A new “silesaurid” from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs

Highlights

• One of the oldest dinosauromorphs is described.

• It is the earliest “silesaurid” with a sacrum composed of three vertebrae.

• The oldest episode of sympatry among “silesaurids” in South America is reported.

Conclusions

Gondwanax paraisensis was a bird-line archosaur that shared affinities with typical “silesaurids”. It comes from the oldest dinosauromorph-bearing beds of South America (i.e., Ladinian-Carnian boundary), comprising one of the oldest “silesaurids” worldwide (Fig. 7). The material preserves elements that are scarce among “silesaurids”, such as the sacrum. This structure is particularly interesting for Gondwanax paraisensis, which is composed of three vertebrae.