In my recent post, How We Pray 1, I talked about how the concept of salah, and some of the postures, existed before Islam. We can understand that salah, when used in the Qur'an referring to human beings (please see Definition of Salah) generally means worship. Looking at Biblical descriptions of the worship of prophets, we see them falling on their faces. But there is even more evidence in the Qur'an as to what salah looked like, or included as far as postures, in the Qur'an.
That's why this is a part 2 post, it's just further elaborating on some points I already discussed.
One thing that the Qur'an describes is praying in the House of Allah, which is the Ka'ba. This is something we can read in Surat al-Baqarah (2:125.) Surah Ale Imran describes Zakariyyah praying in a mihrab, a chamber or private room (3:39.) And Surah Sad mentions a mihrab of Dawud (38:21.) Surah Yunus describes taking houses as places of prayer for Musa and Harun in Egypt (10:87.) Surah Ale Imran includes instructions to Mary about prostrating and bowing, and it tells her to bow along with those who bow, indicating congregatoinal prayer (3:43.) Surat al-Hajj mentions standing, bowing, prostration, and circumambulation (22:26.) Also mentioned is that salah is for dhikr, rememberance of Allah, as in Surah Taha (20:14.)
I mention these references just to point out that some postures and particulars of prayer, in addition to being universal demonstrations of humility and devotion, are also part of the salah in times before Islam, one more thing which gives our daily salah special significance.