3D reconstruction of Koleken inakayali. Image credit: Gabriel Díaz Yantén.
Abelisauroidea is the best known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and some incomplete abelisaurid specimens were also discovered in France, adding evidence to the biogeographical link between southern Europe and Gondwana. The group was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These ceratosaurian theropods exhibit spectacular cranial ornamentation in the form of horns and spikes, short cervical vertebrae, and strongly reduced forelimbs and hands. They also display stout hindlimbs with a robust and short femur.
Traditionally 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. Recent phylogenetic analyses indicate that there are two principal clades within Abelisauridae, ‘majungasaurines’ and brachyrostrans. The later includes mostly South American abelisaurids, such as Carnotaurus and Skorpiovenator. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous, from Cenomanian (Ilokelesia, Xenotarsosaurus, and Ekrixinatosaurus) to Campanian–Maastrichtian (Abelisaurus, Carnotaurus, Aucasaurus, and Noasaurus). A new specimen, Koleken inakayali, from the La Colonia Formation (Maastrichtian, Upper Cretaceous) of Patagonia, expands our knowledge about the dinosaur fauna of the late Cretaceous period.
Fossil remains of Koleken inakayali. Photo: Amalia Villafañe. CONICET
The holotype (MPEF-PV 10826), consisting of cranial, axial and appendicular elements, including an almost complete pelvis and hind limbs, was discovered in 2015 at the Cerro Bayo Norte, east of the Sierra de La Colonia, centre north of Chubut Province, Argentina. The age of this unit has been restricted to the early Maastrichtian. The generic name is derived from the Teushen language (spoken by the native population of central Patagonia) meaning “coming from clay and water”, given the nature of the section where the specimen was found, dominated by claystone representing an estuarine environment. The specific name, inakayali, honors Inakayal, one of the last chiefs of Tehuelches, native people from central Patagonia.
The unique set of characters that distinguish Koleken inakayali from other theropods includes medially smooth paradental plates, dorsal surface of the nasal with a row of foramina orientated obliquely with respect to the longitudinal skull axis; parietal with a mediolaterally concave dorsal surface and lacking a knob-like dorsal projection. Histological and osteological evidence estimate a minimum age of 6 years for the specimen. Phylogenetic analysis indicates that Koleken is clearly nested within furileusaurian abelisaurids. This clade diversified after a major faunal turnover among South American dinosaurs around the Cenomanian–Turonian boundary.
Phylogenetic relationships of Koleken inakayali according to parsimony analysis. From Pol et al., 2024
The team behind the discovery of Koleken, led by Diego Pol, found that abelisaurids and noasasaurids began to rapidly evolve into different body plans between the late Jurassic and early Cretaceous. Different analyses indicates that noasaurids were primarily characterized by early high rates of evolution in the axial and hind limb skeleton, whereas abelisaurids show high rates of evolution in the cranial characters.
References:
Pol, D., Baiano, M.A., Černý, D., Novas, F.E., Cerda, I.A. and Pittman, M. (2024), A new abelisaurid dinosaur from the end Cretaceous of Patagonia and evolutionary rates among the Ceratosauria. Cladistics. https://doi.org/10.1111/cla.12583
, , , and , 2013. Evolution of the carnivorous dinosaurs during the Cretaceous: the evidence from Patagonia. Cretac. Res. 45, 174–215.
Letters from Gondwana. 