Stegosaurus

# Evolutionary Timeline of Stegosaurus Stegosaurus, a plated dinosaur from the Late Jurassic, evolved within the Thyreophora clade of ornithischian dinosaurs. Its evolution was shaped by environmental pressures such as predation from large theropods, competition for vegetation in forested floodplains, and climatic shifts towards seasonality in the Jurassic period. Key ancestors include early ornithischians like *Lesothosaurus* and basal thyreophorans like *Scelidosaurus*, leading to the development of defensive plates and spikes. ### Key Milestones - **Triassic Period ( ~230-200 Mya)**: Origin of dinosaurs from archosaur reptiles; early saurischian and ornithischian split. - **Early Jurassic ( ~200-175 Mya)**: Emergence of Thyreophora with armored dinosaurs like *Scelidosaurus*, adapting to herbivory and predation pressures. - **Middle Jurassic ( ~170-160 Mya)**: Rise of Stegosauria clade, with primitive forms developing dorsal plates for defense and thermoregulation. - **Late Jurassic ( ~155-150 Mya)**: Peak of *Stegosaurus* species, featuring advanced plates and thagomizer spikes amid lush, predator-rich environments. - **Early Cretaceous ( ~145-125 Mya)**: Decline and extinction of stegosaurs, possibly due to changing flora and competition from other herbivores.