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Background  Fossil evidence suggests that extant North American lizard genera (north of Mexico) evolved during the Miocene. Although fossils of the clade Phrynosomatidae (spiny lizards and sand lizards) have been reported, there have been no previously described fossils of the fringe-toed sand lizards ( Uma ). In the extant biota,  Uma  inhabit arid deserts, and members of the western clade of  Uma  are restricted to sand dunes or other habitats containing fine-grained sand.    Results  I describe the first known fossil of  Uma  and refer the fossil to the total clade of  Uma  with an apomorphy-based diagnosis. The fossil is a partial premaxilla that was found in the Miocene strata of the Dove Spring Formation of southern California, dating to 8.77 Ma. The paleoenvironment of the Dove Spring Formation was semiarid and contained ephemeral streams that facilitated deposition, and there is no evidence of sand dune deposits in the strata containing the locality from which the  Uma  fossil was found. Divergence time analyses of a concatenated molecular dataset with four fossil calibrations support a Neogene origin of the total clade of  Uma  and of the crown clade of  Uma . Those analyses also estimated a Neogene divergence between  Uma scoparia  and the  Uma notata  complex. Multispecies coalescent analyses with one fossil calibration inferred a Paleogene origin for the total clade of  Uma  and a Pliocene or Pleistocene divergence between  Uma scoparia  and the  Uma notata  complex. The fossil and the total and crown clades of  Uma  precede the evolution of modern desert ecosystems in the southwestern United States and northern Mexico by millions of years.    Conclusions  The total clade and the crown clade of  Uma  were not restricted to arid deserts throughout their evolutionary histories. I demonstrate that an apomorphy-based diagnosis can be used to identify fossils of isolated skeletal elements for at least one clade of phrynosomatid lizard, and suggest exercising caution when using environmental tolerances of extant taxa to hypothesize paleoecological reconstructions.    Electronic supplementary material  The online version of this article (10.1186/s12862-019-1501-5) contains supplementary material, which is available to authorized users.

The first known fossil Uma: ecological evolution and the origins of North American fringe-toed lizards