The osteology of the holotype of the early erythrosuchid Garjainia prima Ochev, 1958 (Diapsida: Archosauromorpha) from the upper Lower Triassic of European Russia

Erythrosuchids are Early-Middle Triassic bulky, quadrupedal archosauromorphs with proportionally large heads, and they were among the first archosauromorphs to occupy the role of terrestrial hypercarnivores. Recent work has expanded anatomical and phylogenetic knowledge of erythrosuchids, but a thorough understanding is still lacking, and Erythrosuchus africanus is the only species for which a thorough anatomical description of most of the skeleton has been published. Garjainia prima, from the upper Olenekian of Russia, represents one of the oldest known erythrosuchids and includes the best-preserved skull of an Early Triassic erythrosuchid. Here, we expand understanding of erythrosuchid anatomy by providing the first detailed and comprehensive description of the holotype of Garjainia prima. We consider 'Vjushkovia triplicostata' to be a junior synonym of Garjainia prima, because of their extremely similar morphology, with the two character states that differ between them being variable intraspecifically in some other diapsids. A new phylogenetic analysis recovered a monophyletic Garjainia as sister to Middle Triassic erythrosuchids and recovered Fugusuchus hejiapanensis as sister to all other erythrosuchids. Branch support for Erythrosuchidae is low, but the Middle Triassic erythrosuchid clade is well supported by characters with low homoplasy, indicating that their morphology was specialized in ways rarely explored by other Triassic archosauromorphs.