Apex domains cannot have CNAME records.
Question and response
Question
dig iguana.cat. NS
Answer
iguana.cat. 5 NS ns2.iguana.cat.
iguana.cat. 5 NS ns1.iguana.cat.
Authority
The response has no authority records.
Additional
ns1.iguana.cat. 5 A 45.15.139.141
ns2.iguana.cat. 5 A 45.15.139.152
ns1.iguana.cat. 5 AAAA 2a01:57a0:0:0:0:0:0:141
ns2.iguana.cat. 5 AAAA 2a01:57a0:0:0:0:0:0:200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0