Prehistoric because none of them remain and all that is left are fossils and imprints.
Here is a fascinating video of the magnificent steel beast eating out of a ships hold.
http://www.youtube.com/v/1RJfnk2S330
(Embedding unfortunatly not allowed)
Once common all along the southern coast of the Great Lakes, Lake Erie in particular, now all gone.
General information here at Wikipedia: http://en.wikipedia.org/wiki/Hulett

Fearless men actually rode the necks of these beasts at they clawed and tore at the ship's innards:

Jaws wide open:

Some excellent "archeology" resources are available here, drawings and all: http://www.loc.gov/pictures/item/oh0121/
Make sure to check out these magnificent photos and the sheer amount of railroad operations involved: http://www.clevelandmemory.org/glihc/hulett/index.html or http://site.ebrary.com/lib/clevelandstatedr/docDetail.action?docID=10402179 and many more.
Talking Huletts, one shouldn't forget rotary car dumpers, hopper/gondola dumpers with lifts and "marble tracks" and all kinds of other interesting animated machinery involved in coal/ore transportation.

Money and space are no limits on our virtual railroads, it only takes time, skill, lots of determination and a little imagination to model our desires.
Lack of interest also wouldn't be a problem either I'd guess, even if it were a payware pack of say "PRR Cleveland Ore Docks". "PRR Sandusky Line" with the mighty J1's, crossing the C&O with their mighty T1's and H8's at Columbus, Ohio also is like a dream come true.
P&LE and Ohio Steel and Massillon already offer endless operational opportunities for receiving coal and ore trains.
Only RSC should allow merry-go-round trains that don't need to stop to load/unload their cargo.
Hudson River car floats, Lake Michigan train ferries are also nice to model once we have a waterfront and docks. I imagine an operational car float is nothing more than a overlarge flatcar running on tracks laid underwater. A tug with small bowwave and wake is even able to be animated with a few well crafted emitters to suggest motion over the water's surface.
Edit: found that Santa Fe colour photograph here:

The original TIFF is over 140 MB and incredibly sharp! You can see the emblem shining on the boy's beret as he strolls past the engine. It's Albuquerque rather than San Bernardino, the mission style depot had me fooled. B-SB and the Cajon Pass are featured extensively in this collection. If you are into industrial archeology you can spend your every leisure hour looking at all the material. Toledo, Huron, Cleveland, Ashtabula, Conneaut, Wheeling, Gary, Pittburgh, the Monongahela Valley, the Mesta Machine Company where huge machine was built and many, many more subjects of USA's industrial past now all but gone.
I collected all of these and the Hulett photographs a couple of year back and now only need to find them. That Libary of Congress is a pure treasure trove especially the HAER archives which contain excellent drawings and photographs for asset making.
I'd better stop before my enthusiasm and imagination gets the better of me.




















