Apex domains cannot have CNAME records.
Question and response
Question
dig 64.83.in-addr.arpa. NS
Answer
64.83.in-addr.arpa. 1 NS rns1.nameservice.at.
64.83.in-addr.arpa. 1 NS rns2.nameservice.at.
Authority
The response has no authority records.
Additional
rns1.nameservice.at. 3 A 46.125.235.221
rns2.nameservice.at. 3 A 84.115.254.99
rns1.nameservice.at. 3 AAAA 2001:4bc8:2000:703:0:0:0:1
rns2.nameservice.at. 3 AAAA 2a02:8383:d:200a:0:0:0:99
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0