Foramina of bones are beginning to yield more information about metabolic rates and activity levels of living and extinct species. This study investigates the relationship between estimated blood flow rate to the femur and body mass among cursorial birds extending back to the Late Cretaceous. Data from fossil foramina are compared with those of extant species, revealing similar scaling relationships for all cursorial birds and supporting crown bird–like terrestrial locomotor activity. Because the perfusion rate in long bones of birds is related to the metabolic cost of microfracture repair due to stresses applied during locomotion, as it is in mammals, this study estimates absolute blood flow rates from sizes of nutrient foramina located on the femur shafts. After differences in body mass and locomotor behaviors are accounted for, femoral bone blood flow rates in extinct species are similar to those of extant cursorial birds. Femoral robustness is generally greater in aquatic flightless birds than in terrestrial flightless and ground-dwelling flighted birds, suggesting that the morphology is shaped by life-history demands. Femoral robustness also increases in larger cursorial bird taxa, probably associated with their weight redistribution following evolutionary loss of the tail, which purportedly constrains femur length, aligns it more horizontally, and necessitates increased robustness in larger species.

Melanin pigments are central to colors and patterns in modern vertebrate integuments, which inform upon ecological and behavioral strategies like crypsis, aposematism, and sociosexual selection. Over the last decade, melanin has emerged as a valuable tool for predicting color in exceptionally preserved fossil feathers and subsequent testing of paleobiological hypotheses in long-extinct dinosaurs and birds. Yet much remains to be learned about melanin stability, diagenetic alterations to melanin chemistry, and their implications for “paleocolor reconstruction.” Pressure–temperature maturation experiments with modern feathers offer a way to examine these topics but have mostly been conducted in closed-system capsules or open-system aluminum foil. Both methods have operational limitations and do not consider the filtering effect of porous sediment matrices on thermally labile chemical groups versus stable ones during natural fossilization. We use sediment-encased maturation to resolve this issue and demonstrate replication of organic preservation of melanin highly comparable to compression fossils. Our experiments, coupled with time-of-flight secondary ion mass spectrometry, show predictable volatilization of N/S-bearing molecules and increased melanin cross-linking with elevated temperatures. We also suggest that eumelanin is more stable compared with pheomelanin at higher temperatures, explaining why eumelanic colors (black, dark brown, iridescent) are better preserved in fossils than pheomelanic ones (reddish brown). Furthermore, we propose that proteins preferentially undergo hydrolysis more so than forming N-heterocycles in selectively open systems analogous to natural matrices. Thus, we conclude that melanin pigments and not diagenetically altered protein remnants are the key players in promoting fossilization of soft tissues like feathers.

Documenting patterns of evolution and stasis has been a major focus of paleobiology. However, despite substantial knowledge gleaned on this topic, many questions related to the underlying environmental processes that determine the dynamics of evolution and stasis remain unresolved. Therefore, this study focuses on examining these evolutionary patterns framed within an environmental context. Specifically, we test Sheldon’s “Plus ça change” model, which predicts that morphological change is associated with more stable environments, such as in tropical latitudes or greenhouse climates, whereas stasis is linked to less stable environments, like those found in temperate latitudes or during icehouse climates. We examine the role that broadscale climatic variation exerts on evolutionary dynamics by documenting morphological change among nuculid bivalves in shallow-shelf settings from three different climate regimes: (1) the stable Late Cretaceous greenhouse climate; (2) the moderately stable Neogene transitional climate; and (3) the less stable Quaternary icehouse climate. Morphological changes over time were assessed using both bivalve size and outline shape. Comparison among changes in size and outline-shape patterns for Late Cretaceous and Neogene–Quaternary Nucula indicates that morphological change over time and stasis, respectively, dominated these different time intervals. In all cases, morphological change over time coincided with the more stable and less climatically variable greenhouse conditions, whereas stasis was associated with the more variable regimes characteristic of icehouse climates. These data provide strong support for the need to consider broad environmental factors—in this case climate—when assessing evolutionary modes. Furthermore, they point to the relevance of the Plus ça change model to explain patterns of evolution and stasis.