7 – Tyrants Return

Tyrannosaurus rex, by Julius Csotony. This reconstruction depicts “Scotty”, one of the largest and most complete specimens ever found. This is the appearance I’ve chosen for adult T.rexes in this timeline. (1)

Summer was only just beginning, when the world ended.

The asteroid impact that killed Mesozoic dinosaurs - and with them, the vast majority of life on Earth at the time - likely occurred at the tipping point between spring and summer in the northern hemisphere. Possibly, during the early days of June. (2)

It was one of Earth’s worst days, in ways that defy description. The immense size of the asteroid (bigger than Mount Everest) caused cataclysmic damage even before the impact.

It’s hard to communicate the scale of the disaster, beyond listing an increasingly horrifying list of isolated anecdotes.

Fossils from marine vertebrates that died in the impact and were catapulted on land, have their gills filled with tiny glass spheres: rocks that were vaporised and glassed by the sheer energy of the collision.

Any animal or plant to survive the first shockwave would have to contend with the horrifying prospect of being baked alive by infrared radiation and subsequent build-up of heat in the atmosphere.

Within the first day, most vertebrate fauna above very small body size would have been cooked alive. And for survivors, the long, cold, bitter winter set in… All in all, it seems that no terrestrial vertebrate larger than 5kg in body mass managed to outlive the apocalypse. (3)

Such was the cosmic power required to put an end to the reign of the dinosaurs. (4)

Of course, one dinosaur lineage survived into our present, and occasionally grew large again. It even earned our attention, in more ways than one. Birds are everywhere in human life - as food, pets, iconography, or simple objects of study and curiosity.

But the very same traits that allowed birds to survive the asteroid - their small size, peculiar reproductive and feeding habits - confine them to a supporting role in present day’s ecosystems. (5)

Sixty-six million years after the end of her world, Roberta emerged from her egg. And it might as well have been on a different planet, given how much the Earth has changed in the meantime. And yet, with her birth, all the ingredients came together for an incredibly powerful cocktail.

There was the very defiance of extinction itself, of course. This act of human daring - or hubris, depending on who you ask - now relied on more than the manipulation of ancient DNA. In fact, the scientific and technical challenge was morphing.

Sorna’s staff now had to care for a hatchling that literally didn’t belong to the present world. The capitalist necessity to get it done weighed on everybody’s mind. The high-strung, stressed-out, ambitious personalities in play proved to be the final, crucial ingredient.

All in all, it sounds like a description of a disaster waiting to happen.

In so many ways, it was. But at least back then, InGen’s set of killer dice delivered their luckiest roll yet.

The InGen staff had to deal with two conflicting impulses: that of celebration, and the worried anxiety of having to look after a newly born animal. Wu was quick to stamp out any festive initiative, and forced the facility’s top brains into the same room, to tackle a very simple problem.

What the hell would they do next?

Countless hours of thought and analysis had gone into finding, extracting, and computing paleo-DNA; preparing artificial eggs, fertilising them, and hatching them. But what did the staff actually know about Tyrannosaurus rex, as an animal?

Luckily for InGen, Tyrannosaurus in particular had been studied extensively before, to the point of obsession. This is an inevitable byproduct of the animal’s popularity. Research works and papers mentioning, or focusing on T.rex inevitably draw more attention from the public, and more funds. (6)

Roberta’s ancestors lived at the very end of the Cretaceous, in the last two million years of the Mesozoic; they were around to witness the end of the world. At the time, they roamed the forests and floodplains of Western North America: the continent at the time was split by the sea, specifically by the so-called Interior Seaway. From the shores of the Seaway to the heart of the forests, Tyrannosaurus rex was the apex predator of its environment.

In adulthood, the animal grew to truly gigantic sizes, over 12m in length. But the lineage that eventually produced T.rex was not traditionally one of giant predators, on the contrary.

T.rex’s ancestors were lithe, relatively small to mid-sized predators, ranging between two and seven metres in length. Agile, feathered, and built for speed, these animals lived in the shadows of larger predators in their environments, were closer to birds than most, and eventually spread from Asia into Western North America.

Due to a combination of factors - some environmental, some the lucky product of natural selection - the family of tyrant dinosaurs would eventually displace their competitors, which are completely absent from the fossil record after Tyrannosaurus rex takes over. But what made this animal so successful?

The biggest component was a stark differentiation in the life stages the animal went through, from hatching to adulthood.

When mammals are born, they are generally smaller versions of what they will look like when they stop growing. While body proportions do change, there is a very clear and recognisable anatomical similarity between young and old individuals. Moreover, mammals spend the majority of their lifespan as adults.

Not so Mesozoic dinosaurs, as InGen would soon learn: the vast majority of a dinosaur’s life is spent as an immature individual. Moreover, the anatomical differences between the young and old are significant, and sometimes extreme, at least by the standards of land vertebrates. (7)

Tyrannosaurus is a perfect example of that. The very young individuals are gracile and lithe, built for speed, with the hind limbs in particular presenting many cursorial adaptations. The skull is elongated and narrow, with steak-knife teeth made for slicing the meat of smaller prey - say, human-sized prey.

Subadult individuals are large and powerful terrestrial predators, with considerable mobility for their size and weight. The shape of the skull, and the shape and number of teeth, begins to change, thickening and widening, enabling the animal to go after larger and stronger prey.

In adulthood, Tyrannosaurus is a terrifying predator. What used to be the cursorial adaptations of its hind limbs no longer serve for fast running, but rather enable the animal to grow to a tremendous body mass of nine tonnes or more without sacrificing mobility.

The skull becomes enlarged and built to withstand shocks. (8) The neck thickens into a bundle of powerful muscles, to power a bite strong enough to crush a car. The teeth are thick and banana-shaped, no longer meant for slicing, but rather for crushing bone and armour with a single bite - and for holding on to a struggling prey that is the size of an elephant.

And this prey was heavily armoured more often than not, too. Every major herbivore that shared its environment with Tyrannosaurus has an impressive arsenal of defensive and offensive weaponry.

Triceratops’ horns were taller than an adult human being. Ankylosaurus was so heavily armoured that even its eyelids were completely ossified. These extraordinary bodies were crafted by an evolutionary arms race that extended over millions of years, in which Tyrannosaurs and their prey grew larger and more extreme with every new iteration.

But it was the surprising degree of differentiation that proved to be T.rex’s secret weapon.

This strategy has a clear advantage: where normally every species has a very particular role in its ecosystem, Tyrannosaurus could multitask. Need a diminutive predator chasing insects, lizards, and small mammals? Newborn Tyrannosaurs have you covered. What about the niche reserved for fast, agile hunters? Juvenile T.rexes will pitch in. The same logic applies to large, and then to extremely armoured prey.

By differentiating its life stages, Tyrannosaurus could out-compete multiple species across multiple fronts. This surely goes a long way to explaining why it is found in such numbers in the fossil record.

Naturally, this incredibly successful adaptation backfired after the asteroid impact in Yucatan. Where a more generalist species could adapt to living off a single surviving food source - say, seeds surviving underground - Tyrannosaurus was extremely dependent on the entirety of its ecosystem, since it ate different things at different ages.

The same is true of many other contemporary dinosaur species, which ticked off all the boxes to be perfect victims for the asteroid: large in body size, incredibly specialised, and dependent on a complex food web.

InGen also knew Roberta was very likely to be diurnal, (9) among a host of other scattered factoids: it would be endowed with a large brain, even relative to its body size. (10) It was clearly capable of surviving shocking injuries. (11) It was vulnerable to a prehistoric variant of trichomoniasis, an infection that plagues birds to this day, which can cause death by starvation. (12)

While useful and interesting in and of themselves, none of these considerations helped Sorna’s staff with the immediate issue of rearing a T.rex hatchling.

While the top scientists brainstormed and pondered, they’d left young Roberta in the care of the most junior geneticist on site, one Amanda Weaver. (13)

In a way this was of course a simple exercise of seniority, a classic workplace move seen on a daily basis all over the world.

Weaver was no animal handler. She made the point to Wu, but it fell on deaf ears. Robert Muldoon, the gamekeeper for Hammond’s nature reserve in Tanzania, had already been notified and was about to board a plane to Costa Rica, but he wasn’t on hand at the moment. (14)

Wu had reasons beyond simple seniority to burden the junior geneticist with grunt work that had nothing to do with her qualifications, however. Weaver had been the first on the scene when Roberta had hatched from the egg.

No one knew if Tyrannosaurus hatchlings imprinted on anyone upon birth. In fact, it seemed unlikely. Any species with so large a body size difference between adults and newborns is unlikely to exhibit complex parental behaviour.

Nevertheless, Wu wasn’t about to waste the opportunity. If there was any chance Roberta liked Weaver more than the rest of the staff, then he would be sure to take it.

Ever since then, countless words have been spent on this original decision.

Had Weaver not been selected as Roberta’s guardian, would things have turned out different? This is a popular point of departure for people to speculate on different outcomes. (15)

In all frankness, the impact of this initial decision is probably exaggerated. Weaver had plenty of exposure to InGen’s animals, over a period of years. And given the literal forces of nature at play, it’s doubtful how much consequence can be assigned to any one individual.

Nevertheless, if nothing because Wu did select Weaver, her time spent with newborn Roberta ended up having a historical significance all of its own.

As such, it pays to report her account of the encounter, which follows, in her own words. (16) For better or worse, it would prove foundational to what was to come.

Footnotes:

(1) I really like this reconstruction, for a couple of reasons. The vast majority of Tyrannosaurus illustrations fail to depict just how bulky and muscular it was in adulthood. Where most theropods of comparable height and length remained relatively slender figures, an adult Tyrannosaurus was a mountain of muscle with a forward-tipping posture, thick hind limbs, and a relatively low centre of gravity. Add the bone-crushing bite and you have an animal built to tackle and kill extremely strong, large (elephant-sized and up), heavily armoured prey.

(2) It is an old hypothesis, but with relatively decent support. You can read a recent paper about it here. It is perhaps fitting, then, that Jurassic Park’s original theatrical release was 9th June. Given that we’re unlikely to narrow down the timing of the impact even further than “early June”, I have more or less elected 9th June as my own Mesozoic Remembrance Day. Remember to wear some amber on your person to mark the occasion, and press F to pay your respects to the fallen!

(3) Really, seriously. Hollywood has toyed with the notion of asteroid disaster movies in the past, but this is one avenue where they completely fail to portray and encompass the scale of the apocalypse. If you want to get a more vivid picture of what the impact must have been like, take a look at this. For a more detailed breakdown, read here. Fair warning: it is an absolutely horrific and harrowing read.

(4) One that lasted for an absurdly long time, too. You might have seen a meme about it making the rounds: Tyrannosaurus rex is closer in time to the iPhone than it is to the iconic Jurassic herbivore Stegosaurus.

(5) Occasionally birds did and do reverse to larger body sizes - think of ostriches and emus, but also moas and Haast eagles, or the infamous terror birds (phorusracids in particular). Arguably birds retain the dinosaur tendency to gigantism even today, given the anatomical constraints required for flight: after all, flying mammals (bats) don’t even get close on average. But there’s no doubt that the apex of trophic relationships on Earth today is occupied by mammals the overwhelming majority of the time.

(6) There is a joke in palaeontology that T.rex is “the ruler of all dinosaurs”. Not in the sense of “monarch” but in the sense of “measuring reference” :D studies about locomotion and biomechanics, body mass, and sundry other things, which could be performed on literally any species, somehow always end up involving Tyrannosaurus. It is quite literally the measuring rod of the Mesozoic.

(7) Obviously amphibians do one better, with actual life stages that look completely different from one another. Nothing so extreme in the case of dinosaurs, but Tyrannosaurus in particular fulfilled a radically different role in the ecosystem as it grew.

(8) The skull is actually a fantastic way to get a sense of how much Tyrannosaurus changed during its lifespan. Take a look at this ontogram, as well as this one, which is from Carr, 2020.

(9) Like most Mesozoic dinosaurs. Of course a few did have nocturnal adaptations that have made it into the fossil record, and you can definitely name nocturnal birds today - just think of owls. However, it’s important to keep in mind that dinosaurs (both living and extinct) place(d) a lot of emphasis on sight and colour, and if birds and crocodiles are an indication, this extends to vocal communication as well.

(10) Although it’s important to note that a large part of it was devoted to sensory perception, primarily sight and smell, which are among the most developed in the history of Earth’s fauna. A dizzying consideration, given all the other adaptations that made this animal a formidable predator.

(11) Stan, a Tyrannosaurus fossil we’ve mentioned before, managed to survive a direct bite to the neck by another T.rex. The bite broke Stan’s neck, but its muscles were so strong, they acted as a natural bust of sorts, and kept the cervical vertebrae together long enough that they could fuse and heal. This is the kind of absurd factoid that sounds completely made up, and would be straight-up unbelievable if it was in fiction, and yet there it is - Stan survived a broken neck long enough for it to heal, not just outlasting the injury itself, but also managing to drink and eat while recovering. Incredible.

(12) As evidenced in the fossil record.

(13) Character of my own invention. She is the employee that snapped the photo of Roberta shortly after her hatching, but that’s far from the only reason history will remember Amanda Weaver.

(14) Why bother staffing Sorna with a handler in the first place, right?

(15) Great (Wo)Man Theory of history proponents in this timeline pay a lot of attention to this juncture.