We analyzed both mitochondrial (mt-) and nuclear (n) DNAs in a conservation phylogenetic framework to examine deep and shallow histories of the Beaded Lizard (Heloderma horridum) and Gila Monster (H. suspectum) throughout their geographic ranges in North and Central America. Both mtDNA and intron markers clearly partitioned each species. One intron and mtDNA further subdivided H. horridum into its four recognized subspecies (H. n. alvarezi, charlesbogerti,exasperatum, and horridum). However, the two subspecies of H. suspectum (H. s. suspectum and H. s. cinctum) were undefined. A supertree approach sustained these relationships. Overall, the Helodermatidae is reaffirmed as an ancient and conserved group. Its most recent common ancestor (MRCA) was Lower Eocene [35.4 million years ago (mya)], with a approximately 25 my period of stasis before the MRCA of H. horridum diversified in Lower Miocene. Another approximately 5 my passed before H. h. exasperatum and H. h. horridum diverged, followed by approximately 1.5 my before H. h. alvarezi and H. h. charlesbogerti separated. Heloderma suspectum reflects an even longer period of stasis (approximately 30 my) before diversifying from its MRCA. Both H. suspectum (México) and H. h. alvarezi also revealed evidence of historic range expansion following a recent bottleneck. Our conservation phylogenetic approach emphasizes the origin and diversification of this group, yields information on the manner by which past environmental variance may have impacted its populations and, in turn, allows us to disentangle historic from contemporary impacts that might threaten its long-term persistence. The value of helodermatid conservation resides in natural services and medicinal products, particularly venom constituents, and these are only now being realized.
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