The Tyrannosaurs- From Man-sized Jackals to Gargantuan Apex Predators
What makes a theropod a Tyrannosaur:
The Tyrannosaurs are characterized mainly by the shape of their teeth, and the powerful jaws, as well as gracile to heavy stature. The D-shaped teeth are serrated on both sides and usually curve backwards, indicating the ability to rip apart a carcass with ease. This design first started in the earliest known ones like Guanlong wucaii and Dilong paradoxus and then continued in the large, powerful Late Cretaceous members, like T. rex.
Tyrannosaurs, however, are not really known for their gracility (Slenderness) and are more characterized as large, well-muscled, powerful brutes. This heavy stature wasn't evident in the earlier members, but were well defined in the later members like Daspletosaurus, Tyrannosaurus rex, and Tyrannosaurus bataar ( Tarbosaurus). There are a few members that increased in size, yet kept their gacile stature, like Albertosaurus.
What they are known for are their bite force, which is exactly what their jaw is designed for. The majority of the bite force is correlated with the increase in weight and bulk in later Tyrannosaurs.
This group is also known for the small, dual clawed, fore-limbs, whose function is still under controversy. However, the early Tyrannosaurs did not have the dual clawed, small forelimbs, but had the long three-digit, fore claws.
The Early Tyrannosaurs- The Tyrannosaur Dark Ages and "T. rex's Granddaddy"(Jurassic Period-208 million years ago-145 million years ago)
What I mean by "Dark Ages" is that this is the part of their evolution that we are, seriously, in the dark about. It wasn't until Guanlong that we even knew (Or, at least, I knew) the lineage extended that far back and reclassified T. rex from being a Carnosaur as a Coelurosaur. We really don't know much about this time in their evolution, except a large mass grave found by James C. Clark in China with Xu Xing, containing layer upon layer of doomed theropod dinosaurs. That's our only clear indication of the lineage of the Tyrannosaurs.
Let me tell you a little bit about Guanlong, the "T. rex granddaddy," as it is popularly referred to by the public. Guanlong is most noted for that odd crest on top of it's head, similar to Cassowary of Australia. Unlike later Tyrannosaurus is it's notable gracile stature, lengthened fore limbs, that happen to have three digits like most other theropod groups.
The behavior of this animal has been related to the jackles of the African savannah (however, the jackles are the active predators most of the time and not the lions.) in that they were scavengers. I believe that they were active predators with the possibility of pack hunting or family groups.
Other than this limited information, there is not much to say on this part of their evolution, other than check out Wikipedia.
The Reign of the Tyrannosaurs- The Tyrannosaurs At their Prime (Cretaceous- 144 million years ago-65 million years ago)
The Cretaceous points out the success of the Tyrannosaurs as we see them diverge through genetic drift and migration filling in almost every predatory niche in the ecosystem and we see a lot of diversity in the other fauna as well.
Despite the gaps in the fossil record of this period on their evolution, we have a much better idea and a much clearer picture of their evolution than we did of the Jurassic period. Some of the Tyrannosaurs grew larger in size and retained their gracile stature, like Albertosaurus sarcophagus and those that have not grown any larger than Dilong paradoxus and have retained that gracile stature like Nanotyrannus lancensis and the newly discovered, Raptorex kreigsteini. These animals filled in the second level predator status of the ecosystem and, some like Raptorex, are on the direct line to Tyrannosaurus rex.
Others sacrificed their gracility for power and a larger head and, a larger, more developed brain, than other theropod groups, (though not as much as the Dromaeosauridae, or the "raptors."), like Daspletosaurus, Tyrannosaurus bataar and Tyrannosaurus rex.
Another notable fact about this family is that every one is rare. VERY few articulate, complete remains have been found and that is why classification and studying their evolution is so frustrating and difficult.
For those of you who did not mind my, indifferent tone, I hope you enjoyed it! And, those who did not, please let me know of how I could have improved it. ;) I also would like some feedback on accuracy and writing ability! Thanks! :D
Anywho, here are a list of sites to visit for more information on this family:
- Wikipedia-The Free Encyclopedia
- The Tyrannosaur Chronicles-the Palaeo Facts Are A Must!
- Ask A Biologist- Q&A
- University of Berkeley Tyrannosauridae page
- Dinosaur World-Tyrannosaur page