Rhino was the component brand of Dean Cycle Works, a manufacturer of Titanium bicycles that was, and still is, based in Boulder, Colorado, USA.
Dean was established in 1989, but I have a feeling that they did not introduce the Rhino components until, perhaps, 1994. I also have a vague notion that they did not persevere with the Rhino components for very long, perhaps only for 2 or three years. They possibly lost interest after Shimano introduced the top-end XTR groupset - and it started to hoover-up the high-end market. However, you will note my uncertainty about these dates!