Tyrannosaurus Species (Also: 50th Post! Whoo!)

(Picture: Which is the tiger? Which is the lion? Where should we draw the line?)

Today, it's easy to tell species apart from one another, even within the same genus (well, generally). We have the luxury of seeing tigers and lions in the flesh, and of seeing their distinguishing characteristics (stripes and manes, respectively). But in paleontology, to the regret of many, things just aren't that simple.

With dinosaurs, we are dealing with something quite different from big cats. These are animals whose living relatives today, crocodiles and birds (you BANDits are in denial!), are very different from their saurian cousins indeed. Of dinosaurs, we have only stripped, petrified bone (except in some very extraordinary and exciting cases, such as mummified Brachylophosaurus and feathered dino-birds from China), which makes it very hard to use characteristics like these to classify them. For examples of living and extinct animals, I will use lions and tigers, and T. rex as my examples for living and extinct animals, respectively.

Any 3-year-old can tell a lion and tiger apart. The lion, Panthera leo, has a magnificent mane and tawny skin. Its legs are relatively well-suited for running, though not as much so as those of the cheetah (Acinonyx jubatus). A tiger, Panthera tigris, is much bulkier than its African cousin, with stouter legs, an orange, striped coat, and a considerable aptitude for swimming. These two animals are so different on the outside, it's hard to imagine clumping them together as the same beast.

But if we take a dip beneath the cats' skin, things become a bit complicated. There are remarkably few anatomical differences between the two, besides the differences in hair and skin, which, one should think, would make the two quite indistinguishable to hypothetical scientists from after the animals in question are long gone. So how can we assume that dinosaurs were any different?

Tyrannosaurus rex is arguably the most famous of all prehistoric creatures. Yet compared to other dinosaurs, it is relatively uncommon. A single species resides within the genus, and has for the century and more that the dinosaur has been known to science. But some scientists insist that tyrannosaurs closely resembling old Rexie are also a part of the genus.

Tarbosaurus bataar is a very close relative of Tyrannosaurus from the Late Cretaceous of Mongolia. There are some small, if appreciable, differences in the skeletons of the two animals, but many paleontologists (palaeontologists?) feel that Tarbosaurus is naught but another species of Tyrannosaurus. Tyrannosaurus bataar would be the name of the dinosaur if it was reclassified. In short, the afforementioned paleontologists want to "clump" Tarbosaurus into Tyrannosaurus.

Some scientists even go so far as to classify Daspletosaurus torosus, considered by some as ancestral to T. rex, as another species of Tyrannosaurus - T. torosus - despite some major differences in skull structure. Where does it end? When does the clumping stop, and poor Das and Tarbo can live in taxonomic peace?

If we can notice these differences in the species even marginally over 70 million years of geologic time, isn't it clear that they were even more different when they were alive? They were probably even more different than lions and tigers (well, maybe not; dinosaurs didn't have hair, after all). If we can't even tell lions and tigers apart in the bone, but can with reptiles which have been extinct for so long, why should these tyrannosaurs be just as closely related?

We frankly don't have the luxury of seeing dinosaurs in the flesh. So who knows? There could have been plenty of Tyrannosaurus species, all as different and distinguishable as tigers and lions. But the thing is, we'll never know, unless some day, we can see the dinosaurs alive. So please: clumpers, please stop clumping! Tarbosaurus and Daspletosaurus are just not Tyrannosaurus.