Royal Tyrrell Museum

During the Late Cretaceous, the coastline of the epicontinental Western Interior Seaway in North America fluctuated in position, temporarily replacing some terrestrial ecosystems with shallow marine habitats.In southeastern Alberta, the uppermost portion of the Dinosaur Park Formation (Belly River Group, late Campanian) preserves one of these transgression–regression cycles in a marine wedge named here as theJohnson Unit. We report the stratigraphy of the unit based on nine stratigraphic sections over several kilometres of exposure. We describe a diverse assemblage of marine vertebrates from the Johnson Unit, represented by microfossils from a surface collecting survey. Our sample includes 1431 specimens, which we assign to 40 taxa. We identify eight new actinopterygians from the unit: Belonostomus longirostris, Amiidae indet.,Elopiformes indet., Horseshoeichthys sp., Enchodus gladiolus, Dercetis cf. D. magnificus, Acanthomorpha indet., and teleost indet. type O. The acanthomorph specimens, which include isolated spines and centra, represent the second marine Cretaceous acanthomorph reported from Alberta, and the highly ornamented spines are unlike any previously described. We revise several chondrichthyan identifications from previous authors and describe partial tooth plates from the chimaeriform Ischyodus bifurcatus for the first time in Canada. Compared to earlier samples from the same unit that were collected using screen-washing, our sample has ahigher diversity of actinopterygians and tetrapods. We identify several taxa to lower taxonomic levels using more complete specimens. These differences are attributed to our use of surface collection; this method allowed novel biogeographic and taxonomic insights.

Otophysans, known for their enhanced hearing enabled by the complex Weberian apparatus, comprise two-thirds of extant freshwater fish species. Previously, they were thought to have originated in fresh water before the breakup of Pangea, implying a nearly 80-million-year gap between the origin and oldest known fossil. However, the discovery of a Late Cretaceous freshwater otophysan challenges this view. Integrating fossil, morphological, and genomic data, we estimate a younger crown group origin of ~154 million years ago. Notably, ancestral range and habitat reconstructions indicate marine origins for the otophysan crown groups, with at least two transitions to fresh water. Functional simulations of the Weberian ossicles of this fossil suggest that the distinctive hearing capabilities of otophysans evolved in conjunction with fusion of hearing ossicle parts and freshwater adaptations.

ABSTRACT Paromomyidae are a taxonomically diverse family of archaic primates known principally from deposits of Paleocene and Eocene age in North America. While often numerically abundant in local mammalian faunas, the various paromomyid taxa are most often represented by isolated teeth and rare dentigerous cranial and dentary fragments. Accordingly, paromomyid interrelationships are on balance poorly understood, and this is especially true for early branching taxa. We report here on two new species of Paromomys—long considered the earliest diverging paromomyid—from Paleocene deposits in southwestern Alberta. Paromomys borealis sp. nov. and Paromomys ignis sp. nov. bear closest resemblance to Paromomys depressidens and Paromomys maturus, respectively, and represent the first occurrences of the genus in Canada. A phylogenetic analysis of all paromomyid species resulted in overall poor resolution. Paromomys was recovered as non-monophyletic—consistent with previous results—with species either in a polytomy or positioned at increasingly crownward positions. In contrast to previous hypotheses, the position of Paromomys as the earliest diverging paromomyid was rendered equivocal. Notably, two recently described species of Ignacius from the Canadian Arctic resolved as sister to Acidomomys to the exclusion of other paromomyids. The newly discovered species of Paromomys are known from a vanishingly small number of specimens, and paromomyid diversity and overall abundance declined markedly through the Tiffanian in Alberta; in contrast, plesiadapoids—generally rare in the Torrejonian—increased significantly in diversity and abundance during the same interval.

Polar ecosystems are structured and enriched by birds, which nest there seasonally and serve as keystone ecosystem members. Despite the ecological importance of polar birds, the origins of high-latitude nesting strategies remain obscured by a sparse fossil record. We report an extreme-latitude Arctic avialan assemblage from the Prince Creek Formation of Alaska—the northernmost Late Cretaceous terrestrial ecosystem. Numerous three-dimensionally preserved fossils constitute one of the most taxonomically rich Late Cretaceous avialan assemblages, including members of Hesperornithes, Ichthyornithes, and near-crown or crown birds (Neornithes), recording a previously undocumented interval in avialan evolution. Abundant perinatal fossils represent the oldest evidence of birds nesting at polar latitudes, which demonstrates that birds began using seasonal polar environments for breeding during the Cretaceous, long before their modern descendants.

Premise of research. Cycads in the extant Australian flora span both Cycadaceae and Zamiaceae, with Cycas—the sole genus in Cycadaceae—considered to have dispersed into Australia from East Asia and speciated there since the Miocene. This premise is untested because of the lack of a fossil record for Cycas in Australia. Methodology. We describe a pinnate partial cycad leaf impression from a Miocene fossil site in northern South Australia. Diagnostic characters for potential matches with other taxa, such as pinnate ferns, pinnate palms, and the univeined Podocarpus, were assessed against the fossil and eliminated. Multivariate analyses of morphological data from extant Australian Cycas species and likely morphological matches from Asia are used to interpret the fossil’s possible affinities. Pivotal results. The fossil is a pinnate leaf with opposite linear to lanceolate leaflets with a single prominent midvein and no secondary veins, diagnostic of Cycas, and the lamina has few (ca. 20) widely spaced, long, broad leaflets. Apparent parallel veins on two leaflets are interpreted as preservation artifacts. This leaf morphology is more consistent with extant Cycas species of the former section Stangerioides from Southeast Asia than with extant Australian taxa from section Cycas, which are characterized by many (100–410) moderately to closely spaced leaflets with narrow laminae. This fossil is a significant temporal and geographic range extension for Cycas and the first record of a fossil Cycas from Australia. Co-occurring angiosperm taxa from the fossil flora are consistent with this cycad being part of a landscape dominated by sclerophyllous forest or woodland under a wet, though seasonally dry, possibly monsoonal climate. Conclusions. Cycas was present in Australia by the Miocene, although potentially representing a lineage absent from modern Australia, likely under a monsoonal climate consistent with that of extant species of Australian Cycas and Southeast Asian section Stangerioides.

A new metriorhynchid specimen with stomach contents is described here. Assigned to Metriorhynchus cf. superciliosus., this specimen has a clear longirostrine form as indicated by its gracile and elongated mandibular rami. This is the second example of gastric contents described for Metriorhynchidae. This specimen’s preservation allows the identification of the gill apparatus remains of Leedsichthys, the giant suspension-feeding osteichthyan from the Jurassic, including its gill rakers. The gastric contents also contain remains of invertebrates. This specimen indicates that Leedsichthys was not the direct prey of these crocodiles but more that its body was scavenged by them. Longirostrine metriorhynchids were piscivorous but also opportunistic and may have had more of a scavenging component in their lifestyle than previously understood, as all discovered fossils point in this direction.

Mosasaurs (Squamata, Mosasauridae) were large aquatic reptiles from the Late Cretaceous that filled a range of ecological niches within marine ecosystems. The type-Maastrichtian strata (68–66 Ma) of the Netherlands and Belgium preserve remains of five species that seemed to have performed different ecological roles (carnivores, piscivores, durophages). However, many interpretations of mosasaur diet and niche partitioning are based on qualitative types of evidence that are difficult to test explicitly. Here, we apply three-dimensional dental microwear texture analysis (DMTA) to provide quantitative dietary constraints for type-Maastrichtian mosasaurs, and to assess levels of niche partitioning between taxa. DMTA indicates that these mosasaurs did not exhibit neatly defined diets or strict dietary partitioning. Instead, we identify three broad groups: (i) mosasaurs Carinodens belgicus and Plioplatecarpus marshi plotting in the space of modern reptiles that are predominantly piscivorous and/or consume harder invertebrate prey, (ii) Prognathodon saturator and Prognathodon sectorius overlapping with extant reptiles that consume larger amounts of softer invertebrate prey items, and (iii) Mosasaurus hoffmanni spanning a larger plot area in terms of dietary constraints. The clear divide between the aforementioned first two groups in texture-dietary space indicates that, despite our small sample sizes, this method shows the potential of DMTA to test hypotheses and provide quantitative constraints on mosasaur diets and ecological roles.

Abstract Ancient greenhouse periods are useful analogs for predicting effects of anthropogenic climate change on regional and global temperature and precipitation patterns. A paucity of terrestrial data from polar regions during warm episodes challenges our understanding of polar climate responses to natural/anthropogenic change and therefore our ability to predict future changes in precipitation. Ellesmere and Axel Heiberg Islands in the Canadian Arctic preserve terrestrial deposits spanning the late Paleocene to middle Eocene (59–45 Ma). Here we expand on existing regional sedimentology and paleontology through the addition of stable (δ13C, δ18O) and clumped (Δ47) isotope analyses on palustrine carbonates. δ13C isotope values range from −4.6 to +12.3‰ (VPDB), and δ18O isotope values range from −23.1 to −15.2‰ (VPDB). Both carbon and oxygen isotope averages decrease with increasing diagenetic alteration. Unusually enriched carbon isotope (δ13C) values suggest that analyzed carbonates experienced repeated dissolution‐precipitation enrichment cycles, potentially caused by seasonal fluctuations in water availability resulting in summer carbonate dissolution followed by winter carbonate re‐precipitation. Stable isotopes suggest some degree of precipitation seasonality or reduction in winter water availability in the Canadian Arctic during the Paleogene. Clumped (Δ47) temperature estimates range from 52 to 121°C and indicate low temperature solid‐state reordering of micritic samples and diagenetic recrystallization in sparry samples. Average temperatures agree with vitrinite reflectance data for Eureka Sound Group and underlying sediments, highlighting structural complexity across the region. Broadly, combined stable and clumped isotope data from carbonates in complex systems are effective for describing both paleoclimatic and post‐burial conditions.