Lucio Manuel Ibiricu

From the Jurassic to the Cretaceous, most medium- to large-bodied non-avian theropods evolved towards predominantly head-driven predatory strategies. Megaraptorid dinosaurs represent a striking exception, retaining well-developed forelimbs and hypertrophied manual unguals hypothesized as a key adaptation within the clade. However, the macroevolutionary processes underlying the mode and tempo of megaraptorid claw evolution remain poorly understood. Here, we investigate the macroevolutionary trends of the megaraptorid manual claw by quantifying the shape and size of 22 manual phalanx I-2 (= manual ungual I) across different lineages of medium- to large-bodied non-avian theropods, using 2D geometric morphometric and phylogenetic comparative methods. Our results indicate that manual claw shape and size were evolutionarily coupled in Megaraptoridae, supporting a major reconfiguration of allometric trajectories during the evolution of the clade. This evolutionary coupling triggered directional shape modifications towards a distinct adaptive optimum associated with enlarged manual claws. This adaptation emerged following an early phase of rapid morphological divergence near the middle Early Cretaceous boundary and was subsequently maintained, likely under stabilizing selection throughout the Late Cretaceous, resulting in a canalized claw morphology. We further show that medium- to large-bodied non-avian theropods with well-developed forelimbs exhibit strong phylogenetic integration between distal and proximal forelimb elements. Despite this integration, the phalanx-I-2 and ulna–radius complex evolved at substantially higher evolutionary rates than the humerus. These results highlight Megaraptoridae as the only large-bodied carnivorous theropod lineage retaining a specialized forelimb-based predatory strategy until the end of the Cretaceous, with no evidence of overall claw shape convergence.

Recent fossil discoveries have cast considerable light on the palaeobiology of Megaraptora, a group of large-clawed carnivorous theropod dinosaurs known from Cretaceous deposits in Asia, Australia, and especially South America. Nevertheless, many important aspects of megaraptoran morphology and evolution remain poorly understood, due in large part to the fragmentary nature of most fossils of these theropods and the scarcity of anatomically overlapping skeletal elements among the known taxa. Here we report a previously unknown megaraptoran genus and species represented by a partially articulated partial skeleton recovered from an uppermost Cretaceous stratum of the Lago Colhué Huapi Formation of south-central Chubut Province in central Patagonia, Argentina. Pertaining to the derived megaraptoran subclade Megaraptoridae, the taxon is among the most completely represented and latest-surviving megaraptorans. Its stratigraphic occurrence indicates that these dinosaurs likely persisted to the Cretaceous/Palaeogene boundary; moreover, the preservation of a crocodyliform humerus between the dentaries of the new theropod may provide information on megaraptoran dietary preferences and feeding strategies. Megaraptorids appear to have been the apex predators in central and southern Patagonian palaeoecosystems approaching the end of the Cretaceous, in contrast to more northerly areas of South America where these niches were occupied by other non-avian theropod groups.

En el centro-sur de la Provincia de Chubut se exponen excelentes afloramientos de rocas sedimentarias de edad cretácica que conforman el principal relleno de la cuenca del Golfo San Jorge. Dentro de esta cuenca se destacan por su abundancia de vertebrados fósiles, la Formación Bajo Barreal (Cenomaniano temprano–Turoniano tardío) y la Formación Lago Colhué Huapi (Coniaciano–Maastrichtiano). Aunque el registro está mayormente dominado por dinosaurios saurisquios, hallazgos de fósiles de ornitisquios, específicamente ornitópodos, se han incrementado en los últimos años. En esta contribución se pretende ampliar el conocimiento de los ornitópodos basales Notohypsilophodon comodorensis y Sektensaurus sanjuanboscoi provenientes de las formaciones Bajo Barreal y Lago Colhué Huapi, respectivamente. También, por primera vez, se abordan y se describen aspectos sobre la paleohistología de ambos ornitópodos. Asimismo, con las evidencias que se cuentan al momento y a la espera de nuevos estudios que resuelvan mejor las relaciones sistemáticas en la base de Ornithopoda, se sugiere que los elasmarios se habrían originado en el este de Gondwana, probablemente durante el Cretácico temprano, y posteriormente se habrían dispersado al oeste de dicho supercontinente, donde alcanzaron tamaños corporales mayores. Por último, al menos en Patagonia central, se observa una selección del ambiente entre los ornitópodos basales (elasmarios) y los derivados (hadrosáuridos). Los primeros se habrían desarrollado en ambientes tierra adentro con climas con cierta estacionalidad, mientras que los hadrosáuridos habrían seleccionado ambientes cercanos al mar y con un clima más homogéneo.

We describe for the first time in the Lago Colhué Huapi Formation (Coniacian–Maastricthian), south Central Patagonia, Argentina, continental bioerosion traces on dinosaur remains. Specifically, six different morphotypes, showing also different morphologic patterns, were identified. The preliminary identification of the trace makers include: crocodyliform, possibly a peirosaurid notosuchian (morphotypes A and B), a theropod dinosaur (morphotype C), and the activity of arthropod pupation (morphotype D), and insects such as termites and dermestids (morphotypes E and F). This study increases our knowledge about the biodiversity registered to the moment in the Lago Colhué Huapi Formation and specifically for the “middle section” of this formation, probably Santonian–early Maastrichtian in age. These bioerosion traces support a warm climate with periods of semi-aridity or at least drier conditions as it was proposed for this interval of time in this section of the formation. Keywords: bone modification, ichnofossils, Late Cretaceous.

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The presence of stromatolites from Cretaceous outcrops at the headwaters of the río Chico locality in the Golfo San Jorge Basin is reported for the first time. They are present in the uppermost part of the Lago Colhué Huapi Formation (Coniacian-Maastrichtian) of the Chubut Group. The presence of, up to now, four structures interpreted as stromatolites in this locality are not only important because it is the first record in the basin, but because it contributes to the knowledge of these bioconstructions in continental environments. The stromatolite called E1, which is characterized and discussed in detail, is associated with an abundant and diverse fossil record represented by palynomorphs, fragments of silicified trunks, dinosaur remains and eggshells. The study, integrated mainly with the recorded pollen and spores, is important for paleoenvironmental interpretations of the site and contributes to the paleoecological and paleoclimatic understanding of the most modern stratigraphic interval of the Chubut Group.

Peirosaurid crocodyliforms were diverse and abundant in the Cretaceous of the Gondwanan landmasses, especially South America. Here, we describe Colhuehuapisuchus lunai, gen. et sp. nov., a new peirosaurid taxon from the Upper Cretaceous (Campanian–?lower Maastrichtian) Lago Colhué Huapi Formation of southern Chubut Province in central Patagonia, Argentina. Although represented by only the anterior ∼one-third of the mandible with several complete, in situ teeth, the new taxon exhibits a combination of distinctive morphologies that does not occur in other peirosaurids, including several mandibular and dental autapomorphies. The symphyseal region of the Colhuehuapisuchus mandible is transversely wider than that of any other representative of Peirosauridae, and as such the new form may be most closely related to other broad-snouted peirosaurids such as Barrosasuchus neuquenianus, Gasparinisuchus peirosauroides, and Patagosuchus anielensis. The exceptional diversity of snout and tooth shapes among definitive and probable members of Peirosauridae suggests the existence of a variety of ecological and dietary preferences within the clade. Colhuehuapisuchus constitutes the southernmost peirosaurid occurrence worldwide and arguably the youngest record from Patagonia, thereby expanding the paleobiogeographic range of these distinctive mesoeucrocodylians to nearly the end of the Mesozoic and the southern tip of South America.

Is a basal titanosaur from the early Late Cretaceous of central Patagonia, Argentina. Here, we present the reconstruction of the pelvic and hindlimb musculature of this titanosaur, based on the sof...

In dinosaurs and other archosaurs, the presence of foramina connected with internal chambers in axial and appendicular bones is regarded as a robust indicator of postcranial skeletal pneumaticity (PSP). Here we analyze PSP and its paleobiological implications in rebbachisaurid diplodocoid sauropod dinosaurs based primarily on the dorsal vertebrae of Katepensaurus goicoecheai, a rebbachisaurid from the Cenomanian–Turonian (Upper Cretaceous) Bajo Barreal Formation of Patagonia, Argentina. We document a complex of interconnected pneumatic foramina and internal chambers within the dorsal vertebral transverse processes of Katepensaurus. Collectively, these structures constitute a form of PSP that has not previously been observed in sauropods, though it is closely comparable to morphologies seen in selected birds and non-avian theropods. Parts of the skeletons of Katepensaurus and other rebbachisaurid taxa such as Amazonsaurus maranhensis and Tataouinea hannibalis exhibit an elevated degree of pneumaticity relative to the conditions in many other sauropods. We interpret this extensive PSP as an adaptation for lowering the density of the skeleton, and tentatively propose that this reduced skeletal density may also have decreased the muscle energy required to move the body and the heat generated in so doing. Given that several rebbachisaurids inhabited tropical to subtropical paleolatitudes during the extreme warmth of the mid-Cretaceous, increased PSP may have better enabled these sauropods to cope with extraordinarily high temperatures. Extensive skeletal pneumaticity may have been an important innovation in Rebbachisauridae, and perhaps also in saltasaurine titanosaurs, which evolved an even greater degree of PSP. This may in turn have contributed to the evolutionary success of rebbachisaurids, which were the only diplodocoids to survive into the Late Cretaceous