Kashrut

The Torah only gives one instruction on kashrut and all it says it something along the lines of “do as I have commanded” That’s it. That all we have. So the rabbis over the years have passed down the information of what g-d has previously commanded until it was written down one day with the oral Torah. The reason the oral Torah was written down in the first place was because information was beginning to get misconstrued, so how do we know our modern rules of kashrut are accurate at all and haven’t been changed through the generations it has passed down? Edit: I’m referring to unkosher animals specifically