The Triassic period documents the origin and diversification of modern amniote lineages and the Late Triassic fossil record of South America has been crucial to shed light on these early evolutionary histories. However, the faunistic changes that led to the establishment of Late Triassic ecosystems are largely ignored because of the global scarcity of fossils from assemblages a few million years older. Here we contribute to fill this gap with the description of a new tetrapod assemblage from the lowermost levels of the Chañares Formation (uppermost Middle-lower Late Triassic epochs) of Argentina, which is older than the other vertebrate assemblages of the same basin. The new assemblage is composed of therapsids, rhynchosaurids and archosaurs, and clearly differs from that of the immediately overlying and well-known historical Chañares vertebrate assemblage. The new tetrapod association is part of a phase of relatively rapidly changing vertebrate assemblage compositions, in a time span shorter than 6 million years, before the diversification of dinosaurs and other common Late Triassic tetrapods in southwestern Pangaea.
,4bstraet: A large and diverse collection of vertebrate remains from the Campanian-Maastrichtian Allen Formation (Malargiie Group) a t the Bajo de Santa Rosa locality (Rio Negro Province, Argentina) is described hore. The vertebrates arc represented hv: chondrichthvans: di~iomvstid siluriform. le~isosteid, cf oercichthvid and titanosaurid dinosaurs. A now small salt,asaurine tit&saurid, I3onatitan reigigen. el sp. no"., is described. It is diagnosed by the following association of characters: 1) longitudinal groovo located an the suture between pariotals that continues posteriorly over the supraoccipital to the foramen magnum; 2) basisphcnoid tubera long and narrow; 3) dorsalto middle caudal vertebrae with deep oval to circular pits present on both sides of the prespinal lamina; 4) anterior caudal vertebra with spino-postzygapophysiat and spino-prezygapophysiai laminae; 5) neural arch of anterior caudals with deep interzygapophysial fossae with numerous pits; 6 ) anterior caudal vertebra with an accessom sub-horizontal lamina extendine from the antero-ventral oortion of the " postzygapophysis to the mid-portion of tho spino-prezygapophysial lamina; and finally, 7) anterior caudal vertobra with a prominent axial crest on the ventral surftaee of tho cerntrum. The first rocord of sphenodonts and cf carcharodontosaurid theropods is recognized for the upper Late Cretaceous ofpatagonia, as well as the earliest record of perichthylds (Pereiformes). The vertebrate record is mainly composed of terrestrial and freshwater tawa, but a few marine elements are found (olasmosaurids) indicating a marine influence during the deposition of the Allen hrmation in the arca of Baio de Santa Rosa. The vertebrate remains s u~~o r t a Cam~anian-and extra Patagonlan South Amencan records Key words: Late Cretdecous, osteichthyans, chondnchtllyans, anurans, turtles, sphenodonts, plesiosaur^, oph~d-ians, dmosaurs, Patagonla particular those of Argentina, is opening new windows, not only for the infornlation based on new taxa, but also for the evolutionary, paleobiogeographic, biochronoiogical, and compositional aspects of the Late Cretaceous continental assemblages which populated this continent. The fossil remains recovered fkom the CampanianMaastrichtian South American formations such as Los Blanquitos iSalta Province, Argentina; e.g., Powell, 1979,20031, Lecho (Salta Province, Argentina; e.g., Bonaparte & Powell, 1980; Chiappe, 19931 . , " ince, Argentina; e.g., Bonaparte et a;., Bonaparte, 1986a Bonaparte, ,1987 Bonaparte, , 1990 Bonaparte, , 1992 Bonaparte, , 1994 Bonaparte, ,2002 Baez, 1987; Broin, 1987;Albino, 1986 Albino, , 1994Cione, 1987; Salgado et al., 1997b), Loncoche (Mendoza Province, Argentina; e.g., Wichmann, 1927; Gonaaez Riga, 1999), Allen (Rio Negro and La Pampa, Provinces, Argentina; e.g., Powell, 1987b, Gasparini & Salgado, 2000 Salgado & Aspilicueta, 2000;Coria, 2001.), L a Colonia (Chubut Province, Argentina; e.g., Ardolino & Franchi, 1996; Albino, 2000 In addition, Campanian-Masstrichtian noiiSou...
A new mammal, Henosferus molus, n.gen. and n.sp., from the Callovian-Oxfordian (latest Middle to earliest Late Jurassic) Cañadó n Asfalto Formation from Chubut Province (Argentina) is described. This taxon corresponds to a new species clearly different from Asfaltomylos patagonicus from the same locality and stratigraphic level. This new species is based on three lower jaws with relatively well-preserved dentition. The lower jaw shows a primitive morphology having a Meckelian groove, a prominent medial flange associated with a lateral ridge of the dentary, and a deep dentary trough, which possibly indicates the presence, even though reduced, of postdentary bones still attached to the dentary. The lower dental formula is i4, c1, p5, m3. The premolars are simple, bearing a main cusp, while the molars appear to be tribosphenic, with an obtuse to right-angled trigonid and a basined talonid with three cusps. This association of plesiomorphic features in the jaw and derived features in the molars is documented in several taxa of the recently proposed Australosphenida. A phylogenetic analysis of mammaliaforms nests the new species with Asfaltomylos from the same locality and stratigraphic level; Henosferidae, new family, is recognized for Asfaltomylos and Henosferus, representing the basal radiation of Australosphenida. Henosferidae is the sister group to Ambondro from the Middle Jurassic of Madagascar, which, in agreement with previous phylogenies, is the sister taxon to the remaining australosphenidans. Additionally, our phylogenetic analysis does not support
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