Dynamic range is not simply dependent on bit depth when the encoding (translation of light into bits) is not linear.
Example of linear encoding:
Light = {1,2,4,8,16,32,64,128,256,512,1024} scene with 11-bit dynamic range
Output = {1,2,4,8,16,32,64,128,128,128,128} 8-bit camera captures 8-bit dynamic range
Example of non-linear encoding:
Light = {1,2,4,8,16,32,64,128,256,512,1024} scene with 11-bit dynamic range
Output = {1,10,20,30,40,50,60,70,80,90,100} 8-bit camera captures 11-bit dynamic range