Well-preserved microfossils occur in abundance through more than 1000 m of lower Mesoproterozoic siliciclastic rocks composing the Roper Group, Northern Territory, Australia. The Roper assemblage includes 34 taxa, five interpreted unambiguously as eukaryotes, nine as possible eukaryotes (including Blastanosphaira kokkoda new genus and new species, a budding spheromorph with thin chagrinate walls), eight as possible or probable cyanobacteria, and 12 incertae sedis. Taxonomic richness is highest in inshore facies, and populations interpreted as unambiguous or probable eukaryotes occur most abundantly in coastal and proximal shelf shales. Phylogenetic placement within the Eukarya is difficult, and molecular clock estimates suggest that preserved microfossils may belong, in part or in toto, to stem group eukaryotes (forms that diverged before the last common ancestor of extant eukaryotes, or LECA) or stem lineages within major clades of the eukaryotic crown group (after LECA). Despite this, Roper fossils provide direct or inferential evidence for many basic features of eukaryotic biology, including a dynamic cytoskeleton and membrane system that enabled cells to change shape, life cycles that include resting cysts coated by decay-resistant biopolymers, reproduction by budding and binary division, osmotrophy, and simple multicellularity. The diversity, environmental range, and ecological importance of eukaryotes, however, were lower than in later Neoproterozoic and Phanerozoic ecosystems.

Plagioptychids are a conspicuous, although minor, component in uppermost Cretaceous rudist-bearing outcrops of the Caribbean Province, where other rudist families are more abundant and diverse. In the Chiapas Central Depression, the plagioptychid rudist fauna includes the following taxa: Plagioptychus antillarum (Douvillé) and Mitrocaprina sp. from the middle Campanian Suchiapa Formation, Plagioptychus muellerriedi Alencáster from the early Maastrichtian Ocozocoautla Formation, and Plagioptychus fragilis Chubb and Mitrocaprina tschoppi (Palmer) from the late Maastrichtian Angostura Formation. These five species are described in detail and some probable synonymies are discussed. Analysis of the literature on American plagioptychids reveals that the characters of too many taxa are still insufficiently known to attempt any thorough phylogenetic analysis. Other lines of evidence also seem to indicate that American Plagioptychidae diversity is probably higher than recognized today, which might result in a more significant difference to Plagioptychidae of the Mediterranean Tethys.

Early Jurassic marine gastropods are well represented in Argentina by three major taxa: Vetigastropoda, Caenogastropoda and Architectibranchia (=Opisthobranchia). The present paper aims at the description of six new caenogastropod species and one new architectibranch species from the Early Jurassic marine deposits of the Neuquén Basin, namely Procerithium subimbricatum n. sp., Microschiza weaveri n. sp., Naricopsina aequabilis n. sp., Naricopsina ballentae n. sp., Pictavia rothi n. sp., Oonia acuta n. sp., and Cylindrobullina brevispira n. sp. Seven other caenogastropods are reported for the first time in the area, including Cryptaulax redelii Ferrari, Procerithium nulloi (Ferrari), Rhabdocolpus patagoniensis (Ferrari), Rhabdocolpus? sp., Pseudomelania feruglioi Ferrari, Pseudomelania aff. baugieriana (d’Orbigny), and Anulifera chubutensis Ferrari, extending their palaeobiogeographical distribution to the Andean region of Argentina during the Early Jurassic. Caenogastropods such as Globularia catanlilensis (Weaver) and Microschiza? americana (Möricke), and the architectibranch species Striactaeonina transatlantica (Behrendsen) and Cylindrobullina ovata (Behrendsen) are redescribed and discussed based on new specimens from the type and other localities. The new fossils described here expand the known diversity of the gastropod faunas in the Early Jurassic of Argentina and contribute to the paleontological knowledge of the group in the Mesozoic of South America.

The richly fossiliferous Ekspedition Bræ Formation of North Greenland yields a typical oligospecific fossil assemblage with well-preserved trilobites, helcionelloids, and lingulate brachiopods. The trilobites include Itagnostus subhastatus new species, Itagnostus sp. cf. I. gaspensis (Rasetti, 1948), Elrathina aphrodite new species, Elrathina athena new species, Elrathina hera new species, and Elrathia groenlandica new species—a fossil assemblage typical of the Bathyuriscus-Elrathina Zone as known from the Cordilleran regions of Laurentia. Excellent preservation allows a detailed assessment of the prosopon and elucidates aspects of the ontogenetic development of Elrathina and Elrathia. An evaluation of Elrathina includes a redescription of its type species, E. cordillerae (Rominger, 1887), based on the type material, and indicates that most specimens collected from the Burgess Shale and previously dealt with as E. cordillerae represent a new species.

The outcrop at Whiterock Canyon Narrows, Nevada, is the stratotype for the Middle Ordovician Whiterockian Series in Laurentia. Contrasts in the distribution of trilobites and conodonts between two parallel sections at the stratotype demonstrate the presence of an unconformity separating Ibexian faunas (the historic trilobite Zone J, the more recent restricted “Pseudocybele nasuta” trilobite Zone, the Reutterodus andinus conodont Zone) from overlying Whiterockian faunas (Zone L, the Psephosthenaspis pseudobathyurus trilobite Zone, the Orthidiella brachiopod Zone, the Tripodus combsi conodont Zone). The unconformity represents the erosional loss of a minimum of 10 m of shale and bedded limestone within the upper Ninemile Formation. In comparison to more continuous section in the Ibex region, Utah, the equivalent to the thin Psephosthenaspis microspinosa trilobite Zone and, possibly, the uppermost interval of the underlying “P. nasuta” Zone are missing. Illaenus welchi new species is described from the Whiterockian faunas of the upper Ninemile and Antelope Valley formations.

The placoderm Titanichthys from the Late Devonian (Famennian) is based on incomplete and fragmentary specimens that have hindered understanding of its overall anatomy and phylogenetic relationships. A new, nearly complete, articulated specimen from the Upper Devonian Cleveland Shale provides new information about the previously undescribed rostral, postmarginal, postsuborbital, submarginal, posterior superognathal plates, and the nasal capsule. A revised diagnosis is provided for the genus. Three new diagnostic characters are identified, including a transversely elliptical rostral plate that does not contact adjacent plates, a reduced posterior superognathal, and a median dorsal plate that inserts into the posterior dorsal lateral plate. The first comprehensive phylogenetic analysis of Titanichthys indicates that the genus is a basal aspinothoracid arthrodire closely related to the enigmatic taxa Bungartius and Tafilalichthys.

The early Oligocene (Rupelian) sirenian Halitherium schinzii Kaup, 1838, which represents the type species of the genus Halitherium Kaup, 1838, is revised herein based on a morphological re-evaluation of skeletal material originally assigned to this taxon. This study provides new and comprehensive information on the cranial and postcranial anatomy and allows the distinction of two sympatric species. Following a recent approach on the invalidity and subsequent rejection of H. schinzii Kaup, 1838, Kaupitherium gruelli new genus new species is established on the basis of a nearly complete holotype. The second taxon resembles K. gruelli n. sp. in a number of skeletal features, such as reduced nasals and absence of the canines, but can be clearly distinguished mainly by the post-canine dental formula and the supraoccipital morphology. The diagnostic skullcap of a species formerly synonymized under “H. schinzii” is re-validated as the holotype of K. bronni (Krauss, 1858). On the basis of paleoecological implications, a hypothesis is established to explain the overlapping stratigraphic and biogeographic occurrences (i.e., sympatry of both taxa). A diagnosis and up-to-date synonymy complement the taxonomical information. The revision of “H. schinzii” provides new data on the past sirenian diversity and forms the basis for a taxonomic and systematic re-evaluation of species originally grouped in the genus “Halitherium.”