Who would win?

[CoffeeGrunt]

To be fair, I think a Bolter would make a right bloody mess of a T-Rex before it even closed for the kill.

[daboarder]

please the hive tyrant (sorry T-Rex) eats the marine every time

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Oh your one of "those" believers

I thought it was meant to be, the dinosaurs existed at the same time as us, a mere few thousand years ago

[Tuatara]

I thought it was meant to be, the dinosaurs existed at the same time as us, a mere few thousand years ago

Erm....65 Million years ago for the T-Rex, Humans started to humans around 200,000 years ago (don't worry - just me being a geek).

As for the OP - Astartes. If a puny little human like Luke Skywalker can kill a Rancor, then an Astartes would kill a T-Rex without breaking a sweat.

[Wolfshade]

So the dinos existed before the earth was created

[YorkNecromancer]

So the dinos existed before the earth was created

Well, I think we all know what this means.

That's empirical evidence that dinosaurs can survive hard vacuum, which suggests that their hide was actually a lot tougher than previously thought. Based on this finding, I'd have to say that unless the Astartes brought Kraken bolts, I'm now starting to lean in favour of the Tyrannousaur. Anything which can float in space for thousands of years and still evolve into one of nature's fiercest predators (or possibly carrion eaters, the science is inconclusive) has to have at least a shot against the Emperor's Finest.

[Psychosplodge]

An unarmed but power armoured marine would probably use the "swallow me" and then dig his way out method...

[CoffeeGrunt]

I think a T-Rex would struggle to fit an Astartes in its gob.

[Psychosplodge]

Oh.
Aren't they that big?

[CoffeeGrunt]

That documentary with Richard Attenborough in it shows they can barely fit a human in their mouth, not without chewing and ripping a bit.

[Psychosplodge]

Ah. in that case I'd trust in the integrity of power armour. and the strength and tactical acumen of a space marine.