Amazon was Using Dyn, now they added also UltraDNS too:

  Name Server: pdns1.ultradns.net 
  Name Server: pdns6.ultradns.co.uk 
  Name Server: ns3.p31.dynect.net 
  Name Server: ns1.p31.dynect.net 
  Name Server: ns4.p31.dynect.net 
  Name Server: ns2.p31.dynect.net