Fourth extinction event

The Triassic - Jurassic extinction event was 201.3 million years ago.

The extinction was associated with multiple rapid cooling and warming events between global average temperatures of 9 and 22°C over several decades. It marks a major mass extinction of mostly terrestrial animals.

The culprit of these events was the beginning of the split of the massive single continent in the middle. Concomitant with rift tectonics was violent magmatic activity in an area in excess of 10000000 km2 on either side of the rift zone. The volcanic activity ran across the whole continent leading to 2.3 million cubic kilometres of lava covering an area the size of Europe. Huge amounts of carbon dioxide (CO2), sulphur dioxide (SO2), hydrogen sulphide (H2S) and other volatiles were released into the atmosphere in about four volcanic eruption phases over some 600 000 years.
A initial pronounced cooling event 10000 years at each phase related to the release of sulphur dioxide (SO2) which rapidly forms sulfate aerosols in the atmosphere that absorb or backscatter sunlight. These glacial intervals were accompanied by acid rain. Both events killed plants hence the food chain suffered. Most of the amphibians and reptiles became extinct.
Then longer term warming period was related to carbon dioxide (CO2) by volcanic emissions. Global temperatures rose sharply by 3 to 4 °C. In some regions, the temperature rise was as great as 10 °C with humid greenhouse conditions.
Ozone layer depletion occurred due to volcanic aerosols which allowed ultraviolet light from the sun to have a negative effect on biodiversity, oxygen production and growth of plants.
Rapid warming and increase in continental weathering led to the stagnation of ocean circulation and deoxygenation of seawater in many ocean regions what may have locally contributed to marine mass extinction.
Ocean acidification occurred due to the chemical reaction of carbon dioxide CO2 and sulphur dioxide (SO2) with water. A direct effect of ocean acidification is a decrease in the concentration calcium carbonate minerals. It may have lasted 20 000 to 40 000 years and many of taxa with calcareous skeletons became extinct.

Extinction rates:

• 80% species
• 47% genera
• 23% families

Before this extinction, temperatures dropped from 32 to 19°C degrees between 240 and 201.3 million years ago.
Dinosaurs appeared 44 million years and the first true mammals 24 million years before this extinction in the Triassic. As dinosaurs evolved, they adapted to low oxygen levels and extreme heat. Unlike the breathing of mammals, where inhaling and exhaling are two separate processes, the hollow bones and air sacs in the bodies of dinosaurs and birds allow one-way breathing: inhaling and exhaling simultaneously. This also allowed them to cool down during intense exertion. As a result, some dinosaurs could grow large, which was an added advantage because they kept their bodies warm with a lower food intake than warm-blooded animals. Therefore, they could move quickly at lower temperatures. A bigger body volume has less heat loss due to a comparatively reduced body area. A larger body volume has less heat loss due to a relatively smaller body surface area.
However, for warm-blooded mammals with fur and directional breathing, the opposite is true. Instead, they need to lose heat. In addition, they need more oxygen and food per body weight. Therefore, they were not bigger than rats because a small body size has a relatively larger body and lung surface area. This allowed them to get rid of heat better and provided them with more oxygen for their high metabolism.
Most of the small mammals burrowed into the ground which allowed them to escape extreme temperatures during the extinction event.
Some early dinosaurs had developed insulating coats of feathers to access the rich vegetation found closer to the poles. This adaptation may have led them to survive the volcanic winters.