Apex domains cannot have CNAME records.
Question and response
Question
dig jussieu.FR. NS
Answer
jussieu.fr. 3 NS soleil.uvsq.FR.
jussieu.fr. 3 NS ns0.sorbonne-universite.FR.
jussieu.fr. 3 NS ganesh.upmc.FR.
jussieu.fr. 3 NS ns1.sorbonne-universite.FR.
jussieu.fr. 3 NS shiva.jussieu.FR.
Authority
The response has no authority records.
Additional
shiva.jussieu.fr. 3 A 134.157.0.129
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0