Saturday, November 13, 2010

Tyrannosaurus rex- Apex Predator or Lowly Scavenger?

I know this is my first post in months, and I promise I will explain more in due time, readers. However, I keep seeing the controversy over T. rex's ecological trophic level. So, I thought that this "Exhibition Fact," as I'd like to call it, would be a perfect way to add my input on the controversy and bring the questions to a close.

Tyrannosaurus rex is probably the most infamous species in the fossil record. Growing to a length of about 40 feet, 20 feet in height, in addition to an estimated whopping 6-7 tons, T. rex is a monster. It's little wonder why it's embedded itself in our imagination. He has been depicted as a killing machine for well over a century. First described by Barnum Brown around 1902-1903 in the badlands of Montana, Tyrannosaurus rex has both thrilled and frightened us in movies, television shows and literature. However, the old, inaccurate stereotype that embedded itself on the reputation of the Dinosauria had gotten the so-called "King of the Dinosaurs." The first specimen was mounted in the American Museum of Natural History in New York City at the commision of Henry Fairfield Osborn, the curator at the time. The great animal was mounted with it's tail lying on the ground, it's head rising menacingly over 20 feet above the visitor's heads.

But, was T. rex really so terrible? Was the the Apex Predator that we loved to hate or was he a lowly scavenger who's lifestyle was Nature's garbage Disposal? Or, was he both: a scavenger AND a and Apex Predator? Well, that's what I intend to find out, and I invite you, readers to come along on this journey into the life of the most infamous and most loved beast to have ever evolved.

From Cold-Blooded Monster to Warm-Blooded Menacing 6-ton Chicken that would Have eaten Col. Sanders

Ironically, the first view of Dinosaurs had been the correct one. In the late 18th to early 19th centuries, fossil bones began showing up regularly in European towns. No one could explain these bones and many people thought that they must be giant remnants of extant animals, since God created the Earth in the biblical 7 days and everything that was tever created was thought to be alive and God would NEVER allow any of His creations to go extinct, right? The view of the world at the time was a static, unchanging world; extinction was impossible as individual animals might die, but whole species did not.

Enter the Baron Georges Cuvier, the leading Anatomist of his day at the intellectual center of the world: Paris, France. He concluded that the bones were of taxa no longer alive and that animals might become extinct. Cuvier reluctantly accepted extinction but never accepted evolution (however, that's another topic for another time).

In 1841, Sir Richard Owen first recognized the Dinosauria as a distinct vertebrate group; a very hot-blooded, active group, to be more specific. He described the genus, Iguanodon, with the conclusion that the teeth resembled an iguana's (hence the name). His view of Dinosaurs had been accepted for the next several decades until.......larger specimens were being excavated; large sauropodomorphs, Hadrosaurs, and Ceratopsians altered that view. It was the Sauropods that convinced the public that, because they are extinct, they must have been unsuccessful, dumb, clumsy creatures. (One has to keep in mind that this view originated in the Victorian era, where progress was on everyone's mind and those mistakes from the past mattered little. Hence, why Dinosaurs obtained such an unfortunate stereotype).

However, it wasn't until the 1960s did Paleontologists start going back to Sir Richard Owen's depiction of active, intelligent, hot-blooded, socially sophisticated animals on the order of Birds. This became known as the Dinosaur Renaissance (Renaissance means "re-birth") and many Paleontologists, including Robert T. Bakker, John "Jack" R. Horner, led by John Ostrom of Yale University. This change in thinking was soon adopted, rather reluctantly, by most researchers and the public at large and induced a lot of re-positioning of all museum mounts from tail draggers to being balanced by their tails, in addition to more active, life-like positions.

From Consensus to Division- Disputes among Friends about Tyrannosaur Behavior/Trophic Level

Colleagues and friends, Robert T. Bakker and Jack Horner have been among the earliest proponenets of the Dino-Bird Theory and Dinosaur endothermy (commonly known as "warm-bloodedness," these animals are so-called because of their bodies to maintain homeostasis without influences from the environment as in reptiles, fish, amphibians, and athropods.) yet, found a wedge split them apart when it came to T. rex's trophic level/environmental niche. Horner saw the large theropod as a scavenger and pointed to several things:

  • Well-developed Olfactory Bulb provided an incredible sense of smell over long distances which helped him to locate carcasses.
  • "Poorly" developed Optic nerve, inhibits effective hunting.
  • Small, nearly vestigial fore-limbs would have prevented him from catching himself if he tripped and fell.
  • huge bulk made him too sluggish to catch prey.
All of which are absurd as I'll explain in a minute. Robert Bakker, as well as many Paleontologists such as Dr. Philip J. Currie of the Tyrell in Drumheller, Alberta, Canada, Dr. Lawrence Witmer of Columbus Ohio, Dr. Thomas R. Holtz, Jr. of the University of Maryland Geological Dept., Paul Sereno of the University of Chicago, Gregory S. Paul, Dr. Xu Xing, Dr. Mark Norell of the American Museum of Natural History, Dr. Pete Larson of the Black Hills Geological Institute, among others agree, as well as I do, on the following:

  • CT Scans of Tyrannosaurid brain cases show the Optic Nerve was Well Developed and, T. rex had it's eyes facing forward, giving him binocular vision, and great depth perception.
  • The Olfactory lobe  was well developed allowing scent distinction, allowing the animal to distinguish the smell of prey, another predator, or family members.
  • Recurved teeth are designed for hanging on to prey, and the jaw is designed to saw through thick hide. Why is this needed if he was just scavenging dead carcasses?
  • Bite Force has been estimated to be several tons per square inch, enabling bones to be crushed with ease. Again, not necessary to be a scavenger.
  • Then, there's the issue with metabolism. The large the muscle mass, the more energy you burn. This animal could not hope to wander aimlessly looking for a fresh carcass to steal for itself.
  • It's a social animal, with possible complex social structure for a being of it's immense size. Being a scavenger, you really need to be solitary; family is not needed.
Finally, I am in favor of the Opportunistic Hypothesis which means, in a nutshell, predator first, then scavenge if it came across something and it failed to catch a meal (which is a lot more frequent in the animal  kingdom than you might think). Often, in nature, the prey gets away, leaving the he predator, hungry and/or injured......or dead. And, when the predator does make a successful kill, it will hesitate and be alert, checking for competition from another of it's own species. Tyrannosaurus rex, apex predator or lowly scavenger? I say, both! What about you?


Dinorider d'Andoandor said...

yes, I think so too!

cool review!

Raptor Lewis said...

Dinorider- Thanks! It's okay, considering I'm a little rusty. lol. It's been so long. I missed it here. :) I've missed all of you: Traumador, you, Prehistoric Insanity, Andy Farke, Dinosaur George, etc. I'm back! :D Hallelujah! Holy Cretaceous!!

Candace said...

Great to see you blogging again! Interesting post!

Raptor Lewis said...

Hey Mom! Well, I wouldn't say I'm "officially" back (and, If I did, my apologies) yet. Now, if I begin to be consistent again, then and ONLY then would you say I am back. ;) But, of course, thank you! I felt it needed to be addressed as I said.

SS Jothiratnam said...

there are 6 objections to jack horner raised at the end of the piece by the author, but of them, only his/her 2nd point makes any sense, although what the author writes does not actually contradict what horner claims, it merely provides an alternative interpretation of horner’s evidence. the forward facing eyes mentioned in his/her first point sound convincing, until one notes that many scavengers have forward facing eyes (viz, hyaenas, vultures, marabou storks, etc). his/her points 3 & 4 make no sense at all, a scavenger - unless it were to feed exclusively on completely rotted carcasses would have needed to bite through thick hide too, and bone crushing bite force, one could argue, would be even more necessary for a scavenger (consider the jaws and dentition of both spotted & brown hyaenas). the second last point is again nonsense, spotted hyaenas (which admittedly both scavenge and hunt) live in complex societies (n.b., incidentally, we do not really know how ‘social’ t rexes were), and vultures will congregate from time to time near a carcass, or a soon-to-be carcass, but they are not really ‘social’ animals. finally, his/her penultimate point make no sense either, since the proposed excellent olfactory system would allow a t rex to do far better than simply wander aimlessly looking for a carcass to steal.

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