Saturday 31 August 2013

The Truth on the Tyrant- The Facts of Tyrannosaurus Rex

Whenever I ask a child what their favourite dinosaur is, the vast majority of replies are either an enthusiastic "T. rex!!!" or a contemplative "Hmm.... Umm.... T. rex?" Clearly, genuine or not, this dinosaur enjoys perhaps the most popularity of any of the extinct Archosaurs. From the earliest Charles R. Knight paintings to its CGI depictions in modern cinema today, everyone is in love with the tyrant lizard king. Spielberg himself acknowledged that the true star of his film was the Tyrannosaurus. What's surprising, then, is how little the public truly knows its favourite dinosaur. So let's pick on our perceptions of T. rex (and on Jurassic Park, once again) and get to the truth on this tyrant. 

To begin with, everyone knows that Tyrannosaurus was the largest, most ferocious meat-eating dinosaur ever. If there was one dinosaur you did not want to meet in the primeval jungle, it would be Tyrannosaurus. Everyone else comes in second to its size and danger. Well... Not really, actually. I realize I'll be bursting a lot of bubbles here, but Tyrannosaurus was definitely not the biggest carnivorous dinosaur. Now, don't get me wrong, it was one of the biggest, and certainly was the biggest Tyrannosaur (the rex had many earlier, smaller relatives, such as Daspletosaurus and Tarbosaurus). However, bigger Theropods had come and gone by the time T. rex hit the scene. Dinosaurs like Acrocanthosaurus, Gigonotosaurus, and Charcarodontosaurus were all bigger, unrelated Theropods that prowled the Cretaceous before Tyrannosaurus evolved. These creatures certainly would have been impressive in their time, and all of them would have made Tyrannosaurus look a bit shrimpy. However, the dinosaur Spinosaurus towered over all of them, and was likely the biggest meat eating animal to live on land. Spinosaurus was remarkably longer and taller than Tyrannosaurus, and its height was even further exaggerated by its towering neural spines that formed its characteristic sail. Dino nerds may remember that Jurassic Park 3 (for all its many flaws) did acknowledge that Spinosaurus was bigger than Tyrannosaurus (Dr. Grant in fact claims that it "sounds bigger". I'm not sure how one determines that but oh well). The film goes further to drive this point home by showing the Spinosaurus (spoilers) kill the Tyrannosaurus after an epic battle. While, if this match up were to be hypothetically arranged, seems one sided in that Spinosaurus was indeed the larger of the two, Tyrannosaurus fans can take comfort in the fact that T. rex had a much stronger bit. In fact, it had the strongest bite of any known animal, ever. This is aided by T. rex's long, bone-crushing teeth, contrasting the conical, fish grabbing teeth of Spinosaurus. So the outcome, in more ways than one, would be impossible to determine. 

A second misconception involves the seeing abilities of Tyrannosaurus. It's commonly believed that Tyrannosaurus could only see something if it was moving. This is impractical for various reasons, the main one being how an animal who can only see moving objects would be able to avoid trees and rocks and whatnot. But let's assume that it only recognizes prey items by movement. Why on earth would an apex predator who often would have needed to hunt by sight evolve a trait that severely handicapped its ability to find its prey? This makes little evolutionary sense. The truth is that Tyrannosaurus likely had very good eyesight. It had foreword-facing orbits, indicating good binocular vision. It's also reasonable to assume that T. rex had a very good sense of smell, which pokes a hole into the scene in Jurassic Park 1 where the rex is right in front of a very still Dr. Grant and cannot find him. One would assume that, even if T. rex did have terrible eyesight, the sense of smell afforded to most large predators would give away Grants position. 

A third rex myth that's popped up, even in the scientific community, is that Tyrannosaurus was not a hunter but a scavenger, feeding off the bodies of dead dinosaurs like a giant vulture. This theory has gained some popularity, but had largely been discredited by most Theropod experts. There doesn't seem to be much of a reason for a scavenging animal to have such a huge size, an extraordinarily powerful bite, teeth evolved for crushing bone in order to kill large animals, and powerful hind limbs. This contrasts the features of most obligate scavengers. Now, many modern large carnivores will scavenge from relatively freshly killed animals when the opportunity arises, and there's no reason to assume Tyrannosaurus was an exception to this rule. However, its anatomical features suggest that it was an animal that was more than capable of bringing down its own prey. Fossilized bones from various large herbivorous dinosaurs have been found with puncture and lesion marks in them. Many of these marks show signs of healing, indicating that the animal was alive when it received the injury and survived long enough for the injury to heal. This, therefore, shows us that Tyrannosaurus did indeed go after live prey. 

This, obviously, ruins a lot of people's ideas as to what Tyrannosaurus would have looked like and how it would have behaved. If this is somewhat disappointing, it's important to remember that our view of this dinosaur has changed dramatically over the years since it was first described in the early 1900's. Sadly reality doesn't always concede to how we would like things to be, but at the same time each newly confirmed theory brings us closer to the ultimate truth about how things were and are. 

Monday 19 August 2013

Prehistoric Imports: Where Canada's Large Mammals Came From (And Where Some Have Gone)

Canada has an impressive collection of large native mammals that everyone should feel proud about. We can boast five species of deer- the white tail, mule, elk (Wapiti), caribou, and moose. Though much reduced in range, two of Alberta's national parks are home to enormous populations of American bison. Our carnivores are no less impressive. Grizzly bears roam our western mountains, polar bears frequent the Arctic region, and black bears are found all across the country. Dogs like wolves, coyotes and foxes too make their home throughout the land, and cougars, bobcats and lynx make up our elusive wild cat population. We also have very recognizable smaller mammals, such as our emblem, the beaver, as well as small carnivores like weasels, minks, and badgers. These species all give off a distinctly Canadian feeling to those who are from here. It's interesting to learn, then, that most of the species listed here have very close relatives that are found throughout northern Eurasia. Some of these species themselves even occupy ranges that spread across the northern latitudes of both landmasses. Where does some of this overlap come from? Why can you go to Eastern Europe and run into beavers and moose? There's an answer to this: faunal interchange.

If you went back in time to the period where huge glaciation events ended up in most of North America being covered by vast sheets of ice (colloquially dubbed the "Ice Age"), you would find that the Bering Straight, the expanse of water separating the eastern tip of Russia from the western tip of Alaska, is gone. Due to the effects of glaciation, the sea levels have dramatically receded. In place of a frigid cold sea, there would be a great bridge of land joining Asia ands North America, known as Beringia. This land bridge facilitated the movement of both plants (the Boreal Forest, covering most of northern Europe, Asia and North America, has a fairly uniform set of plant species) and animals between Eurasia and North America. What species went where is a subject of interest.

Most people are surprised to learn that both camels and horses first evolved in North America. It's fairly common knowledge that all of our domestic horses here were brought over from Europe by Europeans, and small bands of wild horses still roam their native habitats on the plains of Mongolia. It's also pretty hard to picture a camel running around on the North American prairies. But they were here. When the land bridge connected them to Asia, wild horses made the trek over to the 'Old World'. Why? Possibly food. More territory perhaps. Niches for a medium-sized, galloping, grazing animal were open in Asia at the time. Either way, horses made it to Asia and spread further into Europe and Africa too, eventually going extinct in their ancestral homeland of North America. It wasn't until the Spanish brought them back during early colonization that horses once again got to see the land they (unknown to them) originated in. As for camels- the modern Dromedary and Bactrian camels, which inhabit the Middle-East and central Asia respectively, owe their ancestry to camels that followed horses on the journey from North America to Asia. Meanwhile, their relatives, the guanaco and vicuna (as well as their domestic descendants- the llama and alpaca), come from North American camels that went south into South America when the Panamanian land bridge formed.

So what did the Americas get in return for camels and horses? Well... Beavers, bears, bison, big cats, caribou, elk, foxes, humans, mammoths, mastodons, moose, wolverines, and weasels. To name a few. Yes, the ancestors of these animals which proceeded to diversify throughout North America had their start in Eurasia. These creatures traversed back and forth across Beringia and, when the land bridge vanished beneath the sea, they were trapped on both sides. The grey wolf, as well, followed a similar path from it's original home in North America, spreading widely throughout Europe and Asia. However, the level of similarity between mammals living on one side of the Pacific versus the other has some variation to it.

While beavers in the genus Castor occupy both continents, a different species is present on each landmass (canadensis in North America, fiber in Eurasia). The brown bear Ursus arctos is present on both sides, but each continent has a different collection of subspecies. The genus Bison originated in Eurasia. Although different species spread around that landmass, the only surviving one is the wisent (Bison bonasus). Upon arrival in North America, several other bison species evolved and eventually gave rise to the American bison (Bison bison) that exists to this day. Cats, such as cheetahs, lions and the famous Smilodon ranged across NA but are now extinct (however, the jaguar, a close relative of lions, tigers, and leopards manages to make a living from Mexico southwards). Moose and the relatives of todays American elk (also known as Wapiti) are present on both continents but arose in Europe. Red foxes naturally range throughout most of the Northern hemisphere and it's probable that they too came across on the land bridge (although some have argues that they were brought over by Europeans during early colonization events).

Some of the most well known animals to make it to North America were the hairy elephants- the mammoths and mastodons. Fossils of these creatures have been found from Europe to Siberia, down through Alaska and Canada and further south into the United States. As the vegetation and climate of both continents homogenized, cold-adapted elephants made the trip east across the land bridge, where they survived up until the last 10,000 years, leaving a few remarkably preserved bodies frozen into the ice of the north. It's interesting to note that, up until a certain point in time, some native people of northern Russia and Canada were trading in mammoth ivory, and believed the beasts were still alive out there somewhere. While untrue, it's a tantalizing thought.

Thursday 1 August 2013

Brontosaurus Blues

Name off some of the first dinosaur names you ever learned as a child. Triceratops. Tyrannosaurus. Stegosaurus. Brontosaurus? Yea, of course, everyone knows Brontosaurus. The definitive Sauropod, the one everyone thinks of when people talk about the "long neck" dinosaurs. You see its big round body, long neck and tail and tiny, periscope-like head in countless books and movies and paintings of prehistoric life. Indeed, if there was ever a dinosaur's dinosaur, it would have to be Brontosaurus. 

So what if I told you there was never such thing as Brontosaurus? 

Well, not technically anyway. The animal who's fossils we found and subsequently named "Brontosaurus" certainly existed. But here comes my dark raincloud to hover over the parade dedicated to our love for this dinosaur. To understand why Brontosaurus is no longer used by scientists today, we first have to look at some rules. 

There's a strict set of them guiding how exactly we're allowed to name species. Not their common names mind you. Those aren't always reliable and are subject to variation, as some animals are known by different common names in different areas (for example- the cougar, as it's called in Canada, is also known as the mountain lion in the USA and the puma in South America). It's the species scientific names that have rules attached to them. These names are binomial and are the same everywhere, no matter what. Going back to the cougar, although its common name varies between people, to science it's always known as Puma concolor. That way, there's no question about what species you're talking about. As a side note, as far as dinosaurs go, we don't really have common names for them, so all dinosaurs are known by the genus part of their scientific names. That's the first word in their binomial scientific name. For example, in Tyrannosaurus rex (one of the few dinosaurs often referred to by its full name), the "Tyrannosaurus" part is the animal's genus, while the "rex" part is its species. 

So what does all that have to do with Brontosaurus? Well, back in the late 19th century, there was a very prominent palaeontologist names Othneil Charles Marsh, who discovered a huge Sauropod dinosaur, and named it "Apatosaurus". For those who have never heard of it, Apatosaurus looked a lot like what you think of Brontosaurus looking like. Exactly like it, in fact. Shortly after this discovery, Marsh dug up more, similar fossils from a site close by and, in his zealous attempt to name more dinosaurs than his arch-rival Edward Drinker Cope, he named the animal that these new bones belonged to "Brontosaurus". Everybody immediately thought Brontosaurus was pretty awesome, with artists such as the legendary Charles R. Knight doing several famous paintings of the creature. From a very early point, Brontosaurus became engrained into popular culture along side such celebrities and Triceratops and T. rex.

Then, years later, a scientist named Elmer Riggs made an startling discovery: he was closely examining and comparing the fossils of both Apatosaurus and Brontosaurs. Riggs noticed that the two animals were so similar that they actually should belong in the same genus together (this type of event all too commonly creeps up in palaeontology). Now that it had been decided that the two animals were similar enough to be grouped under the same genus, the question arises- do we call them both Apatosaurus or Brontosaurus? Well, the codes of zoological nomenclature have an answer to this: if two specimens of an animal, once thought to represent two distinct types, are found to be the same thing, the name that was first given to describing the the animal is the name that is kept. Marsh coined the name Apatosaurus in 1877, and Brontosaurus in 1879. So, since Apatosaurus was the first name used to describe the animal, everything that we used to call Brontosaurus now should be called Apatosaurus. That's why there was, in a sense, no such thing as Brontosaurus. 

Obviously the name Brontosaurus is dying a very slow death. While scientific institutions consistently refer to the animal in question as Apatosaurus, it seems like many people are having a lot of trouble breaking the Brontosaurus habit. So should the people who love Brontosaurus so dearly just grit their collective teeth, accept Apatosaurus and throw Brontosaurus reluctantly away? Well, yes and no. It still is technically correct to us Apatosaurus and only Apatosaurus when you're dealing, scientifically, with this dinosaur. The naming system is designed to avoid confusion (although this isn't always the result), so switching between the two names isn't a logically sound solution. We all should learn to love Apatosaurus. However, this doesn't mean the Brontosaurus has to go away completely. I'm acquainted with a few people in the field of palaeontology who make a habit of colloquially referring to the Sauropods in general as the "Brontosaurs" (Brontosaurus does mean "thunder lizard", so it's a pretty fitting name for the group). At the end of the day, when all the politics of naming organisms has got you down and confused, it's worth taking a moment to reflect on the fact that these creatures certainly never knew, nor cared, what names we would later give them.