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January 29 - February 3, 2025
Some of the first dinosaurs were being found around the same time, like the meat-eating Megalosaurus and the beaked herbivore Iguanodon. These were big animals, no doubt, but nowhere near the size of the creatures that left the gigantic sauropod bones. So scientists didn’t make the connection with dinosaurs. Instead, they considered the sauropod bones to belong to the one type of thing they knew could get so huge: whales. It was a few decades before that mistake was corrected.
it turns out that the thickness of the main bone in each limb that supports the animal—the femur (thighbone) for those that walk on two legs only or the femur plus the humerus (upper arm bone) for those that stand on all fours—is strongly statistically correlated with the weight of the animal.
Scientists are starting to build three-dimensional digital models of dinosaur skeletons, add on the skin and muscles and internal organs in animation software, and use computer programs to calculate body weight.
The technique is called photogrammetry, and it’s revolutionizing how we study dinosaurs. The super-accurate models it creates can be measured in precise detail. Or they can be loaded into animation software and made to run and jump, in order to determine what kinds of motions and behaviors dinosaurs were capable of.
There is no evidence gravity was substantially different during the Age of Dinosaurs, and oxygen levels back then were about the same as today, or maybe even slightly lower.
While mammals have a simple lung that breathes in oxygen and exhales carbon dioxide in a cycle, birds have what is called a unidirectional lung: air flows across it in one direction only, and oxygen is extracted during both inhalation and exhalation. The bird-style lung is extra efficient, sucking up oxygen with each breath in and each exhalation.
We know that sauropods had such a birdlike lung because many bones of the chest cavity have big openings, called pneumatic fenestrae, where the air sacs extended deep inside. They are exactly the same structures in modern birds, and they can only be made by air sacs.
If sauropods had lacked any one of these features—the long neck, the fast growth rates, the efficient lung, the system of skeleton-lightening and body-cooling air sacs—then they probably would not have been capable of becoming such behemoths.
It was still a teenager, but it had already lived a tough life. Its body was covered with all types of maladies: broken, infected, and deformed bones that testify to the rough-and-tumble world of the Late Jurassic, when even the biggest predators didn’t have an easy time hunting behemoths like Diplodocus and Brontosaurus, when the sharpest teeth and claws were no guarantee of surviving a whack from the spiky tail of a Stegosaurus. The Allosaurus was nicknamed Big Al,
there were many other predators below it on the food chain. There was Ceratosaurus, a twenty-foot-long mid-tier hunter with a frightening horn on its snout, a horse-size carnivore named Marshosaurus after the Bone Wars pugilist, and a donkey-size primitive cousin of T. rex called Stokesosaurus. Then you had the slashers: a number of lightly built, fast-running pests like Coelurus, Ornitholestes, and Tanycolagreus, the Morrison version of cheetahs. And all of these meat-gobblers, even Allosaurus, probably lived in fear of another monster that reigned near the top of the food chain. It’s called
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These sauropods also had different types of necks: that of Brachiosaurus arched proudly into the heavens with the erect profile of a giraffe, perfect for reaching the highest leaves, but Diplodocus may not have been able to lift its neck much past its shoulders and may have acted more like a vacuum cleaner sucking up shorter trees and shrubs. Finally, the heads and teeth of these sauropods differed as well. Brachiosaurus and Camarasaurus had deep, muscle-wrapped skulls and jaws lined with spatula-shaped teeth, so they could eat harder foods like thick stems and waxy leaves. But Diplodocus had
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the middle Cretaceous Argentinosaurus, which at more than a hundred feet (thirty meters) long and fifty tons in mass was the largest animal known to have ever lived on land.
The plate-backed stegosaurs went into long-term decline, gradually wasting away until the last surviving species succumbed to extinction sometime in the Early Cretaceous, snuffing out this iconic group once and for all. Replacing them were the ankylosaurs,
the gnarly-textured skull of a carnivore called Rugops, which probably scavenged carcasses as much as it hunted.
the carcharodontosaurs. Among the family album are three species—Giganotosaurus, Mapusaurus, and the hauntingly named Tyrannotitan—all from South America, which during the Early to middle Cretaceous was still connected to Africa. Other siblings lived farther afield: Acrocanthosaurus in North America, Shaochilong and Kelmayisaurus in Asia, and Concavenator in Europe. And there’s also another one from the Sahara, called Eocarcharia, which Paul and I described
If two species share many novelties between only themselves, they must be each other’s closest relatives. If those two species share other novelties with a third animal, those three must be more closely related to one another than to the remainder of the dinosaurs. And so on, until a complete family tree has been drawn. This whole process is what we in the business call a cladistic analysis.
tyrannosaurs were an ancient group that originated more than 100 million years before T. rex, during those golden days of the Middle Jurassic
These first tyrannosaurs weren’t very impressive. They were marginal, human-size carnivores. They continued this way for another 80 million years or so, living in the shadows of larger predators, first Allosaurus and its kin in the Jurassic, and then the fierce carcharodontosaurs in the Early to middle part of the Cretaceous.
They reached the top of the food chain and ruled the world during the final 20 million years of the Age of Dinosaurs. THE STORY OF tyrannosaurs
This work was mostly done by the end of 1905, when Osborn announced the new dinosaur to the world. He published a formal scientific paper designating the new dinosaur as Tyrannosaurus rex
Brown was an eccentric. He hunted fossils in the dead of summer in a full-length fur coat, made extra cash spying for governments and oil companies, and had such a fondness for the ladies that rumors of his tangled web of offspring are still whispered throughout the western American plains.
clear proof that tyrannosaurs had gotten an early evolutionary start. Kileskus was found in rocks formed during the middle part of the Jurassic Period, about 170 million years ago, more than 100 million years before T. rex and its colossal cousins
Kileskus was probably only seven or eight feet long, most of that being the skinny tail. It stood a couple of feet tall at most—it would have come up to your waist or chest like a big dog. And it wouldn’t have weighed more than a hundred pounds or so.
forty-foot-long, ten-foot-tall, seven-ton T. rex
Actual descriptions of trexes are surprisingly rare
The story of how these dinosaurs got there could be written into the script of a disaster movie. The teenager was found at the bottom of a pit several feet deep, trampled by the adult. They were both engulfed in mud and volcanic ash. Something terrible had clearly happened,
named their new dinosaur Guanlong, meaning “crown dragon” in Chinese. The name refers to the gaudy Mohawk-like crest of bone that runs along the top of the skull. The crest is thinner than a dinner plate and pierced by a number of holes. It’s the type of absurdly impractical-looking thing that probably had only one function: a display ornament for attracting mates and intimidating rivals,
At best, Guanlong was a second- or third-tier predator, an inconspicuous link in a food chain dominated by other dinosaurs. This would have been the same for Kileskus and for some of the other small and primitive tyrannosaurs that have been found recently, like the tiniest one of all, the greyhound-size Dilong from China, and Proceratosaurus
This happens all too often in the field of dinosaur research: a single fossil emerges that hints at a major evolutionary story—the oldest member of a major group, or the first fossil to exhibit a really important behavior or feature of the skeleton—but it’s too broken or incomplete or poorly dated to be certain. Then another fossil is never found and it’s just left hanging, a cold case waiting to be solved.
With Yutyrannus we got lucky—these skeletons were buried so quickly, after a volcanic eruption, that some of their softer parts did not decay. Packed all around the bones were dense clusters of slender filaments, each about fifteen centimeters (six inches) long. Similar structures were preserved on the much smaller Dilong, which was found in the same rock unit in northeastern China. These are feathers.
Yutyrannus looks like an overgrown version of Guanlong, with its ornamental head crest, big nostrils, and long, three-fingered hands. It doesn’t have the deep muscular skull, thick railroad-spike teeth, and pathetic arms of T. rex.
This book is giving me a new appreciation for Yutyrannus
despite their big bodies, Yutyrannus and Sinotyrannus weren’t very closely related to T. rex, and they didn’t have much to do with the evolution of colossal sizes in the latest Cretaceous tyrannosaurs. Instead, they were primitive tyrannosaurs experimenting with large body sizes independent of their later cousins.
We know that the big switch happened some time in the middle part of the Cretaceous, between about 110 and 84 million years ago. Before this time, there were many small to midsize tyrannosaurs living all over the world, with only a few random bigger species like Yutyrannus. After this time, enormous tyrannosaurs reigned throughout North America and Asia, but only those continents, and no species smaller than a minibus remained.
About 94 million years ago, between the Cenomanian and Turonian subdivisions of the Cretaceous Period, there was a spasm of environmental change. Temperatures spiked, sea levels violently oscillated, and the deep oceans were starved of oxygen. We don’t yet know why this happened, but one of the leading theories is that a surge of volcanic activity belched enormous quantities of carbon dioxide and other noxious gases into the atmosphere, causing a runaway greenhouse effect and poisoning the planet.
A pattern is clearly coming into focus: none of the large predators from this 25-million-year time window are tyrannosaurs. All of them belong to other groups of big carnivores like the ceratosaurs, spinosaurs, and especially the carcharodontosaurs.
when the clock struck 84 million years ago and the fossil record became rich again, the carcharodontosaurs were gone in North America and Asia, replaced by monstrous tyrannosaurs. A major evolutionary turnover had occurred.
by the dawn of the Campanian subinterval of the latest Cretaceous, beginning about 84 million years ago, tyrannosaurs had risen to the top of the food pyramid. During the final 20 million years of the Cretaceous, tyrannosaurs flourished,
they lived so hard that we have yet to find an individual that was more than thirty years old when it died.
Some tarantulas live longer than that
They were a pack; the attacker was their leader, and now the underlings got to share in its victory.
...are you serious
This should go without saying but there is 0 evidence Trex was a pack hunter
may have even been warm-blooded like us. If that was the case, then Rex needed to gobble up some 250 pounds (about 111 kilograms) of grub each and every day. That’s many tens of thousands of calories, maybe even hundreds of thousands, depending on how fatty the King liked its steak. It’s roughly the same amount of food eaten by three or four large male lions,
Wow
Maybe you’ve heard the rumor that T. rex liked its meat dead and rotten, that Rex was a scavenger, a seven-ton carcass collector too slow, too stupid, or too big to hunt for its own fresh food. This accusation seems to make the rounds every few years, one of those stories that science reporters can’t get enough of. Don’t believe it. It defies common sense
I really wish other people would understand this
Many of those Triceratops and Edmontosaurus bones pockmarked with T. rex tooth impressions show signs of healing and regrowth, so they must have been attacked while alive but survived. The most provocative of these specimens is a set of two fused Edmontosaurus tailbones with a T. rex tooth stuck between them,
Surprisingly I have had people deny this
T. rex was different, though. Its bite marks are more complex: they start with a deep circular puncture, like a bullet hole, which grades into an elongate furrow. This is a sign that Rex bit deeply into its victim, often right through the bones, and then ripped back. Paleontologists have come up with a special term for this style of eating: puncture-pull feeding.
That is actually really cool
how much force it required: 13,400 newtons, equivalent to about 3,000 pounds. That’s a staggering number—about the weight of an old-school pickup truck. By comparison, humans exert a maximum force of about 175 pounds with our rear teeth, and African lions bite at about 940 pounds. The only modern land animals that come close to T. rex are alligators, which also bite at around 3,000 pounds. However, we need to remember that the 3,000-pound figure for T. rex is for only a single tooth—imagine
That is crazy
because it’s a measure of the force required to make one observed fossil bite mark, it’s likely that this is an underestimate of the maximal biting power.
modeling provides us with the range of ten to twenty-five miles per hour that I cited for T. rex’s speed.
That is not very fast
T. rex was simply too big to run exceptionally fast. Its sheer size also conferred another liability: the Tyrant King couldn’t turn very quickly, or otherwise it would topple over like a truck taking a corner too sharply. Thus, the reality is, Spielberg had it wrong, T. rex was no sprinter, and it would have ambushed its prey with a quick strike rather than chasing it down
There’s really only one way numerous individuals of the same species can be preserved together: they must have lived and died together.
That is just incorrect, and also that is for albertasaurus not Trex. Even if we assumed they did pack hunt, closely related animals can have very different lifestyles from each other so we shouldn't attribute the lifestyle of one animal to that of another without evidence backing that up.
It’s called the encephalization quotient (EQ). It’s basically a measure of the relative size of the brain compared to the size of the body
Isn't this method notoriously inconsistent? I remember hearing about that since the thing that develops intelligence is the amount of neurons in the brain and not it's relative size
no dinosaur eggs that we know of are larger than a basketball, so even the mightiest species like T. rex would have been, at most, the size of a pigeon when they entered the world.
That is adorable
When T. rex took its crown, just a couple million years before the Age of Dinosaurs ended in a bang, the map was more or less as it is today.
