Accurate, comprehensive data on life expectancy, growth rates, age structure, and sexual maturation are necessary to inform decision-making for conservation action, but they are often difficult to obtain from wild animals. Osteohistology has proven a reliable method for accessing chronological data in extant and extinct vertebrates. Traditional mark–recapture methods require repeated measurements in the field and do not allow comparison with far more extensive data from specimens housed in museum collections, thus reducing statistical power and inviting unjustified extrapolation. We investigate longevity and growth in the large-bodied iguanian lizard Sauromalus ater (Common Chuckwalla). We find highly variable growth to be typical for S. ater occupying a spectrum from rapid growth to sexual maturity within two to three years leading to above-average body size later in life or slow growth early in life with sexual maturity at four to eight years followed by growth to body sizes around the average adult size. We show individual S. ater achieve final body size in about ten years, not decades, and that body size and age in adults are significantly correlated. This study suggests conflicting reports on growth, maturation, longevity, and generation cycle in S. ater are all correct and reflect complex ontogeny in squamates.