Cretaceous Argentina 273 South America 136 Neuquen Basin 116 Patagonia 109 taxonomy 78 Andes 72 biostratigraphy 70 paleoenvironment 52 fossil record 51 ammonite 49 Ammonoidea 44 Bivalvia 42 Antarctica 41 geochronology 40 new species 40 morphology 38 Lower Cretaceous 36 paleomagnetism 36 foreland basin 35 paleoecology 34 Early Cretaceous 33 Jurassic 33 fold and thrust belt 33 bivalve 31 tectonic evolution 31 Neuquén Basin 28 fossil 28 uplift 28 uranium-lead dating 28