ns1.amzndns.com has no CNAME records.
Question and response
Question
dig ns1.amzndns.com. NS
Answer
The response has no answer records.
Authority
amzndns.com. 544 SOA g-ns1.amzndns.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 907
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0