Which came first, sharks or Tyrannosaurus rex?

sharks came first, by 382 million years. Shark-like fish were swimming the oceans in the Ordovician.

Side by side

sharks

Scales from shark-like fish appear around 450 million years ago and unambiguous shark teeth by about 420 million years ago. The first trees appeared roughly 385 million years ago, so sharks predate trees by tens of millions of years. They also predate Saturn's rings on most current estimates, and they have survived all five mass extinctions.

Tyrannosaurus rex

Tyrannosaurus rex lived from about 68 to 66 million years ago, right at the end of the Cretaceous. Stegosaurus died out around 150 million years ago. That means T. rex is closer in time to us — 66 million years — than it is to Stegosaurus, by more than 20 million years. The two are routinely drawn in the same picture and never met.

Deep-time dates are approximate to within tens of millions of years and shift as new fossils are found. Deep-time date, approximate to within a million years or so.