Heck cattle are considered by some the most suitable cattle breed for low intensity grazing systems in certain types of nature reserves, due to their ruggedness and lack of need for human care. Heck cattle today are propagated in some places to fulfill the role of extinct megafauna in the ecosystem.
It's a replacement from the standpoint of humans who want meat and/or labor. From an ecological standpoint, our attempts to create replacements often fail miserably.
Humans also created a similar replacement: http://en.wikipedia.org/wiki/Heck_Cattle#Controversy
Heck cattle are considered by some the most suitable cattle breed for low intensity grazing systems in certain types of nature reserves, due to their ruggedness and lack of need for human care. Heck cattle today are propagated in some places to fulfill the role of extinct megafauna in the ecosystem.
A replacement was also created for the extinct tarpan: http://en.wikipedia.org/wiki/Heck_horse