A replica of a dinosaur fossil newly identified in Hobetsu, Mukawa Town (courtesy of Hobetsu Museum)

Another Great Dinosaur Discovery in Mukawa-Hobetsu!

　On January 6, 2021, exactly one month ago, the news came in that "a new theropod dinosaur fossil was confirmed in Hobetsu, Mukawa Town. The press conference was held by a research group led by Professor Kaiji Kobayashi, a world-class dinosaurologist at Hokkaido University, who is affectionately known as "Dinosaur Kobayashi. According to Professor Kobayashi, the fossil found in the storage room of the Hobetsu Museum is that of a dinosaur, and that this may be an even bigger discovery than the "Mukawa Rhinosaur" or Kamuysaurus! But what exactly is this fossil? Why is it so amazing? I am sure there are many people who have no idea what this fossil is or why it is so amazing. In this article, we would like to explain the message hidden in this fossil.

Professor Kobayashi (left) and Mayor Yoshiyuki Takenaka (right) at the press conference

The New Common Knowledge that Birds are Dinosaurs

　What comes to mind when you hear the word "dinosaur"? As the word "dinosaur" suggests, a fearsome dragon. Monsters that were the prototype for Godzilla and other monsters. In fact, however, these are images of dinosaurs from a long time ago. Today, dinosaur reconstructions have undergone a major transformation. Let me start with the definition of the "latest dinosaurs.
Back in the 1960s, when the hippie culture was sweeping America, a new wind blew among dinosaur researchers. A revolutionary theory emerged: "Dinosaurs may have evolved into birds. In the late 1990s, fossils of various "feathered dinosaurs" were discovered one after another, mainly in China, proving that dinosaurs had evolved into birds (see figure below).

Diagram of a Microraptor gui fossil. Wind-cut feather roots grew on the limbs.
(Illustration by Ryo Suzuki)

　Later, more and more fossils were found that were on the borderline between dinosaurs and birds, and it became impossible to distinguish between the two. Finally, the definition of "dinosaur" changed, and "birds" came to be included in "dinosaurs! In other words, birds are part of dinosaurs.
According to the latest definition, a pigeon sunbathing in the park yesterday is a dinosaur, and a crow pecking at garbage in a back alley is a dinosaur.... In other words, dinosaurs are neither extinct nor slow monsters. Considering that today there are about 9,000 species of birds and 6,000 species of mammals, and that the sky is the bird, it is no exaggeration to say that the age of dinosaurs is still going on today.

Zangi, the soul food of the people of Hokkaido, is also "dinosaur meat.

About the Discovery

　There are two important points about this discovery. First, the fossils newly identified in Hobetsu, Mukawa-cho are a group of dinosaurs called theropods. Theropods are a group of carnivorous and omnivorous dinosaurs that walked on two legs, including the famous Tyrannosaurus. On the other hand, some theropods evolved into birds. The fossils discovered this time belong to small theropods, and the stratum in which they were found is from the relatively recent Cretaceous Period, which is the latter half of the dinosaur era, so there is a possibility that they are dinosaurs similar to birds. Furthermore, the fact that there are few dinosaur fossils in Japan and the theropods in this study may be a new species may lead to new discoveries in the evolutionary history between dinosaurs and birds!　However, the research is still in the ongoing stage. However, it has not yet been announced what exactly will lead to the evolution to birds. That remains to be seen.

Cutting Hokkaido in half! What is the geological stratum where the fossils were found this time?

By the way, both the theropod discovered this time and the whole body skeleton of Kamuysaurus, the "Mukawa Rhinosaur," were found in the Ezo Formation, a geological stratum in Hokkaido. Interestingly, the Ezo Formation is a marine formation (technically called a marine stratum). The Yezo Group runs from Wakkanai to the south, dividing Hokkaido vertically in half. The reason why Mikasa City and Nakagawa Town are famous for finding many ammonites is because the Ezo Formation is a "marine formation.

Distribution map of the Ezo Formation (Map created by Ryo Suzuki)

Ammonites from the Yezo Formation

　The Yezo Formation is a period from 100 million to 66 million years ago, which is the middle to late Cretaceous period (including the period when Tyrannosaurus and Triceratops lived). At that time, dinosaurs roamed the nearby continent, even though here in Hokkaido was at the bottom of the sea. Incidentally, it is thought that after Kamuysaurus died, gas accumulated in its abdomen and drifted across the ocean from the continent to Hokkaido, where it was deposited on the seafloor (see figure below). How did this theropod drift to the bottom of the sea, far from land, after death? This is a point of interest for future research results!

Figure of Camuysaurus being washed to the sea from land (1) Living on the coast (2) Swept away by floods, etc. (3) Deposited on the seafloor
(Illustration by Ryo Suzuki)

　This new dinosaur discovery opens up a new perspective on research from a different angle from that of the Kamuysaurus skeleton, which is the elucidation of its evolution into a bird. Let's look forward to future research announcements!