While it seems entirely coincidental, it is not without some irony that stories about two of the most fierce giant predators in the earth’s history, the Great White Shark, and Tyronnosaurus rex, should surface within the same week.
What makes it even more poignant, is the fact that both monsters were disclosed to have had, not the giant evolutionary great grandparents that had been scientifically assigned to them up to now by paleontologists and other evolutionary biologists, but rather far more modestly sized forebears.
The news stories were largely derived from the more substantial, fossil-based scientific articles cited below, particularly Ehret, Hubble and McFadden in the case of the Great White, and by Sereno et al., for the T. rex.
Megalodon is Not the Ancestor the Great White,
Although Both Evolved into the Apex Predators of Their Respective Times
The Great White’s story essentially has it disinherited by the largest shark ever to have lived , Carcharadon megalodon (hereafter simply megalodon).
This previously favored ancestral link actually had made a lot of sense. Both the Great White and the ancestral megalodon are, or were, apex predators. No other creature ate them. They ate all other creatures. In a sense, they were too big, at least at the adult stage, to be eaten by anything else, or at least, to be swallowed whole.
Scientifically reasonable estimates of the top size of the Great White run as high as 26 feet, although 21 feet seems to be the longest reliably measured. Megalodon is conservatively estimated to have measured between 59-67 ft.
The heaviest Great White is estimated to have weighed 5,000 lbs, although they are more reliably and routinely found to range from 1500-2400 lbs. Megalodons ran up to 100,000 pounds, each.
A Shared Taste for Marine Mammals
The comparison between the Great White and megalodon made even further sense, when one considered their preferred diets. While Great Whites primarily eat large fish, their preferred prey are marine mammals: from small seals to the occasional elephant seals or walrus (although the latter generally frequents waters colder than are commonly frequented by Great Whites). Megalodons also preferred mammals, but in their case, those mammals were actually whales. (See a remarkable study by Orangel, Garcia & Cozzuol , cited below, where fossils of the sharks and their victimized whales, with bite marks in the skeletons, have been found together.)
Teeth That Looked Somewhat Alike, But had Different Modes of Action:
The Serrated Knife That Slashes Versus a Serrated Axe That Buries Itself Deeply Into the Victim
The calculated bite force of both species is also impressive, relative to their contemporaries at least. The Great White has the highest biting force per square inch of any contemporary fish (about 3600 pounds ….about three times the force of a lion’s bite), while the megalodon had a 40,000 pounds per square inch pressure bite. (Meaning that megalodon could literally pierce and crush the skulls of whales, not merely rip into their flesh. )
But ironically, it was ultimately the teeth in that bite that reassigned the Great White to another ancestor, an extinct fish more alike the modest (but still rather fierce) mako shark (Isurus hastalis).
Part of the evidence favoring this reassignment was owing to finding that this fossil Isurus clearly had a substantially intact vertebral column very similar to the Great White (an evidentiary rarity for fossilized sharks since shark spines are made of highly perishable, semi-solid, somewhat elastic cartilage and are hardly ever well preserved).
But even more importantly, examination of this fossil Isurus, disclosed an amazingly well-preserved abundance of teeth, many of which were in exact order, and which under systematic microscopic characterization, were a far better match for the contemporary Great White, and its dentitition, than the teeth and jaws that have been reconstructed for the megalodon, even though the teeth of both the Great White and megalodon are triangular and jagged.
The jaggedness of Great White shark teeth, amplified further when examined closely under a microscope, seem to have evolved independently of megalodon . They seem particularly suited to the Great White’s way of dealing with contemporary marine mammals, such as the most sizeable ( sometimes hundreds of pounds) seals.
Great Whites bite into the flesh of their victims with a slashing motion and then let go: Leaving the prey mammal to bleed out and die, before feasting on it. The particular jaggedness of those Great White teeth are custom made for making cuts into soft tissue that cause profuse bleeding.
As has been demonstrated through the fossil record of the whale victims of megalodon, megalodon’s giant teeth functioned y more like pierce-and-bury-deeply-into-the-victim axe blades, albeit peculiar axes in the sense of the largely triangular shape of virtually all shark teeth, and having axe-heads with plenty of serrations.
Tyrannosaurus Started Out More Like A BMW Smart Car
Than It Did A Souped-Up Abrams Battle Tank
A fossil find that was smuggled from China, and landed in the hands of a Massachusetts eye doctor in the early 1990s, has also turned the story of the evolution of T. rex on its head.
Henry Kriegstein, the aforementioned ophthalmologist, was a hobbyist collector of fossils. He bought a large fossil that was still largely encased in its stone matrix at a Fossil Fair in Tucson. He was told that it had been sold to the exhibitor at the fair, by another dealer in Japan, and made what he assumed was a legal and ethical purchase.
On the assumption that this was a juvenile version of a tyrannosaurus cousin called a Tabosaurus, he sent it off to a firm out West which specializes in identifying and sometimes freeing up fossils from the surrounding material.
Scientists associated with that lab advised Kriegstein that this was no tabosaur, but rather a wholly new species.
Ultimately, Kriegstein decided to turn the fossil over to the man who is arguably the hottest vertebrate paleontologist of the most recent decade, Paul Sereno of the University of Chicago.
The team of Sereno et al. published their formal findings in Science, in an advanced online version available to members of the American Association for the Advancement of Science (AAAS), the publisher of Science, with the conventional print version being made available for the general public several weeks later.
However, popular press reports such as that of Aschenbach in The Washington Post, and the separate news items from AAAS staff writers Berardelli and Bryn (all cited below), plus 27 pages of supplementary material already made available to all, enable us to reconstruct much of the story.
Kriegstein’s fossil turned out to be what has come to be named Raptorex kreigsteini (the Kriegstein being the family name of its donor, something applied in honor of the gift and to honor the donor’s Holocaust-urviving relatives.)
While this new species weighed only about 1% of what an adult T. rex would (100– 150 lbs. versus 13,000 lbs.) its anatomy indicated a very similar hunting style, using the tools which are now understood to have made T. rex so formidable.
These included a head, very large relative to the rest of the body ( a tyrannosaur trait) that had very large teeth, for classic tyrannosaurid attack and prey capture, plus flared nostril openings for the keen sense of smell now attributed to T. rex, appropriate for searching out prey.
The relative size of the legs (front limbs tiny and back limbs immensely large relative to the rest of the body) also matched T. rex. This creature was made for speed in running down and lunging forward onto its victims.
So, how could they be sure they were not dealing with a juvenile T.rex?
Two answers:
First, when the approximate location of the fossil’s original finding was uncovered, a district of Inner Mongolia that once was known for its prehistoric lakes, it became possible to analyze the fossil’s home strata and estimate its having been layed down some 60,000,000 years earlier than the first known appearance of T. rex.
Second, by creating some microthin slices of the one of the bones of the fossil dinosaur --- which indicate age somewhat like tree rings do ----- it was clear that the specimen was a young adult, that was several years old, and that the connections of bones into joints were reasonably mature. In other words, perhaps the specimen had a year of developmental growth left, but that essentially it was at its adult size.
After the articulated fossil Raptorex kriegsteini has been thoroughly studied, it will be returned to the proper authorities In the Peoples Republic of China, the place from which it was surreptitiously taken.
Tony Stankus, FSLA, [email protected] Professor, Life Sciences Librarian & Science Coordinator
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Aschenbach, J. (2009). Unveiled: The surprisingly small precursor of T. rex. Washington Post, September 18, 2009 issue, Section A, page A6.
Berardelli, P. (2009). T. rex, meet your great grandfather. http://sciencenow.sciencemag.org/cgi/content/full/2009/917/1
Bryn, Brandon. 2009. Science: Tiny T. rex started the trend of terrifying traits. American Association for the Advancement of Science News. Newsarchive. www.Aaas.org/news/releases/2009/0917_tyrannosaur.shtml
Caill, G.M., Smith, W.D., Mollett, H.F., & K.J. Goldman. 2006. Age and growth studies of chondrichthyan fishes: The need for consistency in terminology, verification, validation, and growth function. Environmental Biology of Fishes, 77, 211-228.
Carroll, S.B. (2009) In a shark’s tooth, a new family tree. The New York Times, September 15, 2009, final edition, Section D, page 1.
Ehret, D.J., Hubbell, G., & McFadden, B.J. (2009). Exceptional preservation of the white shark Carcharadon (laminformes, Lamnidae) from the early Pliocene of Peru. Journal of Vertebrate Paleontology, 29, (1), 1-13.
Kimley, A, & Ainley, eds. (1996). The Great White Sharks. San Diego, Academic Press.
Nyberg, K.G., Ciampaglio, C.N., & Wray, G.A. (2006). Tracing the ancestry of the great white shark, Carcharadon carcharias, using morphometric analyses of fossil teeth. Journal of Vertebrate Paleontology, 26, 806-814.
Orangel, A.A., Garcia, L., & Cozzuol, A.M. (2008). Giant-toother white sharks and cetacean trophic interaction from the Pliocene Caribbean Paraguana Formation. Paleontologische Zeitschrift, 82, (2), 204-208.
Randall, J.E. 1987. The size of the great white shark Carcharadon carcharias. Science, 181, 169-170.
Sereno, P.C., Tan, L., Brusatte, Kriegstein, H.J., Zhao, X, & Cloward, K. (2009). Tyrannosaurid skeletal design first evolved at small body size. Science, epub ahead of print. Supporting online material already available at www.sciencemag.org/cgi/content/full/1177428/DC1
Shimada, K. (2002). Dental homologies in lamniform sharks (Chondroichtyes: Elasmobranchii). Journal of Morphology, 251, 3-72.
Shimada, K. (2003). The relationship between tooth size and total body length in the white shark , Carchardaron carcharias (Lamniformes: Lamnidae). Journal of Fossil Research, 35, 28-33.
Shimada, K. (2005). Phylogeny of lamniform sharks (Chonricthyes: Elasmobranchi) and the contribution of dental characters to lamniform systematics, Paleontological Research, 9, 55-72.