General:
https://www.buzzfeed.com/hannahcgregg/13-terrifying-monsters-that-will-make-you-happy-you-live-in?utm_term=.koN1ODYavy#.alx64VxOgq
http://all-that-is-interesting.com/terrifying-prehistoric-creatures

Titanboa:
https://www.smithsonianmag.com/science-nature/how-titanoboa-the-40-foot-long-snake-was-found-115791429/
http://www.prehistoric-wildlife.com/species/t/titanoboa.html

Liopleurodon:
https://www.thoughtco.com/things-to-know-liopleurodon-1093791

Megalania Prisca:
https://australianmuseum.net.au/megalania-prisca
http://www.animalplanet.com/tv-shows/lost-tapes/creatures/devil-dragon/

Dunkleosteus:
http://www.prehistoric-wildlife.com/species/d/dunkleosteus.html

Arthropleura:
https://depositsmag.com/2017/03/07/arthropleura-a-prehistoric-bug-hunt/
http://www.prehistoric-wildlife.com/species/a/arthropleura.html

Jaekelopterus:
https://news.nationalgeographic.com/news/2007/11/071121-giant-scorpion.html
http://www.prehistoric-wildlife.com/species/j/jaekelopterus.html

Sarcosuchus:
https://www.thoughtco.com/facts-about-sarcosuchus-worlds-biggest-crocodile-1093333

Aegirocassis:
http://www.latimes.com/science/sciencenow/la-sci-sn-giant-arthropod-7-feet-long-20150310-story.html
http://www.prehistoric-wildlife.com/species/a/aegirocassis.html

Meganeuropsis:
http://www.eartharchives.org/articles/the-biggest-insect-ever-was-a-huge-dragonfly/

Megalodon:
http://www.mamasminerals.com/Carcharodon-megalodon-The-mega-shark-of-the-Cenozoic-Era_ep_62.html
https://news.nationalgeographic.com/news/2013/08/130807-discovery-megalodon-shark-week-great-white-sharks-animals/