Previously, the formation had been believed to be Early to Middle Jurassic in age, although the earlier discovery of the rhynchosaur Isalorhynchus had revised that estimate to the Middle Triassic. The tetrapod fossils recovered in the 1997–99 expedition confirmed the Isalo II was Triassic in age, but instead suggested a younger Carnian age. The age of the formation has also been correlated to the Santacruzodon Assemblage Zone (AZ) from the Santa Maria Formation in South America based on the shared genera of traversodontid cynodonts, with a similar late Ladinian or early Carnian age. The Santacruzodon AZ has been more reliably dated through radioisotope U—Pb dating, suggesting a maximum depositional age of 237 ±1.5 million years in the early Carnian.
