Hi James,
MacBook-van-Mathy-De-Vos:lib sam_elseviers$ otool -L /usr/lib/libz.1.dylib
/usr/lib/libz.1.dylib:
/usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.5)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)