Relict duck-billed dinosaurs survived into the last age of the dinosaurs in subantarctic Chile

In the dusk of the Mesozoic, advanced duck-billed dinosaurs (Hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. From Laurasia, hadrosaurids dispersed widely, colonizing Africa, South America, and, allegedly, Antarctica. Here, we present the first species of a duck-billed dinosaur from a subantarctic region, Gonkoken nanoi, of early Maastrichtian age in Magallanes, Chile. Unlike duckbills further north in Patagonia, Gonkoken descends from North American forms diverging shortly before the origin of Hadrosauridae. However, at the time, non-hadrosaurids in North America had become replaced by hadrosaurids. We propose that the ancestors of Gonkoken arrived earlier in South America and reached further south, into regions where hadrosaurids never arrived: All alleged subantarctic and Antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like Gonkoken. Dinosaur faunas of the world underwent qualitatively different changes before the Cretaceous-Paleogene asteroid impact, which should be considered when discussing their possible vulnerability

Caracterización de una relación alométrica en Theropoda (dinosauria) con énfasis en su extensión e implicaciones evolutivas

Tesis entregada a la Universidad de Chile en cumplimiento parcial de los requisitos para optar al grado de Magíster en Ciencias Biológicas.El origen del vuelo en Aves está marcado tanto por disminuciones significativas en tamaño corporal como por el aumento en tamaño relativo de las extremidades anteriores. No obstante, previo al origen del vuelo, la evolución de ambos caracteres pudo estar asociada mediante de un patrón alométrico evolutivo negativo para las extremidades anteriores de terópodos. Esta relación ha sido descrita para la mayor parte de Theropoda, perdiéndose en la base de Aves (desde Archaeopteryx lithographica), clado donde se describen en su lugar isometrías o alometrías positivas tanto evolutivas como ontogenéticas. No obstante, las publicaciones donde estas alometrías han sido descritas no corrigen apropiadamente la no-independencia estadística presente entre especies emparentadas. Además, a pesar de que se ha sugerido, ningún estudio a la fecha ha evaluado formalmente la posibilidad de la pérdida del patrón de alometría evolutiva negativa para extremidades anteriores en otros taxa pertenecientes a Theropoda. Del mismo modo la posible relación entre el patrón alométrico evolutivo negativo para extremidades anteriores y un patrón equivalente en la ontogenia no ha sido discutida. En el presente estudio se procedió a re-evaluar el patrón alométrico evolutivo negativo para extremidades anteriores en Theropoda, además de posibles desviaciones respecto a este, utilizando datos de longitudes de húmero y fémur correspondientes a 163 especímenes distribuidos en 108 géneros, incorporando variabilidad intraespecífica, incerteza filogenética y dos modelos evolutivos alternativos a las correcciones filogenéticas utilizadas en los análisis realizados. Mediante estos análisis se recuperaron valores de alometría negativa para el conjunto de los terópodos no-avianos encontrándose además que Coelophysoidea, Ornithomimosauria y Oviraptorosauria presentan diferencias significativas respecto al patrón alométrico general bajo ambos modelos evolutivos, exhibiendo isometría. Se encontró alometría evolutiva negativa para extremidades anteriores en Dromaeosauridae, corroborando que, probablemente, este patrón alométrico evolutivo estaba presente en formas cercanas a Aves. Al revisar la evidencia publicada respecto a alometrías negativas ontogenéticas para extremidades anteriores en Theropoda se encontraron patrones similares a los patrones alométricos evolutivos obtenidos, del mismo modo esta correspondencia se encontró en Aves y otros clados cercanos a Theropoda permitiendo proponer que, además de una órbita y caja craneana expandidas, la paedomorfosis observada en el origen de Aves incluyó extremidades anteriores proporcionalmente mayores como otro rasgo juvenil.The origin of flight in Aves is marked both by significant decreases in body size and by the increase in relative forelimb size. However, before the origin of flight, the evolution of both characteristics may have been coupled through a pattern of negative forelimb evolutive allometry in Theropoda. This pattern was lost at the origin of Aves (since Archaeopteryx lithographica), clade where isometry or positive allometry has been described instead for both: the phylogeny and ontogeny. However, the publications where these allometries have been described do not properly correct for the statistical non-independence present among related species. Furthermore, even though it has been suggested, no study has formally tested if other taxa in Theropoda show loss of the negative allometric pattern as well. Similarly, the possible relation between the negative forelimb evolutive allometric pattern and an equivalent ontogenetic one has not been discussed. In the present study we re-evaluated the negative forelimb allometric pattern found in the evolution of Theropoda and tested for significate deviations from it using femur and humerus lengths from 163 specimens representing 108 genera, we also incorporated intraspecific variation, phylogenetic uncertainty and two alternative evolutionary models to the phylogenetic corrections used in the analyses. We recovered an evolutionary negative forelimb allometry for all non-avian theropods; we also identified that Coelophysoidea, Ornithomimosauria and Oviraptorosauria show significative differences from the general allometric pattern presenting isometry. We found evolutionary negative forelimb evolutive allometry in Dromaeosauridae showing that this pattern was, most likely, still present in forms close to Aves. Upon reviewing published evidence for ontogenetic negative forelimb allometry in Theropoda we found similar patterns to the ones obtained through our analysis, we also observed similarities between ontogenetic and evolutive forelimb allometric patterns described for Aves and other taxa close to Theropoda suggesting that, in addition to an expanded orbit and braincase, the paedomorphosis observed at the origin of birds probably included proportionally larger arms as another juvenile trait.Proyecto Anillo ACT172099 y Fondecyt 1150906

Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile

Armoured dinosaurs are well known for their evolution of specialized tail weapons— paired tail spikes in stegosaurs and heavy tail clubs in advanced ankylosaurs1 . Armoured dinosaurs from southern Gondwana are rare and enigmatic, but probably include the earliest branches of Ankylosauria2–4 . Here we describe a mostly complete, semi-articulated skeleton of a small (approximately 2 m) armoured dinosaur from the late Cretaceous period of Magallanes in southernmost Chile, a region that is biogeographically related to West Antarctica5 . Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: a fat, frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail. Stegouros shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters. Phylogenetic analyses placed Stegouros in Ankylosauria; specifcally, it is related to Kunbarrasaurus from Australia6 and Antarctopelta from Antarctica7 , forming a clade of Gondwanan ankylosaurs that split earliest from all other ankylosaurs. The large osteoderms and specialized tail vertebrae in Antarctopelta suggest that it had a tail weapon similar to Stegouros. We propose a new clade, the Parankylosauria, to include the frst ancestor of Stegouros— but not Ankylosaurus—and all descendants of that ancestor.Fil: Soto Acuña, Sergio. Universidad de Chile; ChileFil: Vargas, Alexander O.. Universidad de Chile; ChileFil: Kaluza, Jonatan Ezequiel. Universidad de Chile; Chile. Universidad Maimónides; Argentina. Fundación de Historia Natural Félix de Azara; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Leppe, Marcelo A.. Universidad de Chile; Chile. Instituto Nacional Antártico Chileno; ChileFil: Botelho, Joao F.. Universidad de Chile; Chile. Pontificia Universidad Católica de Chile; ChileFil: Palma Liberona, José. Universidad de Chile; Chile. Pontificia Universidad Católica de Chile; ChileFil: Gutstein, Carolina Simon. Universidad de Chile; ChileFil: Fernández, Roy A.. Universidad de Chile; Chile. Universidad de Concepción; ChileFil: Ortiz, Héctor. Universidad de Chile; Chile. Universidad de Magallanes; ChileFil: Milla, Verónica. Universidad de Chile; Chile. Universidad de Concepción; ChileFil: Aravena, Bárbara. Universidad de Chile; ChileFil: Manríquez, Leslie M. E.. Universidad de Chile; Chile. Universidad de Vale do Rio dos Sinos; BrasilFil: Alarcón Muñoz, Jhonatan. Universidad de Chile; ChileFil: Pino, Juan Pablo. Universidad de Chile; ChileFil: Trevisan, Cristine. Universidad de Chile; Chile. Instituto Nacional Antártico Chileno; ChileFil: Mansilla, Héctor Sebastian. Universidad de Chile; Chile. Instituto Nacional Antártico Chileno; ChileFil: Hinojosa, Luis Felipe. Universidad de Chile; ChileFil: Muñoz Walther, Vicente. Universidad de Chile; ChileFil: Rubilar Rogers, David. Museo Nacional de Historia Natural Chile; Chile. Universidad de Chile; Chil