Do we know in what posture the Buddha sat under the Bodhi tree?

I was reading yesterday this blog by a Zen nun and in this post she casually says in the third to last paragraph that we don't know in what posture the Buddha did sit under the Bodhi tree. I found that curious because I always assumed that the Buddha sat in a full lotus position. Is this claim true? Do we not know the actual posture in which the Buddha sat under the Bodhi tree?