Ave, Tyrannosaurus Rex
Tyrannosaurs, the group of carnivorous dinosaurs that includes Tyrannosaurus rex and its closest relatives, are the most iconic and most studied of the dinosaurs. Made famous by movies, television shows and books, T. rex is the image most people think of when they hear the word dinosaur. The popular image of a tyrannosaur is that of a gigantic meat eater, like the one shown in Spielberg's Jurassic Park, but this was not always the case. T. rex was initially described 105 years ago by H. F. Osborn of the American Museum of Natural History. New fossil finds, including six new species during the past year alone, have shown tyrannosaurs to be a more diverse group that was first thought. A phylogeny that includes recently described species shows that tyrannosaurs originated by the Middle Jurassic but remained mostly small and ecologically marginal until the Late Cretaceous.
Research on tyrannosaurs is undergoing a renaissance according to a review article in Science, entitled “Tyrannosaur Paleobiology: New Research on Ancient Exemplar Organisms.” New discoveries and technological approaches are helping paleontologist to describe the biology and evolution of these animals in unprecedented detail. Stephen L. Brusatte et al. layout the latest advances in T. rex science. Approximately 20 tyrannosauroid genera are currently known, 5 of which were described during the past year. Some of the new specimens are 100 million years older and 1/100 the size of T. rex. Here is how the review introduces its subjects:
Tyrannosaurs are a long-lived group that originated by the Middle Jurassic, ~165 million years ago. The oldest and most basal tyrannosaurs comprise a speciose subclade, Proceratosauridae, which includes mostly small-bodied animals no larger than a human, many of which possessed elaborate cranial crests. Progressively more derived tyrannosaurs form a pectinate series on the line toward Tyrannosauridae, the subclade of multi-ton, deep-skulled behemoths from the terminal Cretaceous (Campanian-Maastrichtian), including Tyrannosaurus, Tarbosaurus, Albertosaurus, and close relatives. Taxa phylogenetically intermediate between proceratosaurids and tyrannosaurids include a range of genera from the Late Jurassic–early Late Cretaceous of Asia, North America, and Europe, most of which have been recently discovered. These taxa run the gamut from small to medium size (~1.4 to 9.0 m in length), and few were likely apex predators in their ecosystems.
Until recently, it was generally thought that tyrannosaur body size gradually increased over time, while signature tyrannosaur skeletal features developed. The proceratosaurid Sinotyrannus, a creature of the early Cretaceous, may have had a body length near 32 feet (10 m), demonstrating that tyrannosaurs attained a large size early in their history. More striking, the closely releated tyrannosaurid Raptorex was only 6.5 to 10 feet (2 to 3 m) in length, suggesting that there was great size variability among close tyrannosaurid relatives and perhaps that the immediate ancestors of tyrannosaurids were small animals. The figure below the latest version of the T. rex family tree.
T. Rex family tree.
The cladistic tree, showing the relationships of 19 tyrannosaurs, scaled to the geologic time scale (in millions of years ago, Ma). Taxa in blue are those that have been described during the past year. Silhouettes indicate relative body size (based on femur length as a proxy). Thick red bars indicate major ghost lineages. Thick black bars represent the finest age resolution for each taxon, not actual duration.
Truly enormous tyrannosaurs did not appear until the latest Cretaceous, when some individuals grew to lengths of 42 feet (13 m) and weighing 5 to 8 tons. “Therefore, for the first 80 million years of their history tyrannosaurs were mostly small- to mid-sized animals that lived in the shadow of other giant predators (e.g., allosauroids, megalosauroids), and only during the final 20 million years of the Mesozoic did they develop into some of the largest terrestrial carnivores to ever live,” state the review authors. “The dominance of tyrannosaurs as megapredators was purely a latest Cretaceous phenomenon.” Hollywood got it wrong, there were no gigantic T. rex running around the Jurassic.
Another interesting tidbit is that a full grown T. rex was not a very fast runner, barely able to hit 25 miles per hour (11 m/s). This is not nearly as fast as modern large animals, such as horses, some of which can hit double that speed. Smaller tyrannosaurids may have been faster than their larger cousins. Regardless of size or speed, there is no doubt that a tyrannosaur had a terrible bite.
The anatomy of a tyrannosaur.
Tyrannosaurid bite marks have been found on the bones of a wide diversity of species, including various other tyrannosaurs, demonstrating that they were equal opportunity predators. “Bite mark patterns show that tyrannosaurids characteristically bit deeply into carcasses, often through bones, and then pulled back, creating long cuts,” states the review. From bite marks and coprolites (fossilized feces) scientists think that T. rex fractured bone, ingested it, and used it for sustenance, a mammal-like attribute not seen in current reptiles. The bite forces needed to crunch through large dinosaur bones would have been enormous. Experiments replicating the size and depth of fossilized bite marks and suggest that T. rex generated bite forces of at least 3,000 pound of force (13,400 N).
No doubt about it, T. rex was a monster's monster. But perhaps the most interesting new information to arise regarding tyrannosaurs is where they roamed. Until recently, all tyrannosaur fossils were limited to Asia and North America, but the discovery and recognition of earlier tyrannosauroids over the last decade reveals a wider distribution during their early evolution. The evolution and distribution of tyrannosauroids reinforces what was happening geologically during the Jurassic and Cretaceous, mainly the breakup of the supercontinent Pangaea into successively smaller pieces.
The well documented fossil history of tyrannosaurs provides information about geological changes during the past and the impact those changes had on species' distribution and survival. Dinosaurs were diverse, geographically widespread, and left a long stratigraphic record. Unfortunately, the biogeographical history of dinosaurs remains unclear and often controversial. This is partly because of differences in the fossil data studied and the methods applied. Because tyrannosaurs are the best documented family of dinosaurs they provide an almost “ideal” case study in Mesozoic biogeography.
According to Paul Upchurch, Craig A. Hunn and David B. Norman, writing in the Proceedings of the Royal Society B, many paleontologist have proposed vicariance as the dominant factor that determined dinosaur distributions, especially during the Cretaceous. Vicariance is defined as the separation or division of a group of organisms by a geographic barrier, such as a mountain or a body of water, resulting in differentiation of the original group into new varieties or species. Under this hypothesis, continental break-up and the formation of new seas created barriers to the dispersal of land based animals. Instead of one big continent where the dinosaurs were free to roam, the separation of the continents began to fragment and differentiate regional animal populations.
Palaeocoastline reconstructions after Smith et al. (1994) and Smith & Rush (1997): (a) Late Triassic (220 million years (Myr)); (b) Callovian (160 Myr); (c) Berriasian–Valanginian (138 Myr); (d ) Aptian (120 Myr). Black regions mark emergent land and the faint lines outline modern continents.
Eventually, each isolated region acquired its own local dinosaur species. However, recent failures to detect this pattern led some scientists to conclude that continent-level vicariance was rare and relatively unimportant. Changes in local animal populations is instead interpreted as the result of extinction events affecting different dinosaurs in each of the isolated areas.
In “An analysis of dinosaurian biogeography: evidence for the existence of vicariance and dispersal patterns caused by geological events,” Upchurch et al. applied cladistic biogeographical methods to a large dataset of dinosaur relationships and distributions. Their analyses reveal biogeographical patterns that closely correlate with palaeogeography, thus strengthening the biogeographic hypothesis. Brusatte et al. reinforce that conclusion based on their review of tyrannosaur fossil evidence. Again quoting from the review article:
Members of the Middle–Late Jurassic proceratosaurid radiation are known from Europe and Asia, whereas the Late Jurassic genus Stokesosaurus is known from both Europe and North America. However, all well-known tyrannosaurs more derived than Eotyrannus and Stokesosaurus exhibit a purely Asian or North American distribution. Faunal interchange between these continents is characteristic of most Campanian-Maastrichtian dinosaur clades and reflects an increasing Laurasian-Gondwanan provincialism during the final stages of the Age of Dinosaurs. Tyrannosaurs, because of their rich fossil record and well-studied phylogenetic relationships, are one of the primary sources of evidence for this long-established biogeographic hypothesis.
There are indications that tyrannosaurs were present on the southern continents during their early evolutionary history, as well. An isolated pubis bone belonging to a derived tyrannosaur was found in Australia that dated from the Early Cretaceous. This discovery aside, tyrannosaurs are absent in the well-sampled mid-Late Cretaceous strata of South America, Africa, and Madagascar. It is possible that tyrannosaurs were rare on the southern continents during the Early-mid Cretaceous, and it is likely that Gondwanan forms did not survive into the latest Cretaceous.
Regardless, Tyrannosaurus rex was king of the dinosaurs at the end of their reign on Earth. Its evolution and range were dictated by the ever shifting continents and the intervention of the changing oceans. The history of T. rex is a great example of how nature raises up species, changes them into new forms and eventually but inevitable casts them into extinction. Even the king of the dinosaurs and the most fearsome predator ever to stalk the land could not escape nature's final judgment.
There are those who would have us believe that man is causing a sixth extinction event, a natural cataclysm on the scale of the extinctions at the Permian-Triassic boundary and the end of the Triassic, which set the stage for the rise of the dinosaurs, or the Cretaceous-Tertiary extinction that wiped out the dinosaurs and made way for the rise of mammals as Earth's dominant lifeforms. These extinctions took place at times when the ocean turned anoxic, gigantic volcanic eruptions took place, continents split apart and new oceans formed. Throw in the odd large asteroid strike and it becomes evident how ludicrous claims of a human caused mass extinction are.
Enviromentalists, they're what's on the menu for T. rex.
While we should take good care of Earth and its indigenous life, humanity is not the interloping, planet wasting plague environmental evangelists would have us believe. The eco-alarmists' stance is self contradictory and betrays a depth of ignorance that is breathtaking. Somehow humanity is supposed to be above nature, being able to recognize the impact of our actions, while at the same time people are to be valued less than the wild creatures we are supposed to feel compassion for. Humanity is a product of nature and our impact on the planet is part of nature.
“Wherever they were present during the Late Cretaceous in North America and Asia, tyrannosaurs were the sole apex predators in their environments,” states the review article. How many species did the tyrannosaurs drive to extinction—through predation or competition—over their 100+ million year span of existence? Just a glance at the history of T. rex shows how insignificant and ephemeral humanity's impact on nature really is. So hail, king of the tyrannosaurs—if you were here today we would gladly feed you all the environmentalists you could eat.
Be safe, enjoy the interglacial and stay skeptical.