Why the Cenozoic?

Hey there every peoples!

It’s been far too long, hasn’t it? Well, between fieldwork, job hunting, and a trip to Canada, I just haven’t had time for the ol’ cyber rag. And I actually did get a job and have been working full time for the last couple months. Plus, I applied for a collections internship at the Denver Museum of Nature and Science. So much on my plate! But people keep following my blog so I have returned to ramble some more.

Why be interested in the Cenozoic? Dinosaurs rule everything prehistoric. Movies, books, television, video games, and even museums. Interest and love in dinosaurs is at an all time peak. They are the biggest, scariest, and strangest things to have ever lived. There is nothing, it seems, that they can’t do. Look at the words of this recent article:

It was this environmental wound that allowed mammals to thrive in new ways, even setting the stage for our own ancestors. But if dinosaurs had continued to hold sway in the terrestrial realm, we never would have evolved. Our early primate forebears would have been shunted along different evolutionary routes we can only guess at.

 

There’s no reason to think that dinosaurs would have vanished and ceded the world to mammals if the extinction had been canceled. There were over 80million years between the time of Brontosaurus and Tyrannosaurus, but it’s only been 66million years since the last of the non-avian dinosaurs disappeared. We could fit the entire age of mammals between those two famous dinosaurs with room to spare.

 

Non-avian dinosaurs had survived sweeping changes to climate, shifting continents, and the ticking turnover of species as evolution and extinction work simultaneously. Of course they would have survived to what we know as the present day.

 

A supersmart dinosaur wouldn’t resemble anything humanoid. If dinosaurs with a mental toolkit similar to ours ever evolved, they’d probably look little different from a crow.

 

Mass extinction or not, we’re still very much in the age of dinosaurs.

So if dinosaurs are so incredible, why study anything else? Well, there are many reasons. We’ll deal with that article later. Now, I want to tell you why I am (and why you should be) interested in the Cenozoic.

First off, it provides us with, by far, our strongest examples of convergent evolution. Convergent evolution is when two animals separated by time and space develop similar traits in response to similar environments.  Dinosaurs followed similar body plans to one another, so similar that they never converged on one another. Stegosaurs never converged on sauropods. Tyrannosaurs never converged on carcharodontosaurs. Hadrosaurines never converged on Lambeosaurines. Almost every major family of of dinosaur lived on every continent. There was never any level of isolation that could separate groups of dinosaurs so much they had to imitate something else .

The dynamic world of the Cenozoic, with it’s complex geology, climate, and continental movement meant that animals could be cut off from each other. This led them down separate paths but often similar ones as well. For example, there were no giraffes in North America. The role of a long legged, long necked browser was vacant. So camels, like Aepycamelus and Megatylopus, evolved to fill the spot (hence why they are often referred to as “giraffe camels”). Conversely, dogs were exclusive to North America  for most of the Cenozoic. So, another group of animals developed similar traits (long legs for running and strong jaws for cracking bones) in their absence: hyenas. Far more varied then their modern cousins, some hyenas were remarkably dog like. And in South America, a dolphin (Odobenocetops) developed tusks and suction feeding like walruses did in the north Pacific.

But in the Cenozoic we find even more extreme cases. For example, here are the skulls of a wolf and a sabertooth cat:

Except those are not a wolf and sabertooth cat. They are the skulls of a marsupial and a sapprasodont (an extinct group of metatherians, the same group that includes marsupials. Sparassodonts were once thought to be true marsupials, but were recently found to be separate ). But if I showed them to the average person on the street, they wouldn’t be able to tell the difference. The marsupial wolf, called a thylacine, is from Australia and the sparassodont (Thylacosmilus, which means “pouched knife”, a reference to it’s former status as a marsupial. Things were so much easier when they were just marsupials. I didn’t have to go into lengthy explanations on what sparassodonts were!) is from South America. Both were cut off from the rest of the world, and so they evolved to mimic placental carnivores to a striking degree. Dinosaurs, as far as I can tell, have nothing even close to the kind of convergence achieved by mammals.

Another reason the Cenozoic is so fascinating is all the stories it tells. The constantly shifting climate and land created some of the greatest evolutionary narratives in earth’s history. The isolation of Australia, South America, and other large land masses allowed the evolution of bizarre forms seen nowhere else in the world. In Australia, marsupials were free of competition from placentals. They evolved into beasts like nothing seen before or since: wombat-like animals the size of rhinos, giant kangaroos, creatures that looked like a cross between a tapir and a ground sloth, and some of the largest birds that ever lived. In the last few million years, it was home to many large reptilian predators, including terrestrial crocodiles and the largest terrestrial lizard that ever lived (and one of my all time favorite prehistoric animals).

South America was no different. Cut off from the rest of the world until only 3–4 million years ago, its fauna was no less bizarre. Groups like perissodactyls (horses, rhinos, tapirs) and artiodactyls (bovids, sheep, deer, antelope, and other even toed hoofed mammals) were absent. So,now-extinct groups found nowhere else rose to rule the continent. Groups like notoungulates (who were recently found to share a common ancestor with perissodactyls), litopterns, xenarthrans (sloths and anteaters), and cingulates (armadillos as well as their extinct cousins, the glyptodonts) all reigned supreme. The carnivores were even stranger. With no placental carnivores to compete with, the archaic sparassodonts were able to fill myriad niches from small opossum-like forms to large cat-like forms. But they were not alone. Sharing the large carnivore guild was a family of large, flightless, carnivorous birds. South America also boasted some of the largest reptiles ever. If ever there was an evolutionary laboratory, Cenozoic South America was it.

Isolation wasn’t the only driver of the Cenozoic’s fascinating tales. The chaotic climatealso created countless enclaves of adaptation. During the late Eocene and through the Oligocene, the earth’s climate began to cool and dry. This caused tropical rainforests to give way to subtropical hardwood forests to open woodlands. It was thought that the first grasslands didn’t appear until around 25 million years ago. However, a 35 million year old fauna found in Chile challenged this. They found many animals with teeth adapted to eating grass and evidence of lots of grass. The higher altitude created an environment for grass to thrive, creating a grassland 10 million years before they would appear in the rest of the world.

Another remarkable story has been teased out of Tibet. The Tibetan Plateau (which includes the Himalayas, the tallest mountains on earth) controls the weather for most of Asia. Its harsh climate has earned it the nickname “The Third Pole”. Research into the geology of the plateau shows that this has been the case for a long time. During the  Pliocene, 2–5 million years ago, the world was warmer than today. But because of its altitude, the Tibetan Plateau was cold, living up to its nickname. Discoveries of fossils from this time period hint at a remarkable concept: that Tibet was the cradle of Ice Age megafauna. It is an idea that is gaining strength. The earliest species of big cat as well as the earliest species of woolly rhino have been found there. Genetic research shows that the closest relatives of American wild sheep live in Tibet. And the sister species (or closest relative) of American bison is the Tibetan yak. The picture that is emerging is that a frozen kingdom in a warm and sunny world led to the evolution of cold adapted megafauna. Then, as the ice ages cooled the rest of the world, they were able to leave the Tibetan Plateau and spread throughout the world. It’s a work in progress, but it is shaping up to be one of the most spectacular sagas of prehistory.

And sometimes both isolation and climate could create things most unexpected. And there might be no better case than New Zealand. Its temperate climate meant reptiles couldn’t grow very large. In fact there are no snakes, turtles, or crocodiles in New Zealand. Only geckos, skinks, and the ancient tuatara call the islands home. At almost two feet long, the tuatara is the largest of these. And being an archipelago (group of islands) meant only two ways for animals to get there: flying or rafting on floating mats of vegetation. This allowed birds to establish themselves before most other animals could, including mammals. Save for two species of bats, there are no native land mammals in New Zealand. Not even rodents, who managed to find their way across most of the globe, were absent here (before being introduced by humans). New Zealand was a land dominated by birds.

During the late Pleistocene and and most of the Holocene, the islands were home to a great diversity of bird life. With no large land predators, many lineages of birds became flightless, and others nested on the ground. Most ubiquitous were the moa, large and flightless ostrich-like birds. The 11 species of moa ranged from 3 feet tall and 40 pounds to 7 feet tall and 500 pounds. While the best known, they were only a part of this bizarre lost world. The adzebill, a large flightless rail, hunted for prey in the brush. The flightless New Zealand goose, the size of a small moa, was the largest goose in the world. The iconic kiwi probed the forest floor for food. An assortment of rails, parrots, waterfowl, and other small birds filled out the ecosystem. Although there were no land predators (save for the adzebill, which probably preyed on lizards, bats, and small birds), prehistoric New Zealand was hardly a carefree place. There were several birds of prey, and the king of them all was Haast’s eagle. With a 10 foot wingspan and talons the size of tiger claws, it was capable of taking down even the largest moa. Eyles’s harrier was the size of an eagle and could take prey far larger than any other harrier could (perhaps even the smallest species of moa). The laughing owl, which survived to the early 20^th century, dined on anything it could catch.

This is what made New Zealand unique. In a world dominated by mammals, it was a place where every megafaunal niche was filled by birds. Instead of giraffes, deer, and antelope, there were moa. Haast’s eagle and Eyles’s harrier filled the role occupied elsewhere by cats and dogs. The grazing niche, occupied in the rest of the world by bovids and sheep, was filled her by takahe and the New Zealand goose. Coyotes, foxes, and jackels are replaced here by the adzebill. Kiwis were essentially the shrews, hunting for invertebrates in the leaf litter. Every ecological role you could think of was taken by birds. As far as I can tell, nothing like this exists in the Mesozoic. There was no isolated land where mammals or crocodiles or even the birds of the time werethe dominant aspects of the fauna. Only in the Cenozoic do such incredible places exist.

Dinosaurs are just plain weird. They are like nothing alive today. That is pretty cool, but the Cenozoic can do one better. What draws me into the Cenozoic so much is how it takes what we think we know about the world and turns it on its head. For example, take the modern guinea pig or hamster. Sure, they’re cute and fluffy little rodents, but other than that nothing to get excited about. But take that guinea pig and blow it up to the size of a grizzly bear. Not so ordinary now, is it? During the Cenozoic,South America played host to a number of giant rodents, with the biggest weighing as much as a bull. And the opposite was true as well. Horses, camels, and even elephants, animals we normally think of as big, had small ancestors. Around 50 million years ago, the biggest horse was the size of a small dog. The earliest camels were smaller than a modern deer. And, extinct elephants living on islands in the Mediterranean were no taller than a goat.

But size was only the beginning. During the run of the Cenozoic, evolution experimented wildly with animals familiar to us and took them in unexpected directions. We think of rhinos as tropical animals because of where they live today. But during the ice ages, there was not one, but two, species of rhinos that lived in the frozen north of Eurasia. They both had thick coats of hair to keep them warm. And wear on horns shows that one species (Coelodonta, the classic woolly rhino) used its horn to sweep aside snow to reach the grass beneath it.

Today, alligators and crocodiles are restricted to watery habitats the world over, not able to venture far from the water’s edge. But this was not always the case during the Cenozoic. Australia and South America were both once inhabited by terrestrial crocodiles . Part of an extinct group called mekosuchines, these crocodiles had left the water behind to stalk their prey on land. They had flat, serrated teeth best suited to slicing than holding and crushing. Barinasuchus of the ancient Amazon had a skull as large as a tyrannosaur’s. And Quinkana was around to have encountered the first Australians!

Many species of ancient elephants had long lower jaws tipped with stout tusks, looking like they were crossbred with a front loader. The Cenozoic gave us an actual unicorn. Except it was a pig instead of a horse. Dogs, horses, camels, rhinos. All animals seen throughout the world actually originated in (and in some cases spent most of their history) in North America. And there are horn and antler arrangements so strange that you’d think they were created by Dr. Seuss. Dinosaurs may be weird in terms of absoluteness. But only the Cenozoic can take familiar faces and make them truly bizarre!

And maybe the most important reason to be interested in the Cenozoic: the changing climate. The dinosaurs had it easy. With few exceptions (Liaoning and the poles) the climate was mostly warm and wet. The Cenozoic, on the other hand, has been a roller coaster of climate change. Life had to adapt to constantly shifting climates. Most of these groups survived to the modern day. And considering we live in an unprecedented time of climate change, one could say that studying the Cenozoic is far more relevant to understanding our world and where it’s going.

The key word here would be more. But why worry about what is relevant? Why not care about all of prehistory equally? Why this sense that the past has to be ranked by whatever asinine criteria you can come up? Nature doesn’t have a sense of competition or care what is dominant or even interesting. So why does the Cenozoic lag so far behind in the public conscience?

I have a feeling it might have to do with those quotes I showed you earlier.

It was this environmental wound that allowed mammals to thrive in new ways, even setting the stage for our own ancestors. But if dinosaurs had continued to hold sway in the terrestrial realm, we never would have evolved. Our early primate forebears would have been shunted along different evolutionary routes we can only guess at.

That assumes dinosaurs could hold their position of dominance. We can’t guess what evolutionary paths early primates would have taken. But we don’t have to guess about how long dinosaurs would continue to rule the earth. We know for a fact they would have.

There’s no reason to think that dinosaurs would have vanished and ceded the world to mammals if the extinction had been canceled.

Maybe not immediately, but how do you know they never would have afterwards? As this whole post has shown, the Cenozoic has a very complicated climatic history. How do you know that dinosaurs would have survived the Paleocene-Eocene Thermal Maximum? Or the ice ages? Would they have been able to cope with the spread and takeover of grasslands?  None of these could have created opportunities for mammals to take over? Mammals, with their complex dentition, couldn’t have ruled the grasslands while dinosaurs retreated to the forests? How do you know dinosaurs could have survived wild shifts in climate they never encountered?

What about the current debate about the K/Pg extinction? Some say it was all the asteroid (which you seem to be implying). Others say it just finished them off. The diversity of dinosaurs seems to dwindle at the end of the Cretaceous. In southern Alberta, we see this in action. 75 million years ago, there were nearly 30 species of dinosaurs. At the 70 million year mark, there were around 20 species. By 66 million years ago, there were only about 12 species. Some scientists blame this decline on the Deccan traps, massive volcanic eruptions in India that were going on during the Late Cretaceous. The debris spewed by these volcanoes into the atmosphere would have wreaked havoc on earth’s climate. How do you know that the dinosaurs wouldn’t have eventually died out? They seemed to be on  their way out anyway. Or are you suggesting that dinosaurs are just so great that they can only be killed by the greatest of calamities? And that if that calamity never happened their continued dominance is inevitable? There is a lot we don’t know here. For example, southern Alberta doesn’t speak for the rest of the world. Was this the trend global or was it just local? How can we say dinosaurs would have stayed the dominant group when we don’t even fully understand why they died out?

There were over 80m years between the time of Brontosaurus and Tyrannosaurus, but it’s only been 66m years since the last of the non-avian dinosaurs disappeared. We could fit the entire age of mammals between those two famous dinosaurs with room to spare.

Oh really? According to you, a group’s age is achieved merely by being present. Since the first eutherian mammals appeared 160 million years ago, that would mean the age of mammals has lasted twice as long as the gap between brontosaurus and tyrannosaurs. So no, you can’t fit it between them “with room to spare”.

Non-avian dinosaurs had survived sweeping changes to climate…

If by “sweeping” you mean broad, then yes, they did. According to a couple of paleontologists and a paleobotanist I know, the changes were very drawn out and not as dramatic as what we see during the Cenozoic. The climate remained pretty stable throughout the Mesozoic. There were some changes to humidity and temperature, but nothing as chaotic as what the animals of the Cenozoic had to endure. The Paleocene-Eocene Thermal Maximum is thought to have lasted thousands of years, far faster than anything in the Mesozoic. There were 22 distinct ice ages during the Pleistocene epoch. A constant cycle of hot and cold that may have eventually done in the animals who had survived it for almost 2 million years. If the animals who were used to it could have been wiped out, then what reason is there to think the animals who never encountered anything close to it would have? All climates are not created equal. Just because something survived one climate does not mean they could survive another.

shifting continents…

You know who else survived shifting continents? The animals of the Cenozoic. What makes dinosaurs so special?

and the ticking turnover of species as evolution and extinction work simultaneously.

What the hell is that even supposed to mean? Faunal turnover, evolution, and extinction aren’t malevolent forces conspiring to wipe out life. They are natural processes. As animals migrate, evolve, and go extinct, faunal turnover happens. Ever since the earliest ecosystems faunal turnover has happened. From the smallest arthropods to the largest mammals and dinosaurs, everything has been subject to faunal turnover. Dinosaurs weren’t somehow singled out by it and survived because they are so highly advanced. They just went with it like all other animals have. That doesn’t somehow give them a unique ability to survive over everything else. The synapsids of the late Permian survived faunal turnover. Does that mean they would have continued to rule the planet if the Permain extinction hadn’t happened? If they did then your precious dinosaurs wouldn’t have evolved. Or would they have evolved anyway because they are the ultimate survivors (according to you anyway). Everything you have listed has been endured by every animal other than dinosaurs. Dinosaurs aren’t anything special by surviving them too.

Of course they would have survived to what we know as the present day.

Yes, but that doesn’t mean they would still be the dominant force. If the constantly changing climate didn’t kill them off completely, then why think they wouldn’t be restricted to the tropics (if they survived that long)? Again, you assume they can survive anything like some turbocharged Bear Grills. We don’t even fully understand how they lived and how they interacted with the world they occupied. There is no way we can say with certainty they would have survived the world after.

A supersmart dinosaur wouldn’t resemble anything humanoid. If dinosaurs with a mental toolkit similar to ours ever evolved, they’d probably look little different to a crow.

Or they wouldn’t. They could look like the dinosaurs of old or something completely different. Just because birds are modern dinosaurs doesn’t mean they are the inevitable result. You never know, another group of dinosaurs could have developed intelligence. Elephants are nothing like primates and yet they show signs of intelligence. Hell, octopi are nothing like vertebrate life, and yet they are remarkably smart for invertebrates. The Hobbit (Homo floresiensis) is quite different from us and yet was intelligent. How do you know the evolution of birds during the Cenozoic couldn’t have been influenced by mammals? If dinosaurs survived the K/Pg extinction, modern birds probably wouldn’t have evolved either. They would be very different. There are no inevitabilities in evolution. Just like we can say a smart dinosaur wouldn’t look like us, we can’t say they would look like a crow.

Mass extinction or not, we’re still very much in the age of dinosaurs.

Are we now? So they don’t have to be the dominant life form, they just have to be present for it to be their “age”. As I mentioned earlier, this would mean the age of mammals began 160 million years ago by your logic. It has been suggested to me that it is still the age of dinosaurs because there are 10,000 extant species of birds versus 5,500 extant species of mammals. But if we follow this guy’s reasoning to its logical conclusion, we find we are not still living in the age of dinosaurs. There was never an age of dinosaurs. We are still living in what always has been the Age of Fish. There are currently 27,000 extant species of fish. That is more than dinosaurs and mammals, living and extinct, put together. And that doesn’t even count all the extinct fish who first showed up over 400 million years ago. That is longer than the age of dinosaurs and the age of mammals put together. Even if fish never came on to land (mudskippers and snakeheads would like a word with you), there was still never an age of dinosaurs. It was the age of insects. Insects appeared 350 million years ago and currently outnumber all vertebrate life by several magnitudes. Hell, there are an estimated 1,000,000 species of beetles alone. You can play this game all you want. You will never win.

So just what the hell is an age? What defines one? Why are we so fixated on what is dominant? As humans, we are fixated on the biggest and best. We are always making things into competitions in a futile bid make us and our opinions #1. There seems to be this infantile need to make the things we like the best and above everything else. “I like dinosaurs, so I must make everything about them and show why they are the greatest things in existance!”. But guess what: nature doesn’t give two shits. It doesn’t care about the best or the most awesome. Life lives by nature’s rules and what happens, happens. Arguing over what’s cool or boring or the most interesting will make not one iota of difference in the long run. So what’s even the point?

And yet you have people like the quoted writer hyping dinosaurs to ridiculous levels. It’s bad enough popular culture does it, but it’s another when the actual scientific community joins in. Suggesting dinosaurs would still be ruling the earth today like they are the ultimate lifeforms is not only stupid but diminishes all other life. We are the only known planet to have life. But we feel the need to rank it according to our arbitrary and meaningless standards, shunning anything that we don’t find “cool” enough. If we only focused on the most interesting stuff, we would be truly ignorant of life’s history. We need to learn to appreciate all life in all times. That little brachiopod may not be as big and flashy as a Triceratops. But it is twice as old as the oldest dinosaur. It survived far more time on the earth to arrive in the modern world. They are different strands in the web of life. Thinking one is somehow better than the other diminishes them both. Life is not a contest to see who is best (ok, it kinda is, but you get what I mean).

I laid out to you why I like the Cenozoic over everything else. But that doesn’t mean I hype it up or shit on other life. I still do like dinosaurs. My last two major field seasons were spent looking for dinosaurs. Went I went to Canada,I made a point to visit (and spent all day at) the Royal Tyrrell Museum of Paleontology, even though it’s all about dinosaurs. And that internship I applied for, if I get it (and that’s a big if), would have me working with dinosaurs. As I pointed out in my Jurassic World review, I don’t have a problem with dinosaurs. It’s their fans I usually can’t stand. And I still appreciate life in the Paleozoic for its role in the history of life. We need to learn to appreciate all life. Because it happened and will continue to happen regardless of our opinions on it.

‘til next time!