In the course of my
blogging, I’ve covered toy dinos, and in the process, I’ve covered a fair
amount of genuine science. This all reminded me that once upon a time, I tried
my hand at actual paleontology. That led me as mar as Youtube and other dark corners
of the internet, where I quickly found people fixated on one question: What
could kill a Tyrannosaurus rex? For something different, I decided to throw my
hat in the ring. So, here goes…
What’s the big deal about
Tyrannosaurus?
Since the time of its
discovery, Tyrannosaurus rex has been the most famous of dinosaurs,
especially in the United States. In the process, however, it has become iconic
enough that comparatively little is known about what made it unique. Here are
the facts about what made T. rex different from other carnivorous dinosaurs.
1. T.
rex
was part of a lineage that lived in the latest Cretaceous period. Its most
notable relative was Tarbosaurus bataar, believed by some to be a second
Tyrannosaurus species. T. bataar is also among the best known of
all carnosaurs by the quantity and quality of specimens.
2. It
was among the largest therepod dinosaurs species by size and weight. It was 12
to 13 meters in length and about 4 meters in height, dimensions probably only
significantly exceeded by the semi-aquatic carnivore Spinosaurus aegypticus
and the herbivorous protobird Therizinosaurus cheloniformis respectively.
Its total weight is estimated as 8 to 10 tons (imperial or metric doesn’t
matter much), roughly twice the size of typical T. bataar specimens and
comparable to Giganotosaurus and Carcharadontosaurus.
3. It
was among the most robust carnosaurs, with an especially heavy skull. The
massive skull would have provided a correspondingly powerful bite and
significant resistance to impacts and other trauma. It may in some cases have
outweighed significantly larger carnosaurs, notably Spinosaurus.
4. The
Tyrannosaurus/ Tarbosaurus line were among the last known large
therepods, with T. bataar dated 70 million years ago and T. rex
found virtually up to the K-T boundary marking the end-Cretaceous mass
extinction 65 million years ago. As a result, most if not all other carnivores
had disappeared, with the exception of the dromaeosaurid and troodontid
protobirds.
Can we make T. rex
mortal???
In the course of looking at material on hypothetical face-offs between T. rex and other dinos, what immediately stood out to me is that lay audiences seem genuinely surprised or confused by the idea of a tyrannosaur being vulnerable to anything, even other dinosaurs. This all goes along with my long-running rant about dinosaur movies. It makes for good drama to have humans powerless against dinosaurs, as they might well be if you simply dropped a band of civilians into a Mesozoic ecosystem without warning. But when it comes to armed and prepared human parties who might face dinosaurs on equal terms, Hollywood’s answer has usually been either to make weapons inexplicably useless (see Planet of Dinosaurs) or just have the only properly armed person(s) get eaten first.
A good start to overcoming the hype is to consider the largest common predator in the present, the African lion. A typical male lion can weigh between 180 and 220 kg, while females weigh 120-140 kg. On further consideration, their size is a major but rarely decisive factor in conflicts with other species. Lions can and do kill considerably larger prey, like the Cape buffalo, which can weigh over 850 kg, as well as the young of even larger hippos and elephants. At the same time, there are plenty of smaller animals that offer a significant threat to a lion. The spotted hyena, the lion’s most numerous competitor, is only about 60 kg, but has literally crushing jaws and often far superior numbers. A warthog is as big as a lioness, with formidable tusks. An ostrich weighing 100-140 kg has claws that can deal with a lion of any size. Even a zebra is capable enough that lions will usually wait until one can be separated from the herd.
The lesson of this
exercise is that the effectively invincible predator simply cannot exist in a
terrestrial ecosystem. Size alone can only decide the issue at 5 to 1 or more,
and to get that kind of difference in a living apex carnivore, you would have
to turn from the big cats to the bears, which alternate between predation,
scavenging and omnivory. The T. rex, as we will see, may have had more
advantages than a lion, but even it could not have existed without other
species large enough to hold their own and conceivably win against it. So,
let’s consider the lineup…
Spinosaurus
This is the one that
simply must be put out of the way. Thanks to the Jurassic Park franchise, this
is the one people think of as a rival to rex. Alas, even setting aside the
problem that the latest spinosaurids predate the tyrannosaurs by over 20
million years, what we have is less like an epic duel than the time Muhammad
Ali fought a sumo wrestler. (Yeah, that happened…) To begin with, the spinosaurs
lived in lakes, marshes and brackish waters, where the tyrannosaurs would have lived
in open plains and even semi-arid deserts. For a confrontation to happen at
all, there would have to be an inciting incident, like a large carcass on the
shoreline or perhaps an intraspecies conflict that pushed a tyrannosaur from
its normal habitat. It would still be the spino’s choice to attack, retreat or
simply let the intruder eat and leave, with the last being far more likely if
the element of surprise was already lost. If it did take aggressive action, the
spino’s advantages would all come from the greater reach of its unusually long
head and claws. Ultimately, it would be on par with a rapier against a battle
axe, and if the first strike did not settle the matter, things would go rapidly
downhill for the side with the lighter weapon. All in all, this simply
demonstrates why large carnivores will usually avoid each other given the
opportunity.
Deinocheirus
This dino, full name D.
mirificus, was once the greatest unsolved mystery in paleontology, known
only from a gigantic pair of arms. It remains the most intriguing of several
herbivorous and omnivorous “mega raptors” to approach the tyrannosaurs’ size
and mass, of further note for coexisting with T. bataar as well as the
similarly armed Therizinosaurus (pun unavoidable). From what we know
now, it was a very large, somewhat primitive ornithimid, as heavy as T.
bataar and comparable to Rex in height. In ecological terms, it was
equivalent to a bear, complementing its plant diet with fish and possibly small
or already deceased dinosaurs. While
several specimens show chomping from T. bataar, their relationship may have
been more complex than that of prey and predator. Under specific conditions,
the species could have fought on equal terms over carrion, territory, and even
access to water. As with the spino, Deinocheirus would have the
advantage of reach in the first exchange, and could easily deal a fatal blow. Against
a tyrannosaur already moving at attack speed, however, this would amount to
mutually assured destruction, and matters would be far worse if the full-time
predator got in a strike from behind. The likeliest outcome is that both
species would have stayed out of each other’s way in all but the most trying
circumstances.
Ankylosaurus
Now, we’re getting into
dinos that actually coexisted with T. rex, and this is another that
would have been best avoided. It was “only” about 5 tons and 9-10 meters long,
but it was the epitome of armed and armored, with plates, spikes, a massive
tail club and a wide, thick skull that by my own assessment would have been
effective for head-butting. With its own massive head, Rex probably would have
had as good a chance as anything at surviving a direct hit from the club, but a
strike to the lower leg or foot could have had even more dire consequences for
its ability to hunt and fight. The only angles of attack would have been to
tear open the belly or cripple a leg. Even in Hollywood, Rex leaves these guys
alone.
Triceratops
This is the most
important one to consider, as these dinos were not only among the most numerous
herbivores in Rex’s habitat, but have been found with clear evidence of being
chomped on by it. As with Deinocheirus, the parameters are favorable if
the predator can get in the first strike from behind, rapidly less so in a
frontal attack. Here, however, the herbivore was about the same mass as Rex, and
had a solid frill that could have actually stopped its bite. The most likely
course of an engagement would have been attrition in the manner of a Komodo
dragon. Most ideally, a first strike to a hind limb would have inflicted both
heavy blood loss and enough damage to limit the trike’s ability to bring its
horns to bear against a second pass. From there, the point-blank grappling
loved by the movies really is about right; however, it was only likely if
something had already gone wrong for the Rex. Ironically, the one thing that
could have driven a tyrannosaur to impatience was if a wounded or dying prey
from going into the territory of another predator or somewhere entirely
inaccessible. Otherwise, it could afford to wait.
Hadrosaurs
These are the dinosaurs
that usually get counted as easy prey, something I personally have found
misguided. At face value, they are the equivalent of a zebra, large but neither
armed nor well-protected. The deeper lesson, however, is that temperament
matters as much as anatomy, especially for social animals, and if there’s one
thing we know about hadrosaurs in particular, it’s that they were among the
most gregarious dinosaurs that ever existed. They were tougher than they look
individually. Among other things, the characteristic beaks were more like that
of a parrot or a snapping turtle than a duck. In terms of size alone, familiar
species like Parasauralophus and Corythosaurus routinely fell in
the 2-4 metric ton range, with outliers like Shangtungasaurus approaching
or even exceeding that of Rex. An entire
herd standing their ground would have been formidable, while a nesting colony
of the kind known for Maiasaura would surely have been highly dangerous
even to approach. The bottom line is, creatures like these do not get to be
among the most numerous in their ecosystems without being very capable of
defending themselves.
Sickle-claws
Another face-off set up
by the JP franchise is that of Rex against the sickle-clawed dinosaurs. What I
have found amusing is that there is little if any suggestion of the raptors
posing a threat to the tyrannosaur in the movies or the original books (and I
read the novel first, dammit). What is true is that these little scrappers were
among the only carnivores that even coexisted with Rex, so they were
“competitors” in that sense. However, this does not mean they were hyenas to a
Rex’s lion. Even the generously sized Velociraptor/ Deinonychus
composites shown on screen and in the novel would be in the 100-200 kg range,
which is only 1-2% of a somewhat conservative 8 metric ton size for Rex. Throw
in more recent finds like Utahraptor and Dakotaraptor, and you
will still only get 300-450 kg, maybe 500 on the outside. Realistically, the
only occasions when raptors would have fought a Rex would be if the
hypercarnivore tried to take their hard-earned food, which is a fair enough
reading of the finale of the first JP movie. For once, Hollywood got this right
the first time; when Rex arrives, the raptors leave or get their tails chewed
off.
Alamosaurus
This was a late-surviving
titanosaur coexisting with Rex, with a mass possibly rivaling the 80+ tons of
now more familiar South American species like Argentinosaurus. Like all
sauropods, it was armed with a powerful tail and clawed forelimbs. By
conventional wisdom, even Rex would only have fed on subadults and carcasses of
the already deceased. However, the sauropod did have significant armor, which
only makes sense if it was at least occasionally threatened by the theropod. By
implication, the absolute power of Rex’s bite was consequential even to an
animal that outweighed it 10 to 1. As with Deinocheirus, it is also
possible that conflicts occurred for reasons beyond simple predation. A clash
between the two would have been rare, terrifying and awesome.
Alioramus
This may be saving the
least for last, yet it is in many ways the most intriguing in its implications.
Alioramus remotus was a tyrannosaurid found with T. bataar, described
from a single set of fragmentary and apparently juvenile remains. More
recently, a second species A. altai was described from more complete
remains. Between the two, size estimates range from 400 kg to 700 kg. As such,
they are quite possibly the largest predators to coexist with either
tyrannosaur species, and the most direct evidence that a carnosaur larger than
the Utahraptor could survive in their habitat. Alioramus would
have remained fairly inconsequential to an adult T. bataar, but would
have been a credible threat to juveniles. Given the poor state of remains, the
apparent rarity of Alioramus must be at least in part an artifact of
preservation bias. By implication, their longevity, range and even size are
fairly likely to have been underestimated. Even so, their absence from later
strata and North America in particular paints a bleak picture of the fate of
smaller theropods once Rex arrived.
In conclusion, what we
come back to is the problem of perspective. To us, T. rex is almost
unimaginably huge, far larger than any existing predator except the whales. It is
only natural that we would see it as an unstoppable monster. To view it as a
living, vulnerable animal need not be a letdown. On the contrary, it should
reinforce the respect for nature that good dino fiction has taught all along. A
bear, a dog, an ostrich, or even an irate parrot can all kill you if you do not
show them respect. So follow the example of the prudent T. rex, and give
all living things the space and care they deserve. That’s all for now, so I’m
signing out with a Rex lineup!
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