Cornalean affinities, phylogenetic significance, and biogeographic implications of Operculifructus infructescences from the Late Cretaceous (Campanian) of Mexico.

IN ENGLISH: Premise of the Study Cretaceous Cornales provide a crucial record of the early history of asterids. Most lineages of the order are well represented in the fossil record, but South African families of Curtisiaceae and Grubbiaceae remain poorly understood. Seventy-three specimens of a fossil infructescence belonging to the genus Operculifructus Estrada-Ruiz & Cevallos-Ferriz emend. Hayes & Smith from the Late Cretaceous (Campanian) El Gallo Formation, Baja California, Mexico bear previously undescribed characters that suggest a relationship to Grubbiaceae. Methods Microstructures of the fossils were examined through light microscopy and x-ray microcomputed tomography (microCT) scanning. Modern Grubbia tomentosa (Thunb.) Harms fruits were scanned for comparison to the fossil material. Phylogenetic analyses using the 77 fruit characters of Atkinson () were performed to test relationships of the fossil to major lineages of the order. Several analyses applied topological constraints to the extant taxa, based on various genetically supported hypotheses of relationship within Cornales. Key Results Novel structures of Operculifructus newly observed here include (1) anatropous ovules, (2) drupaceous fruits, (3) an epigynous disc, (4) and a stylar canal in the center of the disc aligned with the micropylar protrusion of the seed. Phylogenetic analysis consistently resolves Operculifructus as sister to Grubbiaceae. Conclusions Operculifructus provides direct evidence for the occurrence of Grubbiaceae in the Late Cretaceous, much older than previous Eocene evidence. The phylogeny of Atkinson () indicates that the new phylogenetic position recovered for Operculifructus also establishes the presence of the most basal drupaceous cornalean fruits in North America by the Campanian. RESUMEN EN ESPAÑOL Hipótesis de la Investigación Cornales cretácicos representan un registro esencial en la historia de los astéridos. Casi todos los linajes del orden están bien representados en el registro fósil, pero las familias africanas sureñas Curtisiaceae y Grubbiaceae permanecen pobremente entendidas. Setenta y tres ejemplares de una infrutescencia fósil perteneciente al género Operculifructus Estrada-Ruiz & Cevallos-Ferriz emend. Hayes & Smith de la formación campaniana (Cretácico Tardío) El Gallo, Baja California, México, poseen caracteres no descritos previamente y sugieren una relación con Grubbiaceae. Metodología Microestructuras de los fósiles fueron examinadas con microscopio de luz y microtomografía computarizada (micro-CT) de rayos X. Frutos actuales de Grubbia tomentosa (Thunb.) Harms fueron escaneados para su comparación con el material fósil. Se realizaron análisis filogenéticos usando los 77 caracteres de frutos de Atkinson () para probar las relaciones de los fósiles con los linajes principales del orden. En algunos análisis se aplicaron restricciones topológicas a los taxa actuales basándose en varias hipótesis, soportadas genéticamente, de las relaciones dentro de Cornales. Resultados Centrales (Cruciales) Las estructuras novedosas de Operculifructus, recientemente observadas aquí, incluyen (1) óvulos anátropos; (2) frutos drupáceos; (3) disco epígino; y (4) un canal estilar en el centro del disco alineado con la protuberancia micropilar de la semilla. Los análisis filogenéticos consistentemente dan como resultado que Operculifructus es hermano de Grubbiaceae. Conclusiones Operculifructus proporciona evidencia directa de la presencia de Grubbiaceae en el Cretácico Tardío, mucho antes que la previa evidencia en el Eoceno. La filogenia de Atkinson () indica que la nueva posición filogenética recuperada para Operculifructus también resalta la presencia de frutos drupáceos cornaleanos más basales en Norteamérica durante el Campaniano.

Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction.

The fossil record and recent molecular phylogenies support an extraordinary early-Cenozoic radiation of crown birds (Neornithes) after the Cretaceous-Paleogene (K-Pg) mass extinction [1-3]. However, questions remain regarding the mechanisms underlying the survival of the deepest lineages within crown birds across the K-Pg boundary, particularly since this global catastrophe eliminated even the closest stem-group relatives of Neornithes [4]. Here, ancestral state reconstructions of neornithine ecology reveal a strong bias toward taxa exhibiting predominantly non-arboreal lifestyles across the K-Pg, with multiple convergent transitions toward predominantly arboreal ecologies later in the Paleocene and Eocene. By contrast, ecomorphological inferences indicate predominantly arboreal lifestyles among enantiornithines, the most diverse and widespread Mesozoic avialans [5-7]. Global paleobotanical and palynological data show that the K-Pg Chicxulub impact triggered widespread destruction of forests [8, 9]. We suggest that ecological filtering due to the temporary loss of significant plant cover across the K-Pg boundary selected against any flying dinosaurs (Avialae [10]) committed to arboreal ecologies, resulting in a predominantly non-arboreal post-extinction neornithine avifauna composed of total-clade Palaeognathae, Galloanserae, and terrestrial total-clade Neoaves that rapidly diversified into the broad range of avian ecologies familiar today. The explanation proposed here provides a unifying hypothesis for the K-Pg-associated mass extinction of arboreal stem birds, as well as for the post-K-Pg radiation of arboreal crown birds. It also provides a baseline hypothesis to be further refined pending the discovery of additional neornithine fossils from the Latest Cretaceous and earliest Paleogene.