Film format does not have anything to do with dynamic range. You can cut the same emulsion up large, small, or in to paper dolls, the properties remain the same.
Does a digital camera lose dynamic range when you set it to crop mode, only using the middle of the sensor?
The tonal resolution of a print does depend on the format indirectly, through the different degrees of enlargement needed to get a given sized print: please consider what has been said about dithering, and the way that information gets "averaged" to form the signal that the eye eventually receives. Averaging multiple signals increases the SNR of the resulting signal.
And to your second question: Yes, in the important practical sense of signal to noise ratios of the final displayed image (print or on-screen), working with the whole file rather than a crop does allow you to produce a final image with "higher DR" or "finer tonal gradations" because for example the data from more pixels can be averaged to produce output pixels of higher SNR (higher DR).
This should be easy to see: take a high pixel count file (preferably taken at high ISO, so that the raw per-photosite DR is lowish) and first display the whole thing at suitably high PPI, and then view a small crop at the same size, so at far lower PPI. (Two prints of the same size, or just zooming in on screen will do it.) You should be able to see differences in "tonal gradations", or "DR" or whatever one calls it, in part through the more visible noise in the second image.
I plea once again for people to stop taking the engineering measures of
per photosite DR and SNR alone as being direct measures of visual quality without taking account of how pixel count, PPI used when printing/displaying, degree of enlargement, and so on effect on the final visual result.
