WEocene–Oligocene extinction event
WAdapidae
WAmbulocetidae
WAnaptomorphinae
WAndinichthyidae
WArctocyonidae
WBaenidae
WBasilosaurinae
WBrontotheriidae
WCercamoniinae
WCimolesta
WCimolodonta
WCoryphodontidae
WDidolodontidae
WDinocerata
WDinopanorpidae
WDyrosauridae
WEpihippus
WEpoicotheriidae
WFormiciinae
WHallirhoidae
WHapalodectidae
WHaplohippus
WHyaenodontidae
WHyopsodontidae
WMacginitiea
WMiacidae
WNotharctidae
WNotharctinae
WOromerycidae
WPakicetidae
WPalaeochiropterygidae
WPalaeophiidae
WPhenacodontidae
WPlanocraniidae
WPlesiadapiformes
WProrastomidae
WPteridospermatophyta
WPtilodontoidea
WRaoellidae
WRemingtonocetidae
WSclerorhynchidae
WSophiornithidae
WTillodontia
WTriisodontidae
WUintatheriidae
WXenungulata