Laura Codorniú

Palaeobiological Implications of the Bone Histology of Pterodaustro guinazui

This study provides a comprehensive investigation of the bone microstructure of multiple bones of the Early Cretaceous filter‐feeder, Pterodaustro guinazui, from the Largacito Formation of Central Argentina. We provide information regarding the bone histology of multiple elements from single skeletons, as well as a variety of bones from different individuals. In addition, we analysed changes in bone microstructure through ontogeny in growth series of several long bones of the taxon. Our investigation of skeletal and ontogenetic variation in Pterodaustro gives insights into the developmental growth dynamics of this unusual ctenochasmatid pterodactyloid from early ontogeny through to adulthood and also provides information pertaining to histological variability within and between bones of individuals. This study also documents the presence of what appears to be medullary bone tissue within the medullary cavity of a large femur of Pterodaustro. This suggests that, like birds, reproductively active female pterosaurs may have deposited a special bone tissue (medullary bone) to cope with the demand of calcium during eggshelling. Our study supports the hypothesis that small Jurassic pterodactyloids took several years to reach adult body size. More specifically, we provide data that suggests that Pterodaustro attained sexual maturity at about 2 years of age, and continued to grow for a further 3–4 years doubling in size before attaining skeletal maturity. Anat Rec, 292:1462–1477, 2009.

Semionotids (Neopterygii, Semionotiformes) from the Lower Cretaceous Lagarcito Formation, San Luis Province, Argentina

Abstract A revision of the semionotids from the Lower Cretaceous Lagarcito Formation of Argentina leads to the conclusion that only one taxon, Neosemionotus puntanus Bocchino, 1973, is represented, instead of two monospecific genera and one species of Lepidotes as originally thought. Neosemionotus shares with Lepidotes the presence of more than one suborbital arranged in one row and a long posteroventral process of the dentary, features that have previously been thought to be diagnostic of Lepidotes. On the other hand, it shares with Semionotus the presence of conspicuous dorsal ridge scales. However, Neosemionotus is unique in the characteristics of its dorsal and anal fins, which are both flanked only by high and strong paired basal fulcra. These fulcra become gradually higher/deeper posteriorly, reaching approximately the height/depth of the first fin ray. Other probable synapomorphies of Neosemionotus are the presence of a long parietal pit line, a small, approximately triangular interoperculum, the complete absence of fringing fulcra on the dorsal, and anal fins, and the presence of only very few long and slender fringing fulcra on the pelvic and caudal fins. The systematic position of Neosemionotus is still unknown, but the presence of probably primitive features like the high number of extrascapulars, short parietals, the arrangement of suborbitals, and short snout indicate a relatively basal position among semionotids.

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.

First occurrence of stomach stones in pterosaurs

ABSTRACT Two nearly complete skeletons of the filter-feeding pterodactyloid Pterodaustro guinazui from the Lower Cretaceous of Argentina exhibit clusters of poorly sorted coarse sand to fine gravel inside the abdominal cavity. These stones are interpreted as ingested gastroliths (geogastroliths), which are commonly found in a variety of archosaurs (including birds) but have never before been reported in a pterosaur. The geogastroliths found in these Pterodaustro specimens are interpreted as having assisted in the digestion of hard food items such as ‘shelled’ crustaceans that are abundant in the fossil beds of this pterosaur. One of these specimens with geogastroliths has anterior mandibular teeth that are notably thicker than the posterior teeth and are somewhat procumbent. We suggest that these teeth might have facilitated the apprehension of fine gravel.

Reptiles from Lithographic Limestones of the Los Catutos Member (Middle—Upper Tithonian), Neuquén Province, Argentina: An Essay on Its Taxonomic Composition and Preservation in an Environmental and Geographic Context

Abstract. The lithographic limestones of the Los Catutos Member (Vaca Muerta Formation, Neuquén Province, Argentina) (late middle—early late Tithonian) bear a great diversity of marine reptiles. These deposits are unique In the Southern Hemisphere as the record of lithographic limestones from the Upper Jurassic is restricted to the Northern Hemisphere, particularly to Western Europe. Some European basins are very close In age (late Kimmeridgian—early Tithonian) but they do not reach the middle—late Tithonian. Additionally, In the European basins the marine reptiles are mixed with continental biota whereas In Los Catutos Member the biota is exclusively marine, with the pterosaurs being the only exception. The strictly marine biota is composed by ichthyosaurs, two different species of turtles, one crocodyliform, and one plesiosaur. The taxonomic composition of Los Catutos Member is very similar to that found in Cerro Lotena (Portada Covunco Member, middle Tithonian) (Vaca Muerta Formation). These members share the same turtle species and one metriorhynchid genus, while ichthyosaurs only coincide at a family level. The study of marine reptiles from the Los Catutos Member, along with studies from other localities of the Neuquén Basin, have made an important contribution In filling the gaps In the evolutionary history of each of the represented clades. In this regard, they represent the only known marine reptiles from Gondwana throughout the Jurassic/Cretaceous transition, which Is poorly represented in other regions of the world.

Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina

ABSTRACT The braincase anatomy of pterosaurs is poorly known because this region of the skull is rarely preserved, particularly in basal pterodactyloid pterosaurs (Archaeopterodactyloidea). We present new information on the braincase morphology of the Early Cretaceous Argentinean ctenochasmatid Pterodaustro guinazui. Morphological information collected from several specimens permits the description of many features of this area of the skull for the first time. The braincase of Pterodaustro is characterized by a skull roof with subtriangular, elongated frontals and rounded, posteroventrally oriented parietals; low nuchal crest; ossified ethmoidal elements; ossified interorbital septum; short and fan-shaped paroccipital processes with undulating lateral and medial surfaces; occipital condyle formed mainly by the exoccipitals; forkshaped basioccipital; long, anteroventrally directed basisphenoid body with keeled ventral surface and short basipterygoid processes; well-developed rostral tympanic recess; rod-like columella; and separate foramina for cranial nerves XII and IX-XI within a common subdivided recess. We were able to identify foramina for cranial nerves II, V, VI, and VII; vascular foramina, such as the caudal middle cerebral vein, the dorsal head vein, and the internal carotid artery; and the columellar recess. This research reveals many features of the braincase of Pterodaustro—some of which are considered potential autapomorphies—for the first time. It also provides new insights into the neurocranial anatomy of pterosaurs, and in turn, contributes to the understanding of the evolution of the braincase in Pterosauria.