Dinosaurs: 10 Things You Should Know by Dr Dean Lomax.
Title: Dinosaurs: 10 Things You Should Know.
Author: Dr Dean Lomax.
Genre: Non-fiction, science, palaeontology.
Country: England, U.K.
Language: English.
Publication Date: 2021.
Summary: The author brings these prehistoric creatures to life in 10 bite-sized essays, written for people short on time but not curiosity. Making big ideas simple, he takes readers on a journey to uncover what makes a dinosaur a dinosaur, what dinosaurs ate, how they evolved, what caused them to go extinct, and more commonly wondered-about subjects and fun and unexpected facts of palaeontology.
My rating: 8/10
My review:
♥ There are four major chapters of time, known as eons, which comprise, from oldest to youngest, the Hadean, Archaean, Proterozoic and Phanerozoic. The first three are collectively referred to as the Precambrian and account for a staggering 88 per cent of geological time (the first 4 billion years), from the formation of the Earth up until the beginning of the Phanerozoic, 541 million years ago (or 18 November on the one-year calendar). We know that life originated during the Precambrian because the oldest fossil evidence of simple, single-celled microscopic organisms is recorded from rocks that are at least 3.5 billion years old. Fast-forward towards the end of the Precambrian, about 570 million years ago, and here is where the first evidence for complex multicellular life emerged of strange soft-bodied creatures that made their lives on the seabed. Even at this point in geologic time, the story of the dinosaurs remains more than 300 million years away.
The Phanerozoic is the eon that we are currently on, where life evolved and diversified on an enormous scale, and where fossils are abundant. Extending from 541 million years ago until the present day, the Phanerozoic Eon is divided into three eras, the Palaeozoic (meaning "ancient life"), Mesozoic (meaning "middle life") and Cenozoic (meaning "new life"). During the Palaeozoic, life exploded onto the scene, animals with hard shells appeared, the first vertebrates evolved and eventually took their steps on land, and the era ended with the greatest mass extinction event ever known, wiping out as much as 90 per cent of all life. Rising up from the ashes of the extinction, the Mesozoic witnessed the evolution of the dinosaurs, the emergence of mammals, and the first flowering plants. Finally, in the Cenozoic, the very same era of geologic time that we are in today, mammals dominated the world and things appeared more similar to how they are today.
♥ The Mesozoic Era is often labelled as "the age of dinosaurs", when these ruling reptiles ran the world. ..Yet, dinosaurs did not all live at one set time in the Mesozoic Era. In reality, the slice of dinosaur life is split into three periods - Triassic, Jurassic and Cretaceous - and extended a whopping 186 million years, from 252 to 66 million years ago.
Furthermore, although the Mesozoic might be considered "the age of dinosaurs" on the whole, the dinosaurs did not live for the entire length of the Mesozoic and were not always the "rulers" either. See, the very earliest known dinosaur fossils were found in the badlands of Ischigualasto (that's fun to say!) in Argentina, South America. They show that dinosaurs appeared during the latter part of the Triassic Period, from a little over 230 million years ago. That means the Earth's oldest known fossils (from 3.5 billion years ago) are fifteen times the age of the earliest dinosaurs.
♥ To begin to understand this, we have to go back to the 1600s and to a Danish scientist called Nicholas Steno, who came up with a very simple way of interpreting the relative age of rocks (and the fossils therein).
In 1669, Steno proposed what became known as the "principle of superposition", which is today one of the fundamental principles of geology. Simply put, in any undisturbed sequence of rocks deposited in layers (called strata), the oldest rocks are on the bottom and the youngest are on the top. An exceptional example can be observed in the breathtaking and richly diverse geology of the Grand Canyon, where the most ancient rocks are at the very bottom and each layer above gets progressively younger the closer you get to the top.
..Today, Steno's work acts as the starting point for understanding the relative age of rocks, but a new technique developed in the early twentieth century was a total game-changer. Called radiometric dating, this technique enabled geologists to provide solid estimates for the absolute age of certain rock by carefully studying the steady rate of decay of radioactive elements contained inside them. Using a combination of both methods, geologists and palaeontologists can determine the age of rocks and thus correctly identify which of the three periods and exactly where in those periods a dinosaur bone came from. This process is similar to, and is often confused with, the more familiar radiocarbon dating, or carbon-14 dating, where scientists study the decay of radioactive carbon-14 atoms to determine the age of an object. However, radiocarbon dating could never be used to date a multimillion-year-old dinosaur bone because radiocarbon decays rapidly (geologically speaking) and is only used for dating anything in the relatively recent ecological past, within the last ~50-60,000 years or so.
♥ Typically, any given species only lived for a couple of million years before it went extinct. In addition to this, those dinosaurs that did live together at the very same time may have lived on a different continent entirely.
♥ That is because the Jurassic Period began 201 million years ago, ended 145 million years ago, and is split into three epochs: the Early, Middle and Late Jurassic, which are divided into eleven different stages. Fossils of Stegosaurus are from the Late Jurassic, a chunk of time that extended from 163.5 to 145 million years ago. More specifically, the fossil remains come from the last two stages in the Late Jurassic, called the Kimmeridgian and Tithonian, which extended from 157 to 145 million years ago, although Stegosaurus fossils are known only from rocks that are approximately 153 to 148 million years old. (I know that might seem quite complicated but stay with me.)
Now, compared with Tyrannosaurus, which lived towards the very end of the Late Cretaceous, between 68 and 66 million years ago in a stage known as the Maastrichtian, by doing the maths you can see that Stegosaurus was already extinct 80 million years before Tyrannosaurus even walked on the Earth! Even more impressive, the oldest tyrannosaur fossils, aka grandparent rex, are more than 160 million years old. To really hit home the magnitude of geological time, Tyrannosaurus is closer to you and me in time than it was to Stegosaurus or even great-grandparent next. Let that sink in!
♥ The continents have not always been where they are today, and neither has the place where you are reading this book right now. In fact, this is just one piece of the overwhelming evidence that suggests all of the Earth's continents must have been joined together in a single, enormous land mass that eventually separated. And not just once. Rather, Earth's continents have been combined as a supercontinent on multiple occasions.
A supercontinent is defined as an enormous single continent made up of all, or nearly all, of the Earth's land. The first supercontinents formed more than a million years ago. They lasted for a few hundred million years before breaking apart and eventually coming back together again hundreds of millions of years later, where the process started over again. This is called the supercontinent cycle. Scientists have even predicted that the next supercontinent will form within the next 200-250 million years. However, we are interested in the most recent giant supercontinent, called Pangaea, which played a crucial role in helping to shape the story of the dinosaurs and give them a fighting chance at success.
..Stretching almost from pole to pole and shaped sort of like a giant thick "C", Pangaea's name which comes from Ancient Greek and means "Whole Earth", really was an enormous land mass. It was surrounded by a global super ocean named Panthalassa, which was the ancestor of today's Pacific Ocean. The supercontinent actually formed around 300 million years ago, about 70 million years before the dinosaurs appeared, and provided the necessary platform for global dinosaur domination - eventually.
♥ However, it is not that simple and no one species spread throughout all of Pangaea. Animals were restricted from doing so due to things like extreme weather or challenging terrain, although evidence does show that some species did travel far and wide across parts of the supercontinent.
♥ By the end of the Triassic Period, dinosaurs had already spread across various parts of Pangaea. When the mighty supercontinent began to break up during the Early Jurassic, about 200-180 million years ago, it eventually split into two enormous land masses, Laurasia to the north and Gondwana to the south. The land became separated by vast oceans and drifted further apart, where dinosaurs became isolated across the globe on different continents. This meant that dinosaurs in the north were subjected to different environments from those in the south, which led to the evolution of very different species that were better adapted to thrive in their new worlds. Over millions of years the continents continued to split, changing shape and position and eventually the continents as we know them today began to take shape.
♥ But beyond being able to say that dinosaur X was found on one continent and dinosaur Y was found on another, perhaps the more intriguing thing about discovering dinosaurs (or any other fossil) is revealing the story of their world contained within the rocks that entombed them.
Take a moment to imagine you are part of an epic fossil-hunting team trekking deep into the heart of Africa's Sahara Desert, when you come across fossils of animals that once lived in the sea, such as corals. You know that corals are found in the sea today but there is no sea around for miles and miles. What the fossil tells you is that the area in which you are standing was once underwater millions of years ago when the creature was alive. For a palaeontologist, having evidence of past environments and ecosystems like this provides a more complete picture of the animal and the world in which it lived, and, in some cases, these details can be even more important than the fossils themselves.
Using this same approach for dinosaur discoveries, one of the most fascinating and unexpected examples is that several dinosaurs have been found in Antarctica, contained inside rocks that have long since been buried underneath the ice. Better still, an abundance of different fossils has been found alongside them, including numerous species of plants. What these discoveries have revealed is that the ancient environment changed throughout geologic time and was dramatically different from the extreme icy conditions of Antarctica today - during the reign of the dinosaurs, at certain times, it was even a warm and lush rainforest.
Looking at another remarkable discovery, about 70 million years ago in the Cretaceous Period there once existed an island located in what is now Romania, called Hațeg Island. The island was cut off from the rest of the world and was ruled by dwarf dinosaurs - an example of insular dwarfism, where larger animals shrink over generations to adjust to a smaller environment that has less food and fewer predators.
♥ The first rule of dino club is that the word dinosaur is not a catchall name for anything that is extinct. ..Just because dinosaurs are reptiles does not mean that all prehistoric reptiles are dinosaurs.
♥ ..1824. This is a particularly significant year because it is when the very first dinosaur (which is actually from the Jurassic) was formally recognised by science and officially announced to the world.
..dinosaurs are a very recent "invention". Not even two centuries old. The first steam engines were running on rails before the dinosaurs received their name.
♥ The original trio of animals, along with additional fossils, were examined by leading comparative anatomist and palaeontologist, Sir Richard Owen, who was the founder of the Natural History Museum in London. Owen noticed similarities in the hip bones, particularly the presence of five fused vertebrae (called the sacrum), and how the limbs were held under the body. He realised that they belonged to a unique group of animals for which he coined the word "Dinosauria" in 1842, taken from the Greek words deinos, meaning "terrible" or "fearfully great", and sauros, meaning "lizard".
♥ To be a dinosaur you must first be a diapsid, aka a reptile with two holes (openings) on either side of the skull, behind the eye socket. Within the diapsids, dinosaurs belong to a group called archosaurs, or "ruling reptiles", which today include the crocodylians and birds. All archosaurs, including the dinosaurs, then have an additional hole in the skull situated between the eye socket and the nostril called the antorbital fenestra.
Then turn your attention to the hips. Just as Owen had originally highlighted, the hips play a critical role in the modern dinosaur definition. Notably, the presence of a distinct hole in the hip socket, formed between the three hip bones, is especially important and marks the place where the "ball" or head of the thighbone (femur) locked into position. This allowed dinosaurs to adopt an upright stance like mammals, with their limbs held directly beneath their body, unlike crocodiles and lizards whose limbs are sprawled out to the side. This is the primary feature that helps to set dinosaurs apart from other reptiles.
Taking a step back from the bones, based on the evidence we have of countless dinosaur eggs, palaeontologists are confident that egg-laying was ubiquitous among dinosaurs. Furthermore, although some species definitely spent time in the water feeding or swimming, dinosaurs were fully adapted to a life on land and no dinosaur lived exclusively in the watery realms.
♥ Traditionally, based on the shape and position of the hips, the dinosaurs are divided into two specific branches, called the Saurischia and the Ornithischia. The saurischian dinosaurs have "lizard-like hips" and include dinosaur hotshots like Tyrannosaurus and Diplodocus. Whereas the ornithischians have "bird-like hips" and include such dinosaur celebs as Stegosaurus, Triceratops and Iguanadon. Each of the dinosaurs is then placed into a distinct group or family winthin either the Saurischia or Ornithischia based on more specific features.
♥ Although palaeontologists do not always concur on the finer points, one thing that we all agree upon is what does not make a dinosaur. By some distance, there are two main groups of animals that are frequently labelled as dinosaurs but are not. First up, the "flying dinosaurs", aka the pterosaurs or, if you must, pterodactyls. (Pterodactyl is not quite correct because this name refers to a particular pterosaur called Pterodactylus, the very first pterosaur to be discovered.) Pterosaurs were a wondrous group of flying reptiles that lived during the Mesozoic Era. Long before birds or bats, they were the first vertebrate animals to evolve flight and had wings that stretched from the tips of their fingers to their ankles. Like the dinosaurs, pterosaurs are also archosaurs, but differ greatly in their anatomy and are on another branch of the archosaur tree of life. You can think of them as dinosaur cousins.
♥ When you tell people that Velociraptor was actually the size of a turkey but with a long tail, many look at you with a puzzled expression. You can see they are questioning your palaeontology credentials: "Is this person really a palaeontologist? Next they'll be telling me that Velociraptor had feathers..." The issue is that, at least in pop culture, Velociraptor is visualised as being as tall as an adult, although the science very clearly shows otherwise. You see, this idea of an oversized Velociraptor has its roots in Jurassic Park, yet these big-screen "raptors" are not really Velociraptor at all. Instead, they were based on a close cousin, called Deinonychus.
♥ ..Deinonychus is known only from the USA and the first discovery was made in Montana.
♥ While Velociraptor is in the spotlight, I feel it is my duty as a palaeontologist to point out that it did not have the dexterity to open doors, let alone reach the handles. Unlike in the movie, it did not have the infamous "bunny hands," where the palms of its hands face the ground. Rather, the palms faced each other (think about when you clap) and were perfectly positioned for slashing at prey with its three curved claws.
♥ One of the biggest and most common misconceptions about dinosaurs is that they were all large. ..The reality, however, is that dinosaurs varied immensely in size and many of them were tiny, at around the size of a squirrel.
♥ You know the types, those herbivorous behemoths with tremendously long necks and long tails and which include dino-stars like Brontosaurus and Brachiosaurus. It is mind-boggling to imagine, but reliable estimates have shown that some sauropods reached upwards of 30 metres (98 feet) in length and about 70 tonnes in weight - the equivalent average weight of twelve fully grown African elephants. Sauropods were true titans of the past and include the largest animals ever to walk on Earth. By contrast, today the largest terrestrial animals are elephants (for weight) and giraffes (for height).
As for the big meat-eaters, Tyrannosaurus is still one of the largest at about 12-13 metres (39-43 feet) long and 8 tonnes, although the bizarre sail-backed Spinosaurus currently take the top spot for length, being a couple of metres longer still. By comparison, it is quite laughable to consider that the largest terrestrial carnivore today is a polar bear. Yes, a polar bear. Think about the size of a Tyrannosaurus compared with a polar bear, which typically weighs half a tonne and measures about 2.5 metres (8 feet) long.
♥ ..Compsognathus, hailed for decades as the smallest dinosaur in the world (just go and check some of your older dinosaur books) although there are many contenders today for the title of world's smallest extinct dinosaur.
Like Compsognathus, virtually all of these pint-sized dinosaurs are small meat-eating theropods, the same group of dinosaurs that includes such mega-predators as Tyrannosaurus and Megalosaurus. Given that many are roughly the same length, around the 30-50 centimetre (12-20 inch) mark, palaeontologists find it difficult to say for certain which was the king of the tiny terrors, although Epidexipteryx from China comes close. Weighing in at about 160 grams (6 ounces) and measuring approximately 25-30 centimetres (excluding its tail feathers), this Jurassic minisaur named in 2008 was about the size of a pigeon.
♥ Perhaps the major discovery that really announced China on the world stage for palaeontology came in 1996 with the discovery of the world's first feathered dinosaur.
..Named Sinosauropteryx, the fossils of this Cretaceous-aged cousin of Compsognathus were extraordinarily well preserved, containing a plumage of primitive feathers (or "dino-fuzz") and soft tissues. It would eventually go on to become the first dinosaur to have its true colour scientifically established. Multiple studies of tiny colour pigments (called melanosomes) locked inside the feathers showed that it was orangey-red and white, with a striped tail and raccoon-like "bandit mask" on its face. The colouration also showed that it was darker on top and lighter underneath, representing a form of camouflage known as countershading.
♥ We now know, thanks to fossils found in Mongolia, that Velociraptor did have feathers.
♥ So, how do we begin to understand what dinosaurs ate, how they ate, and which species dined on which? The first port of call is to look at the structure of a dinosaur's teeth (if it has teeth) and jaws, which can be assessed alongside those of living animals, and thus provide a basic comparison. Just look at the sharp, thick, heavily serrated steak-knife-like teeth of Tyrannosaurus, for example. These are clearly the teeth of a carnivore, perfectly adapted to tear through flesh and crunch through bone. Compare this tooth type with the tall and thin, forward-pointing peg-like teeth in Diplodocus, which are ideally suited for stripping leaves from trees.
♥ Studies based on the skull of Tyrannosaurus found that it had a bone-shattering bite of more than 60,000 newtons, around 6.5 tonnes of force, making it the most powerful bite known for any terrestrial animal, living or extinct. It is about four times more powerful than the bite of a saltwater crocodile, which has the strongest bite force of any living animal. These findings, coupled with the massive teeth and big jaw and neck muscles, provide further evidence that Tyrannosaurus had the ability to chomp through solid bone.
♥ One sure-fire way of knowing what any animal has been eating is to look a what comes out the other end. Of course, I'm talking about poop, fossil poop. Correctly termed coprolites, these are fairly common as fossils and offer a direct view of ancient diets. Just as it is difficult determining who left their bite marks on bones, there are similar challenges when identifying who dung it. However, one bonus is that coprolites are often found to contain plant or animal remains and this provides a starting point. By looking at the size and shape of a given coprolite and comparing it with the size and type of animal found in the same rocks as the ancient poop, it is possible to reliably link one with the other.
The most famous example by far was an enormous, 44 centimetre (17 inch) long, chunky coprolite found in 66-million-year-old rocks in Saskatchewan, Canada, that contained crunched-up bones. By studying the animals found in the same rock formation as the coprolite, through a process of elimination researchers determined that the only predator both big enough and capable enough of producing such a big scat was a Tyrannosaurus.
♥ Among the most famous of dinosaurs to be found with its last meal was the spinosaur called Baryonyx (my favourite dinosaur), which was discovered inside a British quarry in 1983. Contained inside its gut were the bone of a juvenile Iguanodon-like dinosaur and, more surprisingly, fish scales. This was the world's first confirmed fish-eating dinosaur.
Dinosaurs did not have it all their own way, as demonstrated by a marvellous fossil unearthed in China and reported in 2005. When we think of mammals from the age of dinosaurs, it is easy to imagine them as living in their shadow, scurrying underfoot and staying hidden from view, frightened that they will be next on the dinosaur menu, but one badger-sized Cretaceous mammal was found with a baby dinosaur inside its gut. Closer inspection of the dino dinner revealed that pint-sized dismembered skeleton belonged to a small, bipedal cousin of Triceratops called Psittacosaurus. The discovery of this dinosaur-eating mammal was another world first.
♥ Found in 1971 during an expedition to the Gobi Desert in southern Mongolia, this duelling dinosaur fossil captures Velociraptor and Protoceratops, a boar-sized cousin of Triceratops, in remarkable detail. As preserved, the Velociraptor is lying on the floor on its right side and with its right arm, just below the elbow, tightly clamped in the strong beak of Protoceratops, which is crouched above the Velociraptor. The famous killing claw on the left foot of Velociraptor is held high in the air and in the position of the Protoceratops' neck, as if delivering a fatal blow to the throat.
Palaeontologists have pondered how exactly the exceptional preservation of this specific moment in time came to be. The generally accepted view is that the two were battling it out when a sand dune collapsed above the pair, burying them for all eternity. It is astonishing to think that this epic battle to the death is still to this day locked in time, captured just as they were 75 million years ago.
♥ In actuality, the closest palaeontologists have come to finding any sort of undeniable Jurassic sex scene is an incredibly rare fossil of a pair of mating froghopper insects that were caught off guard and rapidly buried together some 165 million years ago. These froghoppers were found in Jurassic rocks in northeastern China near where many dinosaurs have been discovered, so although we do not have any dinosaurs doing the deed, they were likely to have been somewhere in the vicinity as this pair of froghoppers was caught in the act.
♥ In the animal kingdom today, physical structures such as these, along with other characteristics like size and colouration, can help to distinguish males from females and scientists call this sexual dimorphism. The presence or absence of antlers in deer is one of the most famous examples, with antlers being present primarily in the males of practically all deer species. Beside the obvious, this is one quick way of knowing whether you are looking at a male or a female; the males also tend to be significantly larger than the females.
♥ With that being said, the major finding of colour trapped inside fossil feathers may end up being the shining light of evidence that palaeontologists have long been searching for. Colour plays a very significant role in sexual display today - simply consider the luxurious plumage found in birds, like peacocks for example, and the major differences observed between some sexes. Often it is the males that have more extravagant colours, although occasionally it can be the females. So, even though palaeontologists have yet to find clear-cut evidence of colour differences between a male and female of the same extinct species, the fact that we have dinosaurs preserved with an array of colours suggests that colour payed an important role in wooing the opposite sex.
♥ Sadly, as amazing as the fossil record is, even with soft parts occasionally being preserved, we have yet to find a Tyrannosaurus penis in all its glory. Sorry to disappoint. Though, did Tyrannosaurus even have a penis at all?
To answer that question, palaeontologists looked at the closest living relatives of dinosaurs - the birds and the crocodylians - and inferred that the same features(s) present in both groups would have also existed in their extinct relatives. In this case, both sexes of all living birds and crocodylians have what is known as a cloaca, which suggests that dinosaurs also had a cloaca as well. It is a single opening between the legs used for reproduction and excretion.
The penis remains tucked up inside the male's cloaca and protrudes outwards during sex where it is inserted into the female's cloaca to transport sperm. Although all male crocodylians have a penis, most male birds lack one and exchange sperm through what is known as a "cloacal kiss" (the touching of the male and female cloacae); but some are very well-endowed, like the Argentine lake duck, whose penis can be more than 40 centimetres (16 inches) long!
In reality, we do not need to guess whether dinosaurs had a cloaca because one has been found. Really. It belongs to a Psittacosaurus, that small, bipedal dinosaur related to Triceratops which was mentioned in the previous chapter. The fossil was found in China and represents one of those amazing specimens that is so extraordinarily well-preserved that its skin and colour are present. Tasked with bringing this fabulous fossil to life, along with its colourful cloaca, famed palaeoartist Bob Nicholls built a 3D model of it, which has been hailed as the "most accurate depiction of a dinosaur ever created."
♥ I sort of lied when I said the closest thing to fossilised dinosaur sex was two mating insects, because a phenomenal discovery of a "dancing dinosaur sex show" was revealed in 2016.
While studying large theropod trackways exposed in Cretaceous rocks at multiple sites in Colorado, USA, palaeontologists identified many distinctly shaped scrape marks. These markings were found to match the same scrapings made by many modern ground-nesting birds which display a mating behaviour known as lekking. Males congregate together around breeding season to compete for the attention of onlooking females who judge them on their nest-scraping abilities, to see who can make the best nests and thus be worthy winners in the bid to entice a female. This discovery presents direct evidence that theropod dinosaurs also engaged in this type of sexual behaviour.
♥ We know that dinosaurs reproduced by laying eggs, rather than bearing live young like us mammals, because we have discovered thousands upon thousands of them.
♥ Another approach for sexing a dinosaur is to look inside the bones for evidence of medullary bone, a specific type of temporary bone tissue found in female birds that is strictly associated with reproductive activity and used to make eggshells. In 2005, American palaeontologist Dr Mary Schweitzer and her team stunned the dino community when they reported evidence of medullary bone in a Tyrannosaurus, suggesting that this rex was not only female but that she had died just before, during or after laying her eggs. Later studies also found evidence for medullary bone in other dinosaurs. However, this method has received its share of criticisms and is not yet universally accepted. Besides discovering a dinosaur with eggs inside, it seems that sexing a dinosaur or learning more about their private sex lives will mostly remain an enigmatic subject, at least for the foreseeable future. Still, I hold out hope that one day we will find two dinosaurs preserved in the act of mating.
♥ Dinosaur tracks are fairly common trace fossils that are found around the globe. They were made by living, active animals rather than representing the remains of a dead individual and offer a direct view into the world of a dinosaur. Working with trackways, it is possible to determine how fast the trackmaker was moving, how tall it was, its walking gait, what type of dinosaur left the track behind and much more. The drawback is that no dinosaur has been found dead in its tracks (yet), so palaeontologists deduce which type of dinosaur created the track by comparing its size, shape and structure with dinosaur feet. This is standard dino tracking 101.
Evidence for all sorts of dinosaurs, from small to large and carnivorous to herbivorous, has been captured in the midst of some form of apparently social situation. Th mot famous are those tracks found in exactly the same layer of rocks, suggesting that a large group or herd of dinosaurs might have been travelling together. Even "mega-track sites" have been found consisting of hundreds or ten thousands of dinosaur tracks left behind by numerous individuals, typically produced by herbivorous dinosaurs like sauropods.
Some sauropod multi-track sites have shown that groups were either mixed age, comprising older and younger individuals, or age-segregated, implying that juveniles or young adults may have lived in exclusive groups. In mixed-age groups, there is some indication that the smaller juveniles may have been kept in the centre of a wandering herd, while the larger individuals were on the outside. This could suggest that the adults were keeping a watchful and protective eye on the youngsters. Similarly, theropod footprints made by both large and much smaller individuals have been discovered together, hinting at possible parental care. Some other impressive theropod tracks suggest that even tyrannosaurs and Velociraptor-like dinosaurs may have grouped together.
♥ To be confident what we are dealing with a distinct family or group, palaeontologists look out for several things. Firstly, the skeletons must all be in exactly the same layers of rock. Secondly, they need to have perished due to the same circumstances over a relatively short time (minutes to days) and bear similar styles of preservation (for example, have a similar level of completeness). And, lastly, they should usually belong to the same species and be associated (e.g. by the overlapping of bones from different individuals). A fine example matching this description is an intriguing mini mass death of the dinosaur Sinornithomimus, a member of the so-called ostrich dinosaur family of theropods. A group of over twenty was collected from Inner Mongolia and was revealed to consist entirely of immature individuals, with no hatchlings or adults present, thus representing a distinct group of teen dinosaurs that was hanging out together. Unfortunately for this herd of youngsters, they became trapped inside a drying lake filled with sticky mud that led to their downfall.
One of the world's largest and most famous dino bonebeds is the "Hilda mega-bonebed" in southern Alberta, Canada, which is made up of at least fourteen associated assemblages - hence the title of "mega-bonebed." Therein, the rhino-sized, horned ceratopsian Centrosaurus wad found in an enormous mass graveyard comprising thousands of mixed-aged individuals that drowned together during a catastrophic flooding event. The mass association presents strong evidence that this dinosaur lived in huge herds and cared for its young.
♥ Many modern reptiles abandon their eggs after laying them, leaving the hatchlings to fend for themselves. Just think about turtles, for instance, who lay their eggs ashore and then return to the sea. Although we do not know all the ins and outs of the dinosaur world, if you ever speak to a palaeontologist and ask about dinosaur nests and parental care then one dinosaur will usually take the limelight. The herbivorous "duck-billed" Maiasaura, whose name translates as "good mother lizard" - and for good reason.
In 1977, a major discovery of a Maiasaura nesting ground containing eggs, embryos, hatchlings and young juveniles was uncovered at a site in Montana, USA, which became known as "Egg Mountain". Some of the hatchlings showed evidence of wear on their tiny teeth, indicating that they had been feeding. This suggests that the adults must have brought food back to the nests for them; incidentally, plant matter was also found around some of the nests. The discovery provided the first evidence that at least some dinosaurs gathered together and nested in colonies, perhaps at distinct times in the year, where they raised their young for an extended period. Furthermore, additional nests were found buried in rock layers one above the other, indicating that Maiasaura used the same nesting grounds over and over again. Does this mean that all dinosaurs were good parents? No, not at all. But it does mean that some definitely were.
♥ Among the most famous are those rare theropod dinosaurs from China and Mongolia, found lying atop nests of eggs. Originally, when the first of these parrot-beaked theropods was found it was thought to have been caught red-handed about to dine on the egg of another dinosaur; it was even given the name Oviraptor, meaning "egg thief". However, years after the discovery, the eggs were found to belong to the dinosaur itself, which was brooding them, rather like a bird. This was a seriously dedicated parent that sacrificed its life to guard it would-be offspring, shielding them from a major sandstorm that eventually buried the adult and the eggs. Telling a similar story, although a stage further, is the Psittacosaurus skeleton - also from China - that was found buried with at least twenty perfectly preserved juveniles by its side. The larger individual was initially thought to have been an adult, but later studies showed that it had not yet reached sexual maturity and could not have been the parent of these minisaurs. Instead, this individual appears to have been acting as a "babysitter", left to look after the group while the adults were away.
Perhaps saving the best till last, there was also the surprising discovery of three dinosaur skeletons inside a fossilised burrow in Montana, USA. The dinosaurs all belonged to a Labrador-sized bipedal herbivore named Oryctodromeus. Curiously, one of the individuals was an adult and the other two were about half the adult's size and represented older juveniles. Not only does this discovery suggest that the juveniles stayed with their parent, thus indicating an extended period of parental care, but that Oryctodromeus excavated and lived inside burrows where it cared for its offspring, something that we would never have known were it not for this spectacular find.
♥ The modern concept of extinction has its roots in the late 1790s and the work of a French naturalist widely recognised as the "founding father of palaeontology", Georges Cuvier. Through comparing fossils with living animals, Cuvier came to realise that many fossil animals could not easily be linked to, nor did they belong to, any living species. This played a fundamental role in establishing the idea of extinction. By the simplest definition, if a species dies out, it becomes extinct and is gone forever. There is no turning back the lock on extinction.
♥ Through studying the fossil record, it becomes clear that extinction is a natural process, and scientists estimate that 99.9 per cent of all species that have ever existed are now extinct. Just imagine the sheer volume of species that vanished without leaving a tiny trace or subtle hint. The fossil record as we know it is nothing more than a snapshot of life through the ages.
♥ The most catastrophic extinctions are those that scientists term a mass extinction or biotic crisis. This is a period of rapid and global extinction of very many species over a relatively short timeframe which may take hundreds or thousands of years to play out (a blink of an eye in the geological record). In Earth's long history, there have been five big global mass extinction events, the death of the dinosaurs being the most famous and most recent. However, before we dive further into the dino-destroying asteroid, it is important to know that this is not the most catastrophic event. That title goes to a devastating mass extinction that occurred 252 million years ago before the dinosaurs were even a thing. Scientists call this the end-Permian mass extinction event or, more poignantly, "The Great Dying", where life almost came to a halt. As many as 90 per cent of all species were annihilated, leaving room for new forms of life to emerge, including (eventually) the dinosaurs.
♥ Estimates suggest that a staggering 1 million animal and planet species are at risk of extinction because of human activity. Today, we are the asteroid.
♥ Over the years, more than a hundred theories have been put forward to explain the death of the dinosaurs. A common view during the late 1800s and early 1900s was that their time had just simply run its course. Later suggestions were downright bizarre. According to some, the dinosaurs went extinct due to a lack of sex drive, mass blindness from cataracts, general stupidity, constipation, disease-carrying biting insects, or because mammals ate all of their eggs. More serious theories considered that climate change or intense volcanism might be to blame. None of these held up to scientific scrutiny. Any serious hypothesis needed to be testable and justifiably plausible. Enter Alvarez and the crater of doom.
In 1980, Nobel Prize-wining physicist Professor Luis Alvarez and his team, including his geologist son Walter, proposed that the dinosaurs were shot into extinction by a giant asteroid. As far-fetched and controversial as it sounded at the time, the team was on to something. (FYI, Earth is constantly bombarded by space rocks, though practically all of them are tiny and most break up before they enter our atmosphere.) Alvarez's team had discovered rich levels of a rare metal called iridium in a thin layer of rock that marks the end of the Cretaceous and the beginning of the Palaeogene, called the Cretaceous-Palaeogene (or K-Pg) boundary. Iridium is rare on Earth but is very abundant in space rocks. They predicted that many other K-Pg sites around the world would also show high levels of iridium, hinting at a global cataclysmic event. They were correct.
It was a decade before they had their "smoking gun" - the discovery of a colossal crater whose age coincides precisely with the extinction of the dinosaurs. Stretching approximately 177 kilometres (110 miles) across, the Chicxulub crater, as it came to be known, was found on Mexico's Yucatán Peninsula. This was the impact zone of Alvarez's asteroid, an asteroid thought to have been somewhere in the region of 10 to 16 kilometres (6 to 10 miles) wide - wider than Mount Everest is tall. Sadly, Luis died before Chicxulub was recognised as the dinosaur-destroying impact zone, but he and his team revolutionised our understanding of the dinosaur extinction. Today, palaeontologists and geologists (mostly) agree that the asteroid dealt the dinosaur death blow. This major event known as the Cretaceous-Palaeogene (K-Pg) extinction, where as much as 75 per cent of all life was lost.
..Among the very last of the dinosaurs were the likes of Tyrannosaurus and Triceratops, who genuinely witnessed the sky fall on top of them.
One fateful day, on what may have been a lazy Sunday afternoon, 66 million years ago, disaster struck on the most immeasurably violent scale. The dinosaur-destroying asteroid crashed into the Earth at about 64,000 kilometres per hour (40,000 miles per hour), generating more than a billion times more energy than the most powerful nuclear bomb ever detonated. Any animal in the immediate vicinity was obliterated within seconds, transforming the once-rich dinosaur paradise into a silent dead world. Mega-tsunamis wreaked havoc on the seafloor and coastlines, earthquakes shattered the landscape, scaling hot debris was thrown through the air, and wildfires spread far and wife. Any dinosaur unlucky enough not to have been destroyed instantly had a horrible future ahead.
The full force of the impact immediately began spreading across the globe. The planet was on fire. An enormous sun-blocking dust cloud eventually enveloped the Earth, causing a long, dark period of global cooling (an "impact winter"). Plants needed the sunlight, plant-eaters needed the plants and meat-eaters needed the plant-eaters. The food chain collapsed. Any large land animals were toast. A bigger body means a bigger appetite and, if natural food sources are no longer available, then you are in trouble. Any animals that could not adapt quickly enough to the changing apocalyptic world met their doom.
♥ Having appeared a little over 230 million years ago, they went on to rule the world for an incredible 165 million years, diversifying into an enormous array of species, big and small, and reaching all corners of the globe, only to be wiped out by a huge rock from outer space. It seems almost comical that their mighty reign of supremacy would be stopped by an extra-terrestrial event. Still, dinosaurs were around for far longer than they have been gone.
♥ The mass extinction paved the way for one group of dinosaurs to spread their wings and take over the world in a whole new way: the birds. Birds are dinosaurs. Say it with me: birds are dinosaurs.
Palaeontologists use the term avian dinosaurs to refer to birds and non-avian dinosaurs for the rest. Up until this point in the book, I have used the word "dinosaur" to refer to the non-avian dinosaurs. However, when we hear or use the word dinosaur we should really also think about birds and not consider them as something distinct. Think of it like this: birds are dinosaurs but not all dinosaurs are birds, just as we are primates but not all primates are humans.
♥ The idea that birds are closely related to dinosaurs stems back to Charles Darwin and his revolutionary theory of evolution. When Darwin published his monumental book On the Origin of Species in 1859, he proposed that animals evolve over time through a process called natural selection, where those animals with features better adapted to their environment have a higher chance of surviving and reproducing, thus passing on their genes into the next generation. It's worth noting that a contemporary naturalist called Alfred Russel Wallace also came up with the idea at the same time as Darwin, although the latter is more often credited for proposing the theory.
While the significance of the theory of evolution cannot be overstated - as evolutionary biologist Theodosius Dobzhansky famously put it in 1973, "Nothing in biology makes sense except in the light of evolution" - it was not Darwin or Wallace who linked birds and dinosaurs. Instead it was one of Darwin's staunch supporters and fellow scientists, Thomas Henry Huxley. In the same year that Darwin had published Origin, the little chicken-sized dinosaur Compsognathus (who we met briefly in chapter 4) was unearthed in a Jurassic limestone quarry in southern Germany. As if timed to perfection, just two years later, in 1861, the first skeleton of the infamous "first bird", Archaeopteryx, was discovered in one of the same limestone quarries. Just like a bird, Archaeopteryx had feathers and wings, but it also had a long, bony tail and sharp claws on its hands - a sort of half-bird half-reptile. Studying the skeletons of Compsognathus and Archaeopteryx, along with other fossil (and living) reptiles and birds, Huxley realised that their anatomy was so similar that they just somehow be related. (This Archaeopteryx was missing a complete head, but Huxley predicted that Archaeopteryx would have jaws with teeth, which later discoveries would prove correct.)
..Fast-forward a century to the 1960s and 1970s and we move our attention to US palaeontologist Professor John Ostrom and his discovery of the bird-like dinosaur, Deinonychus. Ostrom revived Huxley's concept that birds are connected to dinosaurs by showing that the skeleton of Deinonychus matched that of Archaeopteryx in its general anatomy. He showed that birds were members of the same generic group of dinosaurs called theropods and must have evolved from a Deinonychus-like ancestor. This sensation led to a renaissance in dinosaur studies. Deinonychus was imagined as a fast-moving, agile and intelligent animal, a far cry from the earlier view of dinosaurs as monstrous lizard-like animals that were slow and stupid. Ostrom's research transformed the way that scientists and the public thought about dinosaurs.
♥ See, the way that scientists define animals and plants today has changed dramatically. Rather than focusing solely on a combination of physical features that untie a group (or "clade") of animals, like those that are used to group dinosaurs together, scientists also look at their evolutionary relationships (or "phylogeny") to understand their ancestry. This approach focuses on the bigger picture of a dinosaur family tree, working out how species are related to each other and which branch of the tree they sit on.
This basically means that, in order for an animal to qualify as a dinosaur on the family tree of life, it must be descended from a common ancestor, and thus each dinosaur derived from that common ancestor will share a unique set of features. Consequently, because birds are descended from dinosaurs, they must be classified as a subgroup of dinosaurs. Not only are birds dinosaurs on the basis of their anatomy, but also through their phylogeny. Looking at it like this, birds are actually a group of reptiles and their closest living relatives are the crocodylians.
Today, palaeontologists classify birds as theropod dinosaurs within the group known as Maniraptora (maniraptorans). More specifically, the birds belong to a subgroup called Paraves, the same wider group that includes dinosaurs like Deinonychus and Velociraptor, which are among the birds' very closest relatives. This means that dinosaurs like Velociraptor are more closely related to a pigeon than to Triceratops despite the extensive separation in time.
♥ Feathers were always thought to be unique to birds, given that they are the only living animals to have them. The discovery of many non-avian dinosaurs with feathers provided conclusive evidence that this was not the case. Even dinosaurs far removed from birds on the family tree - those not closely related - have been found with feathery filaments and some palaeontologists have gone so far as to suggest that most, if not all, non-avian dinosaur were likely to have had some sort of dino-fuzz. Interestingly, the current largest known dinosaur with direct evidence of feathers is the ~9 metre (30-feet) long Yutyrannus from China, which has feathers ranging from 15 to 20 centimetres (6 to 8 inches) long. This is a member of the tyrannosaur family and was discovered with a fluffy coating of feathers which suggests that even Tyrannosaurus was likely to have had some sort of feathery covering. Remarkably, dinosaur feathers have also been found trapped inside 99-million-year-old amber, including a dinosaur tail covered with feathers.
Birds inherited feathers from their non-avian dinosaur ancestors. Recent thinking suggests feathers probably evolved in non-avian dinosaurs for insulation and/or display, with flight coming along later. Speaking of display, as discussed in chapter 6, the discovery of fossil feathers with colour pigments indicates that dinosaurs could see in colour, which suggests colour must have played a key role in display. One crow-sized Cretaceous bird from China called Confuciusornis is known from thousands of specimens with preserved feathers and studies of their feathery fossils have found that two different "types" of Confuciusornis exist, one group with long, showy tail feathers and one without them. The different has been interpreted as strong evidence for sexual dimorphism, with the long tail feather group probably representing the males; thus, these feathers were likely to have been used for display.
♥ The earliest known birds appeared around 165-150 million years ago, in the Jurassic Period. While non-avian dinosaurs reigned supreme during the Jurassic and Cretaceous periods, the birds were just another group of feathered theropods doing their own thing. After the mass extinction that wiped out the non-avian dinosaurs, along with flying animals like pterosaurs, there followed an explosion in bird diversity including the appearance of many modern groups of birds. Today, birds are a richly diverse group of theropods, from the tiny bee hummingbird (the world's smallest known dinosaur, living or extinct) to the largest living dinosaur, the ostrich. Just like their non-avian forebears, they have conquered every continent, are found everywhere on the planet, and have evolved into a wide variety of species capable of surviving in even the harshest of environments, from bone-dry deserts to freezing ice caps and tropical forests.
A sparrow, emu, penguin and pelican are just as much of a dinosaur as a Stegosaurus, Triceratops, Tyrannosaurus or Brachiosaurus. Dinosaurs are the most successful group of land vertebrates alive today. The next time you see a bird, remember that you are looking at a living dinosaur whose origins extend back to the Jurassic. With more than 10,000 living bird species, the reign of the dinosaurs is far from over.
♥ In theory, all the dinosaurs that could ever have been preserved as fossils are already fossilised. This means that there is a finite number of dinosaur fossils that could be found. Long before humans began studying them, countless dinosaur fossils had already been lost and destroyed by natural princesses over millions of years. Couple this with all the talk of new dinosaur discoveries here or new species there and it might seem like we could one day have dug them all up. The reality is that we will never run out of dinosaur fossils, and we will never find them all either.
We are currently living in a golden age of dinosaur discovery. On average a mew species of dinosaur is discovered every other week. Every other week! Up to this point, in almost 200 years of study, palaeontologists have identified around 1,500 different species of dinosaur. However, sometimes new and more complete finds can help to reveal that previously named dinosaurs are actually the same as newly discovered ones and not different species at all. They might be juveniles and adults of the same animal, foe example. Therefore, the total number of known dinosaur species fluctuates depending on the discovery of more dinosaurs, new research, and new information.
♥ With new dinosaurs emerging thick and fast, we must remember that fossilisation is an incredibly rare event. For a dinosaur to be preserved as a fossil, it must have died in very specific conditions, that suited its potential preservation, plus be in a situation that meant no other dinosaur could eat it, or the environment destroy it. We cannot, therefore, expect that individuals of every single dinosaur species that ever lived could have become fossilised. The same can be said for all the animals alive on the planet today. There is zero chance that every single species will be preserved in the fossil record because not all living species exist in environments that are conducive to fossilisation. It is therefore important to consider that the fossil record is biased in that dinosaurs found as fossils were only preserved because they were in the right place at the right time (well, actually, many were in the wrong place at the wrong time and died as a result, but you get the point). Plus, we humans also have to be looking in the right places and in the correct types of rocks to even stand a chance of finding a dinosaur.
..Even Charles Darwin had this view of the ancient world, stating: "I look at the natural geological record as a history of the world imperfectly kept and written in a changing dialect."
Just think about the reign of the dinosaur from ~230 to 66 million years ago and the ~1,500 different species identified. Now compare that figure with the more than 10,000 living species of dinosaurs (birds) today and you will quickly realise that there must have been an unimaginable number of dinosaur species spread over many different intervals of time during their roughly 165-million-year reign. This makes you wonder what other weird, wonderful, and bizarre dinos were once here, but whose stories will never be told. It's quite sad to think about these ancient animals that will be forever lost in time.
♥ Another approach to moving the science forwards is to go backwards by looking at "de-extinction", the process of (apparently) bringing extinct species back to life. As far-fetched and Jurassic Park-like as this may sound, some scientists have made enormous strides. Firstly, I must point out that finding DNA in a multimillion-year-old dinosaur fossils, including in amber, is to this day impossible because DNA breaks down swiftly over time. Even if we did find dino DNA or blood cells (which have been identified), they would still have been altered and damaged through the process of fossilisation and thus could not be used to recreate a dinosaur. However, some groups of scientists have taken an alternative approach by "reverse engineering" chicken embryos, tweaking the DNA so that their beaks become modified reptile-like dino jaws. While others have looked at growing long tails on chicken embryos as well. This process would essentially mean creating an extinct dinosaur lookalike from a chicken. In case you were wondering, none of these "chickenosaurus" have ever hatched. At least, that's what they tell us.
♥ Palaeontology has come a tremendously long way from the early dino discovery days of the nineteenth century. Even within the last thirty years, the science has progressed so radically with new discoveries that our general perception has changed from "dinosaurs are extinct" to "birds are related to dinosaurs" to "birds might be the descendants of dinosaurs" and finally that "birds are dinosaurs", which marks a major revelation in the field. At this pace who knows what we may uncover about the incredible dinosaur world in the next twenty, fifty or hundred years? Realising that we will never have all the pieces of that gigantic dinosaur puzzle is what continues to spark our childlike fascination and natural curiosity with everything dinosaur. There is one thing for sure, our love of dinosaurs will never go extinct.