dmesg empty after shutdown -r

Wed Apr 30 23:58:53 UTC 2008

This is very strange.

After "shutdown -r now" and the subsequent reboot, I have
logged in to my machine
 	FreeBSD qemg.org 7.0-RELEASE FreeBSD 7.0-RELEASE #0: Sun Feb 24 10:35:36 UTC 2008     root at driscoll.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64

Everything seems to be running normally, except "dmesg" produces
no output, and /var/run/dmesg.boot is zero bytes long.

Does anyone have any ideas why this would ever occur?  Or even how
it could occur?

Andrew.