For the first Creature Feature, we will be focusing on one of the largest and most famous predators to ever walk the Earth - Tyrannosaurus rex.
This massive dinosaur is one of the most well-represented giant theropods in the fossil record. There are specimens ranging from juvenile to sexually mature adults, and a few are astonishingly intact - in fact, there have even been specimens with some of their soft tissues still preserved. This relative and extremely fortunate abundance of material has allowed scientists to learn a vast amount about this ancient carnivore.
Tyrannosaurus rex was one of the largest carnivores of all time - the largest specimen known (the famous 'Sue') was 12.29 meters long (~40 feet) and is estimated to have weighed 9500 kilograms, or 10.5 tons (Hutchinson et al., 2011). While there are theropods that were larger than T. rex, it still stands out for its terrifying bite. Its massive and serrated teeth combined with a specially adapted skull to generate the highest bite force of any known land animal - it could slam its jaws down with an estimated 12,800 pounds of force. This allowed it to tear through flesh and bone with equal ease.
The skull of Tyrannosaurus rex was huge (nearly 5 feet in length) had extremely large fenestrae, or openings, to reduce its weight and provide large surfaces for muscle attachment - a characteristic that is observed in all theropods. However, its snout was much narrower in comparison to the back of its head than in other carnivorous dinosaurs such as Allosaurus fragilis; this adaptation results in a large degree of overlap between its eyes and acute binocular vision. The degree of visual overlap in Tyrannosaurus is even higher than that of a modern hawk (Stevens, 2006)!
Tyrannosaurus is in a family positioned in the clade Coelurosauria - due to the fact that at least one member of each of the Coelurosaurian subgroups has been preserved with some trace of feathery integument has led some paleontologists to believe that Tyrannosaurus rex was at least partially covered in primitive feathers (Zanno and Makovicky, 2010). The technique that led to this hypothesis will be the topic in this week's Sci-day post. Not all agree with this hypothesis, as it does not account for the possibility of secondary loss. Until direct evidence of feathers or large preserved remains of scales are found, however, we will be unable to know which of the two is correct. This is why, in Dinosaur Battlegrounds, the player will be given the choice to play either as a feathered or a scaled Tyrannosaurus.
If you prefer, you will have the choice to play as a scaly T. rex in Dinosaur Battlegrounds.
The growth rate of Tyrannosaurus rex was astounding - estimates put the peak rate at 1790kg per year (Hutchinson et al., 2011)! This growth is observed to slow down at approximately 16 years of age, and this was further supported when medullary tissue (only found in ovulating birds) was found in the femur of a 16-20 year old T. rex (Schweitzer et al., 2005).
Interestingly, the survival rate of Tyrannosaurus appears to follow a Type I survival curve, with low mortality among the juveniles, and mortality increasing with age. In fact, most specimens of Tyrannosaurus appear to have died within 6 years of reaching sexual maturity. However, this may not be indicative of reality, as it is also possible that this is due to collecting bias - the larger and more spectacular adult specimens are more appealing for fossil collectors and thus would be harvested in larger numbers even if their relative abundance was lower (Erickson et al., 2006). This may also be due to the fact that adult Tyrannosaurus lived very dangerous lives considering the prey that they hunt, and thus were more likely to be killed by their prey than the juveniles.
Tyrannosaurus had a surprisingly well-developed brain. It had extremely acute senses, with the ability to sense low-frequency sounds and extremely large olfactory bulbs for smell (Witmer and Ridgely, 2009). While these two abilities were extreme on their own, they were also combined with incredible eyesight - its visual acuity was even greater than that of modern eagles (Stevens, 2006)! Its large brain is also believed to have been sophisticated enough for some primitive form of group hunting - while not quite true 'pack hunting', as it lacks the organization of a pack hunt, it is still a step above fully solitary hunting (Witmer, 2011).
Well, I hope this has given you a bit more knowledge about the famous Tyrannosaurus rex!
Acknowledgements:
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 9(5): e97055.
Stevens, Kent A. 2006. Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology 26 (2), 321-330.
Lindsay E. Zanno and Peter J. Makovicky. Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution. Proceedings of the National Academy of Sciences, 2010
Schweitzer MH, Wittmeyer JL, Horner JR. June, 2005. Gender-specific reproductive tissue in ratites and Tyrannosaurus rex. Science 308 (5727): 1456-60.
Erickson GM, Currie PJ, Inouye BD, Winn AA. July, 2006. Tyrannosaur life tables: an example of nonavian dinosaur population biology. Science 313 (5784): 213-7.
Witmer, Lawrence M.; Ridgely, Ryan C. September, 2009. New insights into the brain, braincase, and ear region of Tyrannosaurs (Dinosauria, Theropoda), with implications for sensory organization and behavior. The Anatomical Record 292 (9): 1266-1296.
Witmer, Lawrence. July 13, 2011. Dino gangs: solitary, communal, or cooperative hunting in tyrannosaurs. Pick and Scalpel. WitmerLab at Ohio University. Retrieved January 3rd, 2016.
