Theria

Theria

Diversity of Theria

Theria is a subclass of mammals that includes the vast majority of living mammalian species. Therians are characterized by their mode of reproduction, which involves live birth rather than laying eggs, a trait that distinguishes them from the monotremes.

Characteristics

Therians are divided into two infraclasses: Metatheria and Eutheria. Metatherians include the marsupials, such as kangaroos, koalas, and opossums. Eutherians, also known as placental mammals, include a wide range of species from rodents to primates, including humans.

Reproduction

Therians give birth to live young, a process known as viviparity. In eutherians, the young develop inside the mother's uterus and are nourished before birth via a complex placenta. In contrast, marsupials give birth to relatively undeveloped young that often continue to develop outside the womb in a pouch.

Anatomy

Therians possess several anatomical features that distinguish them from other mammals. These include the presence of a cochlea in the inner ear, which is involved in hearing, and a more complex brain structure that supports advanced behaviors and learning.

Evolution

Therians are believed to have evolved during the Mesozoic Era, with the earliest fossils dating back to the Jurassic period. The diversification of therians is thought to have been influenced by the extinction of the dinosaurs, which allowed mammals to occupy new ecological niches.

Classification

Theria is divided into two main groups:

• Metatheria: This group includes all marsupials. Marsupials are primarily found in Australia and the Americas.
• Eutheria: This group includes all placental mammals. Eutherians are the most diverse group of mammals and are found worldwide.

Related pages

• Mammal
• Marsupial
• Placental mammal
• Monotreme