Scatterplot of dataset characteristics. Each circle represents the characteristics of the complete 2008 data matrix from each of 100 vertebrate clades. The number of species in the dataset (x-axis) refers to the number of species sampled for the clade, not the total described diversity of that clade. The number of character refers to the number of columns (nucleotides) for that matrix, rather than the total number of sequences sampled. The size of each circle represents the density of each dataset measured as the percentage of non-missing data.