The oldest known microsaur is preserved in a nodule from the Kinkaid Formation (Mississippian; Elvirian) collected near Goreville, Illinois. At least eight individuals are represented: three by partial skulls plus vertebral column segments with associated limb elements, and five by postcrania only. Skulls are crushed, incomplete, and exposed mainly in palatal view. Palatal bones are denticulate and the palatine has in addition a single large tooth. The basipterygoid process is laterally directed and the basipterygoid joint is open. The atlas carries large articulating facets for proatlantes, a pair of which are identifiable in one specimen. These features have not been found previously in a microsaur. All vertebral segments are dominated by a biconcave pleurocentrum; sutures between the pleurocentrum and neural arch are visible in presacral vertebrae. Distinctive microsaurian intercentra occur between all presacral pleurocentra. Their presence reinforces the hypothesis that microsaur intercentra are homologous with those of other early tetrapods. Caudal vertebrae retain separate haemal arches and some have ribs.

Observed microsaur synapomorphies include: atlas with large median odontoid; atlas with concave lateral facets for occipital condyle; paired occipital condyles that are broad and concave; and thin, straplike intercentra. No observed features support a sister-group relationship with any other microsaur species, or placement within any higher level microsaur group. Because significant portions of the skeleton are missing or inaccessible, the Goreville microsaur is not formally named. A standardized, hierarchical format for skeletal characters is introduced that facilitates data sharing and comparison and fosters rapid archiving and retrieval.

Analysis of 164 collections from shelf facies of Laurentian North America indicates that three successive trilobite mass extinctions at Late Cambrian stage boundary intervals (“biomere” boundaries) are characterized by a common pattern of change in distributional paleoecology and species diversity. In all cases, the extinction intervals are marked by a shift to biofacies that have broader environmental distributions than those prior to the onset of extinctions, implying a reduction in between-habitat (beta) diversity. Significant declines in within-habitat (alpha) diversity also characterize each extinction and the compositions of shelf biofacies record extensive immigration of taxa from off-shelf and shelf-margin sites. The nature and extent of ecologic disruption of the shelf appears to be comparable to changes associated with major mass extinctions, such as those at the end of the Ordovician and Permian. Unlike major mass extinctions, the Cambrian events are followed by a complete recovery of diversity and biofacies structure within a few million years.

A new species, Bananogmius ellisensis n. sp., known only from the holotype, is described from the Blue Hill Shale Member (Upper Cretaceous, middle Middle Turonian) of the Carlile Shale Formation in western Kansas. The skull and anterior portion of the specimen is well-preserved and was subjected to little post-mortem deformation suggesting rapid burial. The nearly complete skull shows three characters that separate the fish from other species of Bananogmius: a straight, rather than ventrally curved dentary, a narrow band of teeth on the dentary that does not extend onto its lateral side, and a cylindrically-shaped articular condyle of the quadrate. The uncompressed preservation of the skull reveals a pair of long structures ventral to the mandible that are also found, but not described for some other Bananogmius species. Based on the positions of muscles in extant teleosts, these structures are most likely the mineralized protractor hyoidei muscles. Furthermore, these structures may be homologous with ventral structures found in Tselfatia. The presence of Bananogmius adds a new ecological component to the Blue Hill Shale fauna.

A new agriochoerid, Protoreodon walshi new species, from the middle Eocene Santiago Formation, San Diego County, California, is described from the Jeff's Discovery and Rancho del Oro local faunas, considered to be late Uintan in age. It differs from most other species of Protoreodon in having an undivided P4 para-metacone and a P3 protocone connected to the paracone by a buccolingual crest. Associated postcranial material is abundant and well preserved. The postcranial skeleton shows several features which probably represent the primitive oreodont condition, including closely appressed metapodials, hoofed ungual phalanges, the lunar in broad contact with both the magnum and the unciform in anterior view, and having the magnum larger than the trapezoid.

Two specimens of a larger morph, Protoreodon cf. walshi, show a different P3 morphology and might represent another new species. Diversity of agriochoerid oreodonts in California is at least as high as has been reported for the Vieja Group of Texas, although not as high as in the Uinta Basin of Utah, where the genus Diplobunops is also present.

We summarize faunal changes through the thickest and one of the most complete records of terrestrial vertebrates spanning Lancian (∼latest Cretaceous) and Puercan (∼earliest Paleocene) ages, the type Ferris Formation in the Hanna Basin, southern Wyoming. Observed faunal changes predate tectonic definition of local Laramide basins. Nonmammalian vertebrates exhibit no major changes in taxonomic composition below the Lancian-Puercan boundary; diversity of non-avian dinosaurs remains high within uppermost levels of the Lancian section. Nevertheless, dinosaurian extinction was not necessarily “catastrophic” within a biologically relevant interval. Primitive condylarths appear locally above the highest known dinosaurs, probably as immigrants. At least in this part of the North American western interior, the first evolutionary radiation of condylarths was subsequent to the last appearance of dinosaurs, not synchronous with or prior to it. Niche-partitioning among condylarths is first recorded near the boundary between Puercan Interval-zones Pu1 and Pu2 (early and middle Puercan time, respectively), by which time the first great mammalian diversification of the Cenozoic had begun. Major experimentations in dental morphology and increasing ranges of body sizes had developed within 400,000 years of the Lancian-Puercan boundary. We recognize no evidence suggesting that placental mammals were “recovering” from events that led to demise of the dinosaurs. The true diversity of marsupials and condylarths precisely at the Cretaceous-Tertiary boundary, throughout the western interior, remains unknown. We cannot, therefore, evaluate extensiveness of competition, if any, at that time among members of the two groups.

Mixosaurus, a Middle Triassic ichthyopterygian, has traditionally been recognized as a typically primitive ichthyopterygian, but this view was recently questioned. Examination of the skull of Mixosaurus revealed many features to confirm this doubt. Its cranial characters, such as the parietal ridge and short supratemporal process of the parietal, are shared with derived ichthyopterygians from the Jurassic. Mixosaurus also has features that are derived within the Ichthyopterygia and unique to the genus, such as a long sagittal crest reaching the nasal, and an expanded anterior terrace of the upper temporal fenestra that also reaches the nasal. Phalarodon, Contectopalatus, and Sangiorgiosaurus are all considered as junior synonyms of Mixosaurus. The supratemporal, squamosal, and quadratojugal are all present in Mixosaurus atavus, as in basal ichthyopterygians. Because all basal ichthyopterygians, and even some derived ichthyopterygians from the Jurassic, have these three elements, the absence of the squamosal in Ichthyosaurus and Platypterygius should be considered derived if it is not preservational.

The shallow-marine Carmel Formation (Middle Jurassic) in central Utah hosts low-diversity trace fossil assemblages, including Arenicolites, Chondrites, Gyrochorte, Lockeia, Planolites, Protovirgularia, Rosselia, Scalarituba, Skolithos, Taenidium, and Teichichnus. Non specialized ichnotaxa with a remarkably small burrow size dominate the assemblages. The amount of bioturbation is lower than expected in comparison with modern shallow-marine carbonate environments. These ichnological features also are significantly different from those of other Jurassic shallow-marine carbonates. The trace fossils represent an environmentally stressed benthic community in a marginal marine, restricted setting, with salinities above normal marine and with depletion of oxygen in pore waters.

The largest documented cimolestid, Alveugena carbonensis new genus and species, is both morphologically and temporally intermediate between small, early cimolestids (such as Procerberus and Cimolestes) and the earliest documented conoryctid taeniodont Onychodectes tisonensis; this represents a transition between the suborders Didelphodonta and Taeniodonta. Diagnosis and description of A. carbonensis is based upon a partial skull and two isolated upper molars recovered from fluvial sandstones at UW locality V-91005, in upper parts of the Ferris Formation, western Hanna Basin, Wyoming. An earliest middle Puercan age for UW locality V-91005 is based upon: presence of taxa that are morphologically intermediate between characteristic early and middle Puercan species; presence of a species of Ectoconus morphologically more primitive than Ectoconus ditrigonus; and co-occurrence of taxa characteristic of Pu1 and Pu2 stratigraphically below and above it. Morphologic trends in evolution of the upper dentition of cimolestids reflect a relative broadening of the crown. A trend toward increasing body size amongst Puercan cimolestids appears to have coincided with a change from a carnivorous (or perhaps insectivorous) to an omnivorous diet, suggested by increased grinding function of the cheek teeth. Cladistic analyses support A. carbonensis as the sister group to O. tisonensis. No known autapomorphies preclude A. carbonensis from having been a plausible ancestor to O. tisonensis.

Two new species, Mojavemys galushai and Phelosaccomys neomexicanus, are described from the Barstovian of New Mexico. Both of these species are assigned to a new subfamily, the Mojavemyinae. It is uncertain as to whether this new subfamily should be referred to the Heteromyidae or Geomyidae.

Both Mojavemys an Phelosaccomys retain some heteromyid characteristics while developing advanced traits of geomyids. It is possible that these genera represent transitional forms between a heteromyid ancestor and advanced geomyines, thus deriving the Geomyidae directly from the Heteromyidae sometime in the middle Tertiary. It is also possible that the Mojavemyinae are a subfamily of heteromyids only convergent with geomyids. A third possiblity is that the mojavemyines are among a group of middle Tertiary geomyoids from which both Recent heteromyids and geomyids were derived.

Morphometric analyses of silicified and nonsilicified (preserved in shale) specimens of the olenelloid trilobites Olenellus (Olenellus) gilberti Meek (in White, 1874) and Nephrolenellus geniculatus Palmer, 1998, from the Lower Cambrian C-Shale Member of the Pioche Formation show that even well-preserved specimens in shales have undergone significant changes in lateral as well as vertical dimensions as a result of compaction. Analyses of cephalic landmarks show that in both species compaction causes posteriordirected collapse of the anterior lobe of the glabella, adaxial deformation of the ocular lobes, and abaxial and anterior splaying of genal regions. These shape changes are explicable in terms of observed exoskeletal fracture patterns. Landmarks show an increase in scatter around their ontogenetic trajectories that is generally proportional to the degree of lateral shift each landmark has undergone. Interspecific differences in compactional response may depend on the relative convexity of the cephalon. Olenellus (Olenellus) gilberti is a low-convexity species and shows marked lateral shape change, particularly in the genal region. Nephrolenellus geniculatus is more convex and shows less severe lateral shape change. Landmarks of both species exhibit an average trebling of the degree of scatter around their average ontogenetic trajectories in compacted samples. Because even well-preserved specimens in shales differ in shape from their precompactional appearance, results of morphometric studies utilizing metric distances between landmarks in trilobites where compaction can be detected must be interpreted with caution.

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.

Phosphatic microfossils including probable microvertebrates occur in the Early and Middle Ordovician rocks of Wisconsin. The eight types described here include the probable ostracoderm Anatolepis, and six unidentified but possible vertebrate fragments as well as the palaeoscolecid worm Milaculum. These fossils are rare, but at two localities several specimens per kg were recovered over significant stratigraphic intervals. The high concentration of certain fossils in the lower part of the Galena Group suggests that there is stratigraphic value in their description. Identification of similar material or of articulated assemblages of these fossils may eventually lead to identification of biologic affinities.

The graphic correlation technique has been used to directly relate the stratigraphic appearances of key species in the Bashkirian Stage stratotype to those in a North American composite section. The type Bashkirian is separated from the underlying Serpukhovian Stage by an erosional unconformity and associated lacuna of undetermined, but probably minor duration. Accordingly, the base of the type Bashkirian (base of Bogdanovkian Horizon) is only slightly younger than the international mid-Carboniferous boundary. A level within the upper part of the Tashastian Horizon (Upper Bashkirian Substage) most likely correlates with the Morrowan-Atokan boundary. This level roughly coincides with a sequence boundary at the Bashkirian stratotype and with a regional unconformity in the North American midcontinent. The top of the Bashkirian Stage (top of Asatauian Horizon) is lower Atokan in North American terms. On the basis of recent 40Ar/39Ar and SHRIMP zircon geochronology studies, the age of the mid-Carboniferous boundary is estimated at 314 Ma and a horizon of early Atokan age is dated at 310.8 Ma. Accepting the present biostratigraphic correlations, these values suggest a duration for the Bashkirian Stage of slightly more than 3.2 m.y. and a duration of the Morrowan Series of slightly less than 3.2 m.y.

A new genus of mylagaluid rodent from the Miocene of the Great Basin, Hesperogaulus, is described, and to it two new species, H. gazini and H. wilsoni (type species) are referred. This genus differs from all other genera of later Tertiary mylagaulines in having: large bosses of rugose bone on the anterior end of the nasal bones; lower slope of the occipital bone; and unique separation of the anterior branches of the forked parafossette on the upper premolar.

Hepserogaulus n. gen. represents a distinct lineage of mylagaulids that has been separate from other members of the family since the early Barstovian. This genus is geographically limited to the Great Basin. Other later Tertiary genera of mylagaulids show geographic limitations to other parts of the continent as well.

This note presents the first stratigraphic, paleoenvironmental, and systematic account of Silurian foraminifers in Wisconsin, which include nine previously described species of Ammodiscus, Glomospirella, Hemisphaerammina, Hyperammina, Lagenammina, Psammosphaera, Stomasphaera, Thurammina, and Webbinelloidea (Appendix 1). Early Silurian carbonates in this area (Fig. 1) were deposited in shelf and ramp environments in the western part of the Michigan Basin (Harris et al., 1998), and the foraminifers are associated with macrofaunal communities that represent Benthic Assemblages BA3 to BA5 of Brett et al. (1993).

Silicified agglutinated foraminifers were obtained from acidinsoluble residues processed for conodonts, sponge spicules, and macrofauna (Watkins et al., 1994; Kuglitsch, 1996; Watkins and Kuglitsch, 1997; Watkins and Coorough 1997a, 1997b). Silicification of the specimens, rather than a composition of agglutinated siliceous grains, is indicated by lack of detrital silica in enclosing dolostones, variable detail of preservation, and association with other silicified fossils.