Well the modern definition of ATV is different from the 1st ones to come on the market and this;
Arnold Ranger, would be one of the first, was a track unit. The developer, Norbert Arnold of Pengilly MN closed because of legal action from roll over's. That unit would literally climb a tree!
I kinda like that setup!
Was up in the u.p. of Mich. and watched some demo's of ATV's with various track units added to them offered by a company of which I don't remember their name. They were impressive. Didn't seem to bury or dig down making ruts like tires do but gripped the ground like nobodies business. IIRC, the turning radius wasn't as good as with the tires.
I've often considered buying the 'track kit' for my 750 Brute Force. Think it was around a couple grand if I remember correctly.
Yes, the old three wheelers were pretty dangerous. Many years ago, was with a good friend of mine at his cabin way back in the backwoods of Clay Co. West Virginia. He did a burnout on the wet morning grass on his Honda 'Big Red' and was doing okay till the mudders hooked up in the WV red clay. Over it came on top of him makin a mess of his spine, breaking his back and crushing several discs/vertebrae.
Trying to get him to lay still while waiting for the chopper to life flight him out was the worse.