CRS: list of datum?

HI!

While

CRS("+proj=utm +zone=32 +datum=WGS84")

CRS arguments:
 +proj=utm +zone=32 +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0

is correct, the same with ED50 is not:

CRS("+proj=utm +zone=32 +datum=ED50")

Error in CRS("+proj=utm +zone=32 +datum=ED50") :
  unknown elliptical parameter name

Is there any way to get the list of available datum acronyms?

Thanks

Agus