Theories on Dinosaurs

Theories on dinosaurs
A list of theories by Jeremy Herz and Taylor William Jacobson

1. Did Tyrannosaurus and other theropods hunt in packs?  
   It is quite likely that many did. Mapusaurus, Albertosaurus and Tyrannosaurus probably hunted in loose family groups as fossils of these theropods are found in close association with members of their own species. More primitive carnivores like allosaurs may have simply swarmed prey. Unlike later carnivores, allosaurs probably were only smart enough to know not to attack each other unless one of their number had already died. Then they likely would have eaten their fallen comrade as if it was prey.

2. What was the purpose of spinosaur sails? And were they able to take down large prey?
    The sail was most likely a display organ. Spinosaurs probably used them to attract mates and more importantly, as visual defense. Though spinosaurs were often the largest predators in their environments, they also had to contend with the similar sized carcharodontosaurs. The sail would probably be able to change color to deter the vicious attacker so that the larger predator would be left alone. As for hunting, spinosaurs were capable of killing 20-foot coelacanths and midsize dinosaurs, but tended to stay in water most of their lives like crocodiles or hippos, so it maybe that spinosaurs may have ambushed prey from deep water or simply stuck to fish. If ambushing land-based prey, the sail may have been also useful in attracting prey, like the lure on an angler fish, though this is pure speculation on my part.

3. What was the purpose of abelisaur jaws?
   Though scientists do not know all the details, it seems abelisaurs used their jaws to both bite and hold or for rapid snaps that induced large amounts of blood loss. Two good examples are the jaws of Carnotaurus and Majungasaurus. The former had a relatively weak, but very rapid bite that could cause huge amounts of blood loss and the latter predator had a bite similar to a modern big cat, which bites and holds until the prey suffocates or dies of blood loss. But as new research is undertaken, we may find out more about these jaws and how these bizarre carnivores hunted.

4. Why did stegosaurs go extinct?
   The stegosaurs may have gone extinct because of competition from ankylosaurs and the appearance of more powerful predators. It seems they were better able to defend themselves against predators with weaker bites. A stronger predator like a carcharodontosaur or tyrannosaur would have easily killed a stegosaur outright. The plates on the stegosaur’s backs were not much help in deterring more advanced predators either. The plates would have been easily broken by a stronger predator’s bite as easily as a human crunches through a potato chip.



5. What was the actual purpose of the dromaeosaur killing claws?
  The killing claws of dromaeosaurs may have had numerous functions. The claws could have been used for slashing, stabbing, and climbing, the latter being most likely for smaller deinonychosaurs like archaeopteryx. In the larger animals, they would have been used exclusively for latching onto prey. Even if the claw’s inner edge was rounded, their sheer mass could have helped in ripping prey apart and disemboweling them. A new find adds in a fourth possibility; in 2011, Paleontologist Denver Fowler revealed that dromaeosaurs may have used their enlarged claws to pin prey down while they devoured it alive in a technique called Raptor Prey Restraint. The prey would then die from organ failure and blood loss.

6. Where there other tyrannosaur groups aside from Tyrannosaurines and Albertosaurines?  
   There may well have been. Though not many other tyrannosaur groups have been found, there may be a group of midsize predators called nanotyrannines; smaller and faster tyrannosaurs that specialized in prey like ornithomimids or pachycephalosaurids. Their niche would have also helped them to stay out of the way of the bigger Tyrannosaurines. Alioramus might be part of this group and possibly Nanotyrannus, but this is pure speculation until fossils are found to prove this true.

7. Were some carnivorous dinosaurs caring parents?
   Most likely. Dinosaurs were endothermic, or warm blooded, animals, and would have likely been social animals, like mammals today. Carnivorous dinosaurs were also probably fairly intelligent and could use complex skills in hunting and other behaviors. These are skills developed through teaching from parent to progeny, so it is likely that predatory dinosaurs taught their young how to hunt and what to hunt. In the case of Tyrannosaurus rex, the young probably became independent as soon as they were able to hunt on their own.

8. Why did spinosaurs and carcharodontosaurs go extinct?  
  The reason for the decline of these two families is unknown but in the carcharodontosaurs’ case, they may have been outcompeted by the tyrannosaurs, neovenatorid allosaurs, and abelisaurs. Spinosaurs were more generalized so this is an unlikely reason for their demise. Climate change could have also been a factor as there was increased volcanism in the later stages of the late cretaceous and loss of food, but these are tied in to other variables. It may even be that spinosaurs might not have gone extinct and scientists may someday find a spinosaur from the latest late cretaceous (there is fossil material present from a baryonychine spinosaurid dating to the Turonian). Until more evidence is found, no one truly knows. As for Carcharodontosaurids, it seems they only went extinct in Laurasia. Scraps of bone from Maastrichtian carcharodontosaurs have been found in South America. The discovery of Siats in North America reveals that such carnosaurs were present until the end of the Cenomanian and suppressed Tyrannosaurid growth until they disappeared.  

9. How wide-ranging were spinosaurs?                                                                         Spinosaurs were apparently very much a wide-ranging group. Spinosaurs have been found in Europe (Baryonyx), South America (Irritator, Oxalaia), Asia (Siamosaurus, “Sinopliosaurus”), and Africa (Suchomimus, Cristatusaurus, Spinosaurus). A new fossil was also found in Australia; a neck vertebrae belonging to a juvenile or hatchling found in the back of a museum also shows that this group was present in Australia as well.

10. What was the reason for the rise in tyrannosaur diversity during the Campanian?  
    The rise in tyrannosaur diversity has to do with prey and the changes in the environment. During the cretaceous, many herbivores were becoming armored tanks; creatures capable of defending themselves from attacks by roving carnivores. The armor and decrease in speed allowed these defenders to weather out the Carnosaurs and dromaeosaurs and flourish. The Campanian and Maastrichtian stages were the time that display switched to hard-core defense, for example the centrosaurine ceratopsians died out while the ceratopsine ceratopsians evolved thicker and larger frills. The predators that came in to deal with these defenses were tyrannosaurs. And as prey evolved for the ultimate in defense, tyrannosaurs evolved the ultimate to overcome those defenses, and despite a decrease in speed, they became the ultimate predators; able to crunch through armor with the most powerful jaws ever to evolve in any animal, living or extinct. And this increase in tyrannosaurs led not only to aid the Carnosaurs in their eventual extinction, but to a decrease in dromaeosaurid “raptors” and troodontids as well.  
     In Addition to this, the discovery of Lythronax argestes suggests that there were three radiations of Tyrannosaurids that occurred at this time; one in the southern part of Laramidia (which included Lythronax, Bistahieversor, Daspletosaurus, an as-yet-unnamed genus, and Tyrannosaurus), One in the northern part of Laramidia (Gorgosaurus and Albertosaurus) and one in Asia, which evolved from the southern stock (Tarbosaurus, Zhuchengtyrannus). Lythronax’s discovery reveals that Zhuchengtyrannus is the sister taxon of Tarbosaurus, while Lythronax in turn is a sister taxon to the group that consists of Tarbosaurus, Zhuchengtyrannus and Tyrannosaurus rex. There are still pieces that have yet to be fit into this puzzle; namely Alectrosaurus and Alioramus and the unnamed Russian Tyrannosaurid nicknamed “Mashka”, so we do not yet know the full extent of who is related to whom in this new study.  

11. How intelligent were dinosaurs?
    It all depended on the species but the most intelligent dinosaurs were the advanced coelurosaurs. The dinosaurs of this order, and probably a lot of theropods in general, may have been as smart as some mammals since many lived lives similar to mammals. But no dinosaur, no matter how smart, was ever as intelligent as a parrot. Overall, they were capable of some complicated strategies, but none close to the problem-solving capabilities of really intelligent birds like ravens, keas, and parrots.

12. Were the baso-theropods the ancestors of the coelophysoids?
  It is possible. Details in the maxilla and premaxilla seem to point this out, as does the discovery of the dinosaur Tawa hallae and Daemonosaurus. Only more discoveries will verify whether or not this is true.

13. How strong was the bite of a Tyrannosaurus?
   The debate continues, but there are well taken measurements. The bite strength was more powerful than a crocodile’s when the dinosaur was feeding. At around three tons, Tyrannosaurus' bite could easily rip large gouges in bone, as was found in a partial Triceratops sacrum. However, the force of the killing bite is estimated to be anywhere from six to twenty tons. Which is closer to being accurate? A biomechanical test in 2012 by Karl Bates and Peter Falkingham reveals that Tyrannosaurus' bite was around 6 tons of force, the most powerful bite of any land animal, surpassed only by the Pliosaurus funkei (Predator X) and the giant white shark Carcharocles megalodon. However, estimates by Mason B. Meers estimated a bite force equivalent to that of the largest Megalodon specimens: 18 to 23 tons of force. Which is the more likely estimate? That remains to be seen.

14. Which was deadlier; Tarbosaurus or Tyrannosaurus?
  Overall, Tyrannosaurus seems to be the deadliest. It was bigger, stronger, and more robust than its Asian contemporary. But unlike Tyrannosaurus, Tarbosaurus is equipped with a locking mechanism in its jaw and a more rigid skull, an adaptation for hunting the sauropods and therizinosaurs of its environment.  

15. What was the reason for the rarity of gracile morphs of Tyrannosaurus?
   The gracile T. rex morph, believed to be the males by some, is likely due to a bias in the fossil record. My thought on this probably could possibly be considered unscientific, but it is my belief that if the gracile Tyrannosaurus specimens are males, they may have been rarer to fossilize due to their tendency to search for fertile females to mate with and rivals to fight with.

16. Is there evidence for pack-hunting in dromaeosaurs and troodonts?  
   There is, or at least possibly. “Egg Mountain” in Montana is the sight of a Troodon nesting ground. During the Campanian stage of the late cretaceous, the nesting ground, now a hilly knoll, was once an island in the middle of an alkaline lake. There, the Troodon males would sit upon the nests and incubate the eggs and the females would bring food back to their mates and babies. There is also pack-hunting behavior in Deinonychus. Four individuals were found dead around a Tenontosaurus in Montana’s Aptian sediments. What had happened was that a large pack or a mob had attacked their prey and four members of said hunting party were killed in the process. The herbivore was eaten by the remaining pack and the dead pack members were also partially eaten, possibly by lower ranking members of the pack or mob drove that from the main kill by their superiors.

17. Were allosaurs good parents?
   At Como Bluff, Wyoming, there is possible evidence that Allosaurus did care for its young, as the tooth marks of juveniles are found alongside adults as some suggest. However Allosaurus probably abandoned its young much sooner than later theropods like Tyrannosaurus did. As for when feeding at kills, allosaur juveniles were probably at risk from adults whom were not their parents. The rival adults would gladly kill a smaller potential rival to eliminate competition at a kill, consuming them as well to restore energy lost in battles with prey.

18. What was a battle like between Alamosaurus and Tyrannosaurus rex?
   This battle is tough to determine, since Alamosaurus is known from specimens that are not full grown. Isolated vertebrae and limbs however, show that Alamosaurus may have been as large as Argentinosaurus or even Puertasaurus, so it may have taken a pack of Tyrannosaurus to take one Puertasaurus down. Tyrannosaurus rex was definitely big enough though to attack Alamosaurus, even if it wasn't full grown.

19. Did some abelisaurids live in the northern hemisphere?
   Only one possible abelisaur was originally known from the northern lands of Laurasia; Tarascosaurus. And that is only known from leg bone fragments. Then, in 2013, Arcovenator, a close relative of Majungasaurus and nearly as large, was discovered in France from material that includes a braincase.   There may have been others, but it seems they were unable to compete with tyrannosaurids on the mainland, which are better built and much larger.

20. What where the actual purposes of ceratopsian horns and frills?
   This is a mystery that may have many answers. In the earliest frilled forms, the frills were probably used to distinguish species and this may have been the case with horns too. However, ceratopsids, the largest of the ceratopsians, found new uses for these. During the Campanian stage of the late cretaceous, North America was overrun by ceratopsids, both centrosaurine and ceratopsine. Frill shape, horn placement, and number of horns were keys in species recognition, and it was easy to tell a 15-horned Kosmoceratops from a single-horned Centrosaurus. Triceratops proves also that the frill changes with age in its numerous growth stages; babies have small, laid back, underdeveloped frills, while growing juveniles have upward curving horns. As the animal matures, its frill grows longer and broader. Ceratopsians could also use their horns and frills to protect their necks and fight off tyrannosaurs and dromaeosaurs, or in the case of species like Chasmosaurus, they could use them to appear much larger. Gregory S. Paul also theorizes that ceratopsians of both groups may have also reared up on their hind legs, flushing the frill with color and then charged at their attacker. Unlike modern rhino horns, ceratopsian horns are made of bone and are covered in horny keratin along with their frills. Some specimens of Triceratops even have scars from each other and from the deadly predator that hunted them; Tyrannosaurus rex. The injuries inflicted healed which showed the triceratops survived its encounter with the predator. The hard frill of ceratopsines may have also been their saving grace. Centrosaurines were less well protected and with animals like Tyrannosaurus, the “tank destroyer”, roaming around, the centrosaurines likely went extinct as predators became deadlier and as climate changed in the favor of the ceratopsines. Such is the power of nature.

21. Where there any Therizinosaurs in North America?
   Yes. Two are known, the relatively complete Nothronychus and Falcarius, which is known from a massive bone bed. However, there may be more. It may be that therizinosaurs were dwellers of the uplands, where few fossils are found. It is even possible that supposed American therizinosaurs from the Maastrichtian and Campanian are even capable of growing as large as or larger than the giant Therizinosaurus of Asia.  

22. Who would win in a battle to the death? Giganotosaurus or Tyrannosaurus rex?
   Of all the battles that could possibly be thought up, this is the hardest to call, according to my friend Taylor, who is studying vertebrate paleontology. Both predators are separated by 45 million years of evolution and each brings weapons meant to kill with one fatal bite. Giganotosaurus weighs about ten tons and is 43 feet long at maximum. Tyrannosaurus is around 9 tons in weight and 42 feet long. Giganotosaurus has serrated bladed teeth for causing massive blood loss and Tyrannosaurus has conical serrated teeth meant to cause blood loss, crush bone and cause death near instantly. Giganotosaurus is built for steady tracking and ambush, while Tyrannosaurus rex is able to pursue prey for long distances. Tyrannosaurus however has one advantage over Giganotosaurus; it has binocular vision, and can see depth unlike its rival. All in all, this is the closest matched of all theoretical battles: 51/49.  

23. Who would win in a battle to the death? Carnotaurus or Orkoraptor?
   In this battle, both combatants are about the same size, about 25 to 30 feet long, but they are of two different hunting styles. Carnotaurus is a speed demon, able to run very fast thanks to its long legs and thick, stiff tail. Orkoraptor on the other hand is likely an ambush predator that uses its powerful arms to kill prey. Both come from around or close to the same time, so its possible they would have met. A fight like this would be tough to call. Orkoraptor would likely have the advantage in more dense foliage or in a more prolonged fight, because it can turn quicker on its axis, and it has both teeth and claws. Carnotaurus however has speed, and in the open Orkoraptor has little chance against its hatchet-like jaws, which can be utilized in a very fast action repeatedly, which allows Carnotaurus to hunt contemporary sauropods with less risk of being injured in a struggle. Overall, I would give a score of 40/60 depending on where the combatants met.