Copying [dead] reply here so I can reply to it: “This simply can’t be true. The dock first appeared in NextStep 1.0, which was released in 1989, six years before dragthing 1.0 appeared in 1995.”
The NeXT Dock was removed from Rhapsody and Mac OS X DP1/DP2. The Mac OS X DP3 Dock was a new creation.
See http://www.rhapsodyos.org/misc/docs_and_faqs/Misc_FAQs.html which recommends a third-party dock called Fiend —
Q: Is the OPENSTEP Dock going to be available in Rhapsody?
A: It is actually still there in 5.0 to a degree. In 5.1 and later it has been replace with the Applications Menu (but you can get it back using Fiend[0]). Also you have the option to use the minimize to tile for windows like in NEXTSTEP/OPENSTEP instead of window shade.