Eutheria facts for kids
Quick facts for kids Eutheria |
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| Skeleton of Microtherulum, an early eutherian from the Early Cretaceous of China | |
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| Northern treeshrew (Tupaia belangeri), a placental eutherian from Southeast Asia | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Subclass: | Theria |
| Clade: | Eutheria Gill, 1872 |
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see text. |
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| Synonyms | |
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Eutheria (pronounced "yoo-THEER-ee-uh") is a special group of mammals. The name comes from Greek words meaning 'true beasts'. You might also hear them called Pan-Placentalia. This group includes all placental mammals and all other mammals that are more closely related to placentals than to marsupials.
Placental mammals are animals like humans, dogs, cats, and elephants. Their babies grow inside the mother's body, connected by a special organ called a placenta. This placenta helps the baby get food and oxygen. Marsupials, like kangaroos, carry their babies in a pouch. Monotremes, like the platypus, lay eggs.
Eutherians are different from other mammals in several ways. For example, most living eutherians do not have special bones called epipubic bones. These bones are found in marsupials and monotremes. Not having epipubic bones allows the mother's belly to expand more during pregnancy. This is important for the development of placental babies. However, some very old, primitive eutherians did have these bones.
Scientists first named Eutheria in 1872. The earliest clear eutherians lived about 120 million years ago. Their fossils have been found in China. Another possible early eutherian, Juramaia sinensis, might be even older, around 161 million years ago. This shows that eutherians have a very long and interesting history on Earth!
Contents
What Makes Eutherians Special?
Eutherians have several unique features that help scientists tell them apart from other mammals. These features are mostly found in their bones, especially in their feet, jaws, and teeth.
Here are some of the key characteristics:
- They have a larger bump, called a malleolus, at the bottom of their tibia (the larger of the two shin bones in the lower leg).
- The way certain bones in their foot connect is different. Specifically, the joint between the first metatarsal bone and the entocuneiform bone is set further back than in other mammals like marsupials.
- Their jaws and teeth also have special traits. For example, they usually have three molars on each side of their jaws. Their upper canine teeth often have two roots, and their lower molars have specific shapes that help them chew food.
The Eutherian Family Tree
The Eutheria group is very diverse, meaning it includes many different kinds of mammals, both living and extinct. Scientists use fossils and genetic information to understand how these animals are related. They group them into different families and orders.
One very important subgroup within Eutheria is called Placentalia. This group includes all the living placental mammals we see today. However, Eutheria also includes many ancient mammals that are now extinct. These extinct groups help us understand the long journey of evolution that led to modern placental mammals.
Scientists are always learning more about the eutherian family tree. They study new fossils and use advanced tools to figure out the relationships between these amazing creatures. It's like solving a giant puzzle that spans millions of years!
How Eutherians Evolved Over Time
The story of eutherian evolution is fascinating! Many of the earliest eutherians were small, often eating insects. Imagine tiny, shrew-like mammals scurrying around during the time of the dinosaurs!
For a long time, during the Cretaceous period, eutherians remained relatively small. But something big happened about 66 million years ago: the K-Pg extinction. This was the event that led to the extinction of most dinosaurs. After this event, many new opportunities opened up for mammals.
With the dinosaurs gone, eutherians began to evolve rapidly. They grew much larger and diversified into many different forms. This is when we start to see the ancestors of today's large placental mammals. Some ancient eutherians, like the zhelestids, even became plant-eaters (herbivores) very early on. This shows how quickly they adapted to new environments and food sources after the big extinction event.
Scientists continue to study fossils to piece together the complete evolutionary journey of eutherians, from their tiny beginnings to the incredible diversity of placental mammals we see around us today.
Eutherians in Their Environment
Early eutherians, especially those that lived during the Cretaceous period, were generally small. Many of them were insectivores, meaning they ate insects, much like many small, primitive mammals do today.
However, as eutherians evolved, their diets and sizes changed. For example, some ancient groups like the zhelestids are believed to have been herbivorous, meaning they ate plants.
After the K-Pg extinction event, which happened about 66 million years ago, the world changed dramatically. The body sizes of eutherians increased a lot, especially among the placental mammals. This allowed them to fill many new roles in the environment, leading to the wide variety of mammals we have today.
See also
In Spanish: Eutheria para niños
