What are dinosaurs ?
Dinosaurs were a successful group of animals that emerged between 240 million and 230 million years ago and came to rule the world until about 66 million years ago, when a giant asteroid slammed into Earth. During that time, dinosaurs evolved from a group of mostly dog- and horse-size creatures into the most enormous beasts that ever existed on land.
Some meat-eating dinosaurs shrank over time and evolved into birds. So, in that sense, only the non-avian dinosaurs went extinct. (For the purposes of this article, "dinosaurs" will refer to non-avian dinosaurs, unless otherwise stated.)
During the roughly 174 million years that dinosaurs existed, the world changed greatly. When dinosaurs first appeared in the Triassic period (252 million to 201 million years ago), they roamed the supercontinent of Pangea. But by the time the asteroid hit at the end of the Cretaceous period (145 million to 66 million years ago), the continents were in approximately the same place they are today.
The oldest unequivocal dinosaur fossils, dating to about 231 million years ago, are from Ischigualasto Provincial Park in northwestern Argentina, and include the genuses Herrerasaurus, Eoraptor and Eodromaeus. Scientists are still debating whether Nyasasaurus, a genus found in Tanzania that dates to about 240 million years ago, is also an early dinosaur or a dinosauromorph, a group that includes dinosaurs and their close relatives, said Steve Brusatte, a paleontologist at the University of Edinburgh in Scotland.
Whenever they first appeared, the dinosaurs' unique anatomy set them apart from other animal groups. Dinosaurs are archosaurs, a clade (different groups of animals that share a common ancestor) that includes crocodilians, pterosaurs, dinosaurs and birds. The archosaurs emerged after the end-Permian extinction about 252 million years ago. Over time, some archosaurs, including dinosauromorphs, adapted an upright posture, meaning they had legs under their bodies, rather than out to their sides.
"Sprawling is all well and good for cold-blooded critters that don't need to move very fast. Tucking your limbs under your body, however, opens up a new world of possibilities," Brusatte wrote in "The Rise and Fall of the Dinosaurs: A New History of a Lost World" (William Morrow, 2018). As archosaur evolution progressed, dinosauromorphs gained long tails, big leg muscles and extra hip bones that enabled them to move quickly and efficiently, Brusatte wrote.
Some dinosauromorphs evolved into dinosaurs. The differences between the two are small, but dinosaurs' anatomy offered increased benefits, including arms that could move in and out, neck vertebrae that could support stronger muscles than before, and a joint where the thigh bone meets the pelvis, Brusatte wrote.
This unique anatomy helped dinosaurs become successful. Having an upright posture also freed the hands, allowing dinosaurs such as iguanodonts to grasp branches and carnivorous dinosaurs to claw and kill prey, noted Gregory Erickson, a paleobiologist at Florida State University. Ultimately, having free arms "allowed gliding then flight in birds," he said.
Moreover, dinosaurs were likely warm blooded, according to research on their growth rates. "When you become a warm blooded animal, you can operate 24/7," Erickson told Live Science. "You're not at the whims of the environment in terms of being active."
Initially, dinosaurs were not as diverse as the crocodile-like archosaurs they were living alongside, Brusatte noted. In fact, dinosaurs "didn't become too successful right away; the crocs ruled the Triassic, then the end-Triassic extinction hit and the dinosaurs survived and took over."
The clade Dinosauria (which means "terrible lizard" in Greek) was coined in 1842 by the English paleontologist Richard Owen, who included the meat-eating theropod Megalosaurus, the long-necked sauropodomorph Cetiosaurus and the ornithiscian Iguanodon as the first known species in the clade, according to the book "Dinosaurs Rediscovered" (Thames & Hudson, 2019).
Each of these dinosaurs, it turns out, represents one of the three major dinosaur groups.
Any Types Of Dynosaurs
As of 2021, there were 1,545 scientifically described dinosaur species, according to the Paleobiology Database. About 50 previously unknown species are described each year, meaning there's roughly one newfound species described each week, Brusatte said.
All of these dinosaurs fit into one of three groups: Ornithischia, Sauropodomorpha and Theropoda.
Ornithischia dinosaurs include beaked plant-eaters, such as Stegosaurus, duck-billed dinosaurs (also called hadrosaurs), as well as horned dinosaurs like Triceratops and armored dinosaurs like Ankylosaurus. Some ornithischians walked on four legs, while others walked on two.
Sauropodomorpha dinosaurs were long-necked, pot-bellied dinosaurs that had tiny heads and column-like limbs. This group includes sauropods (such as Diplodocus), their smaller antecedents (including Chromogisaurus) and extra-large sauropods known as titanosaurs (such as Dreadnoughtus and Argentinosaurus), which are among the largest land animals that have ever existed.
Theropoda is a group of meat-eating dinosaurs, although some (such as Chilesaurus diegosuarezi) changed their diet to be herbivorous or omnivorous. Theropods include Tyrannosaurus rex and Velociraptor, as well as birds, which evolved from small theropods.
So, how are these groups related? It's up for debate. Ornithischian dinosaurs have a backward-pointing pubis bone in the hip, earning them the name bird-hipped dinosaurs. (However, they are not the ancestors of birds; theropods are.) Meanwhile, theropods and sauropodomorphs have saurischian or "reptile hips," which are also seen in modern crocodiles and lizards, according to the book "Dinosaurs Rediscovered."
Historically, it was thought that the reptile-hipped theropods and sauropodomorphs were more closely related to each other than to ornithischians. However, a 2017 study in the journal Nature uprooted the dinosaur family tree by suggesting that ornithischians and theropods were more closely related, based on analyses of 74 dinosaur species, Live Science previously reported. Shortly after, another 2017 study in the journal Nature found that neither family tree, as well as a third that is rarely considered, is statistically significant from the other, meaning all the suggested family trees are equally plausible until more evidence comes forth.
When did dinosaurs live ???
Dinosaurs lived during most of the Mesozoic era, a geological age that lasted from 252 million to 66 million years ago. The Mesozoic era includes the Triassic, Jurassic and Cretaceous periods.
Dinosaurs arose from small dinosauromorph ancestors in the Triassic period, when the climate was harsh and dry. They faced "competition from the croc-line archosaurs for tens of millions of years, [but] finally prevailed when Pangea began to split," Brusatte told Live Science. At this time, volcanoes erupted along the cracks of the supercontinent, causing global warming and mass extinction, he said.
During the Jurassic period (201 million to 145 million years ago), dinosaurs rose to dominance and some grew to huge sizes. For example, Vouivria damparisensis, the earliest titanosaur, dates to 160 million years ago. It weighed about 33,000 lbs. (15,000 kilograms) and measured more than 50 feet (15 meters) long. Iconic dinosaurs from this period include Brontosaurus, Brachiosaurus, Diplodocus and Stegosaurus. During the Jurassic, flowering plants evolved and birds, including Archaeopteryx, first appeared. There was "a small extinction at the end of the Jurassic that we still know little about," Brusatte said.
In the Cretaceous period, dinosaur dominance continued as the continents moved farther apart. Famous dinosaurs from this period include T. rex, Triceratops, Spinosaurus and Velociraptor. The largest dinosaurs on record, including Argentinosaurus, date to the Cretaceous. The Cretaceous period ended with the Cretaceous-Tertiary (K-Pg) extinction event, when a 6-mile-wide (10 kilometers) asteroid collided with Earth, leaving an impact crater more than 110 miles (180 km) in diameter in the Yucatan Peninsula of what is now Mexico.
The impact area, known as the Chicxulub (CHEEK-sheh-loob) crater, has evidence of "shocked quartz" and small glass-like spheres known as tektites, which form when rock is rapidly vaporized and cooled — geologic clues that a space rock struck there with incredible force, Betsy Kruk, an associate paleontologist with Paleo Solutions, a paleontological consulting company based in California, previously told Live Science. Chemical analyses from the sedimentary rock at Chicxulub melted and mixed together at temperatures on par with an asteroid strike about 66 million years ago, she added.
WHAT IS THE LARGEST DINOSAUR? THE SMALLEST !!!
Some dinosaurs were enormous, but others were pipsqueaks. The smallest dinosaur on record is an avian dinosaur that's alive today: the bee hummingbird (Mellisuga helenae) from Cuba, which measures just over 2 inches (5 centimeters) long and weighs less than 0.07 ounce (2 grams). As for extinct, non-avian dinosaurs, there are a few contenders for smallest beast, including a bat-like dinosaur from China named Ambopteryx longibrachium that measured 13 inches (32 cm) long and weighed about 11 oz (306 g), according to a 2019 study in the journal Nature.
Titanosaurs were the largest dinosaurs. However, because paleontologists rarely find an entire skeleton, and because soft tissues, such as organs and muscles, rarely fossilize, it's challenging to determine dinosaur mass. However, contenders for the title of world's largest dinosaur include Argentinosaurus, which weighed up to 110 tons (100 metric tons), an unnamed 98 million-year-old titanosaur from Argentina that weighed upward of 69 tons (63 metric tons), and Patagotitan, which also weighed in at 69 tons.
The longest dinosaur is likely Diplodocus or Mamenchisaurus — long and slender sauropod dinosaurs that were about 115 feet (35 m) long. The tallest dinosaur is likely Giraffatitan, a 40-foot-tall (12 m) sauropod dinosaur from the late Jurassic, about 150 million years ago, which lived in what is now Tanzania.
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