Apex domains cannot have CNAME records.
Question and response
Question
dig 128-255.66.172.95.in-addr.arpa. NS
Answer
128-255.66.172.95.in-addr.arpa. 5 NS ns-1502.awsdns-59.org.
128-255.66.172.95.in-addr.arpa. 5 NS ns-415.awsdns-51.com.
128-255.66.172.95.in-addr.arpa. 5 NS ns-610.awsdns-12.net.
128-255.66.172.95.in-addr.arpa. 5 NS ns-1974.awsdns-54.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0