For the end of the older synapsid stage, I’d use late caseids as your marker. Caseids are basal/non-therapsid synapsids that persisted into the Middle Permian, with the last known forms around the Roadian–Wordian range, before disappearing as therapsids took over.
STORY
Last Non-Therapsid Synapsids
By Michael Alan Prestwood
Thu 21 May 2026
Published 14 hours ago.
Updated 14 hours ago.
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Last Non-Therapsid Synapsids
~262 Million years ago (+/- 2 million)
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— map / TST —
Prestwood writes on science-first philosophy, with particular attention to the convergence of disciplines. Drawing on his TST Framework, his work emphasizes rational inquiry grounded in empirical observation while engaging questions at the edges of established knowledge. With TouchstoneTruth positioned as a living touchstone, this work aims to contribute reliable, evolving analysis in an emerging AI era where the credibility of information is increasingly contested.
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