ALL grass type starters are based on modern animals and loosely based off extinct animals (mostly dinosaurs) except the Chikorita line where as Meganium you can clearly see it's just a small sauropod. Examples:
Bulba line is a mixture of reptile and amphibian but has features that make it fit into neither like its external ears. This one is only very loosely based off generic dinosaurs.
The pears based off fruit and sauropod.
Treeko/Sceptile gecko feathered dromaeosaur (raptor)
Turtwig/Torterra tortoise (world tortoise myth) and loosely ankylosaur due to how the shell of torterra is more back armour and covered in spikes.
Smugfuck le when sneks had arms and legs but lost them
Chesnuts Glyptodon (weird thing from ice age google images it)
Based Owl the Rowlet line is robin hood some mexican death owl and an extinct species of Hawaiian owl that had long legs like Decidueye
This is the grass theme just like water type starters are semiaquatic animals and weapons and like the fire zodiac