Osteología de peces Chondrostei de la Formación La Cantera (Cretácico Inferior), Sierra del Gigante, provincia de San Luis, Argentina

La Cantera es una de las unidades litoestratigráficas que componen el Grupo del Gigante, cuya asociación fósil fue asignada al Aptiano (110 Ma). Todo el material extraído hasta la actualidad proviene del miembro basal de esta formación lacustre que está compuesto de areniscas finas y de limolitas. Los peces más abundantes del yacimiento fueron asignados mediante estudios preliminares a la serie Chondrostei. Estos fósiles están conservados en forma bidimensional con un estado de preservación delicado, son fusiformes y pequeños (no sobrepasan los 97,5mm). Presentan aperturas bucales amplias, con los maxilares, dentarios, preoperculares, cuadrados-yugales y radios branquiostegos completos. Se observa claramente que todas las vértebras presentan los centros vertebrales sin osificar. Se identificaron las aletas pectorales, dorsal y caudal, esta última de forma heterocerca. El ejemplar MHINUNSL- V-562, tiene bien preservado el basicráneo, observándose el paraesfenoides y dos pequeños prevómeres en su extremo anterior. Se identificaron los siguientes caracteres diagnósticos que confirman su asignación a Chondrostei: apertura bucal amplia, fusión del maxilar con premaxilar, maxilar con expansión postorbitaria, preopercular largo en forma de barra, condición apospondílica de los centros vertebrales y la aleta caudal heterocerca. Análisis más detallados y mayor cantidad de ejemplares, facilitarán una clasificación más precisa dentro de este gran grupo de peces.Sesiones libresFacultad de Ciencias Naturales y Muse

A New Pterosaur (Pterodactyloidea: Azhdarchidae) from the Upper Cretaceous of Morocco

The Kem Kem beds in South Eastern Morocco contain a rich early Upper (or possibly late Lower) Cretaceous vertebrate assemblage. Fragmentary remains, predominantly teeth and jaw tips, represent several kinds of pterosaur although only one species, the ornithocheirid Coloborhynchus moroccensis, has been named. Here, we describe a new azhdarchid pterosaur, Alanqa saharica nov. gen. nov. sp., based on an almost complete well preserved mandibular symphysis from Aferdou N'Chaft. We assign additional fragmentary jaw remains, some of which have been tentatively identified as azhdarchid and pteranodontid, to this new taxon which is distinguished from other azhdarchids by a remarkably straight, elongate, lance-shaped mandibular symphysis that bears a pronounced dorsal eminence near the posterior end of its dorsal (occlusal) surface. Most remains, including the holotype, represent individuals of approximately three to four meters in wingspan, but a fragment of a large cervical vertebra, that probably also belongs to A. saharica, suggests that wingspans of six meters were achieved in this species. The Kem Kem beds have yielded the most diverse pterosaur assemblage yet reported from Africa and provide the first clear evidence for the presence of azhdarchids in Gondwana at the start of the Late Cretaceous. This, the relatively large size achieved by Alanqa, and the additional evidence of variable jaw morphology in azhdarchids provided by this taxon, indicates a longer and more complex history for this clade than previously suspected

Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guiñazui

Life-history parameters of pterosaurs such as growth and ontogenetic development represent an enigma. This aspect of pterosaur biology has remained perplexing because few pterosaur taxa are represented by complete ontogenetic series. Of these, Pterodaustro is unique in that besides being represented by hundreds of individuals with wing spans ranging from 0.3 to 2.5 m, it includes an embryo within an egg. Here we present a comprehensive osteohistological assessment of multiple skeletal elements of a range of ontogenetic sizes of Pterodaustro, and we provide unparalleled insight into its growth dynamics. We show that, upon hatching, Pterodaustro juveniles grew rapidly for approximately 2 years until they reached approximately 53% of their mature body size, whereupon they attained sexual maturity. Thereafter, growth continued for at least another 3–4 years at comparatively slower rates until larger adult body sizes were attained. Our analysis further provides definitive evidence that Pterodaustro had a determinate growth strategy

A Jurassic pterosaur from Patagonia and the origin of the pterodactyloid neurocranium

Pterosaurs are an extinct group of highly modified flying reptiles that thrived during the Mesozoic. This group has unique and remarkable skeletal adaptations to powered flight, including pneumatic bones and an elongate digit IV supporting a wing-membrane. Two major body plans have traditionally been recognized: the primitive, primarily long-tailed paraphyletic “rhamphorhynchoids” (preferably currently recognized as non-pterodactyloids) and the derived short-tailed pterodactyloids. These two groups differ considerably in their general anatomy and also exhibit a remarkably different neuroanatomy and inferred head posture, which has been linked to different lifestyles and behaviours and improved flying capabilities in these reptiles. Pterosaur neuroanatomy, is known from just a few three-dimensionally preserved braincases of non-pterodactyloids (as Rhamphorhynchidae) and pterodactyloids, between which there is a large morphological gap. Here we report on a new Jurassic pterosaur from Argentina, Allkaruen koi gen. et sp. nov., remains of which include a superbly preserved, uncrushed braincase that sheds light on the origins of the highly derived neuroanatomy of pterodactyloids and their close relatives. A µCT ray-generated virtual endocast shows that the new pterosaur exhibits a mosaic of plesiomorphic and derived traits of the inner ear and neuroanatomy that fills an important gap between those of non-monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids. These results suggest that, while modularity may play an important role at one anatomical level, at a finer level the evolution of structures within a module may follow a mosaic pattern