Chapter 2: What is unusual about the existence of dinosaurs?

Imagine a world where a Seismosaurus over 52 meters in length roamed the land, and Quetzalcoatlus, a pterosaur sized like a small plane with a wingspan of 12 meters, flew above.

Traditionally dinosaurs were considered to be poikylothermic like modern reptiles--cold-blooded, unable to adjust its body temperature--and also very clumsy. In pictures of dinosaurs a generation ago, sauropods like Diplodocus were always depicted with their bodies half in the water, as it was thought that such gigantic creatures would not have being able to support their own weight on land. Two typical species of giant dinosaurs are Apatosaurus (Brontosaurus) and Diplodocus, though they can no longer be considered gigantic any more.

New discoveries from the late 1970s and through the '80s and '90s have changed completely the image we have of dinosaurs. The unearthing of gigantic dinosaurs one after the other have rewritten the record books.

In 1985, two enormous dinosaurs that exceed the imagination, Supersaurus and Ultrasaurus, were formally recorded. Both measure from 25 to 40 meters in length and weigh more than 80 tons. Amazing numbers. Judging from the names given to them, it is clear that their discovers had thought they had found the largest dinosaurs in history. Unfortunately that record belongs to Seismosaurus, which may have reached a length of 52 meters and weighed more than 100 tons. Although unconfirmed, there is an extraordinary dinosaur called Amphicoelias that may have measured 60 meters and weighed 150 to 300 tons. In comparison, the largest living animal today is the African elephant, weighing about 7 tons.

The smallest dinosaur was the 60 centimeter long Compsognathus, about the size of a chicken. It may seem small for a dinosaur, but compared to modern mammals, reptiles, and birds, that measure several centimeters, even the smallest dinosaur is far larger than the present average.

Chapter 3: Dinosaur Extinction Mystery

The well-known American palaeontologist Professor Colbert measured the body temperatures of a large and small crocodiles with a thermometer in their anus and monitored their changes throughout the day. He discovered that the body temperature of the larger crocodile dropped much less during the night compared to the smaller one. This method of maintaining body temperatures is known as gigantothermy, as compared to true homeotherms that can actively adjust their body temperatures.

In other words, dinosaurs that were much greater in size than modern crocodiles may not have been homeothermic, but were probably able to maintain internal temperatures through gigantothermy. Some of the active smaller dinosaurs are now believed to have been homeothermic.

Lowered global temperatures due to the "nuclear winter" is now accepted as the most reasonable explanation for why the dinosaurs died out. This was based on the assumption that dinosaurs were poikylothermic. However, if dinosaurs were homeothermic as they are presently believed to be, then this puts that theory into question. Of course one can argue that lower temperatures resulted in food shortages, but even so, it should have resulted in decreased numbers, not total extinction.

However, poikylothermic reptiles, like crocodiles and lizards, have survived to the present day.

So, crocodiles and lizards--creatures that depend on the surrounding temperature to regulate its body temperature--have survived despite drastic changes in the environment. And dinosaurs that were homeothermic and able to adjust its internal temperature were unable to adapt and died out. Ironic, don't you think?

Translated by Rie Ishida