Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large, complex organisms which prospered during the late Neoproterozoic. It represents an iconic Ediacaran taxon, but the relatively few specimens previously known significantly hindered an accurate reconstruction. Discovery of more than 100 specimens of Rangea in two gutter casts recovered from Farm Aar in southern Namibia significantly expands this data set, and the well preserved internal and external features on these specimens permit new interpretations of Rangea morphology and lifestyle. Internal structures of Rangea consist of a hexaradial axial bulb that passes into an axial stalk extending the length of the fossil. The axial bulb is typically filled with sediment, which becomes increasingly loosely packed and porous distally, with the end of the stalk typically preserved as an empty, cylindrical cone. This length of the axial structure forms the structural foundation for six vanes arranged radially around the axis, with each vane consisting of a bilaminar sheet composed of a repetitive pattern of elements exhibiting at least three orders of self-similar branching. Rangea was probably an epibenthic frond that rested upright on the sea bottom, and all known fossil specimens were transported prior to their final burial in storm deposits.

Paleobiological studies of early metazoan evolution are critically dependent on the accurate stratigraphic subdivision and correlation of uppermost Proterozoic and Lower Cambrian sequences. Planktonic microfossils evolved rapidly during this period and are widely distributed and abundant in Vendian and Lower Cambrian rocks; therefore, they provide what is potentially one of the best means of correlating successions of this age. In Ny Friesland, Spitsbergen, tillite-bearing detrital rocks of the uppermost Proterozoic Polarisbreen Group are overlain without apparent unconformity by the Tokammane Formation, a tripartite lithologic sequence consisting of quartzarenites (Blårevbreen Member) overlain by dark shales with subordinate sandstone (Topiggane Member) and dolomites (Ditlovtoppen Member). Salterella, hyoliths, and other invertebrate remains occur in the upper part of the Tokammane succession; trace fossils are found in the Tokammane quartzarenites and shales, as well as in the uppermost few meters of the Polarisbreen sequence. Planktonic microfossils occur throughout the succession. They indicate that the Polarisbreen Group is Vendian in age and that a hiatus corresponding in time to the latest Vendian and (perhaps) earliest Cambrian coincides with the Polarisbreen/Tokammane boundary. Lower Topiggane shale samples contain acritarchs comparable to those found in the sub-Holmia Lontova Beds of Eastern Europe. Upper Topiggane samples contain diverse acritarch assemblages that indicate a late Holmia or Protolenus age, suggesting the presence of a second hiatus within the Tokammane Formation. Planktonic microfossils allow biostratigraphic correlation with other sequences both within (East Greenland) and between (East European Platform) paleocontinents. Like those from other areas, diversity trends exhibited by late Proterozoic and Early Cambrian acritarchs from Spitsbergen indicate a major Vendian episode of extinction followed by Early Cambrian rediversification of planktonic microfossils.

Knowledge of phylogenetic relationships among species is fundamental to understanding basic patterns in evolution and underpins nearly all research programs in biology and paleontology. However, most methods of phylogenetic inference typically used by paleontologists do not accommodate the idiosyncrasies of fossil data and therefore do not take full advantage of the information provided by the fossil record. The advent of Bayesian ‘tip-dating’ approaches to phylogeny estimation is especially promising for paleosystematists because time-stamped comparative data can be combined with probabilistic models tailored to accommodate the study of fossil taxa. Under a Bayesian framework, the recently developed fossilized birth–death (FBD) process provides a more realistic tree prior model for paleontological data that accounts for macroevolutionary dynamics, preservation, and sampling when inferring phylogenetic trees containing fossils. In addition, the FBD tree prior allows for the possibility of sampling ancestral morphotaxa. Although paleontologists are increasingly embracing probabilistic phylogenetic methods, these recent developments have not previously been applied to the deep-time invertebrate fossil record. Here, I examine phylogenetic relationships among Ordovician through Devonian crinoids using a Bayesian tip-dating approach. Results support several clades recognized in previous analyses sampling only Ordovician taxa, but also reveal instances where phylogenetic affinities are more complex and extensive revisions are necessary, particularly among the Cladida. The name Porocrinoidea is proposed for a well-supported clade of Ordovician ‘cyathocrine’ cladids and hybocrinids. The Eucladida is proposed as a clade name for the sister group of the Flexibilia herein comprised of cladids variously considered ‘cyathocrines,’ ‘dendrocrines,’ and/or ‘poteriocrines’ by other authors.

Cores dating back to deglaciation were taken from three lakes in Atlantic Canada and analyzed for arcellaceans and pollen. Paleotemperatures and paleo-precipitation were calculated from the pollen data using transfer functions. A sudden warming is recorded by the pollen around 10,000 years B.P., followed by a general warming to the mid Holocene Hypsithermal, then by a decrease in temperature and increase in effective precipitation to the present. The three lakes, two in western Newfoundland and one in eastern Nova Scotia, contain similar late glacial (13-10 ka), early Holocene (10-8 ka), mid Holocene (8-4 ka), and late Holocene (4-0 ka) arcellacean assemblages. Immediately following retreat of the ice sheets, Centropyxis aculeata, Centropyxis constricta, Difflugia oblonga, Difflugia urceolata, and Difflugia corona were common. The latter part of the late glacial is characterized by sparse assemblages dominated by C. aculeata. The arcellacean record thus suggests a climatic reversal in Atlantic Canada between 11,500 and 10,000 years B.P., analogous to the Younger Dryas, although this is not recorded by the pollen. Species diversity increased sharply at the beginning of the Holocene, and D. oblonga is the dominant taxon in early Holocene sediments. Difflugia oblonga remained common through the mid Holocene, but percentages of C. aculeata were very low, and Pontigulasia compressa and Difflugia bacillifera peaked in abundance during the Hypsithermal. The late Holocene is characterized by a resurgence in C. aculeata at the expense of other taxa. The increase in Heleopera sphagni and Nebella collaris since 5,000 years B.P. at the two sites in southwestern Newfoundland reflects paludification in response to increased precipitation since the Hypsithermal. Because the changes in arcellacean assemblages are regionally synchronous in all three lakes and coincide with climatically driven vegetational successions indicated by the pollen record, arcellaceans appear to respond to climatic change, and thus may be useful paleoecological and paleolimnological indicators. With their quicker generation time, these protists may be better suited than pollen to recording short-lived phenomena, like the mid-Holocene Hypsithermal and the Younger Dryas reversal.

A stepwise approach is employed to determine the phylogeny of the initial crinoid radiation during the Arenig and Llanvirn series of the Ordovician. Parsimony-based character analysis is completed first on Arenig crinoids and then for Arenig and Llanvirn crinoids combined.

The topology from well-resolved trees of this early crinoid radiation indicates that the Crinoidea should be subdivided into six subclasses. A new subclass and new order, Aethocrinea and Aethocrinida, respectively, are proposed for crinoids with four circlets of plates in the aboral cup: lintels, infrabasals, basals, and radials. This aboral cup construction is best displayed by Aethocrinus, one of the oldest known crinoids (?Tremadoc-Arenig). However, this primitive aboral cup construction is also present in two Llanvirn crinoids, Perittocrinus and Tetracionocrinus. The Aethocrinea was a small, short-lived radiation of crinoids with this design that was different from those of other crinoids. Two families in the Aethocrinida are the Aethocrinidae, which includes Aethocrinus, and the Perittocrinidae, which includes Perittocrinus and Tetracionocrinus. In addition to the Aethocrinea, the following crinoid subclasses are recognized based on character analyses of these earliest crinoids: Cladida, Camerata, Disparida, Flexibilia, and Articulata.

A revision of the Early-Middle Miocene anguine, Pseudopus laurillardi (Lartet, 1851), is presented based on a detailed anatomical analysis of one newly discovered articulated specimen and numerous disarticulated cranial and postcranial elements from several localities in Germany, as well as on the restudy of the original skeletal material of Lartet. the articulated specimen represents the first record of an articulated anguine from the Neogene. We demonstrate that the contemporaneous anguine Propseudopus fraasii (= Pseudopus fraasi, Pseudopus moguntinus or Ophisaurus moguntinus) from Germany and elsewhere in Europe represents a junior synonym of P. laurillardi. Three species of Pseudopus can by discriminated in the Cenozoic of Eurasia: P. laurillardi (Early-Middle Miocene of Europe), P. pannonicus (Late Miocene-Middle Pleistocene of central and eastern Europe) and P. apodus (Late Pleistocene-Recent, from Eastern Europe to central Asia). Eleven morphological characters of the skull have been identified that distinguish Pseudopus laurillardi from P. pannonicus and P. apodus. Four of these characters regard the frontal and parietal bones, whereas all other characters regard the dentary and dentition. the genus Pseudopus represents the largest and most robust taxon in the subfamily Anguinae and first occurs in central Europe at the beginning of MN 4 (~18.5 Ma). in contrast to the extant species, P. apodus, the fossils P. laurillardi and P. pannonicus had a greater ecological plasticity and lived in various types of environments. the fossil remains of these taxa are most frequently found in localities characterized by sub-humid to humid climate, which may indicate that their preferential habitats include forested environments.

A new species of protocetid archaeocete, Eocetus wardii n. sp., is named based on material from the late Lutetian (middle Eocene, 43-44 Ma) Comfort Member of the Castle Hayne Formation, North Carolina. This material includes portions of the skull, thoracic, lumbar and caudal vertebrae, ribs, and the right innominate. The innominate (pelvis exclusive of the sacral vertebrae) has some characters in common with the innominata of other protocetids, including sufficient size to support a weight-bearing hind limb. This suggests that Eocetus wardii was capable of both terrestrial and aquatic locomotion. The innominate also includes some features in common with basilosaurid archaeocetes including a shift in the relative positions of the pubis and obturator foramen. In addition, the bone histology of Eocetus is found to be very different from that of other archaeocetes and sirenians (sea cows and dugongs). The ribs and vertebrae are composed of a central area of trabecular bone enveloped by layers of dense cortical bone. Eocetus has previously only been known from a few specimens from Gebel Mokattam near Cairo, Egypt. This identification makes Eocetus the only protocetid archaeocete genus known from both sides of the Atlantic Ocean.

At the well-known fossil mammal locality of Fort Ternan in southwestern Kenya, radiometrically dated at about 14 million years old (middle Miocene), fossil grasses have been preserved by nephelinitic sandstone in place of growth above a brown paleosol (type Onuria clay). Large portions of grass plants as well as fragments of leaves have revealed details of silica bodies, stomates, and other taxonomically important features under the scanning electron microscope. The computer database for grass identification compiled by Leslie Watson and colleagues was used to determine the most similar living grass genera to the five distinct kinds of fossil found. Two of the fossil species are assigned to Cleistochloa kabuyis sp. nov. and C. shipmanae sp. nov. This genus includes one species from low fertility dry woodland soils of New South Wales and Queensland and a second species from “raw clay soils” in western New Guinea. A third fossil species, represented by a large portion of a branching culm, is assigned to Stereochlaena miocenica sp. nov. This genus includes five species of low-fertility woodland soils in southeastern Africa. Both Cleistochloa and Stereochlaena are in the supertribe Panicanae of the subfamily Panicoideae. A fourth species is assigned to Distichlis africana sp. nov. and provides a biogeographic link between the single species of this genus now living in coastal grasslands in southeastern Australia and the 12 species of dunes and deserts found throughout the Americas from Patagonia and the West Indies to the United States and Canada. A fifth species is, like D. africana, in the subfamily Chloridoideae, but its stomata were not seen and it could belong to Cyclostachya, Pogoneura, or Polevansia. This earliest known wooded grassland flora in Africa is taxonomically unlike the modern grass flora of fertile volcanic African landscapes, and may have been recruited from an archaic grass flora of Gondwanan desert and lateritic soils.

Dinoflagellate cysts from the classic mid-Pliocene Coralline Crag locality of Rockhall Wood, Suffolk are described, representing the first systematic treatment of mid-Pliocene dinoflagellates from the North Sea region. The dinoflagellates broadly reflect warm-temperate surface waters whose temperatures were considerably higher than today. Two assemblages are recognized: an older assemblage (late early Pliocene or earliest late Pliocene, possibly not younger than 3.3 Ma) confined to the Ramsholt Member, and a younger assemblage (predating 2.6 Ma) confined to the overlying Sudbourne Member. Assemblages are characterized by quantitative differences and their succession indicates either: 1) slight cooling within a probable warm-temperate range; 2) a slight increase in open marine influence; or 3) a taphonomic effect perhaps related to a change in bottom currents.

Specimens have been observed using light (LM) and scanning electron (SEM) microscopy, and cyst wall ultrastructure is emphasized as a valuable but underutilized character for Neogene dinoflagellate taxonomy. Operculodinium? eirikianum Head et al. is emended and the following new taxa are proposed: Achomosphaera andalousiensis suttonensis new subspecies, Ataxiodinium zevenboomii new species, Bitectatodinium raedwaldii new species, and Operculodinium tegillatum new species. Geonettia? sp. is new to science but formal description awaits detailed analysis of tabulation.

On the western side of the Tjörnes Peninsula in northern Iceland exposures of fossiliferous marine sediments, basalts, and glacial tills record the climatic history of this region of the North Atlantic Ocean. Seventy-five marine ostracode species were recovered from the Pliocene Tjörnes sediments and Quaternary sediments known as the Breidavik beds. The ostracode assemblages contain many warm-water genera that do not inhabit Iceland today and indicate early to middle Pliocene (4.5–3.0 Ma) winter and summer bottom-water temperatures that averaged 5–6°C and 14–16°C, respectively (maximum 20°C in summer, rarely below 3°C in winter except during a brief cooling 3.5–3.2 Ma). An intensified North Atlantic Drift and a diminished or absent East Greenland Current account for warm-water oceanographic conditions at 66°N. Late Pliocene marine climates were cooler with winter and summer averages of about 9°C and 8°C. Early Pleistocene ostracode assemblages dated at 1.7–1.3 Ma contain extant arctic–subarctic species that indicate winter and summer temperatures of about − 1.5°C and 4–5°C. New species Bensonocythere eirikssoni, Robertsonites williamsi, Hemicythere rekaensis, Thaerocythere mayburyae, Thaerocythere whatleyi, Leptocythere tjornesensis, Tetracytherura bardarsoni, and Cytheromorpha einarssoni are described.

Remains derived from owl pellets are a major source of small-animal remains in paleontological and archaeological sites. Pellet remains are examined here to further develop workable strategies for extracting taphonomic information from microvertebrate assemblages. Study of the remains of three wild owl species yielded characteristic patterns of bone fragmentation and skeletal element representation. At the assemblage level, owl-derived assemblages are shown to differ quantitatively from other assemblages. The possible variability to be expected in owl-derived assemblages is examined and the patterns are contrasted with those produced by other depositional agents. The patterns can be useful in the identification of owl-deposited remains in some assemblages; however, overlap with patterns produced by other mechanisms may complicate analysis.

A large ichthyosaur from the Early Tithonian (Late Jurassic) of the Neuquén province, Argentina, represents a new genus and species, Caypullisaurus bonapartei, within the family Ichthyosauridae. The holotype is the most complete skeleton of a mature ichthyosaur known to date from the Jurassic of South America. In comparison with other Late Jurassic ichthyosaurs, the new taxon shares a long and slender rostrum, degenerate dentition in adults, and the enlargement of the orbit with Ophthalmosaurus. Unlike Ophthalmosaurus, the forefin of Caypullisaurus has four major digits composed of tightly packed, polygonal phalanges, and pre- and post-axial accessory digits. Caypullisaurus demonstrates that ichthyosaurs were more diverse during the Late Jurassic than thought previously.

The basal Cambrian marks the beginning of an important chapter in the history of life. However, most paleontological work on the basal Cambrian has been focused on skeletal animal fossils, and our knowledge about the primary producers—cyanobacteria and eukaryotic phytoplankton (e.g., acritarchs)—is limited. In this research, we have investigated basal Cambrian acritarchs, coccoidal microfossils, and cyanobacteria preserved in phosphorites and cherts of the Yanjiahe Formation in the Yangtze Gorges area (South China) and the Yurtus Formation in the Aksu area (Tarim Block, northwestern China). Our study confirms the occurrence in these two formations of small acanthomorphic acritarchs characteristic of the basal Cambrian Asteridium–Comasphaeridium–Heliosphaeridium (ACH) assemblage. These acritarchs include abundant Heliosphaeridium ampliatimi (Wang, 1985) Yao et al., 2005, common Yurtusia uniformis n. gen. and n. sp., and rare Comasphaeridium annulare (Wang, 1985) Yao et al., 2005. In addition, these basal Cambrian successions also contain the clustered coccoidal microfossil Archaeophycus yunnanensis (Song in Luo et al., 1982) n. comb., several filamentous cyanobacteria [Cyanonema majus n. sp., Oscillatoriopsis longa Timofeev and Hermann, 1979, and Siphonophycus robustum (Schopf, 1968) Knoll et al., 1991], and the tabulate tubular microfossil Megathrix longus L. Yin, 1987a, n. emend. Some of these taxa (e.g., H. ampliatum, C. annulare, and M. longus) have a wide geographic distribution but occur exclusively in basal Cambrian successions, supporting their biostratigraphic importance. Comparison between the stratigraphic occurrences of microfossils reported here and skeletal animal fossils published by others suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.

The Cretaceous Kodiak Formation at the northeastern end of Kodiak Island, Alaska, is interpreted to have been deposited in a distal deep-sea fan complex. Facies analysis of the sequence suggests deposition in channels (both major and distributary), lobe fringe (proximal and distal), and interchannel and interchannel/channel mouth environments. The strata contain a diverse and relatively abundant trace fossil assemblage consisting, at the ichnogeneric level, of twenty-six forms: Acanthorhaphe, Chondrites, Circulichnis, Cochlichnus, Cosmorhaphe, Desmograpton, Glockerichnus, Gordia, Helminthoida, Helminthopsis, Muensteria, Neonereites, Nereites, Paleodictyon, Palaeophycus, ?Phycosiphon, Planolites, Protopaleodictyon, Scolicia, Spirophycus, Spirorhaphe, Taenidium, Taphrhelminthopsis, Terebellina, Thalassinoides, and Yakutatia.

Thirty-eight ichnospecies are described, three of which (Acanthorhaphe ichnosp., Cosmorhaphe helicoidea, and Desmograpton fuchsi) are recorded for the first time in North America. Final channel-fill (levee) and interchannel environments contain the most abundant and diverse ichnoassemblages, a reflection of favorable environmental parameters for inhabitation by benthic organisms, but more importantly the presence of diverse lithotypes conducive to the final preservation of their activity. Channel-fill sequences are devoid of trace fossils, a reflection of substrate mobility and lack of shale interbeds precluding toponomic preservation. Lobe fringe sequences contain only isolated trace fossils, a reflection of their poor exposure and largely monolithologic character.

The ichnoassemblage is compared to 20 previously described and taxonomically well-documented deep-water flysch trace fossil studies from the Phanerozoic. Comparison at the ichnogeneric level is favorable with only Acanthorhaphe, Terebellina, and Yakutatia being relatively unique to the Kodiak sequence.

Seven species of oryctocephalids occur in the Lower to Middle Cambrian boundary strata of the southern Great Basin. These include Oryctocephalites palmeri n. sp. and an Oryctocephalinae species from the uppermost Lower Cambrian (upper Olenellus Biozone); Oryctocephalus indicus (Reed, 1910), Microryctocara nevadensis n. gen. and n. sp., and Oryctocephalites rasettii n. sp. near the base of the Middle Cambrian (lower Plagiura Biozone); and Oryctocephalus primus Walcott, 1886, and Oryctocephalus nyensis Palmer, 1979, from slightly higher strata (upper Plagiura Biozone). Oryctocephalus and Oryctocephalites are emended based on a cladistic analysis of Oryctocephalinae Beecher, 1897.

The tarsus and distal end of the tibia are described in Herrerasauridae, a family that includes the oldest known dinosaurs. This tarsal configuration is compared to those of more advanced dinosaurs and to other archosaurs. Through phylogenetic analysis of the morphological characters, a picture emerges of the evolutionary changes in the ankles of early dinosaurs.

The tibia of the herrerasaurids has a quadrangular distal articular surface, with a shallow ventrolateral notch. This morphology is strikingly similar to that of the lagosuchid thecodonts Pseudolagosuchus and Lagosuchus and represents the most primitive tibial condition known for Dinosauria.

Aside from the derived states possessed by Theropoda, Sauropodomorpha, and Ornithischia, respectively, it was impossible to recognize synapomorphies in tibiotarsal anatomy shared by these groups exclusive of Herrerasauridae. The transverse broadening of the distal end of the tibia seems to have been attained independently by ornithischians, theropods, and sauropodomorphs.

The tarsus of herrerasaurids is characterized by an astragalus with a small but conspicuous lateroventral depression, by a pyramidal calcaneum with a ventromedial projection that articulates into the cavity of the astragalus just mentioned, and by a posterolaterally directed calcaneal tuber. These characters are also seen in Lagosuchus (a close relative of dinosaurs), in the prosauropod Riojasaurus and, insofar as the astragalus is concerned, in the primitive dinosaur Walkeria, which suggests that dinosaurs of different lineages shared the same tarsal condition.

By definition, this type of articulation between the astragalus and calcaneum follows the “crocodile-reversed” tarsal condition, suggesting that the tarsus in lagosuchids and dinosaurs could be derived from the “crocodile-reversed” pattern present in Ornithosuchidae and Euparkeria. In contrast, the mesotarsal ankle of lagosuchids and dinosaurs lacks the synapomorphies of the “crocodile-normal” ankle present in Crocodylia, Rauisuchidae, Aetosauria, and other archosaurs.

It is concluded that Herrerasauridae retained the primitive tibiotarsal condition for Dinosauria, from which those of the Ornithischia, Sauropodomorpha, and Theropoda were derived. Furthermore, tibiotarsal anatomy supports monophyly of Dinosauria.

Several specimens of the Late Cretaceous lamniform shark, Cretoxyrhina mantelli (Agassiz), from the Niobrara Chalk of Kansas suggest that the shark fed on teleosts, mosasaurs, and possibly plesiosaurs. These animals are active vertebrates, so C. mantelli probably occupied the apex of the food chain in the Late Cretaceous seas. This top predator, however, was probably scavenged frequently by anacoracid sharks. Carcharodon carcharias (great white shark) and carcharhinid sharks are considered as the modern guild counterparts for Cretoxyrhina mantelli and anacoracids, respectively.

As part of a study of vertebrate trackways in the cross-stratified Coconino Sandstone (Permian) of northern Arizona, trackways made by living salamanders under different substrate conditions were compared. The sample of 230 trackways of the western newt, Taricha torosa, included ten combinations of the following substrate characteristics: 1) sediment: muddy or of fine sand; 2) attitude: level or sloped (25 degrees); 3) moisture content: dry, damp, wet, or submerged.

Trackways in wet mud produced the most accurate representation of the number of toes per foot and the arrangement of toes. All other conditions studied yielded a reduced average number of toes per foot, and a large sample was needed before the data had the potential to indicate the true structure of the trackmaker's feet. Trackways made on sloped, submerged mud or sand, sloped, dry sand, and sloped, damp sand rarely included the full complement of toes. The positions and orientations of the toe marks were distorted if the animals were walking underwater or on sloped, damp sand. Trackways on the slopes of cross-stratified deposits make reliable identification of the trackmaking animals exceptionally difficult.

Carinachitiids, hexangulaconulariids, and Punctatus are distinctive and abundant components of early skeletal faunas from the Lower Cambrian of South China. Carinachitiids are redescribed on the basis of Carinachites spinatus from Kuanchuanpu, Shaanxi, and C. tetrasulcatus and C. curvatornatus from Emei, Sichuan. Tubes of all species are characterized by pronounced quadriradial symmetry, but whereas C. spinatus and C. curvatornatus generally have prominent ornamentation consisting of transverse ribbing, that of C. tetrasulcatus is much more subdued. Neither apex nor well-defined aperture is evident in any of the carinachitiids. Hexangulaconulariids are redescribed on the basis of Arthrochites emeishanensis from Emei and Hexaconularia sichuanensis from Kuanchuanpu. In common with the carinachitiids, the former species shows wide morphological variability. The tubes expand rapidly from a blunt apex, bear prominent ribbing, and possess variably developed lateral grooves that impose a quasi-hexaradial symmetry. Hexaconularia sichuanensis is described from fragmentary material with prominent ribbing and well-defined lateral grooves. Punctatus emeiensis has a tapering ribbed cone, with a stellate ornamentation adapically that is replaced by longitudinal ribbing towards the aperture. Carinachitiids and hexangulaconulariids are widely regarded as related to conularids, and this proposal receives additional support here. An external abortive ?borehole in a specimen of Carinachites also supports the tubicolous interpretation of these fossils. An alternative suggestion that carinachitiids and hexangulaconulariids represent the internal rachis of a sea-pen is also considered. The affinities of Punctatus are more speculative, but the genus may be related to the other two groups. The ecology of Punctatus, however, remains problematic.

87Sr/86Sr chronostratigraphy is an important tool for dating and correlating vertebrate and invertebrate faunas preserved in marginal marine sequences. Freshwater flux in marginal marine environments can influence the 87Sr/86Sr of mollusks and, consequently, Sr-chronostratigraphic interpretations based upon them. To appraise the potential problem we have used a two-component mixing equation to evaluate levels of “measurable effects” (defined as ±5 × 10-5 departure from the marine 87Sr/86Sr ratio) in marginal marine environments. A measurable effect occurs at 12 parts per thousand salinity for a weighted world average river, but can occur at salinity > 34 ppt for rivers draining basins with ancient granitic rocks. Predictions were tested with analyses of mollusks from estuaries in the Mississippi Sound and coastal Florida. Analyses document the largely regular variation in 87Sr/86Sr predicted, but also show that a simple two-component model cannot account for all of the variation. Carbonates formed in restricted marine settings may not record a marine 87Sr/86Sr signal, emphasizing the need to consider freshwater flux for 87Sr/86Sr chronostratigraphy.