t-rex -- 1/3/24

Today's selection -- from The Rise and Fall of Dinosaurs: A New History of Their Lost World by Steve Brusatte. The King of the dinosaurs:

“T. Rex is a celebrity character--the nightmare haunter--but it was also a real animal. Paleontologists know quite a lot about it: what it looked like, how it moved and breathed and sensed its world, what it ate, how it grew, and why it was able to get so big. In part, that's because we have a lot of fossils: over fifty skeletons, some nearly complete, more than for almost any other dinosaur. But more than anything, it's because so many scientists are impulsively drawn to the majesty that is the King, the way so many people are obsessed with movie stars and athletes. When scientists get infatuated with something, we start playing around with every instrument, experiment, or other type of analysis at our disposal. We've thrown the whole toolbox at T. rex: CAT scans to look into its brain and sense organs, computer animations to understand its posture and locomotion, engineering software to model how it ate, microscopic study of its bones to see how it grew, and the list goes on. As a result, we know more about this Cretaceous dinosaur than we do about many living animals.


“What was T. rex like as a living, breathing, feeding, moving, growing animal? Let me indulge you with an unauthorized biography of the King of Dinosaurs. 

“Let's start with the vital stats. 

“It goes without saying, but T. rex was huge: adults were about forty-two feet (thirteen meters) long and weighed in the ballpark of seven or eight tons, based on those equations from a few chapters ago, which calculate body weight from the thickness of the thighbone. These proportions are off the charts for carnivorous dinosaurs. The rulers of the Jurassic--the Butcher Allosaurus, Torvosaurus, and their kin--got up to about thirty-three feet (ten meters) long and a few tons--monsters to be sure, but they had nothing on Rex. After temperature and sea-level changes ushered in the Cretaceous, some of the carcharodontosaurs from Africa and South America got even bigger than their Jurassic predecessors. Giganotosaurus, for example, was about as long as T. rex and may have reached about six tons. But that's still a good ton or two lighter than Rex, so the King stands alone as the biggest purely meat-eating animal that lived on land during the time of dinosaurs, or indeed at any time in the history of our planet. 

“Show a picture of T. rex to kindergartners and they'll immediately know what it is. It has a signature style, a unique physique, or in scientific parlance, a distinctive body plan. The head was enormous, perched on a neck short and stout like a bodybuilder's. Balancing the oversize noggin was a long, tapering tail that stuck out horizontally like a seesaw. Rex stood only on its hind legs, its muscular thighs and calves powering its movements. Like a ballerina, it balanced on the tips of its feet, the arch or sole rarely touching the ground, all of its weight held by its massive three toes. The forelimbs looked useless: puny things with two stubby fingers, comically out of proportion to the rest of the body. And the body itself: not fat like one of the long-necked sauropods, but not the skinny frame of a fast-running Velociraptor either. Its very own body type. 

“The seat of Rex's power was its head. It was a killing machine, a torture chamber for its prey, and an evil mask all in one. At around five feet long from snout to ear, the skull was nearly the length of an average person. More than fifty knife-sharp teeth made for a sinister smile. There were little nipping teeth at the front of the snout and a row of serrated spikes the size and shape of bananas running along the sides of the upper and lower jaws. Muscles to open and close those jaws bulged out of the back of the head near the bottle-cap-size hole that served as the ear. Each eyeball was the size of a grapefruit. In front of it, but covered in skin, was a massive sinus system that helped to lighten the head, and then big fleshy horns at the tip of the snout. Small horns protruded in front of and behind each eye, and another stuck downwards from each cheek--gnarly knobs of bone covered in keratin, the same stuff that makes up our fingernails. Imagine this hideous visage as your last memory before the teeth came crushing down, breaking your bones. Many a dinosaur met its end that way. 

Restoration showing partial feathering

“Covering the body--the head, the wee arms, the stocky legs, all the way to tip of the tail--was a thick, scaly hide. In this way, T. rex resembled an overgrown crocodile or an iguana--lizardlike. But there was one key difference: Rex also had feathers sticking out from between its scales. As mentioned in the last chapter, these were not big branching ones like those on a bird wing, but were simpler filaments that looked and felt more like hair, the larger ones stiff like the quills of a porcupine. T. rex certainly couldn't fly, and neither did its ancestors that first evolved these proto-feathers, way back in the early days of the dinosaurs. No, as we'll learn later, feathers started out as simple wisps of integument, which creatures like T. rex used to keep warm, and as displays to attract mates and scare off rivals. Paleontologists have yet to find any fossilized feathers on a T. rex skeleton, but we're confident that it must have had some fluff because primitive tyrannosaur--Dilong and Yutyrannus; which we met last chapter--have been found coated in hairlike feathers, as have many other types of theropods preserved in those rare conditions that allow soft bits to turn into fossils. That means that the ancestors of T. rex had feathers, so it is highly likely that Rex did too. 

“T. rex lived from about 68 to 66 million years ago, and its dominion was the forest-covered coastal plains and river valleys of western North America. There it lorded over diverse ecosystems that included a bounty of prey species: the hornfaced Triceratops, the duck-billed Edmontosaurus, the tanklike Ankylosaurus, the dome-headed Pachycephalosaurus, and many more. Its only competition for food was from the much smaller dromaeosaurs--raptor dinosaurs a Ia Velociraptor--which is to say it didn't have much competition at all. 

“Although several other tyrannosaurs had thrived in these same environments during the preceding 10 to 15 million years, they were not the ancestors of T. rex. Instead, Rex's closest cousins were Asian species like Tarbosaurus and Zhuchengtyrannus. T. rex, as it turns out, was an immigrant. It got its start in China or Mongolia, hopped across the Bering Land Bridge, journeyed through Alaska and Canada, and made its way down into the heart of what's now America. When the young Rex arrived at its new home, it found things ripe for the taking. It swept across western North America, an invasive pest that spread all the way from Canada down to New Mexico and Texas, elbowing out all of the other midsize to large predatory dinosaurs so that it alone controlled an entire continent.”

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Steve Brusatte


The Rise and Fall of Dinosaurs: A New History of Their Lost World


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