The recently discovered mass mortality of fishes from the Tanis Site in the North Dakota portion of the Late Cretaceous Hell Creek Formation contains many well-preserved, three-dimensional skeletons. Among these are representatives of two acipenseriform families, Acipenseridae (sturgeons) and Polyodontidae (paddlefishes). This paper describes two new monotypic polyodontid genera, expanding our knowledge of polyodontid diversity. The first of the new species described here is †Parapsephurus willybemisi n. gen. n. sp. It is distinguished from all other known species by having a combination of posteriorly elongate parietals, the middle fenestra longitudinalis bordered medially by the parietal and frontal and laterally by the dermopterotic, slender and numerous dorsal caudal fulcra, an elongate hyomandibula that is not hourglass shaped, and gill rakers that are short and widely spaced. The second polyodontid species described here is †Pugiopsephurus inundatus n. gen. n. sp. It is diagnosed by a combination of having stellate bones that are exceptionally poorly developed or absent and having a dermopalatine with a medial expansion and lacking an ectopterygoid process. The two species of paddlefishes described in this paper add to the morphological and taxonomic diversity of Polyodontidae. The presence of these taxa within the Hell Creek Formation hints at substantial diversity of polyodontids at this stage of their evolutionary history.

UUID: http://zoobank.org/08cbf8c5-59ba-41fa-9265-8cb762cf7b13

In a recent communication on carbon isotope chemostratigraphy of the uppermost Cambrian strata, it was claimed that the Top of Cambrian Excursion (TOCE) is (1) an undocumented negative δ13Ccarb excursion; (2) ambiguously defined; (3) deliberately fictitious or, in the authors’ words, a ‘nihilartikel’; and (4) not synonymous with the Hellnmaria–Red Tops Boundary (HERB) Event. As the authors who have been involved in much of the discussion surrounding the TOCE since its introduction and in subsequent clarification, we wish to emphasize that the recent communication overlooks the fact that the TOCE is in fact a well-documented and clearly defined negative δ13Ccarb excursion, and that the term ‘HERB Event’ was originally used informally, without definition or reference data, for a negative δ13Ccarb peak, a peak later shown to occur within the TOCE excursion. Nearly a decade after the TOCE was named, the concept of the HERB Event was modified from a negative δ13Ccarb peak to a negative δ13Ccarb excursion, making it conceptually synonymous with the TOCE excursion. The recently published commentary is misleading and replete with misconceptions, as we discuss here.

Hyneria lindae is one of the largest Devonian sarcopterygians. It was found in the Catskill Formation (late Famennian) of Pennsylvania, USA. The current study focuses on the palaeohistology of the humerus of this tristichopterid and supports a low ossification rate and a late ossification onset in the appendicular skeleton. In addition to anatomical features, the large size of the cell lacunae in the cortical bone of the humerus mid-shaft may suggest a large genome size and associated neotenic condition for this species, which could, in turn, be a partial explanation for the large size of H. lindae. The low metabolism of H. lindae revealed here by bone histology supports the hypothesis of an ambush predatory behaviour. Finally, the lines-of-arrested-growth pattern and late ossification of specimen ANSP 21483 suggest that H. lindae probably had a long juvenile stage before reaching sexual maturity. Although very few studies address the life-history traits of stem tetrapods, they all propose a slow limb development for the studied taxa despite different ecological conditions and presumably distinct behaviours. The bone histology of H. lindae would favour the hypothesis that a slow long-bone development could be a general character for stem tetrapods.

The hypothesis that tetrapods evolved from elpistostegids during the Frasnian, in a predominantly aquatic context, has been challenged by the discovery of Middle Devonian tetrapod trackways predating the earliest body fossils of both elpistostegids and tetrapods. Here I present a new hypothesis based on an overview of the trace fossil and body fossil evidence. The trace fossils demonstrate that tetrapods were capable of performing subaerial lateral sequence walks before the end of the Middle Devonian. The derived morphological characters of elpistostegids and Devonian tetrapods are related to substrate locomotion, weight support and aerial vision, and thus to terrestrial competence, but the retention of lateral-line canals, gills and fin rays shows that they remained closely tied to the water. Elpistostegids and tetrapods both evolved no later than the beginning of the Middle Devonian. The earliest tetrapod records come from inland river basins, sabkha plains and ephemeral coastal lakes that preserve few, if any, body fossils; contemporary elpistostegids occur in deltas and the lower reaches of permanent rivers where body fossils are preserved. During the Frasnian, elpistostegids disappear and these riverine-deltaic environments are colonised by tetrapods. This replacement has, in the past, been misinterpreted as the origin of tetrapods.

The first half of the Mississippian or Early Carboniferous (Tournaisian to mid- Viséan), an interval of about 20 million years, has become known as “Romer's Gap” because of its poor tetrapod record. Recent discoveries emphasise the differences between pre-“Gap” Devonian tetrapods, unambiguous stem-group members retaining numerous “fish” characters indicative of an at least partially aquatic lifestyle, and post-“Gap” Carboniferous tetrapods, which are far more diverse and include fully terrestrial representatives of the main crown-group lineages. It seems that “Romer's Gap” coincided with the cladogenetic events leading to the origin of the tetrapod crown group. Here, we describe a partial right lower jaw ramus of a tetrapod from the late Tournaisian or early Viséan of Scotland. The large and robust jaw displays a distinctive character combination, including a significant mesial lamina of the strongly sculptured angular, an open sulcus for the mandibular lateral line, a non-ossified narrow Meckelian exposure, a well-defined dorsal longitudinal denticle ridge on the prearticular, and a mesially open adductor fossa. A phylogenetic analysis places this specimen in a trichotomy with Crassigyrinus and baphetids + higher tetrapods in the upper part of the tetrapod stem group, above Whatcheeria, Pederpes, Ossinodus, Sigournea and Greererpeton. It represents a small but significant step in the gradual closure of “Romer's Gap”.

The recent developments of phase-contrast synchrotron imaging techniques have been of great interest for paleontologists, providing three-dimensional (3D) tomographic images of anatomical structures, thereby leading to new paleobiological insights and the discovery of new species. However, until now, it has not been used on features smaller than 5–7 μm voxel size in fossil bones. Because much information is contained within the 3D histological architecture of bone, including an ontogenetic record, crucial for understanding the paleobiology of fossil species, the application of phase-contrast synchrotron tomography to bone at higher resolutions is potentially of great interest. Here we use this technique to provide new 3D insights into the submicron-scale histology of fossil and recent bones, based on the development of new pink-beam configurations, data acquisition strategies, and improved processing tools. Not only do the scans reveal by nondestructive means all of the major features of the histology at a resolution comparable to that of optical microscopy, they provide 3D information that cannot be obtained by any other method.

The middle Cambrian Lejopyge laevigata Zone is poorly exposed in Scandinavia. Both this zone, however, and the succeeding Agnostus pisiformis Zone are well exposed at a classic locality at Gudhem, Västergötland, south-central Sweden. The sequences consist of finely laminated alum shale with scattered stinkstone (orsten) lenses. Three measured and sampled sections yielded a diverse fossil fauna, dominated by trilobites, in particular agnostoids, and the bradoriid Anabarochilina primordialis. Fossils are excellently preserved but restricted to the stinkstones. The L. laevigata Zone at Gudhem includes several geographically widespread key agnostoid species, notably Tomagnostella sulcifera, Clavagnostus spinosus, Glaberagnostus altaicus, Lejopyge laevigata and L. armata. The L. laevigata Zone in Scandinavia is here extended to include the traditional Solenopleura? brachymetopa Zone, and its lower boundary is defined by the FAD of L. laevigata. Trilobite evidence shows that the upper part of the Scandinavian L. laevigata Zone approximately correlates with the Proagnostus bulbus Zone of China and elsewhere.

Devonian rhizodontid fishes from East Gondwana include Gooloogongia loomesi Johanson & Ahlberg 1998 from near Canowindra, New South Wales (NSW), Australia and Aztecia mahalae gen. nov., sp. nov. from southern Victoria Land, Antarctica. Gooloogongia loomesi is known from well-preserved cranial and postcranial material, and as such represents the most complete rhizodont known. Newly discovered elements (braincase, pelvic girdle) are described for the first time. Aztecia mahalae gen. nov., sp. nov. is based on shoulder girdle material formerly assigned to Notorhizodon Young et al. 1992, which, based on skull and lower jaw morphology, is a member of the Tristichopteridae. The presence of several plesiomorphic characters suggests that Gooloogongia occupies a basal phylogenetic position within the Rhizodontida, while Aztecia n. gen. possesses a more derived shoulder girdle. We argue that the Rhizodontida evolved on the Gondwanan landmass. Notorhizodon occupies a relatively derived position within the Tristichopteridae, but is contemporary with the earliest and phylogenetically most basal Laurussian members of the group. This shows that the tristichopterids achieved a worldwide distribution considerably earlier than previously thought.