The Canon 5DS and 5DS R (pictured here) boast a 50.6-megapixel CMOS sensor. That's not a typo, it actually has an output resolution of 50.6 megapixels. The sensor is full-frame, just like the earlier 5D cameras. Rather than replacing the 5D Mark III, it will sit above it in the Canon range.
The two models are identical apart from one important feature: the 5DS R has a low-pass cancellation filter inside to deliver the maximum resolution from the sensor. The 5DS R is designed for photographers who need the sharpest image possible, such as landscape photographers.
Sometimes, 50 megapixels is just too much. The cameras allow you to choose a crop ratio that reduces the output to 19 megapixels which is a bit more manageable for certain applications. Select from full (no crop); 1.3x (APS-H equivalent crop); or 1.6x (APS-C equivalent crop). The viewfinder also blacks out around the crop area to show you exactly what is being captured.