Gondwanax paraisensis Müller, 2024 (new genus and species)
(Type femur [thigh bone] of Gondwanax paraisensis, from Müller, 2024)
Meaning of name: Gondwanax = Gondwana king [in Greek]; paraisensis = from Paraíso do Sul
Age: Middle–Late Triassic (Ladinian–Carnian)
Where found: Santa Maria Formation, Rio Grande do Sul, Brazil
How much is known: A right femur (thigh bone), along with several vertebrae and a partial pelvis from the same site. It is unknown whether the other bones belonged to the same individual as the femur.
Notes: Gondwanax was a silesaurid, a group of probably quadrupedal Triassic reptiles that often had adaptations for herbivory (though there is evidence that they also ate insects). Until recently, silesaurids were generally considered to be close relatives of dinosaurs instead of dinosaurs themselves, and I previously excluded them from coverage on this blog. However, multiple recent analyses have suggested that they might in fact be true dinosaurs, specifically early members of Ornithischia ("bird-hipped" dinosaurs), so from here on out I will tentatively include them within this blog's purview. In fact, some of those studies have found that most "silesaurids" may not have formed a unique evolutionary group, but instead a series of lineages with some being more closely related to later ornithischians than others.
Regardless of whether it is a true dinosaur, Gondwanax is one of the oldest known dinosauromorphs (the group containing dinosaurs and their closest relatives). Compared to other dinosauromorphs of similar age, Gondwanax more closely resembles later dinosaurs in having three hip vertebrae (whereas dinosaurs ancestrally appear to have had only two). It is unusual among dinosauromorphs in having a very small fourth trochanter, a attachment point on the femur for muscles that pull the hindlimb backward.
(Schematic skeletal of Gondwanax paraisensis, with preserved bones in orange, from Müller, 2024)
Reference: Müller, R.T. 2024. A new "silesaurid" from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs. Gondwana Research advance online publication. doi: 10.1016/j.gr.2024.09.007
