The 5% overall frequency of the novel genotype across our study samples, representing 34% of all detected picornavirus infections, and its observed global distribution, led us to analyze the accumulating sequence data for insights into their history. Rates of evolutionary change and the Time to the Most Recent Common Ancestor (TMRCA) of the novel clade were estimated by using the Bayesian Markov Chain Monte Carlo approach (BEAST package [14] ; ), applying a relaxed molecular clock with an uncorrelated lognormal distribution of rates, a GTR + I + Γ 4 model of nucleotide substitution (determined by MODELTEST [15] ), and exponential population growth. Statistical uncertainty in each parameter estimate is expressed as 95% highest probability density (HPD) values. The estimated mean rate of evolutionary change was 6.6 × 10 -4 substitutions/site/y (95% HPD = 0.3-14.6 × 10 -4 substitutions/ site/y; 38 dated samples collected over 32 mo (8,16) (S.R. Dominguez et al., unpub. data). Under this rate the mean TMRCA was estimated at 1,800 y, although with wide variance caused by the short sequence available (95% HPD = 279-5,201 y). Despite the inherent sampling error, this analysis suggests that this third clade of rhinovirus has been circulating for >250 years. The diversity observed within the novel clade and its genetic distance from other HRV/ HEV were comparable to those seen for HRV-A, -B, or the HEV species (Table 2) .