According to wikipedia, Canis dirus is latin for "fearsome dog". Dire doesn't imply "bears the size of dump trucks" unless you reference d&d specifically.
Rare miniature animals would be cute. Things like miniature tigers would be silly, as we have matching small animals already (cats). The ideal would be tiny moose, bears, or elephants.
What we are really wanting here is an expansion of the "modifier" system to create more procedural variations. Currently, we have basically two:
* "Giant X": which makes things significantly larger, and usually deadlier as a result
* "X Man": which makes things "more humanoid", changing their size larger or smaller to be closer to the scale of other humanoids; plus giving them grasping ability and various other changes.
A few other scale modifiers might be:
* "Dire": larger than normal, but smaller than Giant; within rationally plausible scale; say 30% - 50% larger.
* "Gargantuan": even larger than Giant
* "Dwarf": Rationally smaller than normal, down to half or one-third size perhaps.
* "Miniature": Dramatically smaller than normal, a tenth size or significantly less. The webcomic Girl Genius has the "minmoth", which is a roughly rat-sized wooly mammoth; perhaps 1/10,000 stock size.
Some modifiers other than scale-based that show up a lot in fantasy:
* "Sabertooth": With specifically increased attacks, especially teeth and/or claws. May include adding them to species that don't have them normally, or not significantly
* "Arctic" / "Polar": Thicker, often white, fur; temperature tolerance; stealth; and omnivores tend toward becoming more carnivorous
Some of these can combine; one eccentric example from reality would be the
sabertooth salmon, which was 9 feet (2.7m) long and had fangs. Considering a modern true salmon maxes out at about 150 cm (0.15m), that's about 18 times the length; so it's had "Giant" and "Sabertooth" applied.
Many other modifiers are possible, once we have a general system in place.