13.2: Mesozoic Evolution - Reptiles and Amphibians
- Page ID
- 50137
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Since the Mesozoic Era begins with the Permian-Triassic mass extinction, the Triassic saw devastated ecosystems that took over 30 million years to fully re-emerge. The first appearance of many modern animal groups that would later flourish occurred at this time. This includes frogs (amphibians), turtles (reptiles), marine ichthyosaurs and plesiosaurs (marine reptiles), mammals, and the archosaurs.
The archosaurs (“ruling reptiles”) include ancestral groups that went extinct at the end of the Triassic, as well as the flying pterosaurs, crocodilians, and the dinosaurs which ultimately dominated this era. Archosaurs, like the placental mammals after them, occupied all major environments: terrestrial (dinosaurs), in the air (pterosaurs), aquatic (crocodilians) and even fully marine habitats (marine crocodiles). The pterosaurs, the first vertebrate group to take flight, like the dinosaurs and mammals, start small in the Triassic.
Where Did Reptiles Come From?
The term ‘reptile’ seems straightforward, but when discussing evolutionary history, the term becomes much more complex. Reptile, as a biologic term, is actually paraphyletic. This means that all reptiles are not in the same simple family tree, or, some members of the group are excluded. For example, consider birds. The term bird includes the first bird (such as Archaeopteryx or a related animal) and all of the descendants, including all living birds. However, birds evolved from dinosaurs, which are reptiles. Does that mean birds are reptiles? This is one reason why the word reptile is problematic. For some researchers, birds are reptiles. For others, they are not.
Amphibians: Precursors to Reptiles
Another issue is where does the ‘reptile’ branch begin in the tree of life? To understand this, first one has to consider how reptiles evolved from non-reptile ancestors. The ancestors of the animals that eventually became reptiles were amphibians.
During the mid-Paleozoic, the first fish to walk on land eventually turned into a common group of animals still alive today: amphibians. Amphibians were the first tetrapods (four-limbed animals) and they took advantage of the warm and tropical climate in the Devonian and Carboniferous and proliferated into many terrestrial niches with large and strange forms, like Eyrops.
