+**Synapsid** is a major group of [amniotes](/wiki/Amniote) that includes mammals and all their extinct relatives, distinguished by a single opening behind each eye in the skull. These "mammal-like reptiles" were the dominant land animals of the Permian period, forming the lineage that eventually led to [mammals](/wiki/Mammal).
+## See also
+- [Reptile](/wiki/Reptile)
+- [Evolution](/wiki/Evolution)
+- [Paleozoic](/wiki/Paleozoic)
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