The gap in time separating humans from Tyrannosaurus Rex in the evolutionary chain is roughly 67 million years. The time separating T. Rex from its Jurassic Era dino counterparts, like Stegosaurus, is approximately 83 million years.
Consider how much life has changed in the past 66 million years. Archaic mammals flourished and ultimately went extinct long before anything like the world’s modern fauna appeared. Saber-fanged, knobbly-headed herbivores such as Uintatherium, lemur-like primates called adapiforms, razor-jawed carnivores known as creodonts and many other strange forms proliferated and disappeared. Even lineages familiar to us today, such as horses, rhinos and elephants, evolved and diversified and are now represented by just remnants of what once existed.
The time between the last Triceratops and now has seen radical evolutionary changes. Now think of the 83 million years between the Jurassic and Cretaceous titans. During that time, the first flowering plants bloomed; the fish-like ichthyosaurs disappeared as plesiosaurs and mosasaurs became the predominant predators of the seas; vast herds of hadrosaurs and ceratopsids occupied places once dominated by sauropods; tiny tyrant dinosaurs transformed into apex predators, and early birds established themselves in ever-greater variety alongside their dinosaurian kin.
We tend to think of dinosaurs as existing at the same time period on Earth’s evolutionary stage. But, that is clearly not the case. Instead, we are reminded that evolution is a heaving, combustible, ever-changing process that is not so easily delineated.
The T. Rex, then, is “minding the history gap” between early dinosaurs and humans on the grand, evolutionary stage played out over millions of years.