Multiple dinosaur egg-shell occurrence in an Upper Cretaceous nesting site from Patagonia

The discovery of hundreds of megaloolithid-type egg-clutches (some including embryos of an indeterminate species of titanosaur sauropods) in several stratigraphical levels of the Late Cretaceous nesting site of Auca Mahuevo (Chiappe et al., 2005) unveiled important aspects of the reproductive behavior of sauropod dinosaurs and stimulated further work at other Patagonian dinosaur egg sites. In November of 2003, a join expedition of the National University of Comahue (Neuquén), the Museo Carmen Funes (Plaza Huincul) and the Museo de Lamarque (Lamarque) conducted fieldwork in several Late Cretaceous localities of Bajo Santa Rosa (center-north Río Negro Province, Argentina) bearing the remains of dinosaur eggs and other terrestrial vertebrates (figure 1). The main focus of this expedition was to assess the diversity of dinosaur eggs, to fine-tune the stratigraphy of the egg-bearing layers, and to document the spatial distribution of the egg-clutches. The overall results of this research were reported elsewhere (Salgado et al., 2007). In this contribution, we make focus in one of the fossil localities worked, Berthe IV, where the association of egg clutches likely belonging to different dinosaur species was detected (figure 1.2). Collected eggshells were observed with a binocular loupe ‘‘Stemi SV6 Zeiss’’, at magnifications of x1.0 and x3.2 (for macrocharacters). Microcharacters were observed in transverse thin section using a polarizing microscope (‘‘Zeiss Axioplan’’) at magnifications of x0.4 and x10. The eggshells were photographed using this polarizing microscope equipped with a digital camera. Prior to analysis, the eggshells were submitted to a process of cleaning using ultrasound (see Salgado et al., 2007 for further methodological details).Fil: Coria, Rodolfo Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Provincia del Neuquen. Municipalidad de Plaza Huincul. Museo "Carmen Funes"; ArgentinaFil: Salgado, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue. Museo de Geologia y Paleontologia; ArgentinaFil: Chiappe, Luis M.. Los Angeles County Museum of Natural History. Dinosaur Institute; Estados Unido

Aerodynamic modelling of a Cretaceous bird reveals thermal soaring capabilities during early avian evolution

Several flight modes are thought to have evolved during the early evolution of birds. Here, we use a combination of computational modelling and morphofunctional analyses to infer the flight properties of the raven-sized, Early Cretaceous bird Sapeornis chaoyangensis-a likely candidate to have evolved soaring capabilities. Specifically, drawing information from (i) mechanical inferences of the deltopectoral crest of the humerus, (ii) wing shape (i.e. aspect ratio), (iii) estimations of power margin (i.e. difference between power required for flight and available power from muscles), (iv) gliding behaviour (i.e. forward speed and sinking speed), and (v) palaeobiological evidence, we conclude that S. chaoyangensis was a thermal soarer with an ecology similar to that of living South American screamers. Our results indicate that as early as 125 Ma, some birds evolved the morphological and aerodynamic requirements for soaring on continental thermals, a conclusion that highlights the degree of ecological, functional and behavioural diversity that resulted from the first major evolutionary radiation of birds

Independent origins for powered flight in paravian dinosaurs?

Política de acceso abierto tomada de:https://www.elsevier.com/about/policies-and-standards/open-access-licenses/userFeathered dinosaurs discovered during the last decades have illuminated the transition from land to air in these animals, underscoring a significant degree of experimentation in wing-assisted locomotion around the origin of birds. Such evolutionary experimentation led to lineages achieving either wing-assisted running, four-winged gliding, or membrane-winged gliding. Birds are widely accepted as the only dinosaur lineage that achieved powered flight, a key innovation for their evolutionary success. However, in a recent paper in Current Biology, Pei and colleagues1 disputed this view. They concluded that three other lineages of paravian dinosaurs (those more closely related to birds than to oviraptorosaurs) — Unenlagiinae, Microraptorinae and Anchiornithinae — could have evolved powered flight independently. While we praise the detailed phylogenetic framework of Pei and colleagues1 and welcome a new attempt to understand the onset of flight in dinosaurs, we here expose a set of arguments that significantly weaken their evidence supporting a multiple origin of powered flight. Specifically, we maintain that the two proxies used by Pei and colleagues1 to assess powered flight potential in non-avian paravians — wing loading and specific lift — fail to discriminate between powered flight (thrust generated by flapping) and passive flight (gliding)

Phylogenetic interrelationships of living and extinct Tinamidae, volant palaeognathous birds from the New World

Tinamous, one of the earliest diverging living avian lineages, consists of a Neotropical clade of palaeognathous birds with a fossil record limited to the early Miocene–Quaternary of southern South America. Here, we conduct a comprehensive, morphology-based phylogenetic study of the interrelationships among extinct and living species of tinamous. Morphological data of fossil species are included in a matrix of 157 osteological and myological characters of 56 terminal taxa. The monophyly of most recognized genera is supported by the results of the analysis. The cladistic analysis also recovers the traditional subdivision between those tinamous specialized for open areas (Nothurinae) and those inhabiting forested environments (Tinaminae). Temporal calibration of the resultant phylogeny indicates that such a basal divergence had already taken place in the early Miocene, some 17 million years ago. The placement of the fossil species within the open-area (Nothurinae) and the forest-dwelling (Tinaminae) tinamous is also consistent with the palaeoenvironmental conditions inferred from the associated fauna.Fil: Bertelli, Sara Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Miguel Lillo; Argentina. Natural History Museum of Los Angeles County; Estados UnidosFil: Chiappe, Luis M.. Natural History Museum of Los Angeles County; Estados UnidosFil: Mayr, Gerald. Forschungsinstitut Senckenberg; Alemani

The Lambeosaurine Dinosaur Magnapaulia laticaudus from the Late Cretaceous of Baja California, Northwestern Mexico

The taxonomy, osteology, phylogenetic position, and historical biogeography of the lambeosaurine hadrosaurid Magnapaulia laticaudus (new combination) are revised. The diagnosis of this species is amended on the basis on two autapomorphies (i.e., longest haemal arches of proximal caudal vertebrae being at least four times longer than the height of their respective centra; base of prezygapophyses in caudal vertebrae merging to form a bowl-shaped surface) and a unique combination of characters (i.e., downturned cranioventral process of the maxilla; tear-shaped external naris with length/width ratio between 1.85 and 2.85; neural spines of dorsal, sacral, and proximal caudal vertebrae being at least four times the height of their respective centra). A maximum parsimony analysis supports a sister taxon relationship between M. laticaudus and Velafrons coahuilensis. Both taxa constitute a clade of southern North American lambeosaurines, which forms a sister relationship with the diverse clade of helmet-crested lambeosaurines from northern North America that includes well-known genera like Corythosaurus, Lambeosaurus, and Hypacrosaurus. According to the results of a Dispersal-Vicariance analysis, southern North American lambeosaurines split from the northern forms via vicariance from a common ancestor that lived in both the northern and southern regions of the continent

Feathering Dinosaurs The transition from Theropods to Birds

Desde el inicio del pensamiento evolutivo, el origen de las aves ha constituido uno de los problemas más polémicos de la biología evolutiva. En la actualidad, un gran cúmulo de evidencia indica que dicho problema se encuentra de gran manera resuelto. La evidencia osteológica, oológica, etológica y tegumentaria sustenta fuertemente la hipótesis que las aves descienden de dinosaurios terópodos, en particular a partir de formas clasificadas dentro de Maniraptora. Los contados investigadores que hoy en día se oponen a dicha hipótesis han sustentado sus críticas en observaciones erróneas o dentro de un marco teórico obsoleto. Este trabajo ofrece una breve discusión tanto de las principales líneas de evidencia en sustento de esta hipótesis filogenética como de los argumentos utilizados en su contra.Since the beginning of evolutionary thinking, the origin of birds has constituted one of the most debated problems in evolutionary biology. Today, a large body of evidence indicates that such a problem is to a great extent solved. Osteological, oological, ethological, and integumentary evidence strongly supports the hypothesis that birds evolved from theropod dinosaurs, in particular from dinosaurs classified within Maniraptora. Todays handful of researchers opposing this hypothesis have either based their criticisms on mistaken observations or they have framed them within dated methodologies. This paper provides a brief discussion of both the evidence in support to this hypothesis and the main arguments against it