Tyrannosaurus rex, the ‘Tyrant Lizard King’, was the thesis-statement of theropod evolution. Discovered in 1905, by Barnum Brown, and named by his mentor, Professor Henry Osborn, T. rex was among the very last dinosaurs to evolve. Exceeding forty feet and six tons, it was the largest of the fleet-footed, strong- jawed tyrannosaurs, it was a super-predator evolved specifically to kill large prey in a single strike. With its firepower focused solely in the massive head, T. rex’ jaws were a biological weapon of mass destruction seen only in the likes of the dromaeosaur sickle-claws or the fangs of saber-toothed cats – present in an animal the size of a large elephant. Known from barely a dozen partial skeletons, and a varied assortment of bones, T. rex was a monster of such terrifying proportion that it continues to exist to this day in the half-life of popular culture, sixty million years after it’s own extinction. Casts of the specimens listed below, are on display all over the world.
KING OF THE TYRANT LIZARDS
Despite the discovery of larger theropods – the carcharodont carnosaurs and the derived megalosaur, Spinosaurus - T. rex remains the single most destructive predatory force that ever evolved on land. In spite of its great size, T. rex retained adaptations for speed similar to its ostrich-mimic relatives. It also had forward-facing eyes, giving it advanced binocular vision, and was the largest-brained of all dinosaurs. It was its jaws, however, that truly separated the T. rex from the field. Tyrannosaurs in general, but most particularly, T. rex itself, represented the most powerful biters in terrestrial Earth history, The wide, heavily reinforced skull boasting jaw and neck muscles nearly as powerful as its legs, with recent studies indicating bite forces approaching seven tons – totally eclipsing the bite forces of even other theropods, (see graph). And as opposed to the slashing blades of the narrow-skulled, carcharodont, Giganotosaurus, T. rex’ banana-thick teeth, arranged like a bladed ice-cream scoop, actually bit OUT huge chunks of flesh. This massive bite, combined with its thick, muscular, shock- absorbing neck, gave the Tyrannosaurus an attack similar to the modern white shark – an especially devilish variation of the theropod attack and retreat strategy - a massively destructive first strike that left its target incapacitated or dead – a necessary adaptation considering the large and dangerous horned dinosaurs that comprised the bulk of its prey. Dated speculation that T. rex was a pure scavenger never really deserved serious consideration, but researcher, Jack Horner recently revived the idea, mostly as a publicity stunt, capitalizing on the concurrent boom in public interest in dinosaurs, ushered in by Jurassic Park, as Horner wrote in his own book that he doesn’t believe T. rex was an obligate scavenger, and only says so in order to deliberately stir debate – and, of course, grant funds.
BITE FORCE OF T. REX (Pounds/Newtons)
CHALLENGERS FOR THE TITLE
T. rex had plenty of competition in the ‘big and terrible’ category. As it turns out, almost every branch of theropod dinosaurs produced individuals in the same size class as T. rex. Torvosaurus tanneri was a forty-foot megalosaur, and Allosaurus amplexis was a similarly large Jurassic allosaur. Two contenders in particular, however, have emerged as the top threats to the title of King of the Dinosaurs. First, is the giant carcharodont carnosaur, Giganotosaurus carolini (along with its close relatives, Carcharodontosaurus, Mapusaurus, and Tyrannotitan) (Page 16), and the other is Spinosaurus aegyptiacus (page 17). But while both of these species likely exceeded T. rex’ largest size (although there was certainly overlap between them), T. rex was a much more advanced, much more powerfully armed animal. One look at the skull of T. rex compared to any large spinosaur (see illustrations) clearly demonstrates that it would be ridiculous for a spinosaur to snap a T. rex’ neck the way it did in Jurassic Park 3 – a battle would likely be more like an alligator snapping the head off a stork. Giganotosaurus, on the other hand, itself a big game hunter, was a more worthy challenge to T. rex’ throne. T. REX VS SUCHIMIMUS But the massive straight razor jaw of the carnosaur, (Spinosaur) designed to attack large, slow sauropods, lacked the one-shot kill-power of a rex jaw – necessary to kill fast, dangerous ceratopsians. And while Giganotosaurus would certainly be capable of inflicting a fatal injury on a rex (which Spinosaurus likely could not), the pairing would be like a muscular pit-bull versus a German Shepard (see Illustrations, photos)
GIGANOTOSAURUS (Carcharodont) TYRANNOTITAN (Carcharodont)
T. REX
CMN 9380, HOLOTYPE: THE FIRST REX
Holotype - CMN 9380 (11.9 m, 5.7 tons): This was the first substantial remains of T. rex ever described. In truth, another specimen, named ‘Dynamosaurus’ was found earlier, but ‘Tyrannosaurs rex’ was described first, earning the species the name, ‘Tyrant Lizard King’. It was on this fragmentary skeleton that Charles Knight based his first famous T. rex mural, incorrectly placing the eye too far forward due to incomplete skull bones - a trait translated into popular culture as Knight’s image became enshrined in paleo art, and was the basis for famous cinematic T. rex, like Ray Harryhausen’s Gwangi, and the King Kong T. rex. ‘Gwangi’ is a good example of the thick-boned ‘robust’ morph, particularly visible in the skull and vertebra.
AMNH 5027: THE FACE OF T. REX
AMNH 5027 (11.8m, 5.7 tons): For nearly a century this specimen WAS the face of T. rex, the basis for Charles R. Knight’s second, most famous T. rex mural, and, in fact, it was researcher/artist, Gregory Paul’s skeletal illustration of this particular specimen (see illustration) that eventually became the Jurassic Park T. rex. The mount at the American Museum of Natural History – a gracile morph - has been combined with the legs and arms of the robust-morph Holotype, to create the world’s first full skeleton of T. rex – albeit a paste-up Frankenstein version made of mixed parts. NOTE: While 5027 is a gracile morph, it is still one of the top four or five largest T. rex ever found, indicating that the robust morph was not necessarily the largest in terms of sheer size, as two of the top four largest specimens are gracile. NOTE: Ironically, while 5027 is the face of T. rex, it is one of the specimens being considered as a second species: Tyrannosaurus x.
BHI 3033: STAN
BHI 3033 (11.8m, 5.6 tons): ‘Stan’ is a large gracile morph, with a particularly large skull, all the more intimidating for the fact that the teeth have partially slid from their sockets, giving Stan a horrific ‘fanged’ appearance. Stan’s large head, perhaps indicates that the gracile morph – male or female – certainly was no less a formidable predator, and might, in fact, have done the bulk of the hunting, just like the lighter, faster modern lioness do today, with the larger male lion only lending its extra strength and bulk when necessary. If tyrannosaurs pair-bonded like many modern birds, a pack of two parents and offspring could have functioned in much the same way. All this is speculative, but Stan is another example that the gracile morph is maintained, even at full maturity and large size, as opposed to being a factor of age.
FMNH PR2081: SUE: BIGGEST T. REX OF ALL
FMNH PR2081 (Formerly BHI 2033) (12.3m, 6.1 tons): Sue is the largest, most complete T. rex in the world – a thickly boned, massive monster, just as famous for the legal wrangling behind it’s ownership and sale (which actually sent researcher Peter Larson from the Black Hills Institute to prison). While complete, Sue is a little bit crushed from top to bottom – particularly its skull - giving mounted casts the impression the animal was more squat and ungainly than it actually was. As the largest T. rex, Sue would have scaled about the same as the type specimen of Giganotosaurus, although would have been several feet shorter (see illustration page 2). And while there have been several reports of even larger T. rex discovered, these have all either been in error, or refer to extremely fragmentary remains, and all indications are that Sue represents the upward size limit for T. rex.
LACM 2345: SAMSON MOR 555: WANKLE REX
LACM 2345 (12.2m, 6 tons): Samson is another large MOR 555 (11.6m, 5.4 tons) “Wankle’’s Rex” named robust morph – often described as ‘large as Sue’, but after discoverer, Kathy Wankle, is a good example of while it is only a biscuit shorter, and taller at the hip, the gracile morph – a scrawny, scarecrow of a T. rex the fellow standing in front of the skeleton below (with that leads one to wonder if it might have simply a T. the disturbingly visible bald spot), is yours truly, and to rex version of a ninety-pound weakling. On the other my eye, Samson is not nearly as massive as Sue. It hand, that’s just compared to a massive rex like Sue, is, however, a good-looking, mostly non-crushed as MOR 555 is still a large animal. No skeletal skeleton (unlike the distorted, albeit complete remains drawings exist, but photographs show a widely spaced of Sue), and might be the second or third largest T. ischium bone consistent with other gracile morphs rex, next to Peck’s Rex (page 9). (page 13), a possible indication that a gracile bone structure was a way to keep weight down, while maximizing body cavity space for laying eggs.
MOR 980: PECK’S REX, RIGBY’S GIANT RSM 2523.8: SCOTTY-BIGGER THAN SUE?
MOR 980 (12.2m, 5.9 tons): Rigby’s Giant, or ‘Peck’s RSM 2523.8 (12m, Unrevealed): A new contender Rex’ after Fort Peck, is the largest example of the claiming to dethrone ‘Sue’ as the largest T. rex, gracile morph, approaching Sue’s size, with a ‘Scotty’ was found in 1991 in Saskatchewan, but only monstrously large head, similar to Stan. Although finally mounted in 2012. While complete, the skeleton gracile, Peck’s Rex is not emaciated like Black Beauty, was disarticulated and the mount – particularly the Stan, or Wankle’s Rex. It is on display at the Carnegie skull – has a paper-machete, muppet-like quality, museum opposite the slightly smaller, robust Holotype distorting the normal T. rex face. With a rather short specimen, CMN 9380, again proving the gracile/robust skull and heavy thighs, it is described as very robust – separation does not preclude sheer size. Again, it is while Larson’s graph records Scotty’s femur at 129 still possible we are looking at individual variation, age, cm, to Sue’s 134 cm, this figure is evidently disputed or even different species. (NOTE: After Sue sold for by curators of the T. rex Discovery Center in Canada. millions, a fossil poacher tried to steal Peck’s Rex’ remains from the ground, damaging several bones.)
RTMP. 81.12.1 : BLACK BEAUTY KING KONG
RTMP 81.6.1 (11m, 4.2 tons): Black Beauty is a 28% ‘KING KONG’ (12 m, Unrevealed): A privately owned complete skeleton, based at the Royal Tyrell Museum fossil discovered in Montana’s Hell Creek Formation. in Alberta. Discovered in 1981. Known for its mineral- 65% complete, the missing bones were cast from resin enhanced shiny black color. One of the smaller molds rather than borrowed from other fossils. adults, not quite the size of Wankle’s Rex (MOR 555), Purportedly very large, at 12 m, ‘King Kong’ has not Black Beauty is also one of the more exaggerated been through scientific review – while it’s difficult to tell examples of the gracile form, looking scrawny and from photos, to my eye it most resembles large gracile emaciated – possibly not even a morphological individuals like Stan or Peck’s Rex – although this is separation at all, so much as a comparatively weak, uncertain without knowing what bones are missing perhaps malnourished animal. from the mount. Its large size and the black color of its bones inspired the name, although on a personal note, naming a T. rex, ‘King Kong’ is just wrong
TRISTAN TRIX
‘TRISTAN’: (12 m, Unrevealed): ‘Tristan-Otto’, ‘TRIX’: (12 m, Unrevealed): In 2013, scientists from named after fossil hunter, Craig Pfister’s two sons, is a the Netherlands, found another large, 80% complete privately-owned specimen, found in the lower Hell T. rex in Montana – named ‘Trix’ after Queen Beatrix – Creek Formation in Montana, in 2011, currently on described as ’12 m’ – evidently the go-to estimate for loan for public display at the Museum für Naturkunde any big rex – robust (and therefore, declared ‘female’ in Berlin (which gave Tristan the specimen number, by Pete Larson, although a side-view of the skeleton MB.R.91216). Tristan is another big, robust speciimen shows a narrow ischium-gap). 30 yrs old at it’s death, tosed off as ‘Sue-sized’, at 12 m, although I can find Trix is also the ‘oldest’ T. rex, older than Sue (28), no official confirmation. which has caused some to suggest the robust morph is actually more a factor of age than dimorphism.
TYRANT LIZARD QUEEN?
While it’s not truly possible to identify dinosaur gender, we can assume they came in two sexes, like their archosaur ancestors and their avian descendants. It is also likely that they exhibited some form of sexual dimorphism. In dinosaurs, many species exhibit what seems to be a ‘robust’ and ‘gracile’ morph within the same populations, a trend that endures in different time periods and geographical areas, suggesting, but not ruling out, that these were not examples of different, similar species sharing an environment. Tyrannosaurs have been found in groups with two adults (perhaps pair-bonded like birds) and juveniles – with one adult gracile, the other robust. MOR 1125: B-REX, THE LITTLEST REX So, which were male and female? In recent years, researcher, Pete Larson, has forwarded the idea that MOR 1125 (9.5m, 4.5 tons) With his chevron theory in T. rex exhibited ‘reverse sexual dimorphism’ – where shambles, Larson needed something to resurrect his the females are larger than males. reverse dimorphism concept, and so turned to a Putting aside a hopelessly small sample size – specimen nicknamed ‘B-rex’ – made famous by the remember, we’re talking about a few partial skeletons discovery of soft tissue within the thigh bone – representing a species that ranged for up to four including what appeared to be ‘medullary bone’ – a million years - this is actually more plausible than the calcium deposit present in nesting birds. Assuming rex-scavenger idea. In many modern birds – such as these finds are accurate (and there has been some raptors – females are larger. However, Chris Brochu, corroborating evidence of medullary bone in other lead researcher overseeing the study of Sue, says that theropods), this suggests B-rex was an ovulating robust/gracile is a measure of shape, not size. female – and also happens to be one of the smallest Female birds, large or small, are gracile compared to known adults (see illustration below). Larson, males, as a way to keep body weight down while however, has declared this a robust morph, based on maximizing body cavity space for laying eggs. In the length/width ratio of its thighbone (B-rex is known eagles, the territorial males are smaller but more only from a partial skull, a femur, and a few other robust, as an advantage in aerial combat. Brochu also loose bones), and where it clusters with other T. rex says reverse dimorphism is least evident in birds that nest on the ground – ostriches and secretary birds, modern ground theropods, exhibit larger males. There is also the gracile specimen, ‘Steven’ (named for its discoverer) found among a nest of eggs, perhaps indicating the gracile form guarded eggs… although in pair-bonded birds, both parents will guard nests. Larson’s theory, however, was that T. rex gender could be determined by the chevron bones underneath the base of the tail – believing females to be missing one chevron – an arrangement thought to exist in crocodiles, which Larson also claimed existed on Sue – the largest, most robust T. rex. The novel idea gained wide acceptance despite a number of problems. First, comparing crocodiles and T. rex is a WIDE separation – they are only basal relatives – the difference between a bird and a reptile – and not just a Class separation, but the very far end of the evolutionary line. Then, Sue’s ‘missing chevron’ turned up, indicating that, by this measure, Sue was male. And finally, it was revealed that the supposedly ‘female’ chevron arrangement didn’t even exist in crocodiles – ten years spent on a wild goose chase.
WHAT SKELETONS CAN TELL US THICKEST PROPORTIONATE FEMUR: Femur Length Femur Circumference MOR 1128 1260 mm 580 mm 46% While the chevron indicator might be debunked, it is BHI 6233 1110 515 46% CM 9380 1200 545 45% not unreasonable to look to the pelvic region for clues, BHI 6232 1180 527 44% as this is where most animals keep their ‘privates’. T. MOR 1125(Larson) 1150 510 44% rex would have laid eggs like birds, with the egg shaft FMNH PR2081 SUE1340 580 43% running along the ischium bone – in the examples LACM 2345 1295 560 43% BHI 6230 1190 494 42% below, both gracile specimens show a demonstrably MOR 555 1275 514 40% wider ischium gap than the robust rex. MOR 1125(Horner) 1070 433 40% Other skeletal traits could also serve as indicators. If M0R 980 PECKS 1232 483 39% RTMP 81:6:1 1210 470 39% the symmetrical comparison to the white shark LL 12823 1200 467 39% remains consistent, the diminutive rex-forelimbs might BHI 3033 STAN 1310 500 38% serve a similar purpose to the white shark’s genital claspers – indicating that whichever morph Again, there are problems, – Larson’s graph includes demonstrated larger arms, would be male – as is the Nanotyrannus – now known to be a separate species case in the robust T. rex. – and the femur length/width ratio is among the least Likewise, heavier bone over the eyes – often the case reliable points of separation between the two morphs; in animals that argue conspecifically with head-butts – Sue, the most robust specimen of all, clusters near the again a more typically male trait – a feature of the middle of the graph, as does Samson. While there robust morph in T. rex. does seem to be convincing evidence for a robust/ gracile separation, again, that is a matter of shape. Femur length/width most likely simply reflects a taller or shorter animal as the smallest animals in the study obviously trend towards shorter limbs. It also turns out that different studies from multiple researchers record slightly different numbers when measuring the same skeletons – which to be fair, is simply wrapping a tape measure around a bone. A growth study from Jack Horner records MOR 1125’s femur length/width ratio as 1070 mm x 433 mm – as opposed to Larson’s 1150 mm x 510 mm – which by Larson’s scale clusters B. rex right next to MOR 555, one of the most gracile specimens. And while I often question, Jack Horner’s conclusions, he gathers data just fine. And when your assessing credibility, it’s worth noting whether data was complied randomly… or with a specific theory already in mind. Pete Larson had over a decade invested in his reverse dimorphism theory, gaining notoriety worldwide – museums dutifully reproducing his findings – and, of course, all the consequent funding. I will also mention that Larson did time in prison after the legal wrangling over ownership of Sue – a heavy-handed miscarriage of justice, perhaps, but an indication he might have a tendency to cut corners. In any case, it’s not hard to imagine, if a difference of 77 mm will confirm or deny your lifetime’s work, that 433 mm can become 510. There is also MOR 1125’s age – she would have been 18 years old – still young, but well past early sexual maturity and the initial rapid growth spurt of adolescence (dinosaurs would have been like birds and mammals in predeterminate growth, as opposed to reptiles that grow their entire lives) and she still remains one of the smallest T. rex adults known.
ALBERTOSAURUS DASPLETOSAURUS
Albertosaurus sarcophagus (8m, 2.5 tons) is very Daspletosaurus torosus (9m, 2.5 tons) is similar to Gorgosaurus, which for many years was considered by some the first and smallest of the assigned to Albertosaurus. Recently the genera have Tyrannosaurus genus, along with Tarbosaurus and T. been separated again (possibly just to preserve the rex itself. While this likely over-simplifies the genera, name ‘Gorgosaurus’). Albertosaurus is smaller, faster D. torosus, is still the first of the ‘heavy-duty’ older relative of T. rex – probably the fastest of any of tyrannosaurs - increasingly powerful, strong-jawed the large theropods. It’s skull was more primitive than predators, adapting specifically to hunt ceratopsians, T. rex, narrower, with a lesser degree of binocular while its more lightly-built cousin Gorgosaurus preyed vision. Albertosaurus has been suggested to have on hadrosaurs – a notion supported by population lived in family groups due to fossils found together. studies, showing a corresponding predator prey ratio.
GORGOSAURUS LIZARD TARBOSAURUS: THE ‘OTHER’ TYRANT
Gorgosaurus libratus (8m, 2.5 tons) (formerly co- Tarbosaurus bataar (9.5m, 4 tons) was the Asian generic with ‘Albertosaurus) is a smaller, faster, earlier cousin of T. rex. Beyond minor differences in the relative of T. rex. It is the first true giant of the clan, skull, Tarbosaurus is a virtual duplicate of T. rex, and with a typically large head, reduced forelimbs, and likely would have been assigned to the genus adaptations for speed. Adult Gorgosaurus were likely Tyrannosaurus if it had been found in America. Some the fastest runners of any large theropod. It’s teeth researchers still believe the two species should be were more blade-like than T. rex, and it’s general reclassified as co-generic – Tyrannosaurus bataar – a structure was more gracile than it’s contemporary lion versus a tiger separation. On the other hand, T. cousin, Daspletosaurus, suggesting Gorgosaurus bataar does have a narrower skull, with a probably specialized in hunting the abundant hadrosaurs, less-powerful bite, along with more bladelike teeth – leaving the heavy-duty horned ceratopsians, to the perhaps a specialization in hunting the medium-sized more solidly-built Daspletosaurus. sauropods that shared its habitat versus the ceratopsians that T. rex preyed upon. The Asian predator is also somewhat smaller, probably due to its more arid environment, and is a couple of million years more ancient, so most modern scientists maintain the separate genus for Tarbosaurus.
GIGANOTOSAURUS: LARGEST LAND PREDATOR EVER
Giganotosaurus carolini (12-13m, 7-8 tons) is the current title-holder as the largest meat-eating dinosaur of all time, displacing the century-long reign of the mighty Tyrannosaurus rex. Giganotosaurus (Gigantic- lizard), stretching over forty-five feet in body length, with evidence of individuals even larger, edges T. rex by several feet and as much as two tons. While Giganotosaurus lacked the extreme skull-strength of the tyrannosaurids, its blade-like teeth, set in its nearly six foot skull were designed to take down the largest prey animals that ever existed – the fantastic 100 ton titanosaur sauropods. Employing a strategy similar to modern Komodo dragons, the Giganotosaurus would attack and retreat, falling back to wait as the slashing wounds would fester, leaving the prey to weaken and die over the following days – providing a mountain of meat with little risk and little contact. Giganotosaurus, and its closely related carcharodont cousins, represented the culmination of the allosaur- carnosaur lineage. It’s resemblance to T. rex with its large head and reduced forelimbs, represented parallel evolution – and had scientists fooled for a while, believing that the ever-increasing skull size and shrinking arms of the allosaurs had led directly to T. rex itself. Claudistic analysis, however, has revealed the tyrannosaurs to be a sister group to the Giganotosaurus carnosaurs, that split in the Mid-Late Jurassic, Skull remaining small until their rise late in the Cretaceous, after the virtual extinction of the carnosaurs
Carcharodontosaurus Skull
SPINOSAURUS: BIGGEST THEROPOD OF ALL?
Spinosaurus aegyptiacus (12-14m, 6-8 tons) was known only from fragmentary fossils, destroyed in WWII, with only photographs as evidence. Nonetheless, extrapolation from related species puts Spinosaurus firmly among the top contenders for largest theropod of all, with high-end estimates suggesting lengths over sixty feet. On the other hand, while Spinosaurus probably attained the greatest overall body length, it was much more lightly-built than T. rex or any of the large carcharodont carnosaurs, and its skull was long and slender – seemingly unsuited for tackling large prey. And because it shared its habitat with Carcharodontosaurus, it is likely Spinosaurus occupied a different ecological niche than top predator – a river-hunting fish-eater – a giant stork, with gharial jaws, and long, clawed arms that could catch fish in the manner of a bear catching salmon. So, even if Spinosaurus was the largest theropod, it probably did not directly compete for top predator. Recent computer reconstructions of Spinosaurus, based on newly discovered remains, have taken the stork analogue one step further, reducing the hind legs to gator-size, preseniting Spinosaurus as an entirely swimming animal that walked on its forelimbs on land. This probably goes too far. Spinosaur arms were robust, but its clawas prohibited walking on them. Critics also suggest that the computer reproduced the hind legs far too small, and that Spinosaurus likely retained bipedal locomotion on land.
JURASSIC PARK
The Jurassic Park T. rex is certainly the most famous face of dinosaurs, its design taken directly from Gregory Paul’s skeletal diagram of AMNH 5027 – itself historically the most famous T. rex in the world. And while the movie takes certain factual liberties – T. rex’ blindness to non-moving prey, explained in the book as a result of frog DNA, is tossed off in the movie as a natural trait – the JP rex still remains the best, most accurate T. rex Hollywood has ever done. Debuting with breakthrough computer animation, the JP rex has assumed icon status and, like so many great villains, has even begun to morph into the role of hero, first saving the heroes from the raptors, in JP1, to teaming with it’s former enemies, the raptors, to defeat the genetically modified ‘Indominus rex’, in Jurassic World.
VASTATOSAURUS: RETRO REX
If AMNH 5027 starred in Jurassic Park, than Holotype CM 9380 – the Gwangi rex – made its own high-tech debut in Peter Jackson’s remake of King Kong. Cast as the remnant species ‘Vastatosaurus rex’, the Kong beast is a throwback to the original Knight painting, complete with plated skin and the forward- oriented eye. The artists also took the liberty of further evolving the V. rex, which is larger, with an even more robust skull – as well as more fanciful details like a feline stalking pose, and giant feet, both adaptations to living on the swampy uneven terrain of Skull Island.