This odd contraption was on the end of a backhoe's hydraulic arm - I have a suspicion that it was used to break up hard clay at the construction site, but I don't know for sure. :)
I believe this is called a 'sheep's foot packer', and is used to compact freshly graded roadbeds. I have worked on jobsites where there were two pairs of these things, each 4 to 4 1/2 feet wide, towed by a D-3 Cat.