Dinosaur Day Date in the current year: June 1, 2024

Dinosaurs are a diverse group of animals that make up the natural group (clade) Dinosauria, which can be divided into two big groups: non-avian and avian (feathered) dinosaurs. According to the currently predominant scientific theory, all birds are feathered dinosaurs. However, hardly anyone ever refers to birds as dinosaurs; when most people say “dinosaurs”, they mean lizard-like non-avian dinosaurs.

Dinosaurs first appeared during the Triassic period and became the dominant terrestrial vertebrates in the early Jurassic period after a major extinction event that marked the end of the Triassic period. Their dominance continued throughout the Jurassic and Cretaceous period, but the Cretaceous-Paleogene extinction event wiped non-avian dinosaurs out.

Dinosaur fossils have been discovered and documented for millennia, but their true nature wasn’t recognized prior to the development of paleontology. In ancient China, for example, they were considered to be dragon bones, whereas in Europe people generally believed dinosaur fossils to be the remains of various mythological creatures.

The first person to provide a full scientific description of a non-avian dinosaur was English theologian, geologist and paleontologist William Buckland. He studied fossil bones of a giant reptile discovered near the village of Stonesfield and named the creature Megalosaurus (“great lizard”).

The second non-avian dinosaur to be identified and described was Iguanodon. Its fossils were discovered by British fossil collector Mary Ann Mantell and described by her husband, surgeon and paleontologist Gideon Mantell. The name “dinosaur” (“terrible reptile”) was coined by English paleontologist and biologist Richard Owen in 1842.

Since the early 19th century, paleontologists have identified and described more than 1,000 non-avian dinosaur species. Some of them were carnivorous, other herbivorous. Studies suggest that dinosaurs reproduced by laying eggs, and that many dinosaurs, avian and non-avian alike, built nests. While avian dinosaurs were (and are) relatively small because otherwise they wouldn’t be able to fly, the largest non-avian dinosaurs are estimated to have been up to 40 meters long and 18 meters tall.

It is unclear who came up with the idea of celebrating Dinosaur Day and why there are two of them, but we hope it won’t stop you from celebrating! Whether you celebrate it in May or June (or twice a year), Dinosaur Day is a perfect occasion to learn fun facts about these amazing creatures and share them with the world, rewatch the Jurassic Park movies, visit a museum that has dinosaur-related exhibits, buy some toy dinosaurs for your kid (or for yourself, we promise we won’t judge!), bake dinosaur-shaped cookies, and post about the holiday on social media with the hashtag #DinosaurDay to spread the word.