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I discovered that theropods ranged in many sizes and had many different body design variations. After spending most of my free time over the past two years focusing on T. rex, I also decided to take a look at a few other theropod species. I was curious to see if the Treeosaur theory could be applied to theropods other than Tyrannosaurs.

The first species I looked at was Giganotosaurus: a large theropod that lived in South America in the late Cretaceous period. Giganotosaurus had a similar body design to T. rex, but with a few noticeable differences. It had a proportionately longer head, neck, arms, and overall body length than T. rex.

I found out that Giganotosaurus lived along side the largest know sauropod: Argentinosaurus. Most paleontologists believe a Giganotosaurus could not have possible brought down a massive adult Argentinosaurus by itself. Some paleontologists believe Giganotosaurus hunted in packs to overcome this problem. I definitely agree that Giganotosaurus hunted in packs, but I don’t believe packs of Giganotosauruses would have randomly attacked herds of Argentinosauruses. I believe packs of Giganotosauruses stealthily used the stand hunting from a tree strategy to effectively bring down Argentinosaurus.

I believe Giganotosaurus was capable of stand hunting from trees inside forests like T. rex, but probably spent most of its time hunting edge habitat. The reason I think Giganotosaurus was more of an edge habitat hunter was because of its pubis boot design and because of its prey, Argentinosaurus. Giganotosaurus’ pubis boot was proportionately smaller and less robust than T. rex’s pubis boot. This suggests to me that Giganotosaurus would not have been able to perform major Treeosaur maneuvering around a tree inside a forest like T. rex. Giganotosaurus’s pubis boot design seemed perfect to have made minor Treeosaur maneuvering around a tree at edge habitat. Most Paleontologists believe that large, mature sauropods were too big to have ventured deep into forests and probably spent most of their time feeding out in open country or on the edges of forests. It seems reasonable to believe that packs of Giganotosauruses may have stand hunted from trees on the forest’s edge and waited to ambush Argentinosaurus.

I can imagine a pack of Giganotosauruses strung along the edge of a forest in a high Treeosaur posture (same posture as T. rex) facing out into open country. Once the pack had detected an incoming herd of Argentinosaurus with its auditory, visual and possible vibration senses, the pack would have made minor Treeosaur sideways maneuvering and waited for the incoming prey. The pack’s only chance of success would have been if one of the Argentinosaurus had fed too close to one of the trees concealing a Giganotosaurus. Once this occurred, that single Giganotosaurus would have exploded off the tree to attack the Argentinosaurus’ exposed weak spots: its vulnerable head and neck, which were low to the ground for feeding.

I believe that Giganotosaurus’s attack zone was a small circular area that surrounded the tree, not a straight line attack zone like T. rex. The Giganotosaurus would have had to quickly attack the Argentinosaurus at very close-range to ensure the Argentinosaurus wouldn’t have had time to lift its head up and out of Giganotosaurus’s attack height. This meant a very short and very low attack zone for Giganotosaurus: a much shorter attack zone than T. rex’s attack zone. The Giganotosaurus’s best bet would have been to bite down hard on top of and directly behind Argentinosaurus’s head and then to grab underneath Argentinosaurus’s neck with its strong, powerful arms. This would have ensured a solid, firm hold for Giganotosaurus. If the Argentinosaurus were small and young, then the single Giganotosaurus may have been able to kill the Argentinosaurus quickly with its jaws. If the Argentinosaurus were large and mature, then the Giganotosaurus would have held on with its jaws and arms and used its strong neck and body weight to keep Argentinosaurus’s head from rising up. Though a very massive animal, the Argentinosaurus would probably not have been able to lift up its head and long neck because of the Giganotosaurus’s body weight bearing down from on top. Giganotosaurus would not have been able to stop the massive Argentinosaurus from walking away, but it could have used its powerful legs to maneuver along with the slow walking Argentinosaurus.

The only chance Argentinosaurus would have to shake off Giganotosaurus would be to spin its body around and try to use centrifugal force to throw off the attached predator. More than likely, Argentinosaurus would not have been able to do this in its current position because of the many trees at its flank sides. Argentinosaurus would have to try to clear these trees or risk injuring its neck during its defensive maneuver. The only chance Argentinosaurus had would have been to walk backwards and pull Giganotosaurus out of the tree line and then attempt to spin its body around. Argentinosaurus would have had to clear the tree line as quickly as possible. Giganotosaurus’s legs and feet would have had to work very hard to slow down the Argentinosaurus as much as possible as it attempted to reverse out of the tree line. I think this resistance would have automatically repositioned Giganotosaurus’s body up against Argentinosaurus and probably forced Giganotosaurus’s arms out from underneath Argentinosaurus’s neck. Giganotosaurus’s powerful jaws and long, strong, flexible neck would have been major advantages in this situation. Giganotosaurus’s strong jaws would have stayed firmly attached to Argentinosaurus as Giganotosaurus’s body was dragged up over and on top of the reversing giant’s head. Now Giganotosaurus could have re-embraced Argentinosaurus’s trunk-shaped head with its long, powerful arms. This new position would have given Giganotosaurus an even stronger grip, more leverage, and more maneuverability than if it had stayed positioned to the side of the Argentinosaurus.

Timing was everything for these battling giants. If Argentinosaurus had managed to quickly pull Giganotosaurus out of the tree line, it would have had a good chance to spin and throw off Giganotosaurus. Argentinosaurus would have then been able to raise its head and neck up to safety and then had plenty of room to defend itself. If Argentinosaurus had been too slow in pulling Giganotosaurus out of the tree line, then the results would have been disastrous for the Sauropod. The rest of Giganotosaurus’s nearby pack would have quickly arrived and attacked the vulnerable neck of Argentinosaurus, which would have been held down low by the attached Giganotosaurus. Like lions, I imagine the first few had arrived to assist with holding down and securing the prey animal while the rest of the pack tore into its flesh. I don’t think it would have taken long for the Giganotosauruses to bite deep into Argentinosaurus’s vulnerable neck and sever major arteries or its airway to bring the giant crashing to the ground.

I believe Giganotosaurus’s arms had all the same Treeosaur functions as T. rex’s arms, but that Giganotosaurus’s arms had one additional important function for dealing with the type of prey it hunted. Giganotosaurus had evolved longer and more powerful arms than T. rex simply because it needed them to assist its jaws in holding onto the head and long necks of large sauropods. If Giganotosaurus had spent most of its time hunting a more compact prey like Hadrosaurs, it probably would have depended mostly on its jaws for attacking and not have evolved long, powerful arms. If this were the case, Giganotosaurus would have evolved smaller arms, like T. rex. These arms would have been just strong enough to help the dinosaur perform its many Treeosaur tree tasks.

There are many other large theropod species that lived among other large sauropod species. One example of a possible predator/prey relationship could be the Allosaurus (theropod) and Diplodocus (sauropod). A lot of these other theropod species had proportionately similar body designs as Giganotosaurus: long necks, long arms, and a decent sized pubis boot. I believe these theropods may have evolved this body design to specialize in hunting sauropods by stand hunting from trees on the edges of forests.

After looking at a few other theropod species similar to Giganotosaurus, a very strange looking theropod caught my eye: Carnotaurus. This medium-sized theropod had also lived in South America in the late Cretaceous period. Carnotaurus had a very different body design than T. rex. Compared with T. rex, Carnotaurus had a smaller head, a shorter muzzle, tinier arms, a smaller pubis, and a thinner overall body profile. Carnotaurus also sported two horns over its eyes. Even though I was doubtful that the Treeosaur theory would work with Carnotaurus, I decided to analyze this theropod further.

I spent a few weeks scratching my head over Carnotaurus. I couldn’t see anything to suggest that this theropod’s biomechanics would have allowed it to sustain the Treeosaur posture against a tree like T. rex. Carnotaurus’s body didn’t seem designed to perform this task. I was about to give up when something finally occurred to me. I realized that the tree I used in my original Treeosaur T. rex model had a large, round trunk design. This tree design seemed reasonable to use since large coniferous and deciduous trees with round trunks had existed in T. rex’s environment. Perhaps trees of other sizes, widths and shapes had existed in Carnotaurus’s environment. Maybe a different type of trunk design would have allowed Carnotaurus to stand hunt from a tree.

I jumped online and started searching prehistoric trees, cretaceous trees, dinosaur trees, etc. Of course there were thousands of hits, but I couldn’t find any definitive website dedicated to prehistoric trees. Carnotaurus is from South America, so I ran a search under “South American trees.” Once again the search produced a countless number of hits. Even though there are hundreds of species trees in South America, I started browsing through photos. I stumbled onto a picture of an amazing tree. “Jackpot!” I think I had found exactly what I was looking for; I literally had goose bumps! On my computer screen was a photo of a modern day ceiba tree.

I didn’t know much about ceiba trees because they don’t exist in North America. However, they did look somewhat familiar to me. Maybe I recognized them from my scuba diving trips to the Caribbean. After reading up on ceiba trees, I found out that my hunch was correct: ceiba trees do exist in the Caribbean. There are about fifteen species of this tree found in tropical regions around the world.

Ceiba trees are very strange looking as far as trees go. Most trees widen slightly at the base, but ceiba trees take this widening to an extreme. Ceiba trees have buttress roots. This unique, wall-like root system can spider far out from the tree’s base. The roots gradually taper up into the trunk of the tree, many feet above ground level. Most of the ceiba tree pictures posted on the web show people standing in between the large crevasses of the buttress roots. There is a good chance that some prehistoric form of the ceiba tree had existed in Carnotaurus’s environment. Maybe Carnotaurus positioned itself in a crevasse of the buttress roots for concealment while stand hunting from a tree.

Carnotaurus, with its small head and thin body profile, may have had a “wedge” technique in contrast to T. rex’s “hug” technique while stand hunting from a tree. Instead of positioning itself more vertically high against a round tree, Carnotaurus may have positioned itself more horizontally low, onto its thick chest, in the crevasse of a buttress root tree. I think the design of Carnotaurus’s pelvis helps support this idea. Carnotaurus’s pubis and ischium were about the same size and both had a small boot. Carnotaurus’s ilium was practically horizontal when its pubis and ischium were resting on the ground. This suggests a more equal weight distribution on Carnotaurus’s pelvis while its body was cradled in a tree crevasse during a low Treeosaur posture.

T. rex’s ilium was positioned at more of an upward angle when its pubis and ischium were resting on the ground. This suggests T. rex had unequal weight distribution on its pelvis. While in a high Treeosaur posture, most of T. rex’s body weight would have been bearing down at the point directly below its upper body mass: the pubis. I believe that was why T. rex had a massive pubis boot and a smaller ischium.

Example of Carnotaurus wedged in the crevasse of
a buttress root tree.
Comparison of Carnotaurus’s pelvis and T. rex’s pelvis. The arrows indicate the distribution of body weight pressure while each theropod was in the Treeosaur posture.

Surprisingly, Carnotaurus had even tinier arms than T. rex. I also learned that Carnotaurus’s arms functioned differently than T. rex’s arms. T. rex’s arms folded in, toward each other. Carnotaurus’s arms worked in reverse by pushing out, away from each other. This arm motion would have helped Carnotaurus stabilize itself while wedged into a crevasse between buttress roots. Though T. rex and Carnotaurus had arms of different size and design, both theropods used their arms for stabilization during the Treeosaur posture.

Carnotaurus’s head was very different than T. rex’s head. It was shorter in length, thinner in width, and had two horns above its eyes. If Carnotaurus had wedged its body into a narrowing crevasse of a buttress root tree, then these unique head features would have worked to its advantage. I think Carnotaurus had a different attack method and attack zone than T. rex. The buttress roots to either side of a wedged Carnotaurus were perfect natural blinds that would have concealed most of its body. I believe Carnotaurus would have attacked its prey at the flank sides of its Treeosaur position, rather than its front sides like T. rex. Once Carnotaurus detected prey at one of its flank sides, it would slowly and quietly pull in its arms and push its head against the tree. Its strong neck and leg muscles would act like a tripod as it slowly stood up. It would make a sideways glance over or around the buttress roots. As soon as Carnotaurus locked onto its prey with its excellent binocular vision, it would launch an attack.

I believe Carnotaurus’s horns may have had multiple functions while wedged in a root crevasse: to protect its eyes, to support and hold up its head, to act as pivot points for its head and neck as it stood up, and possibly to sense prey vibrations. There are a few different types of modern ceiba trees. Some have wide buttress roots and some have narrow buttress roots. Carnotaurus’s horns may have evolved if it had stand hunted from trees with narrow buttress roots. Carnotaurus’s horns (not muzzle or jaw) would have made contact with the buttress roots while wedged into a narrowing crevasse. Carnotaurus’s horns would have protected its eyes, and possibly its muzzle and jaw, by allowing the animal to pivot its forward body weight onto its horns as it stood up. Having a stubby muzzle would also have been an advantage. The horns would have kept its small, stubby head from rubbing against the buttress roots as it rotated slightly on its horns’ axis points. The horns, once wedged in a crevasse, would have also helped support and hold up its head for extended periods of time while in a low Treeosaur posture.

I believe Carnotaurus’s horns also provided the advantage of sensing prey vibrations. While wedged in a crevasse, each horn would tap into the buttress roots on each side of its head to detect incoming prey ground vibrations. Check out the photo below: a close-up of the tip of my vibration meter. I used the vibration meter to run the ground vibration tree experiment in the previous section. Doesn’t it look familiar? Carnotaurus horns and the vibration meter tip have the same basic shape. Maybe its horns performed like a built-in vibration meter for Carnotaurus.

A close-up of the tip of my vibration meter.

The reason I think Carnotaurus was more of a flank side attacker, and not a front side attacker like T. rex, was because of the many restrictive tall buttress roots that surrounded the tree. Carnotaurus would have blended in extremely well while wedged in a crevasse of buttress roots, but the many tall roots around the tree would have been obstacles for Carnotaurus to attack around or over. If Carnotaurus attacked to the tree’s flank sides, it would have minimized the number of buttress roots in its attack path. Carnotaurus would only have to go over or around one buttress root, not multiple roots.

I believe Carnotaurus was a stationary tree hunter. It would not have been able to do the Treeosaur sideways maneuver around a tree like T. rex. The buttress roots were just too restrictive. Carnotaurus would not have been able to see around or over the buttress roots while in a low Treeosaur posture. In fact, Carnotaurus’s eyes would not have been able to see anything while it was wedged into a tree crevasse. In contrast to T. rex’s dominant peripheral vision, some paleontologists think Carnotaurus’s eyes had more binocular vision and less peripheral vision. This seems logical because Carnotaurus did not need wide peripheral vision while wedged in a tree crevasse. Carnotaurus would have depended heavily on its hearing, and possibly its acute vibration senses, to detect incoming prey. After it had detected its nearby prey, Carnotaurus would have slowly stood up, turned sideways and locked in on its prey with its binocular vision.

I believe Carnotaurus’s body design evolved to perfectly wedge itself in the crevasse of a buttress root tree in a low Treeosaur posture. Carnotaurus’s horns were a real surprise to me and may have had multiple functions. Even though they contrasted each other in many ways, I found Carnotaurus to be just as fascinating as T. rex.

Carnotaurus had a small relative, which also lived in the late Cretaceous period: Aucasaurus. This smaller theropod had a very similar body design to Carnotaurus. The only major difference was that Aucasaurus didn’t have horns; however, there were small bumps on its head. Aucasaurus’s small bumps probably had the same function as Carnotaurus’s horns, but in a smaller scale. I believe Aucasaurus and Carnotaurus shared the same exact stand hunting from a tree strategy.

Another unique species was Acrocanthosaurus. This medium-sized theropod had lived in North America in the early Cretaceous period. Its body design was closer to T. rex than to Carnotaurus, but it had a fin running down its spine from head to tail. Since I had just studied up on Carnotaurus, the fin jumped out at me immediately because it reminded me of a tree buttress root. Could it be that Acrocanthosaurus’s fin had evolved to mimic a buttress root? Similar to the Carnotaurus, I think it was possible that Acrocanthosaurus had wedged itself into the crevasses of trees. Its fin would have helped this dinosaur blend in perfectly between buttress roots.

Acrocanthosaurus had a body and pelvis design similar to T. rex: a larger pubis boot and smaller ischium. I think Acrocanthosaurus would have wedged itself into a wide tree crevasse in a high Treeosaur posture. This posture would likely have placed Acrocanthosaurus’s arms just above where the buttress roots tapered up into the trunk of the tree. For this reason, Acrocanthosaurus had enfolding arms, like T. rex, rather than outward pushing arms, like Carnotaurus. Acrocanthosaurus had longer arms than both Carnotaurus and T. rex. Like Giganotosaurus, I believe Acrocanthosaurus may have evolved longer arms for dealing with the types of prey it hunted.

I do not know if Acrocanthosaurus had been a stationary tree hunter, like Carnotaurus, or a mobile tree hunter, like T. rex. I think it would have depended on the size and shape of the buttress roots of the trees in its environment. If the buttress roots were shallow and hadn’t flared out very far, Acrocanthosaurus may have been able to do the Treeosaur sideways maneuver around the tree like T. rex. If the buttress roots were high and had flared out far, Acrocanthosaurus was probably a stationary tree hunter like Carnotaurus. My gut is telling me that Acrocanthosaurus probably did practice the Treeosaur sideways maneuver to some extent because it had a decent sized pubis boot. Another possibility is that Acrocanthosaurus may have hunted from round trees that were mixed in among buttress root trees. If this were the case, Acrocanthosaurus’s back fin design would have visually turned a round tree into a buttress root tree. Acrocanthosaurus would have had open mobility to perform the Treeosaur sideways maneuver. Either way, I believe Acrocanthosaurus, with its mimicking buttress root fin, would have blended in extremely well against a buttress root tree or against a round tree within the vicinity of buttress root trees.

Another medium-sized theropod that I studied was Ceratosaurus. Ceratosaurus lived in North America in the late Jurassic period. To me, Ceratosaurus was the neatest looking theropod dinosaur. Ceratosaurus had centered horns on top of its head and a blade-like crest, which ran from the back of its head down to its tail. Like Acrocanthosaurus’s fin, I believe its horns and crest may have evolved to mimic some part of a tree from which Ceratosaurus hunted. Like Carnotaurus, Ceratosaurus had an equally sized pubis and ischium. Unlike Carnotaurus, Ceratosaurus had long grabbing arms. Its pelvis and arm design suggest that Ceratosaurus had hunted in a low Treeosaur posture from some type of round tree.

I found out there was a very common group of short Jurassic trees called cycads. Maybe Ceratosaurus stand hunted from these trees in a low Treeosaur posture with its long grabbing arms hugging the tree partway up from its base or directly at its base. Ceratosaurus would have been able to rest its head and chin on top of the cycad tree in the upper leaves. Its horns may have evolved to mimic parts of the upper cycad tree. Its blade-like crest may have evolved to mimic the cycad’s rough trunk pattern. Ceratosaurus would have blended in very well against most short cycad trees in a low Treeosaur posture.

I think Ceratosaurus would have been a stationary tree hunter because of its low Treeosaur posture. Ceratosaurus would not have had sufficient leverage to perform the Treeosaur sideways maneuver around a tree. Also, Ceratosaurus’s head would have caused too much leaf movement if it had to rotate through to upper part of cycad tree. Any sort of vegetation movement, especially in a stand of low cycad trees, potentially could have been seen from a distance by incoming prey.

Ceratosaurus may have had a similar attack method as T. rex: to its front sides. However, I think Ceratosaurus would have had a different launching method. Since Ceratosaurus’s head would have been resting on top of a cycad tree, it wouldn’t have had to drop its head to the side of the tree in order to stand up. Similar to Carnotaurus, Ceratosaurus could have simply pushed its head down into the tree and used its neck and legs like a tripod to stand up and then attack.

One more medium-sized theropod I found interesting was Cryolophosaurus, which lived in Antarctica in the early Jurassic period. Cryolophosaurus had a very unique looking head crest; it ran perpendicular across its head. Most head crests on crested theropods ran parallel with their bodies. Some paleontologists believe head crests on theropods were for display. I think it may also be possible that theropod crests evolved to help them blend in by mimicking a part of the tree from which they hunted. If Cryolophosaurus did stand hunt from a tree in a Treeosaur posture, its head crest would have been horizontal with the ground. Perhaps Cryolophosaurus’s head crest evolved to mimic tree fungus, which had the same basic shape and was common on rotting trees.

Tree Fungus

I have applied the Treeosaur theory to a few large and medium-sized theropods. What about the small theropods? Small theropods would have hunted smaller, swifter prey. At first, I thought that the stand hunting from a tree strategy by theropods would not have been effective against swift prey. Then I realized it probably was possible because small theropods were also fast on their feet.

Velociraptor was a small but dangerous theropod, which lived in Asia in the late Cretaceous period. A deadly and intelligent pack of Velociraptors was portrayed in that famous 1993 dinosaur blockbuster movie. I thought it would be awesome if I discovered that Velociraptor had also used the Treeosaur hunting strategy. Well, after reading up on Velociraptor, I came to the conclusion that Velociraptor definitely did not stand hunt from a tree. This became apparent when I found out about the shape of Velociraptor’s pubis. Its pubis was very thin and hatchet-like in appearance. Clearly, it was not designed to have sat for extended periods of time in the Treeosaur posture.

I still wanted to find a small theropod that may have used the stand hunting from a tree strategy. After some more research, I found a promising Treeosaur candidate: Gwanlong. This small theropod lived in Asia in the middle Jurassic period. Gwanlong is thought to have been an early Tyrannosaur. From what I can tell from reconstruction drawings of Gwanlong’s skeleton, proportionately it may have had a decent sized pubis boot and smaller ischium like its relative, T. rex. This leads me to believe that Gwanlong may have stand hunted from a tree in a high Treeosaur posture, but on a smaller scale. Gwanlong had a very prominent head crest. Like Acrocanthosaurus’s fin, Ceratosaurus’s horns, and Cryolophosaurus’s head crest, I believe Gwanlong’s head crest had evolved to mimic part of the tree from which it hunted.

I am very glad that I decided to research and apply the Treeosaur theory to a few theropods other than T. rex. I believe the stand hunting from a tree strategy would have been used in many variations, among the many different types of theropods. Maybe not all theropods had used the stand hunting from a tree strategy, but I think the majority of them had. Even the shapes of trees had possibly influenced the evolution of certain theropod’s body designs.


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