The Mesozoic terminated in boreal spring

Abstract

The Cretaceous–Palaeogene mass extinction around 66 million years ago was triggered by the Chicxulub asteroid impact on the present-day Yucatán Peninsula1,2. This event caused the highly selective extinction that eliminated about 76% of species3,4, including all non-avian dinosaurs, pterosaurs, ammonites, rudists and most marine reptiles. The timing of the impact and its aftermath have been studied mainly on millennial timescales, leaving the season of the impact unconstrained. Here, by studying fishes that died on the day the Mesozoic era ended, we demonstrate that the impact that caused the Cretaceous–Palaeogene mass extinction took place during boreal spring. Osteohistology together with stable isotope records of exceptionally preserved perichondral and dermal bones in acipenseriform fishes from the Tanis impact-induced seiche deposits5 reveal annual cyclicity across the final years of the Cretaceous period. Annual life cycles, including seasonal timing and duration of reproduction, feeding, hibernation and aestivation, vary strongly across latest Cretaceous biotic clades. We postulate that the timing of the Chicxulub impact in boreal spring and austral autumn was a major influence on selective biotic survival across the Cretaceous–Palaeogene boundary.

Late Cretaceous sturgeons (Acipenseridae) from North America, with two new species from the Tanis site in the Hell Creek Formation of North Dakota

“…6). During et al (2022) used carbon isotope analysis, paleohistology, and propagation phase-contrast synchrotron radiation micro-computed tomography to infer seasonal and growth patterns of polyodontid and acipenserid specimens, and concluded that the seiche waves and subsequent inundation of the fishes occurred during the boreal spring. The presence of both marine and freshwater organisms indicates that this site was in close proximity to the shoreline of the Western Interior Seaway.…”

Microstructural and crystallographic evolution of palaeognath (Aves) eggshells

“…Non-avian dinosaurs became extinct at the end of Mesozoic ( During et al, 2022 ), but avian dinosaurs are still extant and flourishing today as the most speciose land-vertebrate lineage ( Jarvis et al, 2014 ; Lee et al, 2014 ; Brusatte et al, 2015 ; Prum et al, 2015 ). For example, their eggshell sizes, shapes, and pigment colours and patterns show phenomenal diversity ( Mikhailov, 1997a ; Hauber et al, 2014 ; Stoddard et al, 2017 ).…”

Microstructural and crystallographic evolution of palaeognath (Aves) eggshells

“…Non-avian dinosaurs became extinct at the end of Mesozoic (During et al, 2022), but avian dinosaurs are still extant and flourishing today as the most speciose land-vertebrate lineage (Jarvis et al, 2014; Lee et al, 2014; Brusatte et al, 2015; Prum et al, 2015). For example, their eggshell sizes, shapes, and patterns show phenomenal diversity (Mikhailov, 1997a; Hauber, 2014; Stoddard et al, 2017).…”