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.
It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.
Sphenodontian reptiles successfully radiated during Triassic and Jurassic times, but were driven almost to extinction during the Cretaceous period. The sparse Early Cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards, their suspected ecological successors. However, recent discoveries in Late Cretaceous beds in Patagonia partially modify this interpretation. Numerous skeletons of a new sphenodontian, Priosphenodon avelasi gen. et sp. nov., were collected from a single locality in the Cenomanian-Turonian Candeleros Formation, where it is more abundant than any other tetrapod group recorded in the quarry (for example, Crocodyliformes, Serpentes, Dinosauria and Mammalia). Adult specimens of Priosphenodon reached one metre in length, larger than any previously known terrestrial sphenodontian. Here we propose, using available evidence, that sphenodontians were not a minor component of the Cretaceous terrestrial ecosystems of South America, and that their ecological replacement by squamates was delayed until the early Tertiary. The new discovery helps to bridge the considerable gap in the fossil record (around 120 million years) that separates the Early Cretaceous sphenodontians from their living relatives (Sphenodon).
Two new crocodyliform specimens found in a recently discovered locality from the Late Cretaceous of Patagonia (Argentina) are described herein. One of them comprises an almost complete skull found in articulation with the lower jaws, while the other consists of the anterior region of the lower jaws and fragmentary remains of the palate. These two specimens differ in the morphology of their lower jaws (e.g., height of mandibular symphysis, pattern of ornamentation on ventral surface of mandibular ramus, concavity of medial surface of splenials, shape of splenial-dentary suture on ventral surface of mandibular symphysis) and probably belong to different taxa. The more complete specimen is considered to be a new taxon, Araripesuchus buitreraensis, diagnosed by the combination of the following characters (autapomorphic characters are indicated with an asterisk): long and acute anterior process of frontals extending anteriorly between the nasals; frontals extending into supratemporal fenestra; narrow parietal dorsal surface between supratemporal fossa; anterior palpebral remarkably broad; large siphoneal fora-men in otic recess; T-shaped choanal septum that completely divides the internal nares, having its anterior end as broad as the midregion of the septum*; pterygoid flanges pneumatic and poorly expanded at its lateral end*; transversely elongated depression on ventral surface of pterygoid flanges close to the posterior margin of suborbital fenestra*; longitudinal groove on flat lateral surface of dentaries below toothrow. The second, more fragmentary specimen might represent a different new taxon, although more material is needed in order to make a justified taxonomic decision. The phylogenetic relationships of both specimens are analyzed through a comprehensive cladistic analysis including 50 crocodylomorph taxa. All the most parsimonious hypotheses depict both specimens as closely related to the previously known South American species of Araripesuchus (A. gomesii and A. patagonicus). This group is depicted as the most basal clade of notosuchians, the most diverse group of Cretaceous mesoeucrocodylians from Gondwana.
The previous oldest known fossil snakes date from B100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional B70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.
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