Vertebrates

The extinction event for the vertebrates was far less severe than for the invertebrates with far fewer species becoming extinct. This has led to less research and literature on these organisms being published, as it was a far less significant event in terms of their evolution and study of their fossils tells us less about possible causal mechanisms behind the extinction.
The tetrapods had colonised the continents with amphibians being the dominant species, and reptiles also being prevalent.

The amphibians had evolved into the most important species group in the preceding eras, as the first animals to venture from the oceans onto the ecological vacuum of the newly greened continents. Thriving in the tropical swamp forests of the Carboniferous they had evolved into giant forms such as the 2-3m long Temnospondyls, and the long snouted Archegosaurs.

As the climate changed, with the continents drying and heating up the amphibians suffered as the pools in which they lived, and in particular laid there spawn, shrunk and dried up. With this decline of a vital habitat many of the amphibians would become extinct.

As the climate got hotter and the amphibians declined through the Permian the Amniota succeeded as the dominant land species. They had the advantage of amniotic eggs, which with their calcium carbonate shell could retain water while allowing the transpiration of gas meaning they didn't have to be laid in the rapidly diminishing pools of water.

The Amniota can be divided into two groups, the Synapsids and the Sauropsids, divided by differences in various large openings in the skull and dentition.

The Synapsids are ancestors of the mammals and became the dominant species in the Permian. The first of these were the Pelycosaurs in the Early Permian. This group contained the finbacks of the Dimetrodon and Edaphosaurus, which had large sails protruding from their vertabrae. Often bundled with dinosaurs in childrens play sets these were in fact ancestors of the mammals, with the large sails functioning as thermo-regulatory structures. There were some Pelycosaur relatives without this sail adaptation which would be more sluggish due to not being able to heat up as fast.
All Pelycosaurs were confined to the equatorial tropics.
By the Mid-Permian the Pelycosaurs were replaced as the dominant species by the Therapsids, known as the mammal-like reptiles. These were more advanced Synapsids which were far more metabolically active, encompassing both herbiverous and carniverous forms.
The most primitive of the Therapsids (Dinocephalians) grew to a huge size (upto 6m in length), but became almost completely extinct at the beginning of the Late Permian, probably due to the changing climatic conditions. Only one species, the Pareiasaurs, survived to the end-Permian where it died in the mass extinction.

They were succeeded as the dominant tetrapod species by smaller Therapsids, which were even more mammal-like. It is believed that some may have even had fur and warm blood. With the reduction in competition as the larger Therapsids died out, these would be the most important species on the continents for the remainder of the Permian. Herbivores such as the especially abundant dicynodont far outnumbering the predatory carnivores.

While the Therapsids were dominating the Sauropsids were also evolving with one group of Diapsids of particular importance; the Archosauriformes. These were small and rare but did manage to cross the taphonomic filter created by the Permo-Triassic mass extinction, and would proceed to diversify into forms which would become the Dinosaurs.

In the Triassic the Archosaurs would come to dominate, probably being better suited to the hot-house environment which would last throughout the Mesozoic. With the proceeding evolution of the dinosaurs, the mammal ancestors would remain relatively insignificant until the extinction of the dinosaurs.
For a Bristol University site on the Age of the Dinosaurs click here.

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