Apex domains cannot have CNAME records.
Question and response
Question
dig 0-27.62.210.62.in-addr.arpa. NS
Answer
0-27.62.210.62.in-addr.arpa. 5 NS dns2.ubunet.es.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0