By Drew Johnson

Left Lane News

It's been a while since BMW engineers have been seen out testing the next-generation Z4, but apparently the sports car's development is still on track--despite being hidden for the last few months--as spy photographers spotted a Z4 prototype out testing on Wednesday. The latest photos don't give too much away as the car is still heavily clad in camouflage, but we've got an illustration of what the final product will likely look like after the jump.

Since the new Z4 rides on the same platform as the 3-series, look for the Z4's engine lineup to mirror that of the 3-series. A high-performance Z4 M will once again be offered and, for the first time, it is believed that BMW will offer a diesel-powered Z4. Unlike the current model, look for the next Z4--due out in late 2009--to sport a retractable hardtop roof to better compete with Mercedes-Benz's SLK roadster. As we have reported before, the Z4's production will shift from the U.S. to Germany when the new model bows. More photos at Left Lane News.