How can dynamic-range be larger than sensor bit-depth?
Dynamic range is the logarithm of the ratio between the brightest and and the darkest intensities on the linear part of the sensibility curve. There may be other definitions, but in general it is derived from the ratio of two intensities, objective physical properties of the scene. It is a real number.
Bit-depth is the number of bits per channel used to quantize the continuous variable. More bit-depth gives more distinct shades of gray in between. It is purely a question of how an image is represented in computer memory.
Dynamic range reflects how much contrast the sensor can register. The bit depth reflects how many distinct colors the camera can “give names” to. Or into how many pieces the camera can divide the range. If a camera were a ruler, then the dynamic range would be the (logarithm of the) length of the ruler, and the bit depth would be the (logarithm of the) number of marks along its edge. And you can divide the length into as many pieces as you like. Similarly, the bit depth does not have to be the same as the dynamic range.
If dynamic range is S EV, and bit depth is n, then it means that the camera can register scenes with contrast at least as large as
(Actually a little more if you use also the non-linear part of the sensor response curve). And you can theoretically distinguish
shades of gray.
I own a compact camera which can write 12-bit RAW. Inspite of the high bit-depth, its dynamic range is very modest. You can imaging an opposite situation, when the sensor can register a high contrast scene, without over- and underexposure, but if the bit depth is low, that scene will be represented with few intermediate colors.