Therian mammals

Therian mammals (clade Theria) are a subclass of mammals that give birth to live young, as opposed to laying eggs. This group includes two major infraclasses:

• Metatheria – Marsupials (e.g., kangaroos, koalas, opossums)
• Eutheria – Placentals (e.g., humans, dogs, whales)

Key Characteristics of Therian Mammals

• Live Birth: Therians give birth to live young rather than laying eggs (a trait seen only in monotremes like the platypus and echidna).
• Mammary Glands: Therians nurse their young with milk produced from mammary glands.
• Middle Ear Structure: They have three middle ear bones (malleus, incus, and stapes) that aid in sensitive hearing.
• Dentition: Specialized teeth suited for various dietary needs, including incisors, canines, premolars, and molars.
• Placenta (in Eutherians): Eutherians have a complex placenta that facilitates nutrient exchange between mother and offspring during gestation.
• Marsupial Pouch (in Metatherians): Marsupials give birth to underdeveloped young that continue their development in a pouch.

Evolution

Therian mammals are believed to have evolved around 160–170 million years ago during the Jurassic period. They diverged from the egg-laying monotremes (subclass Prototheria), which represent the most primitive lineage of mammals.

Examples of Therian Mammals

• Marsupials: Kangaroo, wallaby, wombat, Tasmanian devil
• Placentals: Humans, lions, elephants, bats, whales, rodents

All modern mammals, except for monotremes, are classified as therians.

More information is available at [ Wikipedia:Therian_mammals ]

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