Who are the Tamil Saurashtrans?

I have come across many people who say they are Saurashtran. They speak Saurashtran but it sounds nothing like Gujarati. From what I have noticed, they have assimilated a lot with Tamil culture. Who are these Saurashtrans, when and why did they migrate to Tamil Nadu, what is their culture like? Why is their language so unique? Are there places where their population is considerably high? It would be great to hear some answers