Placental mammals
Kartavya Desk Staff
- •Source: Phys org*
Context: New research from Stockholm University, in collaboration with other institutions, reveals that brown fat, a crucial heater organ in placental mammals, evolved exclusively in modern placental mammals.
What are Placental mammals?
Placental mammals, classified under the subclass Eutheria, are animals that have a placenta, a vascular organ formed during gestation for nutrient exchange between the mother and fetus. They carry their fetus in the uterus until birth at an advanced stage, nourishing them through the placenta. This allows for longer fetal growth, resulting in larger and more mature offspring at birth.
Fossil evidence suggests they evolved around 163-157 million years ago.
Marsupials, on the other hand, give birth to relatively undeveloped young, which continue to grow in a pouch outside the womb, nourished by a short-lived placenta. Over 330 species of marsupials exist, with examples including kangaroos and koalas.
Feature | Placental Mammals | Marsupials
Birth Process | Give birth to relatively developed young | Give birth to relatively undeveloped young, which continue to grow and develop outside the womb, typically in a pouch
Placenta | Have a well-developed placenta | Have a less-developed, short-lived placenta that nourishes their young for a few days before birth
Gestation Period | Longer gestation period, allowing for larger and more mature offspring at birth | Shorter gestation period, resulting in less mature offspring at birth, which continue to develop externally
Heat Production | Possess fully evolved brown fat for heat production | Possess a not fully evolved form of brown fat, lacking thermogenic function
Epipubic Bone | Do not have an extra pubic bone for pouch support | Have an extra pubic bone, the epipubic bone, to support their pouch
Examples | Humans, dogs, cats, elephants, etc. | Kangaroos, koalas, opossums, etc.
Key Phrases: Placental mammals, Marsupials