Ice islands, massive tabular icebergs, are known to fracture as they drift. The footloose mechanism occurs when a large protuberance, known as a ram, develops along the submerged edge of the ice island and induces a buoyancy-driven bending stress. This study investigates the relationship between rams and footloose fracture using finite element models of ice islands with simulated underwater rams. Geospatial polygons of ice islands, derived from remote sensing imagery, were used to create three-dimensional shapes of ice islands at two thicknesses and with various ram sizes. Then, the location of maximum stress and fractures were predicted using finite element analysis (FEA) and the results were compared to remote sensing observations of the actual fractured pieces that calved from each of the 26 modelled ice islands. Accurate simulations of calving were achieved when a synthesized ram was placed along the ice island edge where the calving was observed. An empirical model was developed to predict the magnitude of stress from various ram sizes and shapes. The predictive ability of this empirical model suggests that ice island calving models can be improved and combined with drift forecasting models to help mitigate risks to offshore infrastructure and seafaring vessels.

When studying extinct organisms, which phylogenetic methods are the most useful to determine patterns of evolutionary relationship? How well do current classifications reflect the patterns discovered? Using Athyridida (Upper Ordovician–Lower Jurassic) as a case study, we utilize parsimony, Bayesian Mk, asymmetrical rates, and fossilized birth–death process models, with and without character partitions, to compare results from different methods of inference, to test previous phylogenetic hypotheses and examine morphological character evolution in this long-lived group of extinct brachiopods. Because different phylogenetic methods utilize different models of evolution involving different sets of assumptions, they can result in different patterns of relationship, making it necessary to test multiple methods and then evaluate thoughtfully the various results obtained.

We discovered that the four main athyridide higher taxa we focus on largely maintain their coherence as clades in most of the analyses, but relationships among them vary substantially, with implications for the evolution of characters important in their classification. We were able to characterize in detail the athyridide external valve characters that are more variable than internal characters, quantifying the commonly held impression that internal features are more likely to be homologues and thus more reliable in identifying relationships than external characters. Because taxa in classifications are still frequently used as clade proxies in macroevolutionary studies, it is necessary to obtain and compare the most robust hypotheses of relationship among named taxa in order to evaluate both character homology and homoplasy and taxonomic fidelity to hypotheses of evolution.

Pterygotids were Paleozoic marine and marginal marine large apex predatory arthropods. However, their evolution remains poorly understood due to the scarcity of their fossils and the delicate nature of their exoskeletons. The well-studied Devonian Xiaxishancun Formation in Qujing City, Yunnan, China contains various Agnatha and three eurypterid species. Our study focuses on the eurypterid material assigned to Erettopterus qujingensis Ma et al., 2022 and Pterygotus wanggaii Ma et al., 2023. The two species were discovered from the same locality, both with individuals of different developmental stages (juveniles more common), suggesting that this area could represent a breeding site, in agreement with mass molt behavior and the occurrence of other pterygotids in shallow waters. Moreover, the coexistence of heavily armed Agnatha with Pterygotus wanggaii in the Xiaxishancun Formation, alongside their robust chelicerae, supports the hypothesis that some pterygotids were piscivorous. In addition, due to ambiguity of pterygotid cheliceral dentition nomenclature, we introduce a new framework to define the cheliceral denticle types of pterygotids based on their relative positions: TD, terminal denticle; MD, median denticle (including: MMD, modified MD, and OMD, ordinary MD); BD, basal denticle. A key diagnostic feature in the cheliceral denticles of E. qujingensis is established: movable finger ends in a curved TD, 3 MMD’s present, 9 OMDs between MMD1 and MMD2 (OMD4 and OMD8 slightly enlarged); fixed finger ends in an acute TD’, 3 MMD’s present (MMD’2 being the largest), 8 OMD’s between MMD’1 and MMD’2 (OMD’5 slightly enlarged), 15 OMD’s between MMD’2 and MMD’3 (OMD’1 and OMD’10-12 slightly enlarged). This cheliceral diagnosis distinguishes E. qujingensis from Pterygotus wanggaii by its distinct number of MMDs.

Perna perna mussel is a coastal benthic filter-feeder widely cultivated in mytiliculture farms and serves as a resource for local communities engaged in its harvest along the Brazilian coast. This study presents the isotopic ratios (δ13C and δ15N) in the soft tissues of adult mussels from six natural populations in Rio de Janeiro State, southeast Brazil, to evaluate whether they are sensitive enough to distinguish the origin of specimens. The COVID-19 pandemic served as temporal reference, as the quality of coastal waters was influenced by the restrictions imposed during the pandemic. The mean values of δ13C and δ15N ranged from −19.5‰ to −17.3‰, and 6.2‰ to 10.5‰, respectively. The spatial variation of δ13C-δ15N data in the analysed mussels was greater than the temporal variation. The k-means clustering method correctly identified 80% of populations during the pre-pandemic period, 67% in the pandemic, and 50% in the post-pandemic. In most samples, the spatial variation of δ15N (tracer of food source variability) was the primary variable distinguishing the groups of mussels. The isotopic ratios did not reveal a clear trend when using the COVID-19 pandemic as temporal reference. Consequently, the positive environmental changes brought about by the suspension or reduction of anthropogenic activities in coastal waters during the pandemic had minimal impact on the isotopic ratios of mussels at most sampling sites. The utilisation of δ13C-δ15N data to trace the origin of P. perna mussel from natural banks was only partially effective in distinguishing the origin of natural populations across the studied area.

This study provides the first case reported of Paraprionospio treadwelli (Hartman, 1951) in the Gulf of Mexico. Based on 242 individuals collected between 20.8 and 176 m depth during three oceanographic expeditions, we describe in detail the morphology of the identified specimens, including the description of the pygidium, so far unknown in this species, and provide SEM photographs to support their identification. Paraprionospio treadwelli was originally found in Chesapeake Bay, Northwestern Atlantic, and we now extend its distribution southwards to the Western Gulf of Mexico. Remarks on the environmental conditions where this spionid species was found and the observed abundance seasonal pattern are also provided.

Fossil data are subject to inherent biological, geologic, and anthropogenic filters that can distort our interpretations of ancient life and environments. The inevitable presence of incomplete fossils thus requires a holistic assessment of how to navigate the downstream effects of bias on our ability to accurately reconstruct aspects of biology in deep time. In particular, we must assess how biases affect our capacity to infer evolutionary relationships, which are essential to analyses of diversification, paleobiogeography, and biostratigraphy in Earth history. In this study, we use an established completeness metric to quantify the effects of taphonomic filters on the amount of phylogenetic information available in the fossil record of 795 extinct squamate (e.g., lizards, snakes, amphisbaenians, and mosasaurs) species spanning 242 Myr of geologic time. This study found no meaningful relationship between spatiotemporal sampling intensity and fossil record completeness. Instead, major differences in squamate fossil record completeness stem from a combination of anatomy/body size and affinities of different squamate groups to specific lithologies and depositional environments. These results reveal that naturally occurring processes create structural megabiases that filter anatomical and phylogenetic data in the squamate fossil record, while anthropogenic processes play a secondary role.

The Gulf of California, one of the world’s most biodiverse marine ecosystems, is also heavily exploited by fisheries. Among its fish fauna are species that, although currently underappreciated, may become commercially important in the future. Enhancing our biological knowledge of these species is crucial for monitoring population dynamics and community changes. Fish parasites offer valuable insights into host ecology, including feeding habits and population structure. In this study, we document the metazoan parasite fauna of Trichiurus nitens (Trichiuridae) from four locations in the eastern Gulf of California, Mexico. A total of 165 fish specimens were examined, revealing five parasite species identified using both morphological characteristics and molecular markers: the monogenean Octoplectanocotyla travassosi, the trematode Lecithochirium sinaloense, and three nematodes – Anisakis typica A, Skrjabinisakis brevispiculata, and Spinitectus sp. Among these, L. sinaloense was the most prevalent. Although parasite species richness was similar between small and large fish, overall parasite abundance was higher in larger specimens. Moreover, parasite assemblages did not vary significantly across the study locations. These findings suggest that T. nitens exhibits a specialized feeding strategy, relying on a narrow range of prey throughout its life, and that the oceanographic variability does not limit fish movement in the region. Future studies encompassing a broader geographical scale, additional fish size classes, and different climatic seasons are needed to further elucidate the ecological role of this species. This work provides novel insights into the host-parasite dynamics of T. nitens and establishes a valuable baseline for ecosystem monitoring under global change scenarios.