Apex domains cannot have CNAME records.
Question and response
Question
dig 0-127.77.71.206.in-addr.arpa. NS
Answer
0-127.77.71.206.in-addr.arpa. 5 NS ns-212.awsdns-26.com.
0-127.77.71.206.in-addr.arpa. 5 NS ns-1958.awsdns-52.co.uk.
0-127.77.71.206.in-addr.arpa. 5 NS ns-1059.awsdns-04.org.
0-127.77.71.206.in-addr.arpa. 5 NS ns-732.awsdns-27.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0