While there are several controversial explanations, the leading theory for the actual \u2018kill mechanism\u2019 is that a 10km-wide asteroid smashed into Earth, leaving a crater 180km across at Chicxulub in Mexico. A thermal pulse from heated debris spread across the globe, while the force of collision \u2013\u00a0equivalent to millions of atomic bombs \u2013 created shockwaves that triggered earthquakes, then tsunamis and wildfires.<\/p>\n
The impact launched a vast dust cloud into the atmosphere, which coincided with gas released from volcanic activity and blocked-out the sun for years. That led to a nuclear winter and limited photosynthesis, which ultimately powers most life, and that in turn caused a collapse of our planet\u2019s ecosystems.<\/p>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/04\/GettyImages-1032823218-b1874b4.jpg?quality=90&resize=620%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Did all dinosaurs go extinct?<\/h2>\n
Not quite \u2013 because birds are living dinosaurs! To distinguish birds \u2013 the class Aves \u2013 from prehistoric reptiles, extinct groups are known as \u2018non-avian dinosaurs\u2019. They were the dominant terrestrial vertebrates of the Mesozoic era (252-66 MYA) throughout the Triassic, Jurassic and Cretaceous periods.<\/p>\n
Because the fifth extinction occurred at the boundary between the Cretaceous (K) and subsequent Palaeogene (Pg) period, it\u2019s also called the end-Cretaceous or K-Pg event. Other reptiles commonly mistaken for dinosaurs went extinct during the event, including the winged pterosaurs and aquatic plesiosaurs and mosasaurs.<\/p>\n How to watch Dinosaurs: The Final Day with David Attenborough<\/em><\/a><\/p>\n Five British dinosaurs you\u2019ve (probably) never heard of<\/a><\/p>\n How to watch Prehistoric Planet<\/em><\/a><\/p>\n <\/p><\/div> The word \u2018dinosaur\u2019 stems from the Greek for \u2018terrible lizard\u2019, but dinosaurs aren\u2019t actually lizards. That distinction is based on anatomical features. Most notably, a lizard\u2019s legs stick-out at right angles from its body, producing a sprawling stance, but a dinosaur\u2019s legs are tucked underneath. Keeping a reptile upright requires strong joints between hips and backbone, which ancestors of dinosaurs made after fusing together vertebrae to form a modified structure, the sacrum.<\/p>\n The origin of dinosaurs dates back to around 230 MYA. Dinosaurs emerged from a group of reptiles called archosaurs, which has a \u2018crocodile line\u2019 (Crurotarsi) and \u2018bird line\u2019 (Avemetatarsalia), defined by bones near the ankle. There are a few candidates for oldest species \u2013 including small carnivores like Eoraptor<\/em>, larger Herrerasaurus<\/em>, and omnivores such as Panphagia<\/em>\u00a0\u2013 but no frontrunner for the first dinosaur, which evolved from the \u2018bird line\u2019 of archosaurs. Early dinosaurs walked on their hind legs, but not all their descendants were bipedal, which suggests that walking on four legs evolved several times independently.<\/p>\n Dinosaurs appeared during the late Triassic, a period when present-day land masses existed as a single supercontinent, Pangaea. After Pangaea started to break apart around 200 MYA, dinosaurs were distributed across the globe. They occupied a range of terrestrial habitats, from arid deserts to floodplains.<\/p>\n The dinosaur family tree is split into two branches based on hip-bone anatomy: \u2018bird-hipped\u2019 ornithischians and \u2018reptile-hipped\u2019 saurischians.<\/p>\n Ornithischian species feature the armoured Stegosaurus<\/em> and Ankylosaurus<\/em>, the duck-billed Parasaurolophus<\/em> and horn-faced Triceratops<\/em>. Saurischians include two major dinosaur groups: sauropods and theropods. Sauropods were long-necked herbivores like Brachiosaurus<\/em>.<\/p>\n Theropods are the most diverse group and contained well-known meat-eaters like Tyrannosaurus rex<\/em>, which was as big as a double-decker bus, and turkey-sized Velociraptor<\/em>.<\/p>\n All of the above dinosaurs starred in the Jurassic Park<\/em> movie franchise (although some characteristics were fictional), along with the flying pterosaur Pteranodon<\/em>\u00a0and marine monster Mosasaurus<\/em>.<\/p>\n About a thousand non-avian dinosaurs have been identified in the fossil record, but a mathematical model estimates that around 2,000 species of dinosaur existed during the Mesozoic era \u2013 around 500 ornithischians, 500 sauropods and 1,000 of the more diverse theropods.<\/p>\n Confusingly, birds aren\u2019t descended from the \u2018bird-hipped\u2019 ornithischian group, but \u2018reptile-hipped\u2019 theropods. Add 10,000 species of living birds to the total and you get an even larger number of dinosaurs.<\/p> Some dinosaurs were the heaviest animals to ever walk the Earth, reaching sizes far bigger than the largest land mammals. Giant sauropods known as \u2018titanosaurs\u2019 weighed around 50,000kg, for example, the same mass as 10 elephants<\/a>. Observing cross-sections of fossilised bone under a microscope has provided some insights into how physiology and biomechanics allowed dinosaurs to get big: like those of mammals, dinosaur bones were packed with blood vessels, which may have helped provide the nutrients needed for speedy growth. Juvenile sauropods grew at a rapid rate and their bones became compact in the outer layers: after hatching from an egg, a young 10kg sauropod could become a 10-tonne adult after only a decade or so, a feat that would take crocodiles around a century to complete.<\/p>\n Possibly, but it\u2019s hard to prove. Warm-blooded vertebrates (endotherms) need to eat massive amounts of food to generate enough energy to heat their bodies. One calculation suggests a 40-tonne sauropod would have had to consume over a tonne of plant matter each day, three times that of cold-blooded animals (endotherms) of equivalent size. Instead, large dinosaurs could have been \u2018gigantotherms\u2019 that conserved heat through sheer body mass to maintain a stable core temperature.<\/p>\n Not all, only some. Therapod dinosaurs had feathers, which probably evolved for insulation, serving the same function as feathers on living birds like penguins. Bird feathers were later repurposed for gliding, then powered flight. The other groups of dinosaur, ornithischians and sauropods, didn\u2019t usually have feathers.<\/p>\n Although dinosaurs get almost all the attention, the fifth mass extinction had effects across the tree of life \u2013 not just on land, but in water too. In fact, the Big Five events were originally defined not by mere species, but by dramatic drops in diversity for entire families of organisms, as measured from fossilised marine creatures. For example, all ammonites \u2013 cephalopods with spiral shells closely related to octopus and squid \u2013 disappeared following the fifth event.<\/p>\n That\u2019s the big mystery! Mass extinctions aren\u2019t random, they\u2019re selective, and there are clues that help explain why some species were survivors while others were victims. One contributing factor is characteristics associated with feeding and diet. For example, after the fifth extinction, natural selection was biased against large bony fishes with fast-closing jaws.<\/p>\nYou may also like:<\/h4>\n
![\""Image\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/04\/David-Attenborough.-Dinosaurs-The-Final-Day-f462587.jpg?quality=45&resize=556,556"\" "\\"\"Sir\\"")
<\/div><\/div> <\/div> <\/section>What is a dinosaur?<\/h2>\n
What was the first dinosaur?<\/h2>\n
Where did dinosaurs live?<\/h2>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/04\/GettyImages-1317077652-5ea5c41.jpg?quality=90&resize=620%2C310"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Which dinosaurs appeared in Jurassic Park<\/em>?<\/h2>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2018\/09\/iStock_000045055788_rectangle-83de936.jpg?quality=90&resize=552%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>How many dinosaur species are there?<\/h2>\n
How did dinosaurs get so big?<\/h2>\n
Were dinosaurs warm-blooded?<\/h2>\n
Did dinosaurs have feathers?<\/h2>\n
How were other animals affected?<\/h2>\n
Why did certain species survive?<\/h2>\n