A reassessment of the taxonomic relationships of North American gigantopterids is presented in light of an examination of large populations of specimens housed in the US National Museum of Natural History. Variations in venation and subtle aspects of leaf shape facilitate refined understanding of the relationships and diversity of the North American gigantopterid species leading to an improved understanding of the taxonomic and biogeographic relationships of this group, which are found most abundantly in western equatorial Pangea and Cathaysia. Current literature suggests that there are eight North American genera, however, this study has revealed a morphological overlap of several previously defined genera, leading to the conclusion that Gigantopteridium encompasses the species previously treated as Cathaysiopteris yochelsonii as well as a new species, Gigantopteridium utebaturianum. The transfer of C. yochelsonii to Gigantopteridium yochelsonii suggests that Cathaysiopteris may represent a genus endemic to Cathaysia, limiting the biogeographical connection between the regions to Zeilleropteris, Gigantopteridium, Euparyphoselis, and Gigantonoclea.

The problematic calcified cnidarian Cambroctoconus is described from the Henson Gletscher Formation (Cambrian Series 2, Stage 4—Series 3, Stage 5) of North Greenland, representing the first record from Laurentia of a genus otherwise recently described from China, Kyrgyzstan, and Korea. Internal molds produced by penetrative phosphatization mirror the pervasive pore system of the calice walls and septa. The pore system is compared to the network of gastrodermal solenia that distributes nutrients between polyps and surrounding stolon tissues in present day octocorals. In conjunction with the octagonal form of the individual coralla and eight-fold symmetry of septa, the pore system promotes assignment of Cambroctoconus to the Octocorallia, a basal clade in cnidarian phylogeny. Octocorals (‘soft corals’) are diverse in present day seas, but have a poor fossil record despite the general development of distinctive calcareous spicules. New taxa: Order Cambroctoconida new; Cambroctoconus koori new species.

The mixed carbonate-siliciclastic successions of the Cambrian Series 2–Cambrian Series 3 interval of the Great Basin are well investigated in respect to their trilobite and brachiopod fauna. In contrast, the small shelly fossils have been mostly unreported. Nine sections in eastern California and southern Nevada have produced a small shelly assemblage of low diversity, which likely reflects non-phosphatization and loss of originally calcareous remains. From the Montezuman—Delamaran stages we report Anabarella chelata Skovsted, 2006a, Costipelagiella nevadense Skovsted, 2006a, Pelagiella aff. P. subangulata (Tate, 1892), Microcornus sp., Parkula sp., Hyolithellus? sp., Allonia sp., Chancelloria sp., Archiasterella cf. A. hirundo Bengtson in Bengtson et al., 1990, Archaeooides cf. A. granulatus Qian, 1977, and undefined echinoderms and helcionelloid molluscs. The lower part of the Montezuman Stage delivered a number of lobopodian sclerites as Microdictyon rhomboidale Bengtson, Matthews, and Missarzhevsky, 1986, Microdictyon montezumaensis n. sp., and Microdictyon cuneum n. sp. The occurrence of P. aff. P. subangulata and species of Microdictyon in the lower Montezuman Stage offers a fundamental potential for correlation with the base of Cambrian Series 2/Stage 3 of South China, Siberia, and Avalonia.

We describe a new species of enigmatic stalked filter feeder, Siphusauctum lloydguntheri, from the middle Cambrian (Series 3, Stage 5) Antimony Canyon locality of the Spence Shale of northern Utah. The described specimen is the only one known from the Spence Shale, represents the first occurrence of Siphusauctum outside the Burgess Shale, and is only the second described species from the genus. Siphusauctum lloydguntheri n. sp. differs from S. gregarium O'Brien and Caron, 2012 in the shape of its calyx and the position of the digestive tract. The new species provides some additional information about the possible affinities of enigmatic stalked Cambrian filter feeders, as well as the taphonomic pathways that lead to preservation of Siphusauctum.

Karlsorus n. gen. is proposed in this study as a large, smooth-shelled pentameride brachiopod of the family Pentameridae, based on Pentamerus gothlandicus Lebedev, 1892, from the Wenlock (Silurian) Slite beds of Gotland, Sweden. This species is transferred from Pentamerus to the new genus because of the combination of a Pentamerus-like shell shape and the development of a brachiophorium through fusion of the outer hinge plates in the middle portion, like a dorso-ventrally inversed cruralium. The first appearance of brachiophorium in pentamerids is in the late Wenlock, known also in Brooksina, Pentamerifera, and other related pentamerid genera, marking a significant stage in morphological transformation of dorsal internal structures, as part of the Silurian pentameride diversification in both level-bottom and reefal depositional environments.

The use of different methodological approaches together with an exhaustive qualitative study has helped to recognize important morphological traits to distinguish species in a systematic and phylogenetic framework. Parabolinella triarthroides Harrington, 1938 was described based on two cranidia from the Quebrada de Coquena, Purmamarca, Jujuy province. The generic assignment of P. triarthroides has been questioned by a phylogenetic analysis, which resolves this species as the sister group of Bienvillia Clark, 1924. To explore the generic assignment of this species, a revision of the type material, plus a morphometric analysis including specimens of Parabolinella Brøgger, 1882 and Bienvillia were performed. In addition, the original matrix used in the published phylogeny was reviewed and enlarged, including more species of Bienvillia. Continuous characters were coded in different ways in order to compare how they could affect the ordering of specimens and their phylogenetic relationships. Finally, both methodologies were compared, especially in regard to the behavior of the quantitative characters included in the analyses. From the combined analyses, it is shown that similarities between the cranidium of P. triarthroides and all other Parabolinella species are true homologies instead of a by-product of evolutionary convergence. Therefore, P. triarthroides should be considered a member of this genus. Finally, this study demonstrates that the best strategy for solving systematic problems in groups where the morphological variation is the only source of information (i.e., fossil taxa without living representatives) is the implementation of an integrative approach, combining different methodological techniques and a good description of specimens.

Restudy of the limestone slab containing the type suite of Arthricocephalus chauveaui Bergeron, 1899 (Trilobita), the type species of Arthricocephalus Bergeron, 1899, shows that specimens of three species, each representing a separate genus, are present on the slab and were likely included in the original concept of the species. Besides A. chauveaui, the slab contains specimens of Oryctocarella duyunensis (Qian, 1961) and Duyunaspis duyunensis Zhang and Qian in Zhou et al., 1977. Bergeron (1899) illustrated one exoskeleton from the type suite of A. chauveaui only and apparently based much of his written description on that specimen. This specimen was clearly intended to be the type specimen of A. chauveaui. Subsequently, Lane et al. (1988) designated another specimen, which was not originally illustrated, as the lectotype, and this specimen is referable to Oryctocarella duyunensis. As revised here, Bergeron's illustrated specimen should be regarded as the lectotype of A. chauveaui. Such designation stabilizes the concepts of both Arthricocephalus and A. chauveaui. Arthricocephalites Qian in Lu et al., 1974 and Haliplanktos Blaker and Peel, 1997 are regarded as junior synonyms of Arthricocephalus. Oryctocarella Tomashpolskaya and Karpinski, 1961, which was previously regarded as a junior synonym of Arthricocephalus, is revived as a valid genus. Oryctocarella includes a number of species previously assigned to Arthricocephalus. The type species of both Arthricocephalus and Oryctocarella, together with related species, are described on the basis of new material.

Numerous well-preserved remains of a new limulid species from the Anisian-lower Ladinian (Middle Triassic) of the Tejra section of southern Tunisia are described. Comparisons are made with limulids from the Triassic deposits of Europe and Australia. The new specimens are congeneric with the type species of Limulitella, but show some morphological differences. Here we describe Limulitella tejraensis new species, a small limulid with semicircular prosoma, small and triangular opisthosoma, well-defined axial ridge, and pleurae along both ridges of the opisthosoma. The Tunisian Limulitella fossils are associated with conchostracans, bivalves, gastropods, and microconchids. Sedimentological and paleontological data from the Tejra section suggest freshwater to brackishwater conditions during the formation of the fossil-bearing interval and the influence of marine transgression into a playa-like environment. Supposed adaptation to the stressful environment sheds new light on the origin and survival of the extant limulines. This is the first report of limulid body fossils from the Triassic of North Africa and the first documentation of Limulitella in the Middle Triassic of northern Gondwanaland.

The oldest known fossil mysid (order Mysida) Aviamysis pinetellensis n. gen. n. sp. is described here from two nearly complete specimens found in the Alcover unit from El Pinetell (Catalonia). It differs significantly from other Mysida and is placed in a new genus assigned to the family Mysidae and tentatively to the subfamily Boreomysinae. These specimens represent the first described mysid material from the Alcover outcrops (Middle Triassic, upper Ladinian, 235–242 Ma), extending the known geological range of the poorly understood fossil fauna of the order Mysida by at least 70 Myr.

The crustacean microcoprolite Palaxius floridanus n. isp. is described from shallow-water carbonate platform deposits of Pleistocene limestones of south Florida. Palaxius floridanus n. isp. occurs in moderate-energy packstones and grainstones of the oolite facies of the Miami Limestone, and in skeletal packstones of the Key Largo Limestone, ranging in age from marine isotope stage (MIS) 11 to MIS 5a (ca. 400–80 kyr BP). The new ichnospecies resembles P. decemlunulatus, which has been described previously from Oligocene deposits. Late Jurassic and Late Cretaceous forms described as P. decemlunulatus belong to a new ichnogenus and new ichnospecies, respectively, yet to be described.

Euthycarcinoid arthropods (Cambrian—Triassic) were likely the first animals to transition from oceanic to freshwater and emergent environments. Although their basic bauplan is well known, they have a poor fossil record because their non-sclerotized exoskeleton was rarely preserved. Euthycarcinoids' unusual morphology (varying numbers of body segments, seemingly dichotomous possession of either mandibles or a labrum, specialized or generalized limbs, and possession by some euthycarcinoid species of sternal pores—structures possibly analogous to coxal vesicles in myriapods) contribute to uncertainty regarding their relationship to other arthropod groups; while their poor fossil record masks the evolutionary transitions within and between the separate realms they inhabited (marine, freshwater, emergent). A new euthycarcinoid from a Permian polar proglacial lake is described herein that is morphologically unlike all other euthycarcinoids, and interpreted as being well adapted for a nekton-benthic lifestyle. Antarcticarcinus pagoda n. gen. n. sp. possesses a pair of large wing-like processes that project laterally from the preabdominal dorsal exoskeleton. A trace fossil from the overlying Mackellar Formation, cf. Orbiculichnus, which was previously interpreted as having been produced by insects taking off or landing on wet sediments, is reinterpreted herein as being produced by A. pagoda n. gen. n. sp. due to the high degree of morphological similarity between traces and body fossils. This occurrence indicates that euthycarcinoids were able to adapt to life in temperate freshwater environments, while possible subaerial adaptations hint at an ability to breathe air. Indeed, if euthycarcinoids could breathe air, Cambrian terrestrial forays and rapid transition (by the Ordovician) into freshwater environments might be explained.

The Sinoalidae, as one of the three Mesozoic froghopper families, was recently recognized from the latest Middle—earliest Late Jurassic Daohugou Biota of northeastern China. We herein report some new materials from the same horizon and locality, providing some new insights on morphological diversity and evolution of this family. Shufania hani new genus new species indicates that the relative branching position of veins M and CuA of the forewing is highly variable within the Sinoalidae and not appropriate for family-level diagnosis. The venations of three reported sinoalid hind wings are conservative, likely due to its simplified topology and reduced terminal branches. Color patterns of hind wings are likely variable for different sinoalid froghoppers. However, considering that color pattern is easily weakened or even erased by diagenetic processes for imprint fossils, the morphological character is not reliable for distinguishing different sinoalid taxa. Additionally, our new material suggests that the number of lateral spines of the hind tibia can vary intra-individually for sinoalids, just as in some recent froghoppers.

Twenty-one species of echinoid are reported from Paleocene rocks of the eastern United States along the outcrop belt from Texas to New Jersey. Six of these are strictly early Paleocene age (Danian), nine strictly late Paleocene age (Thanetian), five range throughout the Paleocene, and one previously reported Paleocene species (Diplodetus moscovensis) is most likely a Cretaceous species. Two new species are described, Salenia palmyra n. sp., from the Danian Clayton Formation in Alabama and Georgia, and Ova rancoca n. sp., from the Thanetian Vincentown Formation in New Jersey. One new species from the Clayton Formation in Mississippi, Arbaciella? sp., is left in open nomenclature.

The Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygian Birgeria (Birgeriidae), attributed to B. americana new species and Birgeria sp. Birgeria americana n. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.72–1.85 m, it is among the largest birgeriids. We confirm that Birgeria encompasses species with either two or three rows of teeth on the maxilla and dentary, and suggest that species with three well-developed rows are restricted to the Early Triassic. From the latest Smithian of Palomino Ridge, we present a three-dimensional, partial skull of the longirostrine predator Saurichthys (Saurichthyidae). This and other occurrences indicate that saurichthyids were common in the western USA basin. From the early late Spathian of Crittenden Springs, we describe a posterior body portion (Actinopterygii indet.). This find is important given the paucity of Spathian osteichthyan sites. We provide a summary of Early Triassic vertebrate occurrences in the United States, concluding that vertebrate fossils remain largely unstudied. The presence of predatory vertebrates in subequatorial latitudes during the Smithian confirms that Early Triassic trophic chains were not shortened and contradicts the ‘equatorial vertebrate eclipse’.

Metoposaurids are temnospondyl amphibians that are well known from Upper Triassic deposits in North America, Europe, India, and Africa. Two species of metoposaurids, Koskinonodon perfectus and Apachesaurus gregorii, are among the most common fossils found in the Petrified Forest National Park (PEFO) of the southwestern United States. The two are distinguished on the basis of several cranial traits and the morphology of their intercentra, and are more informally distinguished by their overall size and biostratigraphic range. While material of adult metoposaurids is extremely common in Upper Triassic deposits, described material of juveniles is very rare, which limits the study of ontogenetic trajectories that would assist in assessing whether diagnostic traits of the smaller A. gregorii are also ontogenetically influenced traits in juveniles of K. perfectus. Here we report on material from a juvenile specimen of K. perfectus from the Petrified Forest Member (Norian) of the Chinle Formation in the PEFO. This specimen is significant because it represents the highest known occurrence of the species within the PEFO, documents a rare occurrence of a juvenile specimen of a North American metoposaurid, and records a rare North American metoposaurid specimen that includes associated cranial and postcranial material. Additionally, the combination of cranial features diagnostic of K. perfectus and intercentra of proportions intermediate between K. perfectus and A. gregorii in this specimen raises questions about the utility of several characters for species discrimination in North American metoposaurids.

As many as eight species of the “anchitherine” equid Miohippus have been identified from the John Day Formation of Oregon, but no statistical analysis of variation in these horses has yet been conducted to determine if that level of diversity is warranted. Variation of the anterior-posterior length and transverse width of upper and lower teeth of Turtle Cove Member Miohippus was compared to that of M. equinanus, Mesohippus bairdii, Equus quagga, and Tapirus terrestris using t tests of their coefficients of variation (V). None of the t tests are significant, indicating that the variation seen in Turtle Cove Miohippus is not significantly different from any of the populations of other perissodactyls examined in this study. Data also indicate that Mesohippus is present in the Turtle Cove Member. Additionally, hypostyle condition, used to diagnose all species of Miohippus, was found to be related to stage of wear using an ordered logistic regression. Only two species of equid, one Miohippus and one Mesohippus, in the Turtle Cove Member can be identified, therefore only Miohippus annectens, the genotype and first species described from the region, can be recognized as the sole Miohippus species known from the Turtle Cove assemblage. There are insufficient data to determine which species of Mesohippus is present. The dependence of hypostyle condition on crown height in Miohippus implies that wear stage must also be considered in investigations of dental morphology in the “Anchitheriinae.”

A new genus and species of megalonychid sloth, Zacatzontli tecolotlanensis n. gen. n. sp., is described from the late Hemphillian of Jalisco, Mexico. Comparison and analysis of the type specimen, a mandible, with other megalonychid sloths shows a closer relationship to South American taxa than those from North America or the Caribbean. This suggests that during the early stages of the Great American Biotic Interchange there were two separate dispersal events of megalonychid sloths—an earlier one represented by Pliometanastes and the later one by Zacatzontli n. gen. While the morphology of the spout of Zacatzontli more closely resembles that of Megalonyx, based on the current record, Zacatzontli does does not enter North America until after the evolution of Megalonyx from Pliometanastes. The role of the northern neotropics in South America as a staging area for South American taxa that entered North America is discussed.

Litopterna is represented in the Pleistocene of the Brazilian Intertropical Region by a monospecific genus of Macraucheniidae, Xenorhinotherium. Although most of the knowledge about this family is derived from the dentition, some dental features still remain unknown. This study describes the eruption sequence of permanent dentition and classifies the hypsodonty status of X. bahiense. The specimens studied are from Toca dos Ossos, a limestone cave located in Bahia State. We perform qualitative macroscopic analysis to describe the eruption dental sequence. Additionally, we perform quantitative analysis to determine the hypsodonty index. The dental eruption sequence of the juvenile specimen is M1, M2, I1, I2, M3, I3, P1, P2, P3, and P4. In addition, the analysis of tooth wear in adult specimens provides similar results. The hypsodonty index assigns a mesodont tooth crown for X. bahiense. The dental eruption sequence is most similar to a rapid-growth extant mammal. Moreover, our results do not support afrotherian-like delayed dental eruption to Litopterna. The hypsodonty index can be related to data on vegetation of the Brazilian Intertropical Region and the shape of the premaxilla of X. bahiense, both of which suggest a browsing diet for this macraucheniid.