Note: MYA is a unit of time indicating ‘Million Years Ago’
Dinosaurs are no strangers to us. The Jurassic Park franchise brought these fantastical beasts right into our living rooms, leaving us with a feeling of marvel and awe. We still have a lot to discover about these colossal creatures; this is a brief rundown on what we do know, thus far. Stick around and you just might find something new to add to your dinosaur-fact repertoire.
Dinosaurs ruled the Earth for a whopping 150 million years. The Jurassic Period (which we’re all familiar with) was one of three periods during which dinosaurs called Earth their own. All three periods – the Triassic Period (245-208 MYA), Jurassic Period (208-146 MYA) and Cretaceous Period (146-65 MYA), belonged to the Mesozoic Era.
The Mesozoic Era, spanning a 180 million years (245-65MYA), was anything but idle. Apart from dinosaurs, three mass extinctions marked the era and it coincided with the breakdown of Earth’s massive supercontinent, Pangaea, into several continents that would eventually mirror the Earth as it is today. This change in geography and climate had a substantial impact on the evolution of dinosaurs. The timeline of events is as follows.
Permian-Triassic Extinction (251 MYA)
The Permian-Triassic extinction event is morbidly monikered the Great Dying, and with good reason. It was the most devastating event to have ever taken place. It spanned across 50,000 years causing the demise of 95% of marine species and 70% of terrestrial species. There were no forests left to spare; it took roughly 10 million years for them to recuperate due to the Coal Gap – scarcity of coal on Earth. Siberian volcanic activity was likely the cause here – it acidified oceans and wreaked havoc on the ozone layer, showering the Earth with a deathly dosage of UV.
The Triassic Era
The Triassic Era was thus focused on the reestablishment of ecosystems. Organisms like the Synapsids (mammal-like reptiles from whom we evolved) were dominating the Earth before the extinction event took place; they gave way to other groups, including the reptilian Archosaurs that would eventually evolve into the now-extinct pterosaurs (Flying Dinosaurs that were not actually dinosaurs) and dinosaurs, and the crocodiles and birds of today.
The reptilian skin of Archosaurs had a knack to conserve water which suited them well in a climate that was hot, arid and devoid of polar ice caps. Despite the gradual and homogenous temperature gradient between the equator and poles, life mostly existed towards the Panthalassa (the massive, singular ocean) rather than amid the Pangaea. This was because the land was a spread of unsustainable desert with hot summers and cold winters. At the very least, seasonal monsoons blessed the coast.
The earliest dinosaurs appear to have sprung up 230 MYA and were small – a few meters long. They were bipedal, and walked on their hind legs by tucking them under their bodies. This eventually caused more permanent changes to their anatomy.
These early dinosaurs eventually split into two clades – bird-hipped dinosaurs called Ornithischia and lizard-hipped dinosaurs called Saurischia. During this period the Ornithischians and Saurischians greatly resembled one another but they soon began to diversify.
There’s a doozy here – the birds of today are more closely related to the lizard-hipped dinosaurs than the bird-hipped dinosaurs; the nomenclature had more to do with the positioning of the pubis (and pelvis) amongst other things, than the lineage.
Triassic-Jurassic Extinction (201 MYA)
The Triassic-Jurassic extinction event marked the end of the Triassic era, occurring 50 million years after the preceding event and resulting in the loss of 80% of marine and terrestrial life. It was brought about by the splitting of Pangaea into Laurasia in the north and Gondwana in the south, which still remaining connected, causing an uptick of underwater volcanic activity somewhere in the Atlantic Ocean. This was, however, a blessing in disguise for our ferocious pals, as the loss of terrestrial life, including competing archosaurs, paved the way for the diversification of dinosaurs.
With the competing organisms out of the way, this period became the Golden Age of Dinosaurs, so to speak. It led to an increase in the numbers and diversity of the dinosaur population. There was variety in their sizes, shapes and even preferred modes of travel – there were bipeds, quadrupeds and of course dinosaurs blessed with flight.
The end of dinosaurs aside, this era housed some of our favourite ones, including the Triceratops and the T-Rex. To set the scene, the climate was tropical – warm and humid. As the era drew to a close, Laurasia separated into North America and Eurasia and Gondwana split into South America, Antarctica, and Africa. We’re nearing the end of the tale now, folks!
Cretaceous-Paleogene Extinction (66 MYA)
We’re all aware that a blazing asteroid (and more volcanic activity!) led to the end of the Mesozoic Era (and dinosaurs). This was the Cretaceous-Paleogene extinction, circa 66 MYA. It proved to be the fifth and last extinction event of its kind, until right about now – a sixth extinction event is currently underway with humans as its agent – but I digress. It wiped out 76% of the Earth’s species (including the dinosaurs); although it wasn’t as bad as the Great Dying, the event was monikered the Great Extinction. Thus, after a tumultuous reign over the Earth, the Age of Reptiles gave way to the Age of Mammals and a bunch of birds.
Written by Shweta Manoharan.
P.S. if you’d like to read more about mass extinctions we’ve got you covered – Mass Extinction: Curse or Blessing?