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Alkaline hydrogen peroxide oxidation (AHPO) and HI hydrolysis of extant and fossil tissues. All extant tissues analyzed contain pyrrole-2,3,5-tricaboxylic acid (PTCA) (a eumelanin marker) and 4-amino-3-hydroxyphenylalanine (4-AHP) (a pheomelanin marker). The fossil sample (†torso, P. pueyoi) contains PTCA and abundant pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) (a marker for diagenetically altered melanin), but no 4-AHP. P. pueyoi data from ref. 24.
