12/23/2023 0 Comments Are platypus marsupials or mamals![]() ![]() For example, the red kangaroo gives birth to a baby the size of a jellybean just a month after conception before nursing its young for up to six months. In contrast, marsupials are essentially born in an embryonic state. The gestation period ranges depending on body size but can be up to 22 months in African elephants. Placental mammals are born with their four limbs and skulls already well developed, which grow in size as the animal gets older. Why do marsupials give birth to underdeveloped offspring? It's just a completely different way of developing that marsupials have evolved." "How marsupials reproduce isn't an intermediate form between egg-laying and placental mammals. "What we could clearly show is the marsupial way of developing is the one that's changed the most from the ancestor of marsupials and placentals," says Anjali. However, this study found that this not to be the case. The therians, which is the group containing marsupials and placental mammals, are thought to have diverged from each other quite soon after, around 160 million years ago.Īs the therians evolved away from young being born via an egg, it was originally thought that the live birth of an underdeveloped baby as in modern marsupials was the natural intermediate stage. It is thought that living mammals all descended from an egg-laying common ancestor that lived approximately 180 million years ago. It contains just five species alive today in two families: the platypus and the echidnas. Monotremes are egg-laying mammals and are the smallest of the three groups. Marsupials also give birth to live young but have a very short gestation period and so the offspring are very underdeveloped and so must be looked after by a parent in a pouch. The largest group is the placental mammals, which give birth to live, well-developed young and comprise about 95% of all living mammals, including humans. These are easily distinguished by their methods of reproduction. How did marsupial and placental mammals evolve?Īll mammals alive today can be divided into three groups: placental mammals, marsupials and monotremes. "As a member of the placental mammals, we often have this bias that ours is the group that evolution is directed towards, but that's not how evolution works." "It turns out that marsupials are the ones that are far more evolved from the ancestral form." "For a long time, people have treated marsupials as 'lesser mammals,'" which represent the intermediate stage between placental mammals and egg-layers, explains Anjali. This showed that marsupials have changed more from than ancestor than placentals have. ![]() Using a huge dataset of micro-CT scans of marsupial and placental specimens ranging from embryos to adults, the team measured how their skull shape changes through development and reconstructed how their ancestor would have developed. Professor Anjali Goswami, a research leader at the Museum and senior author of the study, says, "Using this big comparative data set generated from the museum's historical collections, we have been able to flip what we know about mammal evolution on its head." Using this data, they estimated how the common ancestor of marsupials and placentals would have developed and compared it with both groups to see which was the most similar. Micro-CT scans of 165 specimens helped the research team reconstruct the changes of the skull for these species during this early phase. ![]() The study, published in Current Biology, analyzed skulls during different stages of development in 22 living mammal species. However, new research has revealed that the ancestor of both groups was more similar to placentals than to marsupials, meaning that marsupials have modified their method of reproduction more than placentals have. Marsupials have long been considered the intermediate step in evolution between egg-laying and placental mammals, because they give birth to highly underdeveloped young similar to an embryonic state for placentals. By estimating how the common ancestor of mammals reproduced and developed, scientists have turned over the longstanding belief that marsupials are more primitive than placentals. ![]()
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