general problems of the 2000 Toyota RAV4

I bought 4 new goodyear tracker 2 tires size p22570r16 from walmart that are warrantied for 50,000 miles. After about 10,000 I noticed some dry rot and cracking in between the treads. I took my vehicle back to walmart and showed them. The tire manager said he's seen a lot of this with these tires but said they had to contact goodyear before anything could be done. The next day the store manager called me back and said they spoke with goodyear and there is nothing that can be done. In my opinion this is a manufacturer defect and poses a safety hazard. I would like this to be investigated and have something done and the tires replaced before it does cause an accident and/or fatalities.