Synapsids
Mammal-like reptiles that dominated the Permian — the ancestors of every mammal alive today, including us.
Overview
Synapsids — the 'mammal-line' amniotes — include the sail-backed pelycosaurs of the Permian, the diverse therapsids that survived the worst extinction in Earth's history, and the cynodonts that evolved the mammalian body plan. Mammals, including humans, are living synapsids.
Quick Facts
Key Characteristics
- •Single temporal opening (fenestra) behind each eye socket
- •Differentiated teeth appeared early in therapsids
- •Dimetrodon and its relatives had spectacular dorsal sails
- •Cynodonts show the gradual assembly of mammalian features: expanded jaw, palate, and eventually warm-bloodedness
Fossil Record
Permian and Triassic continental red beds of Texas, Russia and South Africa yield abundant synapsid skeletons — the South African Karoo preserves the richest therapsid sequence on Earth, spanning the end-Permian extinction.
Global Distribution
Worldwide in Permian–Triassic continental deposits: North America, South Africa, Russia, China and Europe.
Evolutionary & Scientific Importance
Synapsids are the best-documented example of a major evolutionary transition — the stepwise origin of mammals from reptile-grade ancestors — and their Karoo record ties vertebrate history directly to the end-Permian crisis.