Dinosaurs a concise natural history, Fastovsky Ch.9
“The balance of dispassionate evidence, therefore suggests that the largest theropods [like T-rex] likely were not the fleetest runners of their time. For all that running, it is now known that some theropods, at least, could also swim. In 2007, a trackway was discovered in Spain clearly demonstrating the imprints of a medium sized theropod swimming.” [or rather dragging his tail in very shallow water.]
Theropods footprints are famously rare
Maybe this is because the biggest dinosaur predators mostly moved around in the water 99% of the time, in energy conservation mode, like alligators, the biggest reptile predators today. Maybe they only came out less than 1% of the time to charge at their prey.
See for yourself
1) Compare the A and B images and note how T-rex was vertically proportioned like a fish.
2) Note the giant gut. And imagine the size of the animal (or meat chunk) T-rex could swallow whole with its giant jaws.
3) Look at how the leg bones are wide from the front (image C), but thin from the side (image A).
The Jurassic world moved in slow motion
The Jurassic world was not only a place of giants, but they all moved in slow- motion, the lumbering giant version of the average reptile speeds we see today.
T-rex was aquatic
1) If we take the body proportions of all the known terrestrial and aquatic reptiles. The terrestrial ones have flat and broad bodies. This gives them more belly contact area to better cool and warm with. And the aquatic reptiles have tall and thin bodies to better swim with. Think of an alligator’s tail.
2) What is the average height to width ratio of the average aquatic, and average land lizard-form reptile? (no snakes or turtles) I bet by this metric, T-rex is more aquatic than any living lizard-form reptile.
People and bird bipeds have round leg bones
True bipeds that walk about have round, or at least roundish leg bones. However, T-rex leg bones are proportioned like 2″ x 6″ boards that meet on a 6″ hinge. Now bones evolve to provide rigidity, not to act as leaf springs. So clearly it was horizontal loads that caused the bones to evolve in this way. What are those horizontal loads from?
T-rex had 2 x 6 leg bones
Note how all the parts of the T-rex that ungulate, or move like a fish are tall and thin, suggesting an aquatic environment. This while the leg bones are the opposite. They are proportioned like 2” x 6” boards, and their thick axis is exactly perpendicular to the axis of T-rex’s fish plane — and also the vector of T-rex’s fish undulation forces. So T-rex’s legs seem to have evolved to handle lots of undulation energy, such as T-rex might have when it charged out at its prey. And because we don’t see any of this undulation energy in the T-rex tracks we find, it must have only been initial energy when the predator was accelerating into its charge. So this energy was from when T-rex stopped moving as a fish in shallow water, and started into its bipedal charge like a frilled lizard.
Why are T-rex front limb still there?
With dagger claws on its hind legs, and a crocodile’s jaw, there was little need for front claws as weapons. Yet the front limbs did not evolve completely away, even after millions of years. So having front tiny front limbs did serve some purpose over not having any front limbs at all. The real question is not why T-rex’s front limbs were so small, but why they didn’t they disappear completely. Maybe they helped T-rex occasionally walk on all fours. Or maybe they were helpful in rapidly rearing up. This way its hind legs would have a more vertical application of force. This way the feet would have more traction in the mud, when T-rex jumped into the reptilian version of a cheetah’s charge: A 5-kph rocket charge at the tortoise slow sauropods.
Sauropods have 3×6 leg bones
They also evolved to handle much “serpedal” energy.
True bipeds don’t have tails
In the entire animal kingdom today, are there any true bipeds walking around anywhere on earth with long tails? The closest thing we find are the lizard bipeds. These however do not walk on two legs. They either stand, or run on two legs. So bipedal dinosaurs with tails were probably not true bipeds. They were only bi-ped sprinters like we see with the fringed-lizard today — They charged open mouthed, flailing their feet on the ground.
Most of the time, dinosaurs were maxed out for energy conservation so they could grow bigger to either get at the macro-fruit, or eat the big creatures eating the macro-fruit. Dinosaurs were fundamentally energy-saving belly- draggers, like iguanas, alligators, snakes, and tortoises today. Either that, or they were aquatic. And notably, the frilled lizard is a belly dragger (and tail dragger), except when it is in burst of speed mode… for maybe up to 300 times its length. They simply could not afford to waste energy keeping their weight up off the ground. So most of their weight was frequently dragged along.
True bipeds like humans and birds leave tracks along a single line, but dinosaur “bipeds” walk along two lines. What sort of tracks do lizard bipeds like the frilled lizard leave today on muddy ground? How fast are they moving? Can we make inferences about theropods bipedalism from these footprints?
True bipeds foot prints are in a single line
Look at the tracks of people and birds. The heels almost form a straight line. Look at the tracks of dinosaurs, they are all in two lines. And this is so even for the supposedly bipedal theropods like T-rex. Notice how your own heels form a single line when you walk. Now go and look at a pigeon walking. This appears to be something fundamental about true bipedalism. The pseudo bipedal lizards we observe today does not have aligned heels.
Atrophied T-rex front limbs
Look at a frilled lizard or chuckwalla running. He would run faster without front limbs. Now look back at T-rex. He is so evolved for swimming and the attack dash, he doesn’t even have front legs really. So here is a creature that was never going around on all fours. But here is also a creature that was not walking around like a pigeon or a chicken either.
T-rex footprints are rare
Maybe they are rare because T-rex was not walking around very much.
T-rex lurking like an alligator
Look at a T-rex head, it is 3x as tall as it is wide. Andlookattherestofthe creature. It all looks tall and slim, like an eel, or an alligator’s tail. Rather adapted for swimming, isn’t it? Perhaps its nostrils and eyes stuck up above the rest of his skull, like a crocodile lurking 98% below the water. So it is not hard to imagine that T-rex mostly hung out in rivers and wet places. There it lurked crocodile style, 98% hidden under water. Only its nose, eyes and ears above the water line, like a giant alligator, swimming silently like a snake, conserving energy.
Charging out of the water part-1
When prey came within range, T-rex would charge out of the water in a burst of speed, frilled lizard style, mouth wide open. Here we note the way the Basilisk Lizard can go from swimming in water like an alligator, to walking on water mode. Once up, his tail end— the majority of its mass is drags on surface. Maybe the T- rex did this on land. Here we imagine that T-rex was a two-legged reptilian sprinter, like we observe today with the various species of lizards that run on their hind legs.
Is there any reason to think that T-rex was a true biped?
Maybe most of the supposedly bi-pedal dinosaur predators swam around and then lurked in the water and then only occasionally charging out. And given that there are no true bipeds with tails, it seems more likely that dinosaur bipeds ran like Frilled lizards. With their tails sort of dragged on the ground. The body is held sort of upright like a cobra’s front part, or maybe at 45°. And the huge mouth is held wide open during the bipedal charge. Also, the front arms are held closely to the frilled lizard’s sides when it runs and are completely unused.
Charging out of the water part-2
T-rex never walked around like a giant chicken because of its tail. And because of its small front limbs, it wasn’t ever walking around on four legs like a crocodile. It lurked like a alligator or crocodile in the water, and then charged out of the water like a frilled lizard.
T-rex crouching is under-estimated here. The back was kept just below the water’s surface, and the belly rested on the river bottom. The front limbs helped the T-rex to stay positioned without motion. And they also (perhaps more importantly) helped it rear up faster, shortening the time between visibility and leap.
T-rex arms helped it cheat with its chin-ups
Think of how much easier chin-ups are when your feet can sort-of touch the ground and give your motion even the slightest little start. Now the leg holding racks at gyms, racks for spinal muscle exercise, where you start in a horizontal position and have to “rear-up” like a horse. The average rearing-up speed is much faster when we have something to push off of, even if it it just with our fingers. Now look again at T-rex arms, they are actually ample for this purpose.
Another way of looking at it is that T-rex needed to rear up and get its body centered on the vector of its leap. Until it did this, it could not leap. The tiny arms probably helped immensely with this. And remember that this was a creature mostly buried in water. So its movements were always slowed by water, until it mostly got out of the water.
This is what bipedalism looks like when the creature has a tail and moves around serpedally, like a sperpent. So we should not assume that T-rex walked around like a true biped just because there are bipedal tracks. And the leg bone proportions shout that there were very high lateral energy vectors being applied to the legs. And this clearly describes a serpedally moving animal, or legs on a creature undulating and moving like a snake.
Even alligators sometimes rear up on their hind legs. Note how this one is one his “toes”, and his front limbs are minimized like a T-rex. Also, note how the front half of this alligator is larger than the back half, but it still weighs less.
Fish to amphibian to reptile to aquatic reptile
Look at alligators, turtles, Galapagos iguanas, anacondas, water moccasins. These are all aquatic reptiles. Many reptiles returned to the water.
T-rex and the evolutionary main stream
Dinosaurs had to drink. So here we imagine that there probably were main streams (great long rivers actually) where the feeding opportunities for predators were greatest. And here, the competition for survival was also the toughest, and this pushed evolution to occur faster. So here we imagine rivers as nexuses of dinosaur carnivore evolution, places where adaptation was freshest and hardest to overcome. Here there must have been huge advantages to being amphibious. Swimming, or rather slithering reptilian predators could cover just so much territory expending practically no energy (as with alligators today). They could survey their territory for prey exposing just two nostrils and two eyes (as with alligators today). They could sneak up on their prey, exposing just two nostrils and two eyes (as with alligators today). Then once they were within striking distance, they could charge up onto the land, and lay their giant mouths on their prey (as with alligators today). And of course everything was about the charging speed.
It is worth emphasizing that big-jawed, one-bite, low metabolism reptilians (crocodiles and alligators) are still in this bio-energy conservative, river- based niche today. Here is where the biggest energy conserving slow- metabolism reptiles still live. Here we see what biggest-carnivore T-Rex actually was. It was specialized to take down the biggest macro-fruit sauropods when they came to a stream or a lake for drink. Here being water based allowed the predator to conserve energy, so it could grow to sufficient size to effectively take down the biggest macro-fructivors. And here we see that the alpha predator of this main stream eco-system was also in energy conservation mode. So we can say that the entire Macro-fruit ecosystem was based on scale, and speed really didn’t matter much — Except of course the short bursts of speed we observe in reptilian predators of today. Are T-rex bones, more than other dinosaurs only found in places that could have been river valleys?
Anacondas with legs
T-Rex did not walk around like a chicken. It either swam or slithered like an anaconda in a marsh, then it made a land charge, like a frilled-lizard, mouth open. The tortoise slow sauropods often could not get away.
Lower your expectations
Maybe the giant dinosaurs moved 20% as fast as tortoises today. Or maybe they moved half as fast. And maybe because of their low weight, and low kinetic loads, we over-estimate their muscle strength and mass.
The most extreme biting force? Maybe not
Judging from the muscle attachment points, the biting force of a T-rex was supposed to be greater than any other animal ever. Maybe this wasn’t the case. Maybe the bones were super light and hollow and weak, and the musculature was small and weak as well.
T-Rex teeth angle back
We note that T-Rex’s back-angled teeth frequently broke off and re-grew. So it appears that the T-rex bit once and ‘locked’ (as with crocodilians today), and then wriggled violently (as with crocodilians today) resulting in broken teeth.
It is also not hard to imagine groups of T-rex lurking together (like alligators), and all charging out at once (again like alligators). Once one made a bite, others would also clamp on, sort of like with dogs and a wild boar.
The alpha predator is definitive
The T-Rex was the largest predator, and thus it was probably the #1 sauropod predator. Here was the predator preying on the giant sauropods that were the main macro-fruit symbiot animal. Yet T-rex was in full reptile-style energy conservation mode until the moment he charged his prey. This would only be consistent with an entire ecosystem of cold blooded low metabolism, slow- moving reptilians, living mostly in energy conservation mode — metabolically, they were all tortoises, except that some charged their prey like a frilled lizard. In other words, Dinosaurs were cold blooded creatures where size mattered above all else: This nearly all the time, except for predators, when they had to muster speed.
T-Rex ribs are small at the neck
This suggests a creature that regularly bent its head like a rattlesnake or a cobra, or a frilled lizard.
T-Rex wasn’t running around with a full belly
Judging from the bite and hold nature of its teeth, and from the nature of its rib cage, T-rex seems to have had an expandable gut, like a snake. If it could, it ate a great deal at once and then digested over a long period of time, like a snake.
T-rex lived in the water to save energy
The predators that lived in the water could move around faster and with less energy. Thus they could get bigger than the land predators, big enough to prey on the sauropods. This is why T-rex was so successful as a species.
Whip tail sauropods
Today, most lizards regrow their tails. And these flail wildly when they break off. This was probably the main defense of the sauropods. So the tails were probably how the sauropods made it dangerous for a T-rex to attack. Sauropods were probably turtle slow in general, but if they used their tails for self-defense then it might have moved like a severed lizard tail in spasms. And these spasms were probably quite powerful. Here we imagine a Brontosaurus turned sideways against a charging T- rex. Its neck and tail were on the side of the charging T-rex. This was a tail cocked and ready for the charging T-rex. When the T-rex got to within range, across came that huge, deadly, and disposable tail tip, a tail that would grow back after it smacked a T-rex at say 100-kph. Do we commonly find sauropod skeletons missing their tail tips? Have we found any that broke off and were in the process of growing back? Do we find dinosaur predators with broken bones, as if from a tail impact?
Facts about theropods
1) The head and neck are greatly pneumatized, just like many other dinosaurs, because even as predators, they had to be big.
2) Tracks are extremely rare.
3) T-rex had very large olfactory bulbs, and seems to have the keenest sense of smell around.
4) T-rex had very long cochles, so it had excellent hearing. Evidence suggests that this was particularly so for low frequency sounds.
5) T-rex had relatively the largest brain for its size of any adult non-avian dinosaur, and it was close to that of a modern alligator. So it was dumber than an alligator.