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After The Cretaceous
The Cretaceous period was the last and longest period of the Mesozoic ''era. It lasted around  79 million years, after the Jurassic period 145 million years ago to the Cretaceous-Paleogene (K-Pg) extinction event 66 million years ago.''

The Cretaceous
The Cretaceous Period ended once the dinosaurs died. After evidence shows that the Chicxulub Crater was the main culprit of the extinction of dinosaurs. Once the dinosaurs got wiped out by the asteroid, for a short period of time there was an age of reptiles with animals like the Brontosaurus, Lizards, Crocodiles, etc. It was called the Paleogene period. The world changed drastically after the mass extinction from the land to the type of animals that roamed the world, ones that survived, and plants that were newly formed.

Land
Conifers disappeared almost completely from the new world, tropics, flowers and plants took over. Plant diversity did not recover for about 10 million years after the impact. The Smithsonian Tropical Research Institute determined that pre-impact tropical forest trees were spaced far apart, which ultimately allowed light to reach the forest floor. Within 10 million years after the impact, some tropical forests, flowers, and trees had grown. Trees and vines blocked out most of the light from reaching the smaller trees, bushes, and plants below. The non-avian dinosaurs ate most plants and smaller animals, which was the cause of most destruction during the cretaceous period. The tsunamis that the asteroid caused was a factor in the drifting of the continents. The continents had moved far enough that the world was beginning to change into the present day’s layout. Waves had traveled almost the full extent of the Pacific and Atlantic Oceans and the Indian Ocean from both sides.

Climate change
The asteroid (Chicxulub Crater) jump-started a massive amount of sulfur gasses that was around the Earth for several decades. The gasses from the dinosaurs burping and farting contributed to their own atmospheric change. After the Chicxulub asteroid hit it, its dust and particles of debris from the collision made its way to the upper atmosphere and most likely blocked the sun rays. Insolation was reduced and the climate cooled down because energy from the sun was reflected back into space. A increase temperature also lasted up to several decades, a timescale supported by models and by evidence of species migration. There was a great drop in the global temperature as a result of the asteroid. The sudden cooling would have caused a huge amount of stress on living things and could have been a key contributor to the mass extinction. Dust injected into the atmosphere caused the ocean surfaces would have become acidic, resulting in yet more panic for above surface organisms.

Animals
Animals that lived at the same time as dinosaurs also went extinct, including non-neornithine birds, lizards, snakes, pterosaurs, and crocodyliforms. Tetrapod's such as amphibians and turtles experienced lower losses across the K–Pg. boundary. Organisms in freshwater ecosystems were less affected by the extinction than those on land or marine environments. Freshwater food chains were more reliant on debris feeding than photosynthesis. Due to the fact mainly birds survived the asteroid many animals developed from birds. Neoaves ,Phorusrhacidae (terror birds), and Neognathae birds evolved from them. When non-avian dinosaurs died, mammals survived and continued to grow. The first 10 million years following the wiping out of dinosaurs, the mammals species got thicker instead of growing taller and bigger. This happened because their bodies had began to adapt to the new environment. The Paleogene period. There were dozens of subfamilies grouped by different types of teeth, diets and reproductive styles. Their small bodies, flexible diets, and faster ways of growing and reproducing allowed them to open positions and start building new food webs.

= References =


 * 1) Alvarez, Walter, et al. T. Rex and the Crater of Doom. With a New Foreword by Carl Zimmer, Princeton University Press, 2008.
 * 2) Brett-Surman, M. K., et al. The Complete Dinosaur. 2nd ed., Indiana University Press, 2012.
 * 3) Brusatte, Stephen L., et al. “The Extinction of the Dinosaurs.” Biological Reviews of the Cambridge Philosophical Society, vol. 90, no. 2, 2015, pp. 628–42.
 * 4) Paul, Gregory S. The Princeton Field Guide to Dinosaurs. Princeton University Press, 2016.
 * 5) Prothero, Donald R. Vertebrate Evolution from Origins to Dinosaurs and Beyond. First edition., CRC Press, 2022.
 * 6) Qiu, Jane. “PALEOCLIMATOLOGY. Dinosaur Climate Probed.” Science (American Association for the Advancement of Science)
 * 7) Rivera-Sylva, Héctor E., et al., editors. Dinosaurs and Other Reptiles from the Mesozoic of Mexico. Indiana University Press, 2014.

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