Abstract Shelf-edge-derived boulders in debris-flow conglomerates of the Shallow Bay Formation of western Newfoundland are relicts of a Cambrian–Lower Ordovician margin of Laurentia that was largely obliterated during the Taconic Orogeny. As such, they are an important archive of trilobite faunas from the edge of the continent. In this paper, we document Cambrian trilobites from the mid-Steptoean Stage (upper Paibian of global nomenclature) in the Downes Point Member. Most of the species are from three boulders assigned to the agnostid Acmarhachis kindlei Fauna and include Dunderbergia Walcott, 1924, Pterocephalops Rasetti, 1944, Quebecaspis Rasetti, 1944, Bathyholcus Rasetti, 1961, Glyptometopsis Rasetti, 1961, and Tholifrons Palmer, 1968. These trilobites are assigned to a new biostratigraphical unit, the Quebecaspis conifrons Fauna, which can also be identified in shelf-margin-derived facies in Quebec, Vermont, and Maryland. Comparison with the shelf interior is more difficult because of ecological and biogeographical differences, but the Q. conifrons Fauna most likely correlates into the Dunderbergia Zone of the traditional Laurentian trilobite zonation. New species are Bathyholcus punctatus , Bellaspidella crocalae , Dunderbergia astropletha , D. bovicephala , D. magnatubercula , “ Eugonocare ” arquatum , Glyptometopsis parilimba , Onchopeltis anconis , and Tholifrons maritima . UUID: http://zoobank.org/9c381131-a457-45d1-bbab-1b839c6b2812
Abstract Paleopathologies and tooth marks observed on bones have long been used for behavioral interpretations of extinct organisms, including non-avian dinosaurs. However, our understanding of this behavior is limited by the rarity of large-scale surveys of recovered material. Here, we present a systematic survey of tooth marks across 148 hadrosaurid jugals from various Late Cretaceous formations of Alberta, Canada. Across 20 of the elements (13.6%), we observed 48 tooth marks, restricted to the lateral surface, 40% of which were located on the middle jugal body and showed no preferred orientation of the mark long axis. Across taphonomic modes, tooth marks are most common on isolated specimens, followed by bonebed specimens, with few articulated/semi-articulated/associated specimens showing marks. The proportion of tooth-marked to non-tooth-marked jugals is comparable to tooth-marking frequencies observed for modern mammalian carnivores. Although tooth marks were likely produced postmortem during feeding, it is unclear whether tooth marks were produced when the jugal was removed to access underlying adductor musculature or during the removal of extraoral tissues or a combination of these behaviors. Future large-scale surveys of hadrosaurid cranial elements could help clarify which of these explanations is more likely and elucidate Cretaceous carnivore carcass-processing behaviors. Our survey also identified an additional two specimens showing elongate healed marks extending anteroposteriorly across the lateral surface of the jugal body that are of unknown, but potentially the same, origin. Further specimens with similar paleopathologies could help decipher a likely mechanism of injury.
The presence and spatial distribution of intraspecific variation impact the evolvability of a species. Understanding this variation may shed light on the natural history and ecological breadth, realized and potential, of specific taxa. Insights from the paleontological record can provide additional information on potential phenotypic variation for species that have adapted to past and present environments. Here, we use the American mink, Neogale vison (Schreber, 1777), as a case study to understand the extent and pattern of mandibular shape variation among extant populations (n = 290) and fossil assemblages (n = 13). We use these data to examine whether the role of N. vison has changed in response to environmental conditions or through time. We found that some fossil N. vison mandibles lie outside the morphospace occupied by extant N. vison and are distinct from modern mink. Fossils from Conard Fissure, Arkansas (n = 8), represent a unique morphotype that likely had higher bite forces than modern N. vison. This morphotype may have allowed N. vison at this site to take advantage of larger or different prey. These results demonstrate both the adaptive potential of N. vison and the fossil record’s ability to reveal unique variation in a lineage.
Abstract A number of echinoderm groups lack representation in the Silurian fossil record, which becomes especially clear when considering the echinoderm fossil record of the Ordovician and Devonian. This paucity constrains our ability to resolve echinoderm evolutionary dynamics and biogeographic pathways during the Silurian, thereby underscoring the significance of newly discovered species. Herein, we describe a new species of blastozoan diploporan echinoderm, Eucystis charlotteae new species, from the Silurian of Missouri, USA, representing the first example of this genus described from Laurentia, which now makes this one of the most broadly distributed genera within diploporans. Within this paper, we compare and contrast this new species to other known species within Eucystis Angelin, 1878 . Eucystis charlotteae n. sp. is characterized by having five ambulacral grooves that branch three times into unequal lengths and each end in large, tumid facetal scars. Eucystis charlotteae n. sp. is also relatively large when compared to other named species of the genus, which could lend insight into body size trends of diploporan echinoderms in the early Paleozoic. This new occurrence also lends insight into the biogeographic dynamics of diploporan taxa across the early Paleozoic. UUID: http://zoobank.org/4e64fd0d-f7f5-4f0e-a310-438bad08f046
