The juvenile's body was dismembered…a shocking development in a mammal's molars that allowed it to 'eat and swallow a dinosaur' that was larger than itself (Blue Bucks Editorial Department) | Blue Pax | Kodansha (1/2))

What did our ancestors gain, what did they lose and what did they diverge during their long evolution?

The history of the Earth is said to be about 4.6 billion years, and life is said to have arisen about 3.95 billion years ago at the latest. The first humans appeared about 7 million years ago. From the perspective of Earth's long history, this is “very recent.”

However, Homo sapiens did not suddenly appear. You were born at the end of continuous evolution from the beginning of life to the present. If we focus on one species, Homo sapiens, and trace its history, what kind of journey will we see? A fascinating story of such a journey, focusing on 70 signs, is “The Prehistory of Sapiens: 500 Million Years of History from Vertebrates to Humans“(Bluebacks).

this”Sapiens prehistoric times“The mosquitoLet us introduce the “highlights” of the 70 signs you should pay special attention to. This time, we'll focus on molars, an essential characteristic of mammals. At first glance, the topic may seem simple, but in fact, he says, it is “a very important piece of evidence” for the study of evolution and biology, to the extent that “molars can be used to identify living organisms.” Classify.'' Let's take a look.

*This article is based on “The Prehistory of Sapiens: 500 Million Years of History from Vertebrates to Humans(Bluebacks) has been rebuilt and re-edited.

“Molar teeth” that can even distinguish seeds… 3 representative species

In heterotrophic mammals, molars in particular have a variety of shapes. Their shape is such that an expert can recognize the species.“It is “singularity”.

If you are reading this article and are interested in the evolution of organisms, you may want to learn about some types of molar teeth, even if you are not interested in “endemism” at the species level. Molars, which are particularly noteworthy as a marker (the 32nd feature) of evolution into Homo sapiens, areTrypophynic typeThis type is called “.

The word comes from two words “tribo” which means “to grind” and “seven” which means “to cut”. It is important to note that “triple” does not mean “three”. As the word suggests, tribosphenoid molars have the role of “grinding” and “cutting.”

The basic shape of the tribosphene type has three cusps. In the tribosphenoid molars of the upper jaw, these three heads are triangular in shape, with a pelvic-like structure between them. The mandibular tribosphenoid molars have three additional cusps, or six in all, with pelvic-like structures between them. This complex structure makes it possible to “grind” and “cut”.

They were molars of monotremes or were similar to this tribosphenic molar.

Tribosphenoid molars. It has the role of “grinding” and “cutting”. The basic shape of molars in euthanasia. Illustration by Hidenori Yanagisawa

After unilateralism“The group that separated from the “lineages that led to humans” had narrow molars and three heads lined up in a straight line.“Shear specifications setTrue three cone type(Shinsansui Shirui)” The low protrusions are lined up in rows.““Group Specification Set”PolydontiaTakeo Shiroi, a group whose vertices are arranged in an isosceles triangle.Sparacotherium“And so on and so on.

• Lineages leading to humans = Tribosphenian type: There are three cusps in the upper jaw and six in the lower jaw, with a valley-like structure between them.
• Disperse group
  • Triconid: Three heads lined up in a straight line
  • Polydonts: Low protrusions lined up in rows
  • Sparacotherium: Vertices arranged in an isosceles triangle

And the,“The molars of the lineage leading to humans are of the tribosphenic type.

“Convergent evolution” leads to “similar” forms.

The fact that we have similar molars with monotremes, the most primitive group of mammals, suggests that molar shape evolved independently in each group.“It is believed that the two groups in the lineage that led to humans had similar shapes.

This can be called “convergent evolution.” “Convergent evolution” refers to two different groups that have become similar in appearance as a result of evolution.

However, the diversity of molar teeth greatly influenced Mesozoic mammals.“Mesozoic mammals may not look very distinct or different from each other, but inside their mouths they were undergoing a revolutionary evolution.