Saturday, September 24, 2016

Night Stalker Rex Part I: Sue Is Built Like A Brickhouse

Here it is folks - the king of all kings, the prize fighter of antiquity, the grand poobah, good ol' sexy rexy himself - as you have never imagined before. Some say that we know more about Tyrannosaurus rex than other extinct animals - or even extant ones - and it is high time other lesser known animals should receive attention. Until recently I was of the same notion. However a new flurry of T.  rex research - highlighting it as an intelligent "super senses" endowed predator - has stirred a quiet but growing mumbling on what it really meant to be the tyrant lizard king. Emerging from the haze of past interpretations a more resolute and astonishing picture of T. rex has been forming in my mind. It is a startling beast quite distinct from past visages but not without a newfound ghoulish and nightmarish quality all of its own. Ladies and gentleman I give you Night Stalker Rex.

credit Robin Liesens

"Now wait a second here" you might be thinking "I have heard about likely nocturnal behavior in T. rex and other theropods before - nothing new here." And you are right, it has been suggested before. Indeed a central tenet of this hypothesis - the specialized detection and predation of sleeping dinosaurs by T. rex - has been at least cursorily mentioned at least once on the interwebz.  But you will not find the idea sold to you with quite the same zest and zeal that you will get from me. And you will not find several new and compelling lines of evidence put forth by me that further leverage and embellish the night stalker rex hypothesis.

To get the cognitive gears pumping I want to address a potential role of nocturnal hunting in a modern day T. rex sized predator - the killer whale (Orca orcinus).

This video is astonishing. What really captures my interest is not so much the explosive action and graphic violence but the more economic questions of foraging efficiency. The pod of orcas has obviously positioned themselves at depth - maybe even partially concealed by features we can't discern from the surface - and execute a precise ambush on a large pod of common dolphins. The orcas - which combined as a predatory arsenal must weigh several dozens of tons with appetites to match - expend much energy, foresight, and effort to snatch up just one small dolphin. For what amounts to basically a hard won "snack" for one orca much less for the whole pod the question arises "how efficient is such a foraging tactic for these massive, hot blooded, predators?" Now that the pod of dolphins is aware of the orcas seems the chance for another capture is remote... Not a great optimal foraging capability for the oceans top predator... Or are we looking at how orcas hunt - or more precisely "when" they hunt - in totally the wrong manner? Ask yourself this: for a predator that utilizes stealth to hunt a very agile and intelligent prey would it not be even more efficient for orcas to utilize the cloak of darkness for better tactical advantage? In diurnal predatory events in orca are we not in fact witnessing the exception to the rule of a generally nocturnal predator?

It is paramount to take heed of the obvious bias in wild orca research. Humans are diurnal. Humans are not marine. Most studies of wild orca will be conducted during the day for obvious reasons of practicality, safety, and ease of observation. Working from a research boat on difficult seas it is patently obvious why the overwhelming majority of wild orca research would occur during the day. Because wild orca are mainly observed during the day and because predation events are therefore only observed during the day the emerging bias becomes reinforcing - Orca are diurnal and do their hunting during the day.

However all may not be as it seems with the blackfish and an emerging trickle of data might in fact point to a more nocturnally active hunter than previously suspected.

By recording vocal activity at night at St. Paul island in the Bering Sea researchers K. Newman and A.M. Springer were able to elucidate not only heightened vocal activity at night in transient marine mammal hunting killer whales but they attributed this to predation events. Not only were calls recorded during the night but vocalizations peaked 1 hour after sunset and were more common from midnight to noon than noon to midnight (keep in mind the long days of the northern summer). Although transient killer whales remain silent during the hunt, after a chase or kill is initiated a flurry of calls commences - which when combined with the nocturnal foraging of the prey animal (northern fur seal) - led the researchers to conclude that nocturnal foraging was very important for these transient killer whales.

Could we be on the cusp of recognizing the importance of nocturnal foraging in many or even most populations of killer whales? The obvious utility of ambush technique shown in the above video suggests that such tactics would only be more adventitious at night, especially for an acoustically sensitive predator. The possibility is certainly there and it is easy to see why a bias of diurnal activity in these animals took root. Such a reversal in our thinking is certainly not without precedent.

Nocturnal hunting in great white sharks was only recently documented overturning the diurnal dogma that afflicted the nature of these fish; spotted hyenas long assumed to be solely scavengers from day time observations but long term studies including night time observation elucidated their predatory nature; and the king of beasts has long been known to be a primarily nocturnal hunter - what is less appreciated is that the male lion - long regarded as the inferior hunter compared to females - can actually hold his own as a nocturnal ambush predator of thick brush.

from here
Game cameras are revealing startling and explosive predatory action that occurs under the cloak of night such as this wild chase and capture of feral pigs by an American black bear - an animal not usually noted for stalk, ambush, and predatory technique.

Hunting dangerous, elusive, and quick quarry by predators under the cloak of night is a time honored tradition. Intuitively this makes sense, better to stalk and ambush prey from darkness. Nothing particularly revelatory about that. However there is a seldom mentioned facet of nocturnal predation that - when your prey is herbivorous - consistently tips the balance of power in favor of the predator. It is an inherent advantage the predator has that the herbivore can really do nothing about. One has to ask the question before one can come to an answer: "Why, if nocturnal vision is so advantageous for nocturnal predators, have not herbivorous prey answered the evolutionary arms race by evolving excellent nocturnal vision themselves? I mean, its not like they have not had enough time to evolve excellent night vision as this nocturnal depredation has been going on for some time likely. Darwinian evolution would almost predict such an advantageous adaptation arising."

The answer to be blunt is that herbivores can not, and likely never have, equalled the superior night vision of their predators because they can't. And it's because of what they eat.

Luckily enough through the power of google search I was able to source this little free preview snippet which I will provide below from Essential Fatty Acids and Eicosanoids: Invited Papers from the Third International Congress (ed Sinclair & Gibson 1992) from none other than the American Oil Chemist's Society:

Vitamin A is concentrated in animal tissue but scarce in plants. It is essential for night vision and because predators have a ready and pre-made form of it they will always have a greater capacity for night vision relative to herbivores. Not because herbivores would not benefit from good night vision but because of biochemistry. Yeah science!! If the present is the key to the past and the same unequal playing field occurred in dinosaurs (no reason to think that it didn't) there was likely a high bias of nocturnal theropods stalking the Mesozoic nights. T. rex - as an obligate hunter - certainly slots in nicely to this realm.

The question then becomes "well if T. rex was a nocturnal hunter what type of hunting strategy did it use?". Various methods could and likely did take place such as ambush  at known prey "hot spots", stampeding prey into confusion, stalking of prey in dense foliage, pursuit etc etc. Long story short I think all of these tactics were utilized during the different ontogenetic stages of T. rex. The more light and leggy youngsters utilizing more athletic, running pursuit strategies morphing into a more stealthy, ambush style predatory tactic with the onset of robust build and large mass.

For this hypothesis I want to concentrate on the onto-morph of the adult T. rex. We are talking about Sue sized rex here. And this is an important distinction because a tenet of this hypothesis is that the hunting strategy of other, smaller  tyrant lizard species was encapsulated in the ontogenetic history of T. rex. Essentially in moving up in size through sprightly large coelurosaur sized juveniles, to Albertosaurus like teenagers, to Daspletosaurus sized subadults the behavioral ecology of these respective tyrants was mimicked. But by the time we get to "Sue" sized adults T. rex was playing a different predatory ball game altogether.

Sue Is A Brickhouse - Built Like an Amazon

First of all time to talk about the elephant in the room when it comes to T. rex. And I literally mean elephant in the room. Sue not only was big, she was a certifiable fatty. Sue was not just a tad bit on the hefty side, she would have in life appeared ponderous and round to an almost cumbersome degree. Seriously T. rex as depicted in paleoart is probably the most shrink wrapped, trimmed up, and "wishfully" sveltely depicted  prehistoric animal of all time. Its like there is a collective denial of T.  rex's true body type. T. rex paleoart is the equivalent of gaining a few pounds (or a lot) and keeping that selfie around on social media from when you were trim. And I am not just discussing fan art or deviantart renderings of T. rex - I am talking about the big name "world renowned" paleoartists. You can take your pick, I say that they all underestimate the genuine "girthiness" of ol' sexy rexy. Not by a little, but by a lot mind you. It's time we embrace the big rex and stop the body shaming denial. Big is beautiful!!

If you want to move towards a more realistic countenance of T. rex draw an animal fatter and more rounded than pretty much all other depictions. Now make that animal 20% larger still!!

Have your doubts? Remember there was that little study published a bit ago by Hutchinson & Makovicky? They found that previous estimates were substantially low and their computer modelling suggested an increase of about 30% pushing Sue up to about 18,000 lbs or 9 tons - and they call this size on the conservative range!!

I got a chance to visit with Sue and talk to her about her self image and eating issues as she recently stayed at the Santa Barbara Museum of Natural History. Let me tell you that song "Brickhouse" (She's a brickhouse, just letting it all hang out") does not even come close to doing her justice.

"Sue" credit Duane Nash

When you really look at Sue - and to a lesser extent smaller adult rexes - once you get past the huge maw, lethal bananas, and overall size - you have to be impressed with that barrel chest. I mean come on now, if you take the perspective of the above photo and add on even just a smattering of integument, skin, muscle, and fat to the torso you quite literally would not see the hips from behind that thick barrel chest!!

"Sue" torso credit Duane Nash

I mean really now, it's just ridiculous. Especially when you compare the torso against other slab chested theropods or even other herbivorous dinosaurs for crying out loud. Go look at the various museum mounts of T. rex mounted in pursuit of herbivorous prey - the degree of roundedness in the torso of rex even crushes the giant, rear fermenting sauropods, ceratopsids, and hadrosaurs it was hunting. While not as wide as ankylosaurids T. rex certainly had a deeper chest than they did. Also compared against the torso of canids, felids, and even ursids T. rex looks unambiguously ahead of the curve in terms of a massive torso.

The real elephant in the room is not that T. rex had a massive barrel chest - that has been known and commented upon for some time - the issue is that no other terrestrial tetrapod predator has such a barrel chest!! You really have to go into the aquatic realm to find such girthy predators, animals that have escaped the burdens of gravity. Obviously T. rex is no whale or aquatic animal - it still had to operate under the confines of 1 G - but I do think it had escaped the traditional limits of what it means to be an agile, cursorial predator. No longer hemmed in by ecological and functional constraints of maintaining high degrees of speed and agility other evolutionary pressures dictated an increase in general size, robusticity, and overall swelling of the tyrannosaurid bauplan. These evolutionary pressures included territorial defense, intimidation of rivals, garnering mating privileges, and storage of fat for lean times. All of these Darwinian benefits would dictate and be benefited by increase in size/girth but only after the evolutionary pressures that necessitated speed & agility were lifted. In other words T. rex only could become the T. rex we know and love after it developed uncanny predatory technique as a cryptic, nocturnal, super senses equipped, arch predator specializing in detecting, infiltrating, and apprehending sleeping dinosaurs.

So how fast was T. rex

Obviously this is not a full on review of the research into tyrannosaurid speed. But it is my personal reconciliation of the data and not at all incongruent with accruing data and more coming down the pike suggesting that for T. rex (and probably many gigantic theropods) they were NOT SO FAST (or more importantly agile).

People love to ask this question, and paleontologists love to give eternally "sitting on the fence type answers" - as they should because we really don't know. Not only that but solid, concrete speed numbers on most extant animals is lacking. What I will say is this. Unless Usain Bolt is a secret paleo fan and reader of antediluvian salad, T. rex is probably faster than anyone reading this blog. Now, one statement I hear again and again is that "it does not really matter how fast T. rex was as long as it was faster than its prey". Which on the face of it seems like a reasonable answer, if you are assuming that T. rex was a bit of a pursuit predator and that leg length is a prime determinant of speed. But I am not quite so sold on this line of thinking because there are some notable exceptions - chiefly bears - which constantly fly in the face of the dogma that dictate long lower legs equal high speed.

Based on relative leg length we should expect camels to thoroughly smash bears when it comes to speed...

If both bears and camels were extinct based on comparing lower leg elements the camel would be asserted to be faster. The camel can indeed move pretty fast - indeed I was astonished when actually seeing them get into a full on gallop in the video below - but I would not by any means be confident that in short bursts bears are not just as fast as the longer legged camels.

When it comes to speed in T. rex, its likely prey base, and what it means to be a good & efficient predator I think the questions we ask play a big role in the solutions we seek. When we ask "how fast was T. rex?" implied and embedded in this question is that pursuit was important for T. rex and however fast it was it had to have been faster than its prey base in order to make a living. Instead of trying to get to answers based on the question of speed - which may in fact be a wash when compared against its prey base because of bears and how they break the rules - let us instead ask a more incisive and telling question: "how agile was T. rex?" This line of thinking has more merit to it than simply asking "how fast?" because when you couple the agility of T. rex with the attributes of its prey base there are some significant conclusions to be drawn.

T. rex was horrendously not agile. Indeed it is hard to imagine nature coming up with a design less equipped to handle tight turning. A tall biped, long and heavy all over. Once it gets a head of steam going in one direction it has horrible turning ability. Kind of like running while carrying a big heavy, long log and being asked to twist and turn. Hutchinson (yes the same Hutchinson form the revised mass estimate paper) came to this conclusion when he looked at the turning ability of rex. Ultimately the study concluded that T. rex took a full 1-2 seconds to make a quarter turn (45 degrees).

Past assertions have all resorted to the stock answer that T. rex was "just good enough" to chase down its gigantic prey base are lacking. First of all we don't have reliable speed indexes of modern animals much less extinct ones. The ability of short legged bears to sprint at the speed of long legged ungulates casts doubt on the mere long legged argument to infer high speed. We can't be confident that T. rex was faster than Edmontosaurus, Triceratops, or hell, even Ankylosaurus!?! Short legs, if well muscled and full of bouncy tendon can still do the same job of long legs. But one thing we can be certain of - more than the relative speed argument - is the relative agility index between T. rex and its presumed prey. And here we can see - unequivocally - that T. rex is not on a level playing field with its prey, all of which were quadrupedal with a lower center of gravity and better turning ability. If we combine this with the possibility that some of these herbivores were as fast or even faster (da' bears) than ol' sexy rexy we come to the distinct possibility that these animals could run circles around ol' rexy. Indeed if T. rex was a pursuit predator of gigantic and dangerous prey that could easily outrun, outmanoeuvre, and kill it T. rex would have quickly become erased from the fossil record. An obsolete and inefficient design with glaring flaws that can not be ignored or explained away.

Quite a predicament for rexy to be in if it somehow had to make a living off of catching these animals and - especially in the case of gigantic hadrosaurds, ceratopsians and ankylosaurids - these animals could out manoeuvre you and potentially mortally wound you too!! What is a T. rex to do?

The answer is that (adult morph) T. rex did not chase much of anything down except maybe another T. rex. Ol' sexy rexy eschewed the whole speed game altogether and in doing so achieved both great hunting prowess and great size. It snuck up on dinosaurs both awake and asleep - although sleeping dinosaurs became more of a specialization in larger rexes - under cloak of darkness. The average "chase" was measured in just a few meters or even centimeters. This opened up rexy to exploit not just the large ceratopsians, hadrosaurids, and ankylosaurids that it shared its habitat with but rex could now exploit all the smaller and even more agile dinosaurs it shared its habitat with. A true ruler - a tyrannical rex in every sense of the word - that by highlighting stealth and negating speed it could demand caloric tribute from every underling in its kingdom. Literally nothing was safe in the kingdom of rex - everything from armored ankylosaurids to speedy ornithomimids - could and did end up in the belly of the tyrant ruler king.

I guess I was a little naive in imagining I could get through this hypothesis in just one post. In this post I wanted to concentrate on the unparalleled girth of rex, highlight the fundamental underestimate of rex's size both in both paleoart and technical literature, and show why, if there is any sort of consensus on rex speed & agility, it should be moving in a direction of caution with regards to extremes in both of these dimensions. 

Up next I want to delve into the super senses of T. rex, how to be a giant stalker, and why T. rex had a "childhood".


Hutchinson JR, Ng-Thow-Hing V, Anderson FC. A 3-D interactive method for estimating body segmental parameters in animals: application to the turning and running performance of Tyrannosaurus rex (2007) Journal of Theoretical Biology vol 246 Issue 4. 21 June 2007 abstract

Hutchinson JR, Bates KT, Molnar J, Allen V, Makovicky PJ (2011) A Computational Analysis of Limb and Body Dimensions in Tyrannosaurus rex with Implications for Locomotion, Ontogeny, and Growth. PLoS ONE 6(10): e26037. doi:10.1371/journal.pone.0026037

Newman, K, Springer, AM. Nocturnal activity by mammal-eating killer whales at a predation hot spot  in the Bering Sea (2008). Marine Mammal Science, 24(4): 990-999 (October 2008)

Zelenitsky, DK, Therrien, F, Yoshitsugi, K. Olfactory acuitty in theropods: paleobiological and evolutionary insights (2009) Proceedings of the Royal Society of Biological Sciences. link

"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Anonymous said...

Not to burst your idea, but Sue could probably catch up to a Triceratops and Anky without the help of the night. I've heard some estimates of Sue putting it at about 17-18 mph, and the Saurian team said Trike and Anky could both run at 15 mph. Young E.annectens/Anatos were probably to fast (Top speed of 24 mph) for a Sue sized T.rex, but Super Adult E.annectens/Anatos were probably slow enough to be taken down by a mob of rexes.

Needless to say, this is an interesting hypothesis and maybe it would have worked on certain prey items
Day: Young Trikes, Young Ankys, Adult Ankys, E.annectens/Anatosaurus adults
Night: Super Adult and juvenile E.annectens/Anatosaurus, Ornithomimids, Super Adult Trikes.

Bk Jeong said...

The lack of agility raises major implications towards what could T. rex kill, because it limits the prey size.

Andrew Raymond Stück said...

Thank you for emphasizing the girth of T. rex! I've heard the barrel-chested label tossed out casually several times before, and simply looking at Sue's skeleton really slaps one in the face with that impression, and yet it is frustratingly absent in paleoart. Many T. rex restorations look rather laterally compressed.

Jonathan Atkinson said...

Hi Duane, in relation to the whole limb length and curosiality deal John Hutchinson has a beginners article titled "Animal Speed and Size: Big/small Data vs Errors". It's not really long but it has some small nuggets related to the whole what is speed and curosial stuff, either way it seems to be quite the crap shot and follows a similar line of thinking to your ideas about speed, activity etc. wondered if you had seen it.

Duane Nash said...

@Anonymous please leave a name!! I don't think we can confidently determine the speed of any of these animals - regardless of what the "Saurian team" states. There just throwing out ball park figures anyways. That is why I posit agility as a better measuring stick against how to judge predatory interactions, In all cases rex fails the agility test against any one of those animals.

@Bk Jeong I'm not sure if I follow how lack of agility limits prey size? Anyways my whole argument is that superb stalking technique negated the need for agility in rex.

@Andrew, Indeed she is a brickhouse!!. Well it is ironic how the chunky dino images before the dino renaissance might have a bit of truthiness to them after all. Not hard to follow a line of descent from GSP to modern imagery which tends to borrow a lot from his athletic looking theropods...

@Jonathan No I had not but I should look at that - thanks for heads up!!

babehunter1324 said...

Would the fatness of an old Tyrannosaurus rex also helped them subdue prey more easily once they manage to catch it?

Modern bears very often use their bulk and claws to bring down their prey and restraint it. It seems as though T. rex would be able to do with sheer bite force and bulk.

Duane Nash said...

@babehunter yes bears use their size and strength to grapple and subdue prey, However bears are mainly omnivorous and are not even as barrel chested as rex - rex was an obligate hunter and still had an unparalleled physique for a terrestrial predator, This is the enigma I am exploring.

Trilobite Cannibal said...

With these new thoughts on rex does your vision of the creature change? Perhaps a sinister solid black on the caruncles akin too a black vulture?

Duane Nash said...

@Trilobite Cannibal Yes, yes it does. New pic coming - less facial features prominent, just a general "thickening" of facial skin, upper shoulders & neck. Harkens a bit towards other contemporary depictions but with some weird new stuff. Next post.

Ryan Dempsey said...

I've always appreciated your blog diving into the "non-mainstream" area of Dinosaurs and prehistory, but it's cool to finally see it touched on. Can't wait to see T. Rex as "Nocturnal Predatory Defensive Linemen" explored further.

Duane Nash said...

Thanks Ryan. "Nocturnal Predatory Defensive Linemen" - LOVE THIS!!

mrplcole said...


Bk Jeong said...

With regards to prey size:

Looking at predators that engage prey significantly bigger than themselves (many by night-see:Savuti lions), most of them are focused more on maneurability than speed.

IIRC herbivorous dinosaurs were focused on being able to block an attack from all directions, either by turning quickly or by kicking in all directions. To deal with these defences, a predator would have to be able to dodge quickly and pivot around to get past counters.

Comparing the foot anatomy of carnosaurs or dromaeosaurs to tyrannosaurs, their feet and ankles are more flexible, lacking an arctometatarsus. This costs a bit of speed but increases overall agility, because the foot is able to flex as the animal is turning.

With tyrannosaurs the arctometatarsus binds the ankle joints and the toes tightly. This provides rigid structural support, but at the cost of flexibility.

Combine that with a T. Rex's heavy build and you end up with an animal that will get kicked to death when it engages an animal several times its size, because it would be unable to dodge the kicks.

Stevie Moore said...

While I don't doubt for a second the size and bulkiness of adult morph rex's nor their highly attuned senses of particularly vision and smell, I can't help but wonder if their likely prey items would not be nocturnally active themselves.
How much do we really know about the active hours of operation for the prey items? If we were to go back to the Lion comparison, or even the whales, do their prey items keep one eye open after dark simply because there is a stalker in the night? Certainly the dimness provides an advantage for night sensory adapted predators regardless of whether or not the prey are awake at night, but being alert during the dark with senses of smell and hearing might help them from becoming a midnight snack.
Looking forward to the next chapter.

Duane Nash said...

Thanks for comment Stevie. With regards to vision due to deficiency of vitamin A in herbivore diets predators will always have an advantage over herbivorous prey at night, see in my post where I went into this. If anything nocturnal activity should be our bias our null hypothesis as goes tetrapod predators.

Future posts will elaborate and yes smell and vision are key but it is really the feet, hearing, and delayed adolescence that tie it all together.

khalil beiting said...

Great post Duanae, and I had no clue how effecient black bears were at hunting. Most people just take them as some kind of "Pooh Bear" that just eats berries all day long. And nocturnal hunting Orcas make perfect sense, and it's a shame that we are only now just devling into their nocturnal habits.

And a note about barrel chested Theropods, Tyrannosaurus definitely wasn't the only one for the title of "Brick House with Teeth". I went to the downtown library here in Cincinnati, and because our museum is under renovation a mounted Polar Bear and a sub-adult Allosaurus were on display in the library temporarily. When I looked at this medium sized Theropod at no more than 25 or so feet long, I realized that it too is rather barrel chested. You can clearly see that the body itself encompasses the front viewing,and it blocks the front viewing of the thighs and tail by a good 5 inches or so. 5 inches isn't too much for a 25 ft. animal, but it would be even wider in the real animal when it's covered in fat, muscle, feathers, etc. I have a feeling that most medium to large sized Theropods were barrel chested to a certain degree, in must have been like modern Felids and Ursids in that they too must have somehow used their own sheer weight and girth to subdue prey.

Duane Nash said...

Good point about Allosaurus being relatively barrel chested, I now recall that it has been noted for its relative girth. But if all you have to do is run down sauropodlets and scavenge giant carcasses not much need for agility too.

Jonathan Atkinson said...

Although I totally see how trex would be a good example of nocturnal large theropods I was honestly thinking you would cover cryolophosaurus what with being in 5 months of mostly darkness. Another time maybe (poor cryolophosaurus).

khalil beiting said...

@Jonathan Atkinson Don't forget Nanuqsaurus and Australovenator!

Jonathan Atkinson said...

I didn't mention them because they seemed like the obvious and more recent choices, but no doubt just as important.

Alexander Ruger said...

Very interesting ideas! It reminds me of Phil Tippet's "Prehistoric Beast." I'm largely in agreement with you here: we've long attached this Hollywood vision of the Mesozoic to our speculated behaviors for these animals. A stealthy tyrant is not exactly something we're used to thinking about, but even modern day multi-ton animals can be stealthy - I recall a survivor's account from a program concerning elephant attacks, where a villager in India was attacked from behind by an elephant he didn't even know was there. Imagining a much more svelte predator at that size doing the same is not hard.

My only concern here is that some of your observations are dependent upon the quality of the mounted skeleton - this is not always consistent across museums and companies that work with fossils. There's probably a reason the Sue mount looks ridiculously bulky, whereas other displayed specimens are not so chunky. Peck's Rex and the Trix specimen are nearly as large, and the latter is also of the robust morph. Looking at their skeletons, you have what is most certainly a large, robust animal, but not one that is nearly as square (or brick-house-ish).

Do you think that the one-way breathing system Tyrannosaurus had might have made it a more efficient pursuit predator? Obviously, you aren't attuned to the idea of Rex being a pursuit predator, but it might not have had to run faster, just longer. Food for thought!

Duane Nash said...

Thanks Alex. Indeed the comparison between T. rex and the stealth behavior of elephants is something I will delve deeply into for the next post. Large animals can be cryptic not so much by hiding behind or blending into the environment but by reason of their size just looking like a natural feature of the environment.

I get your point about being careful on drawing too much from mounted skeletons. In the case of Sue though since "she" is the most complete large rex I see less reason to question her general build than other mounted specimens. I do suspect that the "gracile" vs "robust" split in rex is a sexual characteristic - something I will build upon in the future.

Maybe I need to restate my idea - and why I concentrated on Sue - more succinctly in the next post: that in the ontogenetic trajectory of rex we would see the complete gamut of predatory tactics that other smaller tyrannosaurids utilized. From small game coelurosaur hunter/scavengers, to teenage pursuit tactics, to subadult mixed bag ambush/chase and finally at the "Sue" level a complete mastery of stealth technique refined to the point that she may have specialized in not only short ambush tactics but actually detecting, infiltrating, and abducting sleeping dinosaurs. That is why emphasized Sue so much as I see in her a culmination of size, experience, super senses, and limited agility that necessitated the specialized tactic of catching not only dinosaurs under the cloak of dark - but while they were actually asleep. Of course will build on this in future.

I have pondered the long distance pursuit tactic but find it lacking. Again, why pack on so much girth if you want to run for long distances? Furthermore the ginormous jaw muscles speaks to animal that needs to get one good shot in, not something that it harrying and nipping at fleeing dinosaurs over distance. And finally the survival of hadrosaurids after failed predatory attacks is in line with relatively slow ambush predator that - if it doesn't get the first strike in properly - probably loses its quarry.

khalil beiting said...

Just a note about the robust morphs of Tyrannosaurus, I remember the Saurian devs talking about how the gracile and robust morphs are actually seperated over time. So one is found in the lower Maastrichitian and eventually evolves into the other morph over the course of the mid Maastrichitian and onwards. Don't take my word for that though. I don't have a scource to link right now and honestly I lean more towards sexual dimorphism myself seeing as how there aren't any full fledged papers on the matter. Just people alluding to it amongst the deeper parts of the paleo community. And I've learned over the years to not trust random conjceture simply because others have said so online. The whole commotion about the "Spike-backed" Dimetrodon is the best example since people hopped onto that bandwagon simply because one or two people started it. The whole unpublished remains of that "piscivorous" Psittacosaurus sp. is another example that I still hear about from time to time.

khalil beiting said...

Just an update after asking around, it turns out that there are "reports" of the more robust morph being found in the lower Maastrichitian and gracile morphs being found farther up. There are no actual papers on this so take this with a grain of salt, though a famous and (usually) well made* Japanese blog on Dinosaur skeletals talks of this. Here's the blog post from Saurian talking it about it as well with the help of Scott Hartman and Get Away Trike (the info's under the dection called Reference Specimen), so it is even more trust worthy:
Though don't get it wrong, even the more gracile morphs were incredibly bulky. Basing it off of Stan, the animal itself is more "scrawny" than the average Rex simply because of individual variation. Also keep in mind that it was a young adult so it still has some growing to do. So sexual dimorphism isn't likely.

travislyonsgary said...

I do have one question though.Would the morph truly be that big? The estimates you showed seemed to make the arms rather inefficient. The discovery of the amount of muscle on the arms of the Rex, seems to be in place for helping it control itself/and or its prey into an angle it can get that bite in. At that size it looks to be rather tough though I suppose using the weight it could still get a proper angle one the prey item. Do you believe in the use of the arms for predation? I have talked to some paleontologist, one admitting that he cannot take back his position as he is entrenched in the arms being uselss.

Duane Nash said...

I don't really understand the dilemma. T rex - and really all other theropods - have a head that is ahead of the reach of the forelimbs, Whatever the forelimbs were doing it was after the prey had been engaged with by the head.

travislyonsgary said...

But to get into a proper position of control the forelimbs are needed. A bite is only as strong as its ability to reach the targeted area. Not always neccesary but most definitely part of hunting as otherwise there is a massive hole in the defense and control ability of the animal. The head,arms,and legs combine at least partially for the kill and consumption right? An example being that without the use of arms a T.Rex killing an Ankylosaur would be extremely hard to do. Even while asleep it's dangerous as there's a chance of deadly collision.

ted said...

How much would Sue have massed in your opinion? More than any other recorded theropod?

Duane Nash said...

Hi ted. I tend to avoid asserting any concrete suggestions on weight. There are many variables that make even the most rigorous assessments of weight prone to less certainty than we might be comfortable with. Even coming to good weights in living animals is fraught with difficulty. For instance what about skin thickness? The hide of a hippo can weight over a ton... What would this imply for the weight of spinosaurus? If it, as I have argued, had a similar skin thickness - with much more surface area the skin of spinosaurus alone may have weighed 2-3 tons alone possibly!! My final answer for something of a Sue sized rex is it most likely weighed substantially more than a bull African elephant. That is my broad side of the barn best guess answer. In other words - fucking heavy.

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