T. rex vs. Spinosaurus: The Truth

Edit: Portions of this post’s text were updated 23 July, 2019.


It’s the prehistoric showdown that’s swept the world since Jurassic Park III in 2001 – rivaled only by the legendary conflicts of Tyrannosaurus vs. TriceratopsVelociraptor vs. Protoceratops, and Allosaurus vs. Stegosaurus.

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Immortalized by a one-minute fight, Tyrannosaurus vs. Spinosaurus was the first time two reasonably modern versions of predatory dinosaurs got violent on the silver screen. Initially with the upper-hand with its bone-crushing maw, T. rex was bested by the durability of its opponent. Using its dextrous front limbs, the Spinosaurus gripped the rex by the neck and snapped it – leaving the other dead on the ground.

It makes for a tense moment, sure, but as we’ve mentioned before – dinosaurs couldn’t pronate their hands like that. So, the MK-finishing move that the spino used was moot.

Let’s talk about the real Tyrannosaurus and the real Spinosaurus. Let’s do a breakdown of what makes each dinosaur tick as well as some of their defining characteristics. Ignoring the fact that they lived thousands of miles and millions of years apart, let’s beg the question: If they could ever meet, who would win in a fight?

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Going by alphabetical order, Spinosaurus is first. S. aegyptiacus, discovered in Egypt, was a semi-aquatic predatory theropod. I’ve restored it with plumage* that resembles the common loon (and the individual in question is named Becky, for those of you people who like to watch movies featuring anthropomorphic blue tangs). It’s an awfully big animal, and that seems to strike most people. Upper estimates of Spinosaurus‘ size go upwards of some twenty meters in length and over 7.25 tonnes (8 US tons). The animal pictured before you is a more conservative size estimate (somewhere in the neighborhood of 17-18 meters).

*(2019 addendum: this animal probably wouldn’t feature significant, if any, feather coverage)

Your Dinosaurs Are Wrong, while also functioning as one of my favorite YouTube series of all time, has done a segment on Spinosaurus that explains spinosaur locomotion. The center of gravity for this animal, were it to walk bipedally instead of doing its typical swimming, would’ve been too far forward. It would’ve fallen on its chest (a quite possibly fatal injury!). To compensate, the dinosaur would’ve needed to adopt a more tripodal stance with its neck reared back to provide proper balance. So, the animal probably wasn’t all that graceful on above water. Imagine a giant duck that kind of struggles to retain its balance, stumbling about from place to place as it did whatever it needed to on land.*

*(2019 addendum: new restorations of Spinosaurus show this animal as biomechanically competent in the “typical” theropod pose)

We can say, with confidence, that Spinosaurus was an at least semi-aquatic animal based on oxygen isotope analyses of it and several of its relatives. The hook-like talons on its hands were also perfect for swiping and scooping up aquatic prey. Consider it the prehistoric equivalent to a polar or grizzly bear.

Also, the raised vertebrae on the back was likely not a thinly-covered sail used for thermoregulation. It was more likely covered in a large “hump”* of soft tissue and used to make the animal look bigger or for intraspecies identification.

*(2019 addendum: it was more of a thinly-covered sail than a hump; whoops!)

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Tyrannosaurus rex, however, was very much a terrestrial predator built for high-shock, high-risk attacks on heavily armored prey such as Triceratops and Ankylosaurus. Size estimates of this dinosaur also vary, but never exceed 12-13 meters in length (weights are all over the place, but it’s safe to say that it was at least ~5.44 tonnes*). Stalking the environments of North America during the Upper Cretaceous, it probably saw the very end of the Mesozoic with the catastrophic K-T extinction event. Widespread and effective as it was, how did it manage to make it so far into the game?

*(2019 addendum: nope, let’s up that to 7-10 tonnes — also, T. rex’s potential for plumage is still up in the air as of July 2019)

We talk about T. rex‘s bite force here, a lot, but we should note that it could exert 8,273 Newtons-per-square-cm (12,000 PSI*). It could pretty much (withholding injury to the soft tissue in the mouth as a result) bite through cars, metal, and the like. Once again, this is a product of its environment and the available prey. The particularly skittish hadrosaurs of its time, though likely plentiful, were also easy pickings for competing predators. Going after the bigger, more dangerous game gave T. rex a slight edge in an untapped resource.

*(2019 addendum: it’s more along the lines of 8,000 PSI)

The growth series of Tyrannosaurus may also illustrate changes to its lifestyle as it matured.

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I recently visited the LACMNH in…well…Los Angeles. They have a rather impressive cast+fossil skeleton mount of three (they have four, but the other one’s in the main lobby) Tyrannosaurus of differing ages. Youthful T. rex – like the one in the center – had proportionally long legs. As they matured, their legs would actually get proportionally shorter until their growth peaked. What does this imply? Slimmer, lankier tyrannosaurs could’ve pursued faster, more agile prey than older ones. Where they lacked the muscle power and pure force to take down a Triceratops, young T. rex would’ve had ample prey in the form of quick Ornithomimus, juvenile Alamosaurus, and so on.

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And so, we have these two titanic raptorial theropods illustrated side-by-side. Let’s return to the question: Who would win in a fight?

The answer?

They wouldn’t.

Both Spinosaurus and Tyrannosaurus were very specialized predators whom have rule over different terrain and target different quarry. Most fights between predatory animals occur over resources, such as a recently-killed prey animal, territory, etc., and are often intraspecific. A T. rex is more likely to fight another T. rex for food, and so on. T. rex and Spinosaurus developed specializations that allowed them to live without worry of competing with any predators other than themselves, for the most part.

We’ll also consider Spinosaurus‘ environment for this conclusion. It lived in an area full to the brim with large predatory dinosaurs that rivaled T. rex in size. The high density of large carnivores in the same environment led to the local spinosaurs adopting an aquatic lifestyle, where food and space was abundant and unclaimed. In T.  rex‘s case, Utahraptor, Dakotaraptor, and young Tyrannosaurus took on fast and skittish quarry, leaving adult T. rex to seek other sources of meat – namely dangerous terrestrial herbivores.

In a scenario where an adult T. rex and an adult Spinosaurus could have crossed paths with one another, the chances of a fight breaking out would have been slim to none. Seeing two fearsome animals casually stride by each other is definitely a strange thought to stomach, but it makes sense.

There are more fish to catch and more Triceratops to behead, anyway. Who has time for a movie fight?

Until next time!

TL;DR – NeitherSpinosaurus and Tyrannosaurus evolved to fit different ecological niches, seeked different prey, and took up different resources. If they ever could meet (and they couldn’t, since they didn’t exist at the same time), there probably wouldn’t be a fight – since they’d have nothing to fight over!

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