PLOS ONE: Burst of Young Retrogenes and Independent Retrogene Formation in Mammals
Burst of Young Retrogenes…in Mammals. Discusses much
retro-transposition ~40 Mya, relevant to proc. #pseudogenes
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0005040
Also, ref #11 provides more detail on this.