Spinosaurus

Oh boy, let's hope we can find a complete skeleton of this badboy! Can't wait! RAWR! 
Spinosaurus probably could outrun a Tyrannosaurus and out-kill a Carcharodontosaurus and and and... ohhhhhhhhhhhhhh....

Huh...

Well....

Would you look at that...

And for the longest-ever-o-philes, given the proportions in my restoration, this animal would be roughly 12,5 metres long.

A long meaty tail makes sense in keeping the animal from falling on its face. Quadrupedalism seems impractical, but then again, staying any length of time on dry land would probably be impractical as well.

Spinosaurus!

Edit: Aaand, would ya look at that, again. Seems I was right about a very long tail, but who coulda foreseen a tail with a sail? Oh boy!