During the scene with Amelia in the biology lab, Wei-Chen has an affinity to the teacher's lipstick-wearing monkey, who will not leave him alone. Wei-Chen can easily recognize that the monkey is actually a male, just as the monkey can actually recognize that Wei-Chen is a monkey himself.
Did the first vertebrates evolve during the mesozoic era? No. The 1st vertebrates appeared in the fossil record about 525 million years ago during the Cambrian Period.
The Carboniferous period (360-300 million years ago) is famous for its dense coal swamps that eventually turned into modern coal deposits. It was during the Carboniferous that the first true amphibians appeared, evolving by the start of the ensuing Permian period into the first reptiles and lizards.