A replica of the new dinosaur fossil confirmed in Hobetsu, Mukawa Town (Photo courtesy of Hobetsu Museum)

Another Major Dinosaur Discovery in Hobetsu, Mukawa Town!?

On January 6, 2021, just a month ago, news broke that a new theropod dinosaur fossil had been identified in Hobetsu, Mukawa Town. The press conference was held by a research group led by Professor Yoshitsugu Kobayashi of Hokkaido University, a world-renowned paleontologist affectionately known as "Dinosaur Kobayashi." According to Professor Kobayashi, a fossil that had been lying dormant in the Hobetsu Museum's collection has been identified as a dinosaur, and it could be an even greater discovery than Kamuysaurus, also known as "Mukawaryu"! But what exactly is this fossil? And why is it so significant? Many people might be completely new to this. So, this time, we'd like to explain the hidden messages within this fossil.

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

The New Common Knowledge: Birds Are Dinosaurs

When you hear the word "dinosaur," what comes to mind? A terrifying lizard, as the name suggests... A monster that became the prototype for Godzilla and other kaiju... However, that's an outdated image of dinosaurs. Today, dinosaur reconstructions have undergone a major transformation. Let's start with the latest definition of a "dinosaur."
Going back to the 1960s, a time when hippie culture was sweeping across America, a new wind was also blowing through the world of dinosaur research. It was the emergence of the revolutionary theory that "dinosaurs may have evolved into birds." This phenomenon was later called the "Dinosaur Renaissance," an event that dramatically overturned the concept of dinosaurs. In the late 1990s, numerous fossils of "feathered dinosaurs" were discovered one after another, mainly in China, proving that dinosaurs did indeed evolve into birds (see figure below).

Illustration of a Microraptor gui fossil. It had flight feathers on its arms and legs.
(Illustration by Ryo Suzuki)

Subsequently, more and more fossils were found that straddled the boundary between dinosaurs and birds, making it impossible to distinguish between the two. Eventually, the very definition of "dinosaur" changed, and "birds" came to be included under the umbrella of "dinosaurs"! In other words, birds are a part of the dinosaur family.
So, according to the latest definition, the pigeon you saw sunbathing in the park yesterday is a "dinosaur," and the crow pecking at garbage in an alley is also a "dinosaur." This means dinosaurs are not extinct, nor were they sluggish monsters. In modern times, there are about 9,000 species of birds and about 6,000 species of mammals. Considering that the skies are dominated by birds, it's no exaggeration to say that the age of dinosaurs continues to this day.

Zangi, the soul food of Hokkaido residents, is also 'dinosaur meat'

About This Discovery

There are two key points about this discovery. First, the newly identified fossil in Hobetsu, Mukawa Town, belongs to a group of dinosaurs called "theropods." Theropods are a group of bipedal carnivorous/omnivorous dinosaurs, which includes the famous Tyrannosaurus. On the other hand, some theropods evolved into birds. The fossil found this time is from a small theropod, and the geological layer it was found in is from the Cretaceous period, a relatively recent era in the age of dinosaurs. This suggests it could be a dinosaur closely related to birds. Furthermore, given the scarcity of dinosaur fossils in Japan and the possibility that this theropod is a new species, it may bring new insights into the evolutionary history of dinosaurs and birds! However, the research is still ongoing. What specific features link it to avian evolution has not yet been announced. That's something to look forward to.

Splitting Hokkaido in Two! What is the Geological Layer Where the Fossil Was Found?

By the way, both the newly discovered theropod and Kamuysaurus, whose complete skeleton was found, were discovered in a geological formation in Hokkaido called the "Yezo Group." What's interesting is that the Yezo Group is a layer formed in the sea (technically called a marine stratum). This Yezo Group runs from Wakkanai southward, splitting Hokkaido vertically in two. The reason why cities like Mikasa and Nakagawa Town are famous for their abundance of ammonite fossils is also because the Yezo Group is a "marine stratum."

Distribution map of the Yezo Group (Map by Ryo Suzuki)

Ammonite collected from the Yezo Group

The Yezo Group dates from the mid-to-late Cretaceous period (which includes the time when Tyrannosaurus and Triceratops lived), from about 100 million to 66 million years ago. At that time, this part of Hokkaido was at the bottom of the sea, but on the nearby continent, dinosaurs roamed. Incidentally, it is believed that after Kamuysaurus died, gas built up in its belly, causing it to float from the continent to Hokkaido and settle on the seabed (see figure below). How did this theropod's carcass drift from land to the bottom of the distant sea? This is a key point to watch for in future research findings!

Diagram of Kamuysaurus being washed from land to sea. ① Lived on the coast ② Washed away by floods, etc. ③ Settled on the seabed
(Illustration by Ryo Suzuki)

This new dinosaur discovery opens up a new avenue of research from a different angle than the complete skeleton of Kamuysaurus, promising to shed light on the evolution of birds. Let's look forward to future research announcements!