Apex domains cannot have CNAME records.
Question and response
Question
dig 171.207.65.in-addr.arpa. NS
Answer
171.207.65.in-addr.arpa. 4 NS auth40.ns.uu.net.
171.207.65.in-addr.arpa. 4 NS auth62.ns.uu.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0