RESUMEN
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.
Asunto(s)
Fósiles , Frutas , Magnoliopsida , México , FilogeniaRESUMEN
This work presents a detailed structural and morphological analysis of different dinosaur eggshells such as Spheroolithus (sample 1, 2), lambeosaurinae, Prismatoolithus, and one unidentified ootaxon performed by high-resolution scanning electron microscopy (HRSEM). These ancient eggshells of Late Cretaceous dinosaurs were collected in the coastal area of El Rosario, Baja California in Mexico. Additionally, a thorough study was performed on the elements present in the samples by different techniques such as energy-dispersive spectroscopy (EDS), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS). The XPS technique was performed to make an accurate identification of the compounds of two different types of eggshells (Spheroolithus sample 1 and Prismatoolithus). This contribution compares the surface of five different dinosaur eggshells of 74 Ma and their inner section to determine the morphology, distribution of the chemical elements present, as well as their relationship. The observed morphology of the ornithopod eggshells of the herbivorous species shows that the mammillary cones are in the form of columns with microaggregates and irregular pores. In contrast, in the theropod eggshells, the mammillary cones are observed in different forms with wider pores. Finally, the chemical components present in the structures of each of the samples were estimated using the information obtained from SEM-EDS, evidencing the presence of calcite, quartz, and albite in each of the samples. The composition reveals that eggshells contain Si, P, S, K, Ca, Mn, Fe, and Sr and trace elements such as Cr, Cu, and Zn. The presence of heavy metals may be an indication that the eggshells presented diagenetic alterations.