morris and Collins, 1991, is referred to Hexapus de Haan, 1833. Viapinnixa new genus has been erected to accommodate material previously assigned to Pinnixa (Palaeopinnixa) nodosa Collins and Rasmussen, 1992, and Orthakrolophos has been named to accommodate three species of Palaeograpsus Bittner, 1875. Asthenognathus urretae new species is described from the middle Eocene Centinela Formation of southern Argentina.

The progress achieved in trilobite systematics over the last 75 years is briefly reviewed. Different approaches to phylogenetics have influenced the way trilobites have been classified. Classical evolutionary taxonomy, the stratigraphical approach, and cladistics have all contributed in different ways to the current classification, which has evolved piecemeal, and is still unsatisfactory is some ways. Nonetheless, progress towards a phylogenetic classification has been made, especially as the result of information from ontogenies provided by well-preserved silificified material. Trilobites are a well-defined clade within a larger arachnomorph group. Agnostida have been excluded from Trilobita, but are perhaps best considered as specialised trilobites, at least until limbs of eodiscids are described. The outstanding problems in classification of each trilobite order are reviewed. Most are concerned with the recognition of the appropriate Cambrian sister taxa, and the discovery of the relevant ontogenies. It is very likely that post-Cambrian clades “root” deeply into the Cambrian. The coherence, or otherwise, of Proetida, Asaphida, Corynexochida and the lichid/odontopleurid groups will be resolved by such studies. The problems of paraphyly in Ptychopariida and Redlichiina may prove more obdurate. The temporal brevity of certain Cambrian family ranges may be partly a taxonomic artefact. The possibility of a late Cambrian gap in the record on some clades should be considered.

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.

Exceptionally well-preserved Late Mississippian colosteid amphibian specimens occur in southern Illinois; the mandible is described here. Unexpectedly primitive features include toothed adsymphysial and intercoronoid fossa with fenestrate floor. The large adsymphysial bears teeth, forms 50 percent of the symphysis, and meets its antimere in a very coarsely rugose suture. These and other characters are shown to occur also in Greererpeton burkemorani, to which we refer the Illinois specimens. Colosteid mandibles from a Late Mississippian locality in southern Iowa resemble G. burkemorani closely, although they are not conspecific. Our findings are summarized in a PRESERVE-format data table containing 226 characters. G. burkemorani's adsymphysial suture morphology is shared with the baphetid Megalocephalus pachycephalus. However, the relationship of colosteids to other Paleozoic amphibian groups remains unclear, beyond their position as stem tetrapods. The single elongate Meckelian fenestra of colosteids is likely primitive for tetrapods. A three-stage model is proposed for the evolution of Meckelian fenestrae in tetrapods. Based on sutural morphology, G. burkemorani is considered to have a kinetic joint between skull table and cheek. A functional hypothesis is outlined in which movements at this joint are accommodated at the symphysis. A phylogenetically based test of this hypothesis is proposed.

Although Middle Cambrian trilobites of the Braintree Member in eastern Massachusetts were among the first published on in North America, re-examination of this fauna has led to wholesale taxonomic and biostratigraphic re-evaluation. This low diversity fauna now includes at least seven species, with the first report of agnostoids (three poorly preserved taxa) and the ellipsocephalid Kingaspis avalonensis new species. Paradoxides (Acadoparadoxides) harlani Green emend., a senior synonym of P. (A.) haywardi Raymond, allows correlation into the lowest Middle Cambrian elsewhere in Avalon. However, all the polymeroid species are endemic, and this precludes a highly resolved correlation into other Cambrian paleocontinents. A breakdown of provincial barriers in the late Early Cambrian as western Gondwana passed from equatorial to the higher south latitudes of Avalon led to faunal exchanges between these continents. Paradoxides (Acadoparadoxides) and Kingaspis of the Braintree fauna are shared with western Gondwana, while Braintreella and “Agraulos” quadrangularis are closest to genera known from the Spanish, Moroccan, and Perunican (Bohemian) margins of Gondwana.