Tracks are not verifiable evidence.
A skull would be verifiable evidence.
If someone writes a paper about the Bigfoot skull they found, another scientist could go to the skull take measurements and reach the same conclusion.
If someone writes a paper about the Bigfoot DNA they found, another scientist could go to the DNA and see where the specimen fits on a Cladogram.
If someone writes a paper about a Bigfoot foot print in the ground, another scientist can not go and look at the foot that made it and see if it is from an actual Bigfoot.