The earliest dromaeosaurid theropod from South America

Abstract

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, China, 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 America, Africa and Madagascar. Their affinities remain contested, 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.

A short-armed dromaeosaurid from the Jehol Group of China with implications for early dromaeosaurid evolution

“…Within the context of the phylogeny proposed in figure 3, the distributions of Laurasian and Gondwanan dromaeosaurids could be explained by a vicariant hypothesis (Russell 1993;Upchurch et al 2002;Makovicky et al 2005;Novas & Pol 2005). However, in the early evolution of the dromaeosaurids, a dispersal event from Asia to North America occurred at least as early as the middle Early Cretaceous (Xu & Norell 2006), and thus Asia could not have been isolated from other continents at this time.…”

“…Synapomorphies supporting this phylogenetic Liaoning dromaeosaurids share several unique morphological features and are suggested to form a monophyletic Microraptorinae (Senter et al 2004;Xu & Wang 2004;Makovicky et al 2005;Senter 2007;Turner et al 2007b). Tianyuraptor possesses some of these features, including a laterally sculpted maxilla, a significantly shortened manual phalanx III-2 and a spatulate pubic symphysis, but it lacks many other microraptorine features, such as a large oval fenestra in the coracoid, shortened penultimate manual phalanges with their distal end curving ventrally, the posterior end of the ilium being significantly ventral to the ischial peduncle, and a lateral projection on the mid-length of the pubic shaft.…”

“…As in other Liaoning dromaeosaurids, unenlagiines (Novas & Puerta 1997), and basal paravians (Xu 2002), the ischium is significantly shorter than the pubis in length (less than 40% of the pubic length) and as in most other derived coelurosaurians Osmolska et al 2004), the large, triangular obturator process is located at the mid-length of the ischium (figure 2e). The posterior margin of the ischium is strongly concave and bears no distinct posterodistal process seen in other basal paravians (Novas & Puerta 1997;Forster et al 1998;Makovicky et al 2005).…”

“…The furcula is small in comparison to that of most other dromaeosaurids (Norell & Makovicky 1997;Xu 2002;Burnham 2004), about one-fifth of the femoral length and one-third of the scapular width, respectively. It has an interclavicle angle of about 1108 and, as in Buitreraptor (Makovicky et al 2005), the apophysis appears to be flat (figure 2c). No hypocleidium is present.…”

“…Dromaeosaurids are a group of small to medium theropods with a highly specialized pedal digit II (Ostrom 1969;Makovicky et al 2005). Most phylogenetic analyses posit the Dromaeosauridae as the sister taxon to the Troodontidae, forming a monophyletic Deinonychosauria, which in turn is the sister taxon to the Avialae (Ostrom 1969;Gauthier 1986;Sereno 1999;Norell et al 2001;Xu 2002;Senter et al 2004;Senter 2007;Turner et al 2007b), although some analyses suggest that the dromaeosaurids themselves are the closest relatives of birds (Xu et al 1999;Holtz 2000).…”