I wouldn't want to testify to it, but I think that the line converts from cast iron to clay. See the material change in picture 3, and how it appears to be shorter sections with very obvious joints in Picture 4? As long as clay pipe doesn't get damaged, offset/broken joints, or roots don't find their way in through the joints, clay pipe lasts a long, long time. But I have only ever heard of it being used on the outside sewer line. Though it doesn't make sense that it would be used on the new sewer line, as far as I know Chicago is the only place that still uses clay for sewer lines, most places use PVC. Still, the joints look much too close to be 20' or even 10' lengths of PVC, and the inside looks a little rough.
Something caused the cast iron that you have dug up to be very corroded, and I would be concerned that all of the rest of the cast iron is in similar condition. At the very least, I would advise you to have the rest of the line jetted thoroughly then re camera inspect to get a better idea of it's condition.