Anywho, as I don't have much time for this one, I should tell you this one is a brief overview of the Evolution of Theropods according to the Fossil Record. So, Lets get started!!
What is a Theropod?
Because of the possibility that there are new readers, and those who are not familiar with the technical vocabulary, allow me to explain what "Theropod" means, simply. Simply, and briefly, the term "theropod," literally "beast-feet" is the term referencing to the dinosaurian bi-pedal carnivores that, literally dominated the landscape of the Mesozoic. Theropods, as will be covered shortly, according to the Fossi Record (despite the obvious gaps) branched off into a number of different groups based on certain aspects of their skeletal anatomy.
Theropods Emerge- Late Triassic (~208 million years ago):
Despite the evidence of carniverous dinosaurs somewhat earlier, (i.e. Eoraptor, and Herrarasaurus), "true" theropods, like Coelophysis bauri, didn't evolve until later. Coelophysis is considered the earliest known theropod, because of some pretty crucial reasons, namely his body plan. If one were to actually examine a C. bauri skeleton, then one would think he/she was, perhaps, looking at a bird, which, because of it's hollow bones, is it's namesake. This animal had a long flexible vertebrae in the S-shaped neck and tail. The joints of the limbs to the torso allow for fluid movement, and, though, primitive, Coelophysis forelimbs were essential for the manipulation of prey. Though, not heavy and powerful as some of it's predecessors or the reptiles of the time, C. bauri is built for speed and his upright posture gave him the advantage over it's archosaurian neighbors.
Syntarsus, and Dilophosaurus to Ceratosaurus and Allosaurus- Theropods Diverge (Jurassic period, 208 million years ago-145 million years ago):
The Jurassic was not only the reign of the Theropods, but other groups as well. Of course, this post is covering the Theropods. At the beginning of the Jurassic, change was in the air as the Dinosaurs have control of the land. Although, one may not realize it, but many groups that appeared in the Triassic were beginning to branch away from each other, as animals began to migrate and the continents shifted during this period. Pangaea was now breaking up, though the modern continents still haven't arrived.
During the start, we have little predators similar in size and design as Coelophysis, Syntarsus. These animals still have the build: not for power, but for speed. Syntarsus, despite being the same build and no longer has to compete with the primitive archosaurs of the Triassic, is not the terror on the block. Even at the beginning major animal groups were branching off, with some becoming larger, and heavier, while others are remaining gracile. One of the stars of the book and film Jurassic Park, is around, without the frill and the poison glands, and about 2-3 times larger, yet still slender and gracile, Dilophosaurus. Still primitive, because of the five fingered fore-claws, indicating that he just became a biped from a quadroped. He looked like he just started walking upright. Also, his build is like the smaller Syntarsus and the Triassic Coelophysis. His most unusual feature are the two, thin, blood-vessel, filled crests at the top of it's head, possibly for display, hence the name. This theropods jaws were very unusual, as they're pretty slender and the teeth are long and blade like. (The bone crushing teeth of the Tyrannosaurs, do appear during this period, though they won't appear until the mid to late Jurassic.) This jaw design suggests to me that Dilophosaurus wasn't built for hunting the large prosauropods like Anchisaurus. Since behavior doesn't fossilize, I can only go on what I have read, heard and seen in the documentaries and books on the subject (For example, most of this information, is based off of the Discovery Channel documentary When Dinosaurs Roamed America, which covers MOST of the Mesozoic and goes into it more deeply than Walking with Dinosaurs and shows us the fossil evidence of each scene of the show.). So, readers, bare with me, I haven't been around enough specimens to really get my own opinion, thanks to KY.
Anywho, as the animals continue to branch off, we have the carniverous Ceratosaurus of North America, and the tyrannosaurid Guanlong wucaii, of Asia. In the Late Jurassic, we have large, more robust animals like Allosaurus and the Torvosaurus. In the mid to late Jurassic, we see the transitional form of Archaeopteryx. The Jurassic founds an evolutionary boom, similar in size to the Cambrian, only this boom continues into the Cretaceous.
Tyrannosaurs, Birds, Mammals, Raptors, and Flowers- The Peak of their Reign and, Sadly, their Tragic End (Cretaceous period, 145 million years ago to 65 million years ago):
The Cretaceous is one of the most famous periods of the Mesozoic and Prehistory with the public, yet the most commonly misunderstood, as it is second only to the Jurassic period, in terms of popularity. This is where the world starts to look more modern and less alien.
Here is a quick overview of the Cretacous Predators:
Tyrannosauridae- This family emerged in the Jurassic period as medium sized, gracile, feathered animals. One of the most unique feature of this family are the design of their teeth. The D-shaped, serrated, banana-sized teeth bagan in Guanlong and Dilong, and taken into extremes in Tyranosaurus rex. This family belongs to the same group as the "Raptors" (The Dromaeosauridae and the Troodontidae), the Coelurosauria (the most bird-like group of theropods.) As such, they are some of, if not, the most advanced animals of the time.
(i.e. Guanlong wucaii, Dilong paradoxus, Raptorex kreigsteini, Daspletosaurus torosus, Albertosaurus sarcophagus, Gorgosaurus libratus, Alioramus altai, Nanotyrannus lancensis, Tyrannosaurus bataar (Tarbosaurus) and, of course, Tyrannosaurus rex.)
The "Raptors"- Called such because of Michael Crichton's Jurassic Park, this group includes more than just the Dromaeosaurs. These also include the Troodonts. These families share a similar body plan, such as the retractable "Killing claw" and large complez brains and bird like features. Some even have feathers. (Fauna include: Velociraptor mongoliensis, Deinonychus anhtirropus, Utahraptor, Troodon, Jinfengopteryx, Microraptor gui, Dromaeosaurus, among others.)
The Spinosauridae- The odd crocidilian-snouted theropods. Not much to say other than this group is poorly understood, as there is not much fossil evidence for these guys. (Fauna: Spinosaurus aegyptiacus, Suchomimus tenerensis, Baryonyx walkeri, and the others, who are still controversial, that I won't mention to have this post be as accurate as it can be.)
The Allosauroids and the Carcharodontisaurs- There is a long standing debate about how the Carcharodontisaurs emerged. Some say they emerged from the Allosaurids of the Jurassic period. Others say they have a separate lineage. Other than that, I can't say much about them other than they include the largest carnivores that have ever walked the Earth!
Birds-This is obviously, still controversial, but I'll stil mention them anyway.
Those are some of the major groups that inhabitated and terrorized the Cretaceous landscape. Hope you enjoyed and learned something today. ;)
NEXT: THE FAMILY TREE OF "SUE" AND TRAUMADOR!!!!! STAY TUNED!!!!