Synapsid refers to any of the animals belonging to class Synapsida. These animals first appeared in the late Permian period (299 to 251 million years ago). They are presumed to have evolved from the basal amniotes. They are characterized by having temporal fenestra (i.e. the temporal opening on the sides of the skull), front teeth different from the back teeth, and limbs under the body. Mammal-like synapsids are now referred to as stem mammals or proto-mammals. Many of them became extinct by the Permian-Triassic extinction. Those that survived led to the more advanced therapsids. Cynodonts including Mammaliaformes were the only synapsids to survive after the Triassic period.
- “New proto-mammal fossil sheds light on evolution of earliest mammals”. (August 7, 2013). University of Chicago. Retrieved from http://www.uchospitals.edu/news/2013/20130807-megaconus.html
- Greatest mass extinction responsible for the making of modern mammals. Retrieved from http://www.nasmus.co.za/museum/news/greatest-mass-extinction-responsible-making-modern-mammals
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