DIAGNOSIS We refer two specimens to the genus Phryno-soma. The fossil maxilla (DMNH 44766; figure 11.2) shows an anteroposteriorly restricted, triangular ascending process that terminates in a sharp dorsal tip; this morphology is a synapo-morphy of Phrynosoma and is not known for any other lizards native to North America. The dentary (DMNH 44767) is referred to Phrynosoma based on the distinctive, pronounced mediolateral curvature with a flattened ventral portion at the posterior end; this morphology is widespread in Phrynosoma (Montanucci, 1987; Mead et al., 1999), and we consider it to be a synapomorphy of the group.

FIGURE 11.2. DMNH 44766; right maxilla referred to Phrynosoma shown in lateral (top), occlusal (middle), and medial (bottom) views. Scale bar = 3 mm.

R emarks Phrynosoma cornutum, P. hernandesi, and P. mo-destum inhabit Colorado today (Hammerson, 1999), but none of the species is reported from Park County. Of the three, P. hernandesi has the widest geographic distribution and the widest elevational occurrence in Colorado; it is reported to occur as high as 3355 m (Hammerson, 1999) in La Plata County. The Porcupine Cave specimens thus document a wider geographic distribution for Phrynosoma in the past, but one that is within the known elevational tolerance of extant members of the genus.

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