Li Y, Tsoi S, Mannen H, Shoei Lung Li S. Phylogenetic analysis of vertebrate lactate dehydrogenase (LDH) multigene families. J Mol Evol. 2002;54:614-24 pubmed
..Other gene duplication events were also discovered in Xenopus, the first duplication occurring approximately 60-70 mya in both Ldh-A and Ldh-B, followed by another recent gene duplication event, approximately 20 mya, in Ldh-B. ..