Goannas are the best burrowers! Also, a conclusion that heartily pleases me:

....these new finds have shown that living reptiles.... are doing some incredibly complex things. Co-operatively built family burrows (McAlpin et al. 2011), warrens formed of numerous individual burrows, and – now – deep, deep, spiralling corkscrew-like burrows. The expectation that complex structures of this sort can only be attributed to mammals.... ha, it’s dead.