Lourinhã Formation Research Articles

Multiproxy approach reveals evidence of highly variable paleoprecipitation in the Upper Jurassic Morrison Formation (western United States)

Elemental analyses of paleosol B horizons in the Upper Jurassic Morrison Formation of the western United States provide estimates of mean annual precipitation (MAP) and allow determination of humidity regimes. Samples were collected from the lower Morrison Formation in New Mexico and the upper Morrison Formation in Wyoming and Montana. The chemical index of alteration minus potassium (CIA – K) and the calcium and magnesium weathering index (CALMAG) were used to estimate paleorainfall. CIA – K values calculated for paleosols without shrink-swell (vertic) features correspond to MAP estimates between 800 and 1100 mm yr –1 , with an average of 1000 mm yr –1 . CALMAG values, calculated for vertic paleosols, correspond to MAP estimates between 50 and 1200 mm yr –1 , with an average of 700 mm yr –1 . MAP estimates from the older New Mexico strata indicate that early Morrison environments were relatively arid. MAP estimates from the younger Wyoming and Montana deposits reflect wetter conditions in the northernmost part of the Morrison Formation, but the transition from arid interior environments was abrupt. Humidity provinces inferred from geochemical proxy-based estimates of evapotranspiration and energy influx from precipitation range from semiarid to superhumid, suggesting wetter conditions than the MAP estimates, but supporting the relative differences in moisture among the three study areas. Paleoprecipitation patterns within the Morrison depositional basin do not match the modern latitudinal distribution of rainfall that arises from zonal atmospheric circulation. Comparison with the Upper Jurassic Lourinha Formation in Portugal and the Vega Formation in Spain reveals that MAP in Late Jurassic Portuguese environments was similar to that in the wet northern part of the Morrison Formation, although more arid conditions prevailed in some areas of Portugal. Inferred humidity regimes for the Lourinha Formation, which range from semiarid to superhumid, also indicate small-scale geographic variability in climate, although less pronounced than that observed in the Morrison Formation. Paleoenvironments in northern Spain were similar to the drier Morrison environments in the continental interior. Given the abrupt climatic transitions inferred here for the Morrison Formation, paleoprecipitation estimates derived from a geographically restricted sample may reflect only local conditions and should not necessarily be extrapolated to larger areas.

Osteology of the Late Jurassic Portuguese sauropod dinosaurLusotitan atalaiensis(Macronaria) and the evolutionary history of basal titanosauriforms

Titanosauriforms represent a diverse and globally distributed clade of neosauropod dinosaurs, but their inter-relationships remain poorly understood. Here we redescribe Lusotitan atalaiensis from the Late Jurassic Lourinha Formation of Portugal, a taxon previously referred to Brachiosaurus. The lectotype includes cervical, dorsal, and caudal vertebrae, and elements from the forelimb, hindlimb, and pelvic girdle. Lusotitan is a valid taxon and can be diagnosed by six autapomorphies, including the presence of elongate postzygapophyses that project well beyond the posterior margin of the neural arch in anterior-to-middle caudal vertebrae. A new phylogenetic analysis, focused on elucidating the evolutionary relationships of basal titanosauriforms, is presented, comprising 63 taxa scored for 279 characters. Many of these characters are heavily revised or novel to our study, and a number of ingroup taxa have never previously been incorporated into a phylogenetic analysis. We treated quantitative characters as discrete and continuous data in two parallel analyses, and explored the effect of implied weighting. Although we recovered monophyletic brachiosaurid and somphospondylan sister clades within Titanosauriformes, their compositions were affected by alternative treatments of quantitative data and, especially, by the weighting of such data. This suggests that the treatment of quantitative data is important and the wrong decisions might lead to incorrect tree topologies. In particular, the diversity of Titanosauria was greatly increased by the use of implied weights. Our results support the generic separation of the contemporaneous taxa Brachiosaurus, Giraffatitan, and Lusotitan, with the latter recovered as either a brachiosaurid or the sister taxon to Titanosauriformes. Although Janenschia was recovered as a basal macronarian, outside Titanosauria, the sympatric Australodocus provides body fossil evidence for the pre-Cretaceous origin of titanosaurs. We recovered evidence for a sauropod with close affinities to the Chinese taxon Mamenchisaurus in the Late Jurassic Tendaguru beds of Africa, and present new information demonstrating the wider distribution of caudal pneumaticity within Titanosauria. The earliest known titanosauriform body fossils are from the late Oxfordian (Late Jurassic), although trackway evidence indicates a Middle Jurassic origin. Diversity increased throughout the Late Jurassic, and titanosauriforms did not undergo a severe extinction across the Jurassic/Cretaceous boundary, in contrast to diplodocids and non-neosauropods. Titanosauriform diversity increased in the Barremian and Aptian–Albian as a result of radiations of derived somphospondylans and lithostrotians, respectively, but there was a severe drop (up to 40%) in species numbers at, or near, the Albian/Cenomanian boundary, representing a faunal turnover whereby basal titanosauriforms were replaced by derived titanosaurs, although this transition occurred in a spatiotemporally staggered fashion. © 2013 The Linnean Society of London

A diverse Upper Jurassic dinosaur ichnofauna from central-west Portugal

Mateus, O. & Milan, J. 2009: A diverse Upper Jurassic dinosaur ichnofauna from central-west Portugal. Lethaia, Vol. 43, pp. 245–257. A newly discovered dinosaur track-assemblage from the Upper Jurassic Lourinha Formation (Lusitanian Basin, central-west Portugal), comprises medium- to large-sized sauropod tracks with well-preserved impressions of soft tissue anatomy, stegosaur tracks and tracks from medium- to large-sized theropods. The 400-m-thick Lourinha Formation consists of mostly aluvial sediments, deposited during the early rifting of the Atlantic Ocean in the Kimmeridgian and Tithonian. The stratigraphic succession shows several shifts between flood-plain mud and fluvial sands that favour preservation and fossilization of tracks. The studied track-assemblage is found preserved as natural casts on the underside of a thin bivalve-rich carbonate bed near the Tithonian–Kimmeridgian boundary. The diversity of the tracks from the new track assemblage is compared with similar faunas from the Upper Jurassic of Asturias, Spain and the Middle Jurassic Yorkshire Coast of England. The Portuguese record of Upper Jurassic dinosaur body fossils show close similarity to the track fauna from the Lourinha Formation. □Dinosaur tracks, Lusitanian Basin, Portugal, skin impressions, Upper Jurassic.