Mega fauna downsized?

I saw this film called "The Meg' about a prehistoric shark from c.2-3 million years ago that was not as extinct as everyone thought. It wasnt all that great,but it was far from the worst I had seen. 

I read some articles about megladons and noticed that all of the artist impressions looked like a great white shark. I also looked up giant elks and cave bears and I noticed that all of them looked like bigger versions of today's animals.

Is it possible that a lot of ther mega fauna from the Ice Age did not die out, but merely downsized?

Some of those animals, like the terror birds, clearly became extinct,but grizzlies are still bears and mountain lions could easily be smaller sabre tooth cats and the pretty big elks of today look the same as the giant elks of c.10,0000 BC.  Wooly rhinos mammoths lost their hair and moved south too?

Or chased south by humans....

Just random thoughts floating around in my head on a rainy day!