| Phrynocephalus frontalisi and P. versicolor are two morphologically similar, small sized toad-headed lizards. Although lizards of these two species are locally very abundant in Inner Mongolia, data on life-history traits and thermal ecology are largely absent. In May 2004 and 2005, I collected lizards in Ordos and Wulate, Inner Mongolia, trying to fill this gap. The two species differ in body size (SVL, snout-vent length), with adult P. versicolor being on average larger than adult P. frontalisi. Sexual size dimorphism (SSD) is evident in P.frontalis but not in P. versicolor, with males of the former species being the larger sex. In both species, males have longer tails as well as larger heads than do females of the same size, whereas females have longer abdomens than do males of the same size. Adult P. versicolor have wider heads than do adult P.frontalis of the same size (SVL).In our sample, the minimal reproductive female was 44.1 mm SVL in P.frontalis, and 47.7 mm SVL in P. versicolor. In both species, clutch size varied from 2-6 eggs, and clucth size, egg size (clutch mean egg mass), and clutch mass were all positively correlated with female SVL. A principal component analysis (eigenvalue ≥ 0.5) on seven SVL-adjusted female reproductive variables resolved three components, accounting for 76.2% of total variance in the original data. Egg size was negatively correlated with relative fecundity in both species, indicating that females with higher fecundity lay smaller eggs. When removing the influence of variation in relative fecundity using ANCOVA, the egg size-number trade-off line is higher in P.frontalis than in P. versicolor, signifying that female P. frontalis lay relatively large eggs than do P. versicolor.Embryonic stages at oviposition, varying from Stage 30-32 in the Dufaure and Hubert's developmental series, did not differ between both species. I incubated eggs at four constant temperatures (24, 27, 30 and 32 ℃) to examine the effects of...
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