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Fossil Record

The oldest known member of Anapsida is
Acleistorhinus, a small reptile from the lower Permian of Oklahoma, about 270 million years ago. However, the presence of
romeriids (the sister-group, or closest relatives, of anapsids) in the upper Carboniferous indicates that Anapsida originated no later than this, around the same time as the very first amniotes were found - Hylomonus and Paleothyris from Nova Scotia, around 310 million years ago. Anapsids can therefore be traced right back to the dawn of the reptiles. This implies that there is a long period of ancient anapsid history unknown from fossils.

Most known ancient forms of anapsid originated in the mid to late Permian and became extinct at the Permian-Triassic boundary, at about 250 million years ago (with the exception of the Procolophonoidae), a range of up to about 20 million years.

The fossil record of the anapsids is good, as their typically unfenestrated, strong skulls are generally well preserved. In later forms, the shells of the Testudines are also easily preserved.