Fun with Liquid Nitrogen

Meanwhile on land during the Eocene epoch, the terror bird was meeting up with some fierce competition for the limited open grasslands. Carnivorous mammals have finally reached apex predator status! No more hiding in the trees and in burrows for these mammals. And here he is, arguably the largest mammalian land predator of all time:

We’ve only ever found one skull of Andrewsarchus, a monstrous 2.7-foot long skull resembling the skull of a carnivore ( For contrast, a modern lion’s skull is about 15 inches long and the extinct great cave bear’s skull is 21 inches). Based on creatures of the time with similar skulls, such as Mesonyx and Synoplotherium, scientists can infer what Andrewsarchus might have looked like and how large it was. Estimates place Andrewsarchus at about 6-6.6 feet at the shoulder and 11-17 feet long, not including the tail. The weight of Andrewsarchus could be anywhere from 1,000-2,000 pounds. We don’t know for sure because Andrewsarchus might have been a slender, gracile creature or stocky and compact like a bear. At any rate, it was a monster predator the size of a rhino, if not as heavy.

There is of course, debate on whether Andrewsarchus was a loathsome scavenger or an admirable hunter, but as I’ve said before, very few animals are obligate hunters and nearly every carnivorous mammal that has ever lived will do whatever it takes to survive, whether it be hunting or scavenging. They don’t care about impressing you. Most hunt or scavenge depending on the opportunity they face at any given time. I think it’s a silly debate.

When I first saw some pictures of Andrewsarchus, I thought it was a massive prehistoric hyena. It turns out though, that Andrewsarchus was not related to hyenas at all. It couldn’t be- the order Carnivora was only just beginning to evolve from their ancestral family Miacidae. It would be a few more million years before large Carnivores appeared on the scene.

So Andrewsarchus was a carnivore but not a Carnivore. The way to make sense of this is to understand that an animal can hunt or scavenge other animals and be carnivorous, but not of the official Order Carnivora, which includes all hyenas, cats, wolves and other canids, seals, weasels, and some offbeat members like the civet and the otter.

One way that Andrewsarchus was similar to Carnivores was that he appeared to have carnassial teeth. Nearly all Carnivores have them- they’re the cheek teeth in front of the molars on the upper and lower jaw that occlude in a special way to ensure maximum crushing and shredding. Dogs are no exception. If you ever need to stick your hand in a dog’s mouth for any reason- maybe he’s like my dog and has a tendency to get tennis balls stuck in his throat- you need to be sure to enter only from the front and NEVER take a lateral approach. In front, you have some incisors and some canines, but if you put your hand between a dog’s carnassial teeth, you may not have much of a hand left afterward. If you’ve ever seen a dog or a hyena chew on a grisly bone, you might have noticed that they don’t use their canines or incisors to shred and crush it. They’re always chewing on it from the side. Andrewsarchus probably crushed and chewed bones the same way.

So if Andrewsarchus was not a Carnivore, what was he?

The short answer is that he was kinda-sorta a pig. An ungulate. Most likely the scariest thing with hooves the world has ever known. He was of the order Mesonyx, of which all members are now extinct. This order was a group of wolfish, carnivore-like hoofed mammals, somewhat related to pigs and ruminants. You can see his family tree here:

Andrewsarchus’s order is in the third column, center- Mesonyx. I found this family tree pretty interesting. You can see that also in the third column on the top we have Pakicetus, who was an ancestor of our friend Ambulocetus- as you can see, their kind evolved into the modern walvis, who also share some ancestry with modern zwijn and other hoofed mammals. He’s even related to the unfortunate paard, who always seems to be getting eaten.

Despite being a hoofed mammal, though, Andrewsarchus didn’t show any family loyalty to horses, the most delicious prey animal of the Paleogene period. Things still aren’t looking so good for horses.

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It’s been awhile since we’ve had a good, solid transitional fossil. Transitional fossils are fossils that show a combination of primitive or plesiomorphic traits, along with newer, derived traits, which illustrate the progression of evolution in the fossil record. The last good transitional fossil we showed off here was the famous Archaeopteryx. But my favorite transitional fossil was from the Devonian Period, the Paleozoic Medal of Honor recipient, the indomitable Tiktaalik. Tiktaalik was a pioneer in learning to breathe air and using his flippers and brand-new wrists to make some strides on land for the first time. This changed everything.

So if an ancient fish-tetrapod intermediate worked so painfully hard to make it possible for vertebrates to live on land, why would any vertebrate ever go back to the water?

For some, it was an easier opportunity to catch horses.

Ambulocetus means “walking whale”, and he possesses a variety of both plesiomorphic traits of terrestrial mammals and derived traits of modern marine mammals. Some of his plesiomorphic traits you can obviously see for yourself- he’s got legs, for one. He also has a nose, rather than a blowhole. Other evidence that Ambulocetus had terrestrial origins are still present in modern whales, such as a complete set of wrist bones and bones of the hands and feet. Unlike whales though, Ambulocetus’s wrists were visible on the outside. Also, the alignment of Ambulocetus’s spine only allows vertical undulation. All fish, salamanders, lizards and snakes (if you drop one into water) move through the water by undulating their bodies sideways, whereas all marine mammals- including seals, whales, mermaids, and dolphins move through the water by arching their body up and down. If whales had never once been terrestrial, their spines would be configured more like fish since the vertical spine articulation was an adaptation for terrestrial life.

The more derived traits that made Ambulocetus well-adapted for aquatic life include his lack of external ears and his periotic bones, similar to those of whales, that help him hear underwater. He can walk around on land but he’s more agile in the water, since his legs aren’t well-suited to running fast or climbing. However, he lacks a few adapations found in true whales that make him not quite ready for life at sea. Instead, Ambulocetus preferred to wander the wetlands and hunt in a fashion similar to that of a crocodile- that is, he would hover around shallow water and wait for an unsuspecting mammal, such as a horse, to come along for a drink. Much like the Paleocene epoch, the Eocene epoch was not a good time to be a horse. They were still small and insignificant back then.

This seems like a decent way for an early carnivorous mammal to make a living, but it doesn’t explain why Ambulocetus evolved to aquatic life and returned to the water after his ancestors had been living on land since the Paleozoic era. What happened was that at the end of the Paleocene epoch, the earth experienced one of the most rapid and extreme global warming events in history (except maybe for the one happening right now- we’ll see), called the Paleocene-Eocene Thermal Maximum. The earth’s temperature shot up by 6°C (11°F) in just 20,000 years, with a number of results. Of course, as in every point in natural history when the earth underwent major changes, there were extinctions, which resulted in new ecological niches to fill.

The water levels rose all over the earth, which was nearly uniformly warm. Temperate forests extended all the way to the poles and the tropical regions extended to 45 degrees latitude- along the northern Vermont/Canadian border. The earth now had far more forests and swamps than it used to. This is bad news for animals that preferred dry, open grasslands with large stretches to chase down prey- the terror bird survived, but his habitat was reduced and he was no longer the uncontested apex predator. By this time there were carnivorous mammals on land- we’ll meet one next- but the strategy of Ambulocetus was to exploit the new niche that could be found hunting along the shores and shallows.

This niche was already occupied by the crocodile, of course. That guy never goes anywhere. But with increasing competition for hunting on dry land, and with the new abundance of wetlands, there was plenty of room for both Ambulocetus and crocodiles to fill the same role without running into eachother and competing. Good news for Ambulocetus. Bad news for horses.

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I know it’s been awhile, but you may remember when I first wrote about the Cretaceous period, I mentioned that the mammals were present throughout the age of the dinosaurs. I said “Also during the Cretaceous period, the mammals were around, but they were primarily in hiding, tucked away underground and in the shadows. They were definitely Up To Something throughout that period, but that will be revealed later.”

It’s time to talk about exactly what it was that they were up to.

They were beginning to diversify! They were tucked away indoors, weathering out the great storm of dinosaurs and forming a game plan once they were able to go outside again. Animals that had been developing some mammalian characteristics had been around since the Permian Period. If you”ll remember, Dimetrodon was a synapsid, a proto-mammal that had differentiated teeth- two measures of teeth- that allowed the animal to tear and shear its meat, allowing for mammal-like animals to learn how to chew and digest food more efficiently. Synapsid jaws had a different shape from other vertebrates; the three small inner ear bones common to mammals are believed to have evolved from the synapsid jaw bones. Synapsids also had very exciting skin- it has a thick dermal layer lacking in reptiles that produces leather. It’s also full of glands! Tons of glands! Sweat glands, sebaceous glands, mammary glands- all those might come to be useful some day.

So we have an ability to chew, keen hearing, and thick leathery skin. The skin is useful because it’s protective but more pliable than armored, scaly skin. Better ways to chew and digest food is useful because it leads to more food sources, and keen hearing is very useful if you’re a mammal and you only go out at night to avoid the terrible lizards that dominate the daylight hours. Mammary glands allow an efficient way to supply nutrients to your offspring while minimizing the amount of time you need to go out and forage and expose yourself to danger. What’s also useful for nocturnal activity is a self-regulating body temperature, ie, being endothermic.

All the basic groundwork for mammals was quietly being laid out during the Permian and Triassic periods. The first true mammals evolved during the Jurassic period, right under the noses of the great dinosaurs. But it was during the Cretaceous that the mammals finished their quiet and subversive fine tuning.

The first marsupials and placental mammals developed during the Cretaceous periods. Before mammals diversified into placentals and marsupials, they were all egg-laying, just like dinosaurs and just like the platypuses and echidnas of today. Carrying the unborn offspring inside the body kept it safer than being in an egg in the outside world, plus it was a more energy-efficient way to supply it with nutrients. Marsupials had the right idea with this method, but it was the evolution of a placenta that optimized pregnancy. The placenta provides such an effective way to supply nutrients to the unborn that the offspring could stay in the womb for much longer than a marsupial, and so the animal could be fairly well-developed at birth.

There’s one other feature of placental mammals and marsupials that set them apart from monotremes- their butts. The term “montreme” means “one hole.” That one hole refers to a monotreme’s all-purpose hole, or the cloaca. The monotremes, just like birds and reptiles and dinosaurs, do all their dirty business with just that single hole. But the rest of the mammals have several holes around the butt. We’ve got a poopin’ hole, a sexin’ hole, a peein’ hole- we’ve got holes up the patootie! Holes all over the place! Brilliant, functional holes!

And all these specializations and holes and nipples all came out during the Cretaceous period, during the age of the Dinosaurs. And let’s not forget the the development of a neocortex, found only in mammals. This new-fangled neocortex was involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning, and one day far into the future, the neocortex would be used for conscious thought and language. The mammals were going to become intelligent. Go mammals! You rock!

Nevertheless, mammals had very little opportunity to show off all these holes, neocortices and other new adaptations living in the shadow of the great dinosaurs. It took a giant asteroid to wipe out the dinosaurs and give the mammals an opportunity to come out of the burrows and show themselves. And what a day that was.

The picture above is straight from my all-time favorite childhood book, Ranger Rick’s Dinosaur Book. I loved that book more than I can describe. Of course, at the end of the book there is a chapter called “Death of the Dinosaurs” that features an ankylosaurus lying dead by a swamp. This was an emotional chapter for me. The following chapter was entitled “A New Day Dawns”, with the picture of the small mammals emerging in the morning light to explore the triceratops skull. If you go back to my Epidendrosaurus post, you might notice that I ended the post by saying goodnight to the dinosaurs and the Mesozoic era, following with a promise that “Tomorrow a new day dawns…” That was my personal shout-out to Ranger Rick.

That picture was also the inspiration for my first serious mammal painting in this series:

Most people with some familiarity with mammals know that there are three major divisions of them: the monotremes or prototherians, egg-laying mammals with only one hole; the metatherians or marsupials, the ones with the pouches and two holes; and eutherians or placentals, the ones with the placenta and holes all over the place. At least the females have a lot of holes.

But there was once a fourth major division of mammals- the allotheria or the multituberculates. The most unique feature of multituberculates is their teeth. You may think it’s frivolous to define an entire subclass based on unique teeth, but in the history of mammals, teeth are very important. In fact the first mammal-like feature to come about that set synapsids apart from reptiles was their heterodont teeth. Remember Dimetrodon?

And no other mammal has ever had teeth like those of the multituberculates. Let’s have a look:

At first glance you may think this looks like a set of rodent teeth, but there’s a difference. Rodent teeth are characterized by a prominent set of incisors, then a wide space called the diastema, followed by molars. No rodent has canine teeth, and no mammal at all other than multituberculates has a wide diastema followed by a strange, wide, sharp premolar. It looks like it would be useful as a slicer or a crusher. Like many rodents, multituberculates probably had a varied diet and may have been opportunistic omnivores. After the disaster of the K-T extinction, being able to eat almost anything and having a nice, diverse set of choppers was most likely critical to survival.

And survive they did. Multituberculates threw parties on the remains of their now-dead oppressors, smiling their peculiar, toothy smiles and enjoying this new dawn- while still keeping clear of terror birds. Multituberculates were so good at surviving that they are considered to be the most successful group of mammals in natural history, sticking around for over 100 million years. They never grew larger than about beaver-sized and never reached an apex predator status, but maybe that’s part of the secret to their success. We have already seen that the bigger they are, the harder they fall once the earth undergoes major changes.

But if they were so successful, why are they no longer with us today? Well, right around the early Paleocene, a group of animals evolved that resembled multituberculates. These animals are known as rodents, and they make up 40% of all mammals today. Just like multituberculates, rodents had prominent incisors, generally do not grow any larger than beaver-sized (except for the capybara), and tend to be adaptable and opportunistic feeders. Other than that peculiar premolar, rodents had one major difference from multituberculates- they were placental mammals. The narrow hips of the multituberculates suggest that they gave birth to tiny, grub-like young just like marsupials, and those young were helpless and required the mother’s care for a long time. It’s possible that the longer pregnancy of the rodents, leading to relatively more developed young was the key for the rodent outcompeting the multituberculate in all their ecological niches. The rodents are alive and well with us today, while the multituberculates left us for good by the Oligocene epoch.

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Welcome to the Cenozoic Era, the Age of Mammals. Before we get started here, I want to mention that from here on out, there’s a more specific way of doing things here in the Cenozoic. We’re going to be sub-dividing each period within the Cenozoic into the next division down the line, known as an epoch. We might even further subdivide to stages if any particular epoch is exciting and varied enough- goodness, the Pleistocene epoch is subdivided practically into discrete hours of the day. This is a good thing because the Pleistocene epoch has just about the craziest mammals we’ve ever seen. But let’s not get ahead of ourselves here; the Pleistocene epoch is practically 63 million years from now.

The Cenozoic era is divided into three periods: The Paleogene, formerly known as the Tertiary Period*; The Neogene, and the Quaternary Period, the last of which was only officially recognized as a period by the International Commission on Stratigraphy in 2009.

We’ll start with the Paleogene Period, but there will be one or two species from each epoch within that period. We need to do it this way because 1) it’s more awesome and 2) If we stopped subdividing at the period level of time, there would only be three more species in this entire series and we certainly don’t want all this to end just yet. Here is a handy chart of the geologic time divisions of the Cenozoic era, to make things more clear:

*The Tertiary is now considered a “sub-era”.

And here is how the Paleogene Period breaks down:

Well, now that we have all that straightened out, let’s find out what was going on in that first stretch of time during the aftermath of the great KT Extinction Event. You have to imagine that immediately after the impact event that ended the Cretaceous Period and Mesozoic era was a smoking, scorched ball of earth and every single [non-avian] dinosaur was dead. If you’re like me, you’ll be moved to tears at the imagery of dead dinosaurs all over the place, with some sad music playing in the background. Maybe it’s Rock, playing Beethoven’s Pathetique Piano Sonata No. 8 in C Minor. At the point where the music picks up tempo, you see a few flashes of life here and there, peering out from behind dinosaur skulls and and slowly emerging from their burrows. Life begins anew.

As true as it is in modern times, so was it true in the Paleocene epoch that the first plant species to recover and take over the forest after a fire is the fern. In the geographic strata immediately covering the K-T boundary, there are numerous fern fossils. And insects, too- ferns and insects can survive almost anything (except for that one time and only time that they suffered heavily, the insurmountable Permian-Triassic extinction event). But a lot of plants did not recover, including every member of the Gingko class except for the hardy Gingko biloba that we know and love today. For every species of plant that was wiped out, a new kind of plant evolved quickly during the Paleocene to fill in the empty niche. And so the Paleocene brought about more plant favorites of today- the cactus and the palm tree.

The K-T extinction event’s main casualty was dinosaurs, most other taxa weathered this event fairly well. Yet this was still an extremely notable extinction event because at the time of the Cretaceous, dinosaurs were astoundingly diverse and filled up exactly 9 gadzillion ecological niches. After the impact event, there were suddenly 9 gadzillion empty niches and the animals that survived evolved very quickly to fill them in a period of punctuated equilibrium. Now that the skies were emptied of pterosaurs, birds took over the sky. Crocodiles stayed where they were, but the absence of the great reptilian sea monsters allowed sharks to once again reclaim their title as Kings of the Sea. Without Epidendrosaurus to patrol the trees and stick long appendages into them, rodent-like and primate-like creatures were free to mimic the Aye-Aye.

And of course the land of the Cenozoic era belonged to the mammals.

Wait wait wait, what’s going on here? What kind of Age of Mammals is this?

Unfortunately, while the mammals were experiencing an explosion of diversification, those non-avian dinosaurs, ie, birds, never went anywhere. Mammals were doing a great job of hiding in the trees and in burrows underground throughout the Mesozoic era, always lurking in the shadows, only coming out at night when the giant beasts had gone to bed. These habits were great for developing large tarsier-like eyes for better night vision, for growing fur and a fast metabolism to keep warm at night, and the ability to lactate to feed their young in order to minimize the need to leave the burrow or the nest, but none of these mammalian habits was much good for growing enormous and becoming an apex predator.That niche had yet to be challenged and an avian theropod still held the crown.

The Terror Bird enjoyed chasing down and eating tiny horses and giant guinea pigs, both of which were abundant in the Cenozoic era. I have to confess that my depiction of the horses in this painting are somewhat artistic license. The horses of the Paleogene period didn’t much resemble our horses of today. The hyracotherium, formerly known as the eohippus, looked more like this:

The guinea pig, however, did resemble today’s guinea pigs. Or at least they resembled the capybara. I hope they squealed like modern guinea pigs do when the terror bird swallowed them- “Wheet! Wheet! I’m delicious!”

These early beginnings of the mammals’ rise to power may explain why certain large, powerful animals of today are unusually skittish. A modern horse flies off the handle when a newspaper blows in the wind. A hippo goes on a terrified, defensive rampage and tears humans in half when one goes canoeing in the river in hippo territory. It’s as if they don’t realize that they’re huge. Both these animals, along with the skittish and mighty rhino, were all once small, practically defenseless and cheerfully swallowed by terror birds on a regular basis throughout the Paleocene. It’s been 60 million years and they’re still not over it.

The Terror Bird family survived all the way into the Pleistocene epoch, but it wasn’t long too long before their dominance was to be challenged and usurped. The mammals are a resourceful, adaptable bunch and they were certain to come up with a new model of fearsome land predator.

And as for the Terror Bird, their ultimate, disappointing fate that you may be familiar with was a little underwhelming.

This might have been the way things went down, but I hope it’s at least a small consolation that the horses, guinea pigs, rhinos and hippos millions of years later haven’t forgotten about them.

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Pay attention, this is the last dinosaur we’re going to see.

What happened to the dinosaurs? Why did they leave us? Well, by now most everyone is familiar with the KT-Extinction Event, even if not everyone knows it by name. While not as utterly apocalyptic at the Permian-Triassic Extinction Event we became familiar with during the time of Lystrosaurus, it is definitely the extinction event that has struck the greatest chord in the minds and hearts of humans.

I can tell you that as a child, any film or video about dinosaurs invariably seemed to end with their demise, the narrator in the filmstrip often saying “Nobody knows for sure why the dinosaurs died out…” This being the 80s, we hadn’t yet [mostly] settled on the impact event being the cause for their extinction. Instead all narrators of the 80s assumed it would forever be a mystery. At any rate, once the images from the educational film or video closed with a few images of dead dinosaurs collapsed by the water’s edge, I would struggle to fight the tears welling in my eyes, embarrassed and in fear that someone would catch me crying. Once or twice another kid noticed and would announce jeeringly to the table “Becky was crying at part where the dinosaurs died out!” Of course to save face I would protest indignantly “I was not!” But I was.

No need for embarrassment, though. The K-T honestly was a heartbreaking extinction events to the sensibilities of humans. Dinosaurs fire our imagination the way no others prehistoric creatures can, especially to children. Their fossils prove that giant scary monsters actually did once exist on earth. They were real-life dragons. How could anyone be blase about real dragons?

The reason we’re mostly convinced that this extinction event that ended the Mesozoic Era, the Age of the Dinosaurs, is because all over the earth the layers of sedimentary rock at the Cretaceous-Tertiary boundary contain many, many times a greater concentration of the element iridium than anywhere else in the earth’s crust. Iridium bonds very easily with iron, so most of the earth’s iridium is found with the great concentration of iron in the earth’s core, and not in the earth’s crust. Since iridium is abundant in asteroids and comets, this strongly suggests that the unusual concentration of iridium at this specific geologic layer was deposited there by a large asteroid striking the earth.

The consequences of an impact event are un-pretty for whatever life happens to be around. The impact causes a massive cloud of dust and sulfuric acid aerosols all over the earth for years. This blocks out sunlight and inhibits photosynthesis, which means plants don’t grow and creatures that feed on plants starve. In turn, the predators that feed on those herbivores starve as well. But it doesn’t stop there. In addition to severe famine, the impact would have caused ejecta to fly and then re-enter the earth’s atmosphere, causing a pulse of infrared radiation, from which the heat caused global firestorms. Every time I see a dramatization on the Discovery Channel of these events, complete with dinosaurs screeching and fleeing in terror with no place to run, I still struggle to hold back tears just like I did when viewing the filmstrips of the 80s. I still get laughed at for it, too- by Jon. Even now I’m having a hard time writing about it.

Who died from the impact? Well, we definitely know that the dinosaurs didn’t survive, but nowadays we’re more specific and say that the KT-Extinction Event wiped out the “non-avian dinosaurs.” In short, birds survived and birds are dinosaurs. I still think that the survival of birds is a disappointing consolation for losing our real-life dragons and monsters, but we’ll talk more about birds a little later. For now, it’s all about who didn’t survive.

All cephalopods except for squids, nautiloids, octopodes (you know, octopuses) and cuttlefish went extinct. This is upsetting as cephalopods are enchanting animals based on the ones that survive today. All North American marsupials went extinct except for one- our own Virginia Opossum. But the ones who tend to suffer the heaviest during any great extinction event are the animals that are the largest and most majestic, particularly any apex predator. So of course the King, T. rex, was among the first to go. Triceratops was one of the last dinosaurs to walk the earth. Ankylosaurus, mosasaurs (ie, sea monsters), plesiosaurs (ie, Nessie), pterosaurs, duckbills, and the great sauropods of the Cretaceous- all of them succumbed to the asteroid. Nigersaurus, too- although he was so dumb he would have soon gone extinct even without an impact event.

It is literally an end of an era. I’ve called in one final dinosaur to bid us farewell.

We’ve seen Epidendrosaurus’s kind before in Jurassic intermediates such as Archaeopteryx. Like Archaeopteryx, Epidendrosaurus lived an intermediate life- mostly arboreal, making strides at pre-flying and paving the way for birds.

You might have noticed that Epidendrosaurus seems to be flipping us the bird in a big way. Part of it is because Epidendrosaurus is a drama queen, but we think the other purpose of the enormous fingers is similar to how the Aye-Aye uses that hyperelongated finger: to stick it into things. Just as a woodpecker inserts a long, long tongue into the hole it has drilled in a tree to find grubs, both the Aye-Aye and probably Epidendrosaurus use their sharp little teeth to create holes in the tree and then worm that finger around inside, looking for treats. The fingers are also good for perching birds.

It’s sad that Epidendrosaurus is doomed. That yellow canary will have to find new fingers to perch on.

Good night, Epidendrosaurus. Good night, dinosaurs. Good night Cretaceous Period, good night Mesozoic era. Tomorrow a new day dawns.

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We’re up to the Cretaceous Period already. My my, how quickly the millions of years just fly by. The Jurassic Period came and went, and unlike more rattling periods of time, the Jurassic period did not end with a major extinction event. Instead Pangaea just slowly and delicately finished breaking up into continents and the temperatures changed so that it snowed more at higher altitudes, then it gently warmed up again over a few more million years, and not too many species of dinosaurs went completely extinct. Instead they evolved and flourished and started becoming more and more showy and “experimental”, and thus more and more awesome. As I’ve mentioned before, the dinosaurs of this period are the ones most frequently drafted to be reincarnated as plastic toys.

Another noteworthy point about the Cretaceous Period is that it was the longest period of the Phanerozoic Eon (if you’ll remember, that’s everything from Rock at 542 MYA to right now): 80 million years- the longest period by 20 million years. Who knows how much longer the Cretaceous Period and its undisputed dinosaur overlords would have lasted had this period not come to an abrupt end 65 million years ago, the most famous mass extinction event to date, if not as catastrophic as the Permian-Triassic event. But there’ll be more on that later.

What else was remarkable about the Cretaceous Period? Angiosperms! Flowering plants! Before angiosperms came about, all the earth had as far as plants go were algae, conifers, ferns, mosses, cycads, and something that sounds unappetizing- the liverworts. How dull. With the Cretaceous Period came plants that came to fill in numerous ecological niches and dominate the earth much like the dinosaurs dominated through the Mesozoic era. It’s just that flowering plants continue to dominate today. Flowering plants never took over the ginkgo tree’s niche, though. The ginkgo lived alongside dinosaurs just as it lives along the city streets today. Seeing as the ginkgo was hardy enough to survive the Cretaceous-Tertiary extinction event, so is it hardy enough to withstand city pollution and that’s why it’s often selected to ornament the streets.

Oh- and bees! If we have flowers, we have a niche for bees now. Along with bees, we now have ants, termites, grasshoppers, butterflies and moths. Beetles and dragonflies finally have some competition.

Also during the Cretaceous period, the mammals were around, but they were primarily in hiding, tucked away underground and in the shadows. They were definitely Up To Something throughout the Cretaceous, but that will be revealed later. For now it’s still all dinosaurs.

Let’s meet our first Cretaceous ambassador!

As mentioned, the Cretaceous Period was the point at which dinosaurs were most diversified, which meant that sometimes they evolved some really silly-looking designs. Rock here thinks Nigersaurus is hysterical. He has not seen anything this hilarious and foolish-looking since Diplocaulus, back in the Permian Period some 110 million years ago.

Nigersaurus may not be very bright, but he’s decently evolved for what he does. His skull articulates with his neck in such a way that his head always hangs down, suggesting that he was a ground-grazer. That’s in contrast to the other sauropods of his day with long necks adapted for reaching high-up vegetation. But the vacuum- mouth? It’s wide like that so he can run that thing along the ground and mow up large mouthfuls of plants on the forest floor. He tells us that he likes ferns. He grinds them up with his 50 columns of teeth- some 500-600 teeth total- that are arranged in a row to act like scissors. All those extra teeth lie behind the cutting teeth and are replacements for when any particular cutting tooth is spent and wears out.

Nigersaurus was talented at eating low-growing plants, but unfortunately he lacked the defensive headgear and other creative defenses of herbivores of his day. He was lightweight but slow, and a lot of his bones were found in the same fossil beds as Sarcosuchus, the 40-foot long crocodile that hung out in Nigersaurus’s watering holes. If only he had extensive body armor or a set of horns- even a club tail would have done the trick. But all Nigersaurus could do was attempt to vacuum the croc to death. It didn’t work.

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Q: What’s a pirate’s favorite transitional fossil?

A. Arrrrrrrrchaopetryx!

You’ve seen this fellow before, right?

This is archaeopteryx, another Jurassic classic and the world’s first bird. What makes him so important to us is that the above is a transitional fossil, an intermediate form- that is, he shares some characteristics of birds and some characteristics of reptiles, thus providing powerful evidence for the origin of birds and for evolution by natural selection. The first Archaeopteryx feathers and skeletons ever discovered were unearthed with impeccable timing as well-in the 1860s, shortly after Darwin published his On the Origin of Species, and these discoveries strongly supported his theory. In Darwin’s 4th edition of the book he included Archaeopteryx in his book. It was as if God knew that Darwin needed someone to back him up so he made sure the paleontologists of the day knew where to look for these elegant fossils.

Archaeopteryx has also been used to study the possible origins of flying. Being the world’s first bird and all, he hadn’t yet nailed down the swift, graceful flight of the birds of today, but he was working in it. He lacks a strong, bony breastbone that the best fliers of today possess, and the angle of his shoulder joints didn’t allow him to lift his wings above his back, meaning he wouldn’t be able to flap like a modern bird, either. He was more likely a glider, as his asymmetrical feathers and broad tail feathers would have given him a lot of lift. he could probably flap with a “downstroke only” sort of motion to give him further lift. So two ideas arise from Archaeopteryx over how modern flight may have evolved. The “trees-down” model suggests that Archaeopteryx and his kind were first tree-dwellers and used their wings to glide to the ground in a flying squirrel-like way. The “ground-up” model proposes that Archaeopteryx ran swiftly on the ground, and gliding upward. Still the most accepted idea today is that not particularly specialized for either running nor tree-dwelling, and escaped predators by gliding with shallow downstrokes, evading predators by reaching higher and higher perches in the trees and gliding between cliffs and treetops.

But let’s not forget that Archaeopteryx remained awesome by retaining some of its characteristics of theropod dinosaurs. It had a hyperextensible toe on each foot, known as the “killing claw” in creatures such as Deinonychosaurs. It had jaws (rather than a beak) and lizard-teeth, a bony tail and hands with long fingers and claws.

Here’s what Archaopteryx looked like with all the feathers on:

I found out that some scientists believe that Archaeopteryx did not have a bald lizard head, as he is always depicted. They think that in all the specimens ever found, they’d been sitting in oxygen-poor sediment for a long time after having drifted in the sea, and so the stronger, larger feathers of the wings and tail remained attached, while the finer, softer feathers of the head all fell off. I know from my own failed attempts at bird taxidermy that head and body feathers of dead birds fall off with the slightest provocation, so it’s reasonable to think Archaeopteryx once had a ‘do before he died.

You might notice that Archaeopteryx, along with a lot of other fossils, are found assuming a lot of unlikely contortions not found in life (particularly the backward-twisted neck) is because they’re frequently known to assume a death pose. The characteristic death pose of Archaeopteryx may be caused by floating around in water after death, which jumbles the animal around in an unnatural-looking way, or possible various tendons and ligaments dry out after death and draw the neck backward. Or possibly it’s due to death throes during the end of the animal’s life, causing hypertension and jerking of the neck.

But not this particular Archaeopteryx. He’s not dying, he’s very much alive. He’s just dancing, that’s all.

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