Introducing Guemesia ochoai

Right lateral view of the braincase of Guemesia ochoai. Scale bar: 5 cm. From Agnolín et al, 2022.

Abelisauroidea is the best known carnivorous dinosaur group from Gondwana. The clade was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes, and strongly reduced forelimbs. Abelisauroidea has been divided into two main branches: the Noasauridae and the Abelisauridae. The Noasauridae are known from Cretaceous beds in northern Argentina, Madagascar, India, and Niger. They are small and slender with sizes that range from 1 to 3 metres in length. The Abelisaurids are medium to large, robust animals, such as the Carnotaurus and the Majungasaurus of Madagascar. The group exhibits short, round snouts; thickened teeth; short, stocky arms; and highly reduced forearms. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic with Eoabelisaurus mefi, and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi, Viavenator exxoni, Niebla antiqua, and Llukalkan aliocranianus. All of them are from the Cretaceous of Patagonia.

Map indicating the locality that yielded Guemesia ochoai. From Agnolín et al, 2022.

Guemesia ochoai is the first definitive abelisaurid theropod from Northwestern Argentina. The holotype (IBIGEO-P 103) is represented by a nearly complete braincase, with parietals, frontals, supraoccipital, basioccipital, exoccipital-opisthotic complex, basisphenoid-parasphenoid, prootics, laterosphenoids, and orbito-sphenoids. It was recovered from Los Blanquitos Formation (Campanian, Late Cretaceous), near Amblayo town, Salta province, Argentina. The name honours General Martin Miguel de Güemes who defended northwestern Argentina during the War of Independence, and Javier Ochoa, technician of the Museo Regional “Florentino Ameghino,” who discovered the specimen. The braincase of Guemesia is small compared to other abelisaurids. Unfortunately, the absence of postcranial elements makes impossible to perform histological analysis and to corroborate if the specimen reached somatic maturity. The cranial endocast has a total length of 73 mm from the base of the olfactory tract to the foramen magnum, and the volume is ∼47.6 cm³ (almost 70% smaller than the cranial endocasts of Carnotaurus and Viavenator). But the most striking feature of Guemesia is a row of foramina close to the midline of the fused frontals that is unknown in other abelisaurids. These rows may be linked to a zone of thermal exchange.

References:

Federico L. Agnolín et al, First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina, Journal of Vertebrate Paleontology (2022). DOI: 10.1080/02724634.2021.2002348

Meet Dearc sgiathanach

 

Dearc sgiathanach. Scale bars: 30 mm. Adapted from From Jagielska et al., 2022.

Pterosaurs were the first vertebrates to evolve powerful flight. Their reign extended to every continent and achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. The oldest-known pterosaurs appear in the fossil record about 219 million years ago. Most Triassic and Jurassic pterosaurs are small but already had a highly specialized body plan linked to their ability to fly: shoulder girdle with strongly posteroventrally enlarged coracoid braced with the sternum and laterally facing glenoid fossa; forelimb with pteroid bone and hypertrophied fourth digit supporting a membranous wing; and pelvic girdle with prepubic bone and strongly developed preacetabular process. Pterosaurs have traditionally been divided into two major groups, “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail. Dearc sgiathanach, a newly described rhamphorhynchine pterosaur from the Isle of Skye, Scotland, is the largest known Jurassic pterosaur.

Postcranial skeleton and dentition of Dearc sgiathanach. From Jagielska et al., 2022

Discovered in 2017 by Amelia Penny, the holotype (NMS G.2021.6.1-4), a well preserved, articulated, skeleton, was found at Rubha nam Brathairean (Brothers’ Point), Isle of Skye, in north-west Scotland, in the Lonfearn Member of the Lealt Shale Formation (Bathonian, Middle Jurassic). The specimen is almost complete with the exception of the anterior and dorsal portions of the cranium, the end of the tail, hindlimbs elements, and parts of the wings. The name comes from the Scottish Gaelic language and has a double meaning: “winged reptile” and “reptile from Skye.”

Dearc sgiathanach includes the following autopomorphies: vomers with “trident-shaped” precapillary contact, a pre-choana depression on the palatal surface of the maxilla, and enlarged optic lobes. Bone histology indicates that the specimen belong to a juvenile individual. Based on the proportions of humerus length and skull length of Rhamphorhynchus and Dorygnathus, the research team lead by Natalia Jagielska, estimated the wingspan of Dearc sgiathanach at >2.5 m. Phylogenetic analysys places Dearc sgiathanach within the clade Angustinaripterini. The new specimen suggests that many “pterodactyloid” features convergently evolved in other groups, and hightlights that the Middle Jurassic was a time of increasing diversification in pterosaur history.

References:

JAGIELSKA, Natalia, et al. A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs. Current Biology, 2022. DOI: 10.1016/j.cub.2022.01.073

Introducing Abditosaurus kuehnei, the ‘forgotten reptile’

Abditosaurus kuehnei. Image credit: Oscar Sanisidro / Museu de la Conca Dellà

Towards the end of the Cretaceous, France, Spain and Portugal formed the Ibero-Armorican Island. This region holds one the most complete sauropod dinosaur communities and provides clues to understand the events that differentiate the Ibero-Armorican vertebrate assemblages from those of other European islands. The recently described Abditosaurus kuehnei from the Late Cretaceous of Catalonia is the most complete titanosaur skeleton discovered in Europe so far. The new taxon support the migration hypothesis and shed new light on the palaeobiogeographic events between the European archipelago and Godwana. 

Abditosaurus reached 17,5 meters in length (57 ft) with a body mass of 14,000 kg. The holotype, an associated, semi-articulated, partial skeleton, includes several isolated teeth, 12 cervical vertebrae, 7 dorsal vertebrae, 3 chevrons, scapular and pelvic bones, right tibia, parts of the femurs and a complete humerus. The new specimen exhibits an unusual combination of characters not seen in other Ibero–Armorican titanosaurs, like a very robust humerus with a distally expanded deltopectoral crest, a synapomorphy of Saltasauridae. The generic name is derived from the Latin word ‘Abditus’ (means forgotten), and the Greek word “sauros” (lizard). The specific name ‘kuehnei’ honours Professor Walter Georg Kühne who discovered the specimen.

Fossil elements of Abditosaurus kuehnei collected during the 2012-2014 excavations. Image credit: Rubén Contreras. From Vila et al., 2022.

Phylogenetic analyses indicates that Abditosaurus is a saltasaurid lithostrotian titanosaur. Saltasaurinae, a clade from South America and Africa, includes Neuquensaurus, Saltasaurus and Paralititan. The arrival of Abditosaurus to Europe via a dispersal event from Africa ocurred after a regressive event during the Early Maastrichtian(70.6 Ma) that affected the central Tethyan margin and northern Africa.

The history of Abditosaurus began in 1954. Walter Kühne, one of the most renowned specialists on fossil mammals in Europe, found the bones near Orcau (Tremp Basin, Catalonia, Spain), and sent to the Instituto Lucas Mallada in Madrid. In 1955, Kühne revisited the site and collected ten more bones. Unfortunately, the site fall out in oblivion until 1986. when a team led by Josep Vicenç Santafé from the Institut de Paleontologia de Sabadell (Barcelona) found part of a sternal plate and three dorsal ribs. Between 2012 to 2014, a team from the Institut Català de Paleontologia, the Universidad de Zaragoza, and the Museu de la Conca Dellà re-excavated the locality and recovered the remaining axial and appendicular elements. Finally, after 6 decades, the sauropod discovered by Kühne was completely collected in 2014.

References:

Vila, B., Sellés, A.G., Moreno-Azanza, M., Razzolini, N.L., Gil-Delgado, A., Canudo, J.I., Galobart, À. Nature Ecology & Evolution (2022). DOI: 10.1038/s41559-021-01651-5.

Fondevilla, Victor, et al. Chronostratigraphic synthesis of the latest Cretaceous dinosaur turnover in south-western Europe. Earth-Science Reviews (2019) https://doi.org/10.1016/j.earscirev.2019.01.007