Apex domains cannot have CNAME records.
Question and response
Question
dig 1.131.85.in-addr.arpa. NS
Answer
1.131.85.in-addr.arpa. 5 NS ns1.fv.fi.
1.131.85.in-addr.arpa. 5 NS ns2.fv.fi.
Authority
The response has no authority records.
Additional
ns1.fv.fi. 5 A 217.78.192.1
ns2.fv.fi. 5 A 62.78.96.1
ns1.fv.fi. 5 AAAA 2001:14b8:1000:0:0:0:1:11
ns2.fv.fi. 5 AAAA 2001:14b8:1000:0:0:0:1:12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0