|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.
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.
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