Frankly, although I've quite enjoyed some of the digging, I can't spare the effort to do more. I also have a problem in that I believe your answers have said that this animal has a single hoof (hoofed , not split). My sources state specifically that the only animals with a single hoof are related to horses, but you have said that is not the case.

Raak asked if it was an extinct species of horse. I said it wasn't an extinct species of horse, but distantly related, i.e. it belongs in the order Perissodactyl, like horses do.
There is a very important piece of identifying information that no-one has really tried to ascertain.

[All who haven't drifted off] Here is a roundup of all helpful facts so far known:
A non-human, extinct, quadrupedal mammal, of the order Perissodactyla (odd-toed ungulates). Died out more than 100,000 years ago, rhinoceros-like and larger than a toaster.

[irach] Not with two horns.

Has this creature evre been featured in a film?

[Projoy] YES Baluchitherium.
A prehistoric relative of the rhinoceros, featured in an episode of Walking With Beasts and the largest mammal ever to have existed. I would also have accepted Paraceratherium or Indricotherium. And I honestly thought it was fairly well known.

[Spangle] Yes that is the answer.
Should I have added *Audience go wild, not untinged with relief* for avoidance of doubt?
[GL] Is this a rhetorical question?

Come to think of it, there's a talking baluchitherium in Brian Aldiss' short story "Old Hundreth".

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It will not suprise onlookers to know that that was a triumph for Google rather than my prior general knowledge, but I for one am glad to know it now. Getting it to stick in memory will be the challenge...

The next is MINERAL (there might be odd bits of the other two in there, I'm not sure).

[Rosie] A Structure? STRICTLY, YES
[CdM] Unique? YES
[INJ] Primarily metal? YES
[Software] Manufactured? YES