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Pleistocene
Vertebrate Fossils
Phylenogenic analysis of Horned Lizards
Some info I found on a website. The original author wasn't credited.
Most horned lizard species are well represented in the fossil record by the Pleistocene (1 million years ago, mya), P. cornutum is found in the upper Pliocene (3 mya), and P. douglasi is known from the mid Miocene (15 mya). Three species went extinct in the late Pliocene-early Pleistocene, long before there were any humans. The genus is thought to have split from an ancestor shared with the sand lizards (Uma, Callisaurus, Cophosaurus, and Holbrookia) during the late Oligocene-early Miocene (23- 30 mya).
