Dimetrodon Limbatus

Dimetrodon is an extinct, mammal-like animal that lived during the Early Permian Period, around 295–272 million years ago. Several ancient animal fossils have been discovered in the southwestern part of the US. Although it is commonly mistaken for a dinosaur, the Dimetrodon is older than the earliest dinosaurs by about 40 million years.

Dimetrodon was an apex predator known for the prominent spine sail on its back which was used for balance and thermal regulation. The sail would have given an advantage to the reptile in cold weather conditions, by enabling the reptile to warm up quicker in the morning and attain a higher temperature by about 4°C compared to a reptile without a sail. A sail bearing reptile would also lose heat at a higher rate in the evening compared to a reptile without a sail, so maximum benefit would have been obtained if blood flow to the sail was restricted during night-time hours. The sail could have been of great value in environments that would have had a maximum temperature of around 25°C. A possession of a heat absorbing surface in a high temperature environment would have been dangerous. This could be one of the reasons why the sail bearers did not survive in the next geological period, the Triassic.