The number of tRNAs showing each of several numbers of steps (T-arm losses) when mapped over the Shultz (2007) phylogenetic tree of chelicerates. Light gray shading indicates that the characters were reconstructed without homoplasy; dark gray shading indicates that loss of the T-arm required 2 or more steps. One-letter amino acid abbreviations are used to indicate tRNA identity, with numerals used to designate the anticodons: L1 = CUN, L2 = UUR, S1 = AGN, and S2 = UCN.