The Cutler Formation in San Juan County, Utah, with its alternating units of red beds and light-colored largely eolian sandstones, is ideally suited to the study of Permian terrestrial vertebrate chronofaunas. Fossils have been collected from stream deposits in the lowest unit, the Halgaito tongue, in the vicinity of Mexican Hat. Forms referable or close to known Four Corners genera are: Xenacanthus aff. X. texensis, Eyrops sp., Platyhystrix cf. P. rugosus, Diadectes sp., a limnoscelid, Ophiacodon cf. O. navajovicus, and a sphenacodontid pelycosaur. Of 3 kinds of paleoniscoid scales, one is like scales known from the Cutter Formation in New Mexico. Finds of Etosteorhachis aff. E. nitidus and, possibly, a nectridian help to reduce the faunal difference between the lower Permian of the Four Corners and the midcontinent. There is evidence of a variety of limnoscelids in the Four Corners early Permian. The Halgaito tongue in the vicinity of Mexican Hat is probably Wolfcampian in age.

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