It’s hard to imagine life on Earth without mammals, swimming deep in the oceans, burrowing in deserts, and incredibly diverse.
Studies suggest that this diversity can be deceptive, at least in terms of how mammals develop in the next generation. Almost all mammals living today fall into two categories: placental mammals and marsupials.
Placental mammals, including humans, whales, and mice, have long gestation periods, give birth to well-developed young with all major organs and structures in place, and relatively short weaning or suckling when the offspring are breastfed. their mothers.
Marsupial mammals such as kangaroos and opossums are the opposite: they are characterized by a short gestation period, the birth of little more than fetuses, and a long lactation period, or marsupial, during which the offspring are eats and grows in the mother’s pouch for several weeks or months. .
For decades, biologists viewed marsupial reproduction as the most “primitive” state and assumed that placentas developed their “most advanced” method after these two groups diverged, but new tests in the research was published in a paper by researchers at the University of Washington and the Burke Museum of Natural History and Culture. Published on July 18 in The Journal of The American Naturalist, a team led by a team provides evidence that another group of mammals, the extinct multiple tubers, likely reproduced in such a way placenta attitude.
Because many tubercles diverged in other mammalian lineages before the development of placentas and marsupials, these results call into question the view that marsupials are “less evolved” than their placental cousins.
Fossil evidence indicates that these creatures were the most numerous mammals in western North America before and after the mass extinction that killed the dinosaurs 66 million years ago.
“This study challenges the prevailing view that the placental reproductive strategy is more advanced compared to a more primitive follicular strategy, and our findings suggest that reproductive placental-like is either ancestral reproductive tract of all mammals which gives birth, or which resembles the placenta. Reproduction evolved in many species and placentas.
Polytubers appeared about 170 million years ago during the Jurassic period. Most are small-bodied, rat-like creatures. During their long history, Polytubers were the most numerous and diverse group of mammals.
But scientists know very little about its life history, including how it reproduces. Because of the generally poor fossil record, the last many tubercles died out about 35 million years ago.
Working under the supervision of co-author Gregory Wilson Mantella, professor of biology at the University of Washington and curator of vertebrate paleontology at the Burke Museum, Weaver concluded that the microscopic structure of fossilized bone tissue may contain useful life history information about many creatures. tubercle like growth rates. Weaver and colleagues found 18 fossilized femurs, cross-sections of femurs from multiple tubercles that lived in Montana about 66 million years ago.
All 18 samples showed the same structural organization: a layer of irregular bone ‘hidden’ between the inner and outer layers of organized bone.
Irregular bone or woven bone means rapid growth, and under the microscope, the layers of bone tissue are named oblique because of organized bones, the layers are parallel, showing slower growth . each other.
The researchers examined femur sections from 35 species of small-bodied mammals, 28 placental animals, and seven living marsupials, all from the Burke Museum’s collections.
All of the choroidal femurs showed a similar “sandwich” organization as the multiple explants, but all of the follicular femurs were composed almost entirely of organized bone, with a small amount of irregular bone, and believed team that the big difference is likely. reflect different life stories.
Source: indiaeducationdiary
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