Argentinosaurus.

Argentinosaurus, whose partial skeletal fossils were discovered in Argentina’s Neuquén Province, is believed to have been one of the largest terrestrial animals in history. Although no complete skeleton has been found, comparisons between the discovered bones and those of closely related dinosaurs suggest it measured around 40 meters in length and weighed about 90 tons—an astonishing size.

Megalosaurus.

In the world of dinosaurs, the first one recorded to be named was Megalosaurus. “Megalo” means “large,” and “saurus” means “lizard.” In the past, there was a tendency in dinosaur naming to give similar names to dinosaurs of the same kind as the first one, so many were named by adding “-saurus” after a term describing each dinosaur’s characteristics.

I don't know.

The most widely supported explanation for why dinosaurs went extinct is the asteroid impact hypothesis, but it is not fully understood. Rock layers from the time of the extinction have characteristics not seen in other periods, which are said to indicate an asteroid impact, and traces of a massive crater have been found. However, there are also other hypotheses, such as massive volcanic eruptions and climate change.

Fukui Prefecture.

Fukui Prefecture is known as a dinosaur kingdom. About 80% of the dinosaur fossils discovered in Japan have been found in Fukui, and the largest dinosaur fossil excavation site in the country is located in Kitadani, Katsuyama City. There are also many dinosaurs bearing the name “Fukui,” such as Fukui-saurus, Fukui-raptor, and Fukui-venator, which were first discovered in Japan.

Reptiles.

Dinosaurs belong to the same group of reptiles as lizards and crocodiles. Based on characteristics of the pelvis, they are broadly divided into two groups: Ornithischia and Saurischia. They were named because their pelvic structures resemble those of modern birds and lizards, respectively.

Tooth.

“-don” comes from the Greek word for “tooth,” odont. For example, Iguanodon means “iguana tooth,” and Pteranodon combines “ptera” (wing) with the negative “-anodon,” meaning “it has wings but no teeth.” Its mouth was beak-like, without teeth.

Dinosaur.

In English, "恐竜" is called "dinosaur." Incidentally, most dinosaur names are based on Latin: "saurus" means "lizard," "tyranno" means "tyrant," and "rex" means "king." Dinosaur names are given by making use of these characteristics.