They would need a warmer climate and less oxygen, anything back too far would die off in hours, imho.
Try a giant land scorpion, Pulmonoscorpius:
https://www.youtube.com/watch?v=4JK2IEM4zzk 0:21
Even if they couldn’t survive in the wild, evil overlords would pay top dollar to stock their scorpion pits. Kim Jong-Un alone would buy 1,000.
ETA: video also features several other creatures mentioned in this thread. Worth a look!
T. Rex. Because *hell *yeah!
Neanderthals. Not least because it would shut the creationists up once and for all. But also because I think they might actually thrive today. There is reason to believe they were both smarter and stronger (relative to size) than we are. And I read somewhere (just googled, can’t find it to verify) that the genetic mutations which make some people less susceptible to HIV tend to be found in people with higher levels of Neanderthal genes.
Someone above asked about how we know their language skills were less than ours - it has to do with the area of the brain that provides language ability. The skull fragments we’ve found indicate that that brain area is smaller and less developed in Neanderthalis.
But we know they were creative, and painted. We know they made tools, and traded. I think they’d do OK, at least in the second generation.
If I could have two, I’d add the Irish Elk. Because shame on us; that’s why.
Maraapunisaurus, nee Amphicoelias fragillimus. Go big or go home.
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I know they wouldn’t survive in the current atmosphere and oxygen levels. But ever since this thread started, I keep thinking about those gigantic prehistoric dragonflies.
“… Meganeuropsis had a body roughly 47 centimeters long, with a wingspan of 75 centimeters across.” So almost 30 inches wide, wingtip to wingtip. Man, I’d love to see one of those.
Something like this?
You can just call me Megan.
Those would be sooo cool to se. 
I would not. No, I am definitely quite sure that I would NOT enjoy seeing one of those.
I’m betting you would not either, unless it was behind glass, or, you know, maybe weighed down somehow. In fact, I can’t think of a better way to view one of those than if you could somehow be provided with a particularly detailed statue or a life-mold of some sort. . .
They’d be harmless. Now, the giant spiders and scorpions :eek:…but all those things would die in a short time.
I don’t know about that. Dragonflies are pretty fierce predators. They don’t eat things larger than they are, so I don’t think they’d attack people. But I could see them eating small pets.
Actually, even ignoring the issues with the atmosphere not supporting them today, I think they’d quickly go extinct. They would naturally pretty on birds. But birds are much smarter than normal dragonfly prey. And those wings are fragile, and don’t heal. My guess is that just as small birds mob crows and raptors to drive them away, they would mob giant dragonflies and break their wings.
In fact we can probably thank birds for the absence of giant arthropods in general.
“Prey” on birds, not pretty.
That and the atmosphere wont support them anymore.
♪♫ It’s raining Meganeuropsishads, hallelujah… ♪♫
Hm, doesn’t quite scan.
Even the current dragonflies are not harmless. I take it you’ve never been bitten by one? They absolutely deserve their name.
Now, I will grant you that I was a child at the time, and was probably trying to play with the dragonfly, who demonstrably did NOT want to play with me, so I don’t argue that they are aggressive toward humans.
But they hurt. They hurt quite a lot.
I had no idea dragonflies could bite a human.
Well, first you have to try hard to get bitten. And then most species can’t even manage to bite you. And then it’s only an minor thing. Nothing more. Horse flies are nastier bitters.
I played a lot with dragonflies as a kid. I often held them. I might have gotten nipped once or twice. Or not. That sounds vaguely familiar.
I’m going with “dragonflies are harmless”. No, the giant ones wouldn’t be, but ours? Harmless.