At https://phys.org/print450409594.html … giant dinosaurs lived on Earth much earlier than thought. The recently discovered dinosaur graveyards in Argentina are throwing up facts not envisaged as we now have a very large herbivore dinosaur dating from the Triassic period. Gigantism originated earlier than the Jurassic it would seem. Some clarification on gigantism is necessary as it cannot occur as a gradual process – unless the Triassic has been underestimated.
Dinosaurs appeared in the fossil record in the Triassic – but they were regarded as small specimens. The big dinosaurs are thought to have evolved in the Jurassic – but this view has now been upended.