Maniraptora

Abstract: Fossil evidence for changes in dinosaurs near the lineage leading to birds and the origin of flight has been sparse. A dinosaur from Mongolia represents the basal divergence within Dromaeosauridae. The taxon's small body size and phylogenetic position imply that extreme miniaturization was ancestral for Paraves (the clade including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier than where flight evolution is strongly inferred. In contrast to the sustained small body sizes among avialans throughout the Cretaceous Period, the two dinosaurian lineages most closely related to birds, dromaeosaurids and troodontids, underwent four independent events of gigantism, and in some lineages size increased by nearly three orders of magnitude. Thus, change in theropod body size leading to flight's origin was not unidirectional.

Abstract: Sickle-clawed predatory dinosaurs, known as dromaeosaurids, are close relatives of birds. Until a decade ago, members of this group such as Velociraptor were known only from northern continents, but a few fragmentary specimens have been found in the Southern Hemisphere in recent years. The cover shows a life reconstruction of Buitreraptor gonzalezorum, a newly discovered dromaeosaurid from La Buitrera in Patagonia, which is known from a nearly complete specimen. It is geologically oldest of the southern dromaeosaurids, and its completeness provides evidence that they are a distinct lineage that split from their northern relatives after the breakup of the supercontinent Pangaea towards the end of the Jurassic. The individual in the foreground is shown holding a juvenile Priosphenodon (see Nature 425, 609–612; 2003), a relative of the living tuatara, and another relict of a group with a global Jurassic distribution. The evolutionary history of Maniraptora, the clade of carnivorous dinosaurs that includes birds and the sickle-clawed Dromaeosauridae, has hitherto been largely restricted to Late Jurassic and Cretaceous deposits on northern continents. The stunning Early Cretaceous diversity of maniraptorans from Liaoning, China1,2,3, coupled with a longevity implied by derived Late Jurassic forms such as Archaeopteryx, pushes the origins of maniraptoran lineages back to Pangaean times and engenders the possibility that such lineages existed in Gondwana. A few intriguing, but incomplete, maniraptoran specimens have been reported from South America4,5,6,7,8, Africa9 and Madagascar10. Their affinities remain contested11,12,13, however, and they have been interpreted as biogeographic anomalies relative to other faunal components of these land-masses. Here we describe a near-complete, small dromaeosaurid that is both the most complete and the earliest member of the Maniraptora from South America, and which provides new evidence for a unique Gondwanan lineage of Dromaeosauridae with an origin predating the separation between northern and southern landmasses.

Abstract: Troodontid dinosaurs form one of the most avian-like dinosaur groups1,2,3,4,5. Their phylogenetic position is hotly debated, and they have been allied with almost all principal coelurosaurian lineages6,7,8,9,10,11,12,13. Here we report a basal troodontid dinosaur, Sinovenator changii gen. et sp. nov., from the lower Yixian Formation of China. This taxon has several features that are not found in more derived troodontids, but that occur in dromaeosaurids and avialans. The discovery of Sinovenator and the examination of character distributions along the maniraptoran lineage indicate that principal structural modifications toward avians were acquired in the early stages of maniraptoran evolution.

Abstract: Dromaeosaurus albertensis was one of the first small theropods described that was based on reasonably good cranial material. It was realized from the beginning that this animal was significantly different from other Cretaceous theropods, and the Dromaeosauridae was created for its inclusion. In the intervening years, a number of genera were assigned to this family, which came to assume an important position in discussions on theropod relationships and evolution, and the origin of birds. It is now known that many of the dromaeosaurids are different enough from Dromaeosaurus to be included in a distinct subfamily known as the Velociraptorinae. In spite of intensive collecting activity, the holotype of Dromaeosaurus albertensis is still the most complete specimen, and it is apparent that this genus is even rarer than other small theropods. Repreparation and restudy of the holotype has produced new anatomical information useful for evaluating the relationships of dromaeosaurids. Contrary to previous ...