Image: Mark A. Klingler/Carnegie Museum of Natural History
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Most humans think of the placenta as something that gets tossed out after childbirth. In fact, its appearance millions of years ago was a significant evolutionary development that gave rise to the vast majority of mammals alive today, from bats to whales to humans.
Until now, scientists believed that placental mammals first appeared some 125 million years ago. At that point, they branched off from the lineage that developed into modern marsupials, which nourish their young in their pouches instead of through placentas. Yet a recent fossil find backdates that divergence by about 35 million years, showing that mammals with placentas, known as eutherians, shared the earth with dinosaurs much longer than previously thought.
The fossil, described in August in the journal Nature (Scientific American is part of Nature Publishing Group), belongs to a tiny, shrewlike creature known as Juramaia sinensis that roamed China 160 million years ago. It appears to be the oldest known ancestor of placental mammals, according to a research group led by Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History.
Placental nourishment allows a more rapid and efficient transfer of nutrients from mother to offspring, which can result in faster brain development, larger mature brains and increased metabolic rate—all of which have had broad implications for the evolution of the behavioral and social complexity observed among today’s mammals.
The Juramaia fossil also yields important clues about the life of early eutherians. This animal appears to have been an insectivore, judging from the shape of its teeth, and it had robust forelimbs, which could have helped it to climb trees. This ability may have enabled it to take over as yet unexploited territory for both safety from predators and access to insects among the foliage. Any opportunity to reduce competition with other Jurassic mammals by staking out higher ground may have helped strengthen
Juramaia’s divergence from marsupials, leading it to become the ancestor of an extremely diverse group of animals.
The discovery of this fossil corroborates previous molecular studies, which estimated the divergence between eutherians and other mammals to have occurred around 160 million years ago—yet such estimations are often taken with a grain of salt until they are bolstered by hard physical evidence in the form of fossils. This is a prime example of the way in which multiple lines of scientific investigation can work together to draw robust conclusions and make well-supported hypotheses, thereby highlighting the value of integrative approaches to answering scientific questions.
This article was originally published with the title Meet Your Newest Ancestor.
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17 Comments
Add CommentAgain, if this creature was the first known to have a placenta, can you tell us how humans got the placenta from this shrewlike creature known as Juramaia sinensis? Wouldn't all warm blooded mammals come equipped with a placenta with their first induction on the Earth? The way you worded the article, it sounds like all warm blooded mammals sprang from this creature.
Reply | Report Abuse | Link to thisWow, that does look like some of my relatives...
Reply | Report Abuse | Link to thisLOL @ Gatnos your satire is funny...
Reply | Report Abuse | Link to thisThe genes that code for an eggs ability to cling to the placenta wall were stolen from a virus...
The article just says the creature is "the oldest known ancestor of placental mammals, according to a research group." The wording is very clear. And what an exciting discovery!
Reply | Report Abuse | Link to thisIt's funny how you prefer the mythology of a culture that was primitive even by the standards of its age, a culutre which was mostly ignored by its more advanced neighbours (Egyptians, Greeks, Babylonians, Persians all were vastly more advanced in all aspects of technology, society and literature), rather than accept one of the most elegant and well tested fruits of human intelect. Evolution is a well proven and documented natural law that has provided us with far, far more profound insight in our nature than jewish mythology. It has stood the test of time, it has provided testable predictions, it has led to huge advances in biosciences and in all measurable sense, it is the most complete scientific theory ever devised.
Reply | Report Abuse | Link to thisModern mammals can be broken down into three groups; Monotremes (Platypus, Echidna), Marsupials (Kangaroo, Opossum, Tasmanian Devil, etc) and Placentals (Carnivora, Cetacea, Chiroptera, Primates, Ungulates, Etc). All placental mammals would have evolved from a small population of animals closely related to this animal. If you go further back you will find the common ancestor of all mammals. You go back further still and you will find the common ancestor of mammals and reptiles. And so on. The way we got it from this animal is that the genes for Placental mammals first arose in these animals and because this conferred an advantage to that population the genes got passed on.
Reply | Report Abuse | Link to thisi evolved from a pikachu! not a rat-a-tat silly!
Reply | Report Abuse | Link to thisKinda looks like Sara Palin... looking for a tea bagger! Sorry, not scientific but needed to be said!
Reply | Report Abuse | Link to this@Gatnos - what on earth are you doing reading Scientific American?
Reply | Report Abuse | Link to thisIt is sad that not only Gatnos, but evidently quite a number of other readers here, don't realize that history, as we know it, is a field of study that developed long after the Bible.
Reply | Report Abuse | Link to thisThe Bible is theology, and as a Christian I happen to think it is quite fine theology, but it simply isn't history. Not history in the way that we think of history.
For that matter, since Gatnos thinks the Bible gives us history of the modern kind, Gatnos almost certainly doesn't realize there are TWO accounts of creation in Genesis. That's not a problem when you realize they are giving us theology. But Gatnos almost certainly thinks they are instead historical accounts.
Sorry, Gatnos, but the Bible is a lot more than you seem to realize. As for the rest of you, if you commented, you obviously have some interested in these topics. If you want to be better educated, they DO teach about the meaning, role, and formation of Bible in university. They also teach about the study of history.
This user suggests that a book that has been around for less than 3000 years (less than 2000 in its current iteration) and has been documented to have been edited and changed multiple times is an accurate recorded history. Nothing could be further from the truth. Only the most die-hard religious fanatics take the Bible at face value. It's a collection of parables and metaphors. I'm curious why someone who is so vehemently anti-science is surfing/reading scientific articles and is the second person to comment. Is it because of genuine interest, or simply because you have to seek out every article on evolution ASAP so you can be the first to dismiss it.
Reply | Report Abuse | Link to thisBut you're right. Evolution (or more accurately Natural Selection) is a Theory, not a Fact. Because it takes place over such a long time scale, we can't prove that humans or other mammals evolved in a particular pattern. However, there is such a preponderance of evidence from multiple fields (fossils, structural anatomy, physiology, developmental biology, genetic data, etc.,) that you have to be willfully ignorant not to believe it. The type of people that typically read current science magazines are intellectually curious people, the exact opposite of willfully ignorant. I think anyone who trolls these sites just to poo-poo anything that appears about evolution are wasting their time. But hey, if people want to do that it's their time to waste.
At least juramaia sinensis did not overpopulate the planet and threaten all life thereon. See the previous article on 7,000,000,000 of its descendants.
Reply | Report Abuse | Link to thisIs evolution a hypothetical theory? Or is evolution a verifiable fact? The two Oxford definitions of what "Theory" means define the difference, and are is worth repeating.
Reply | Report Abuse | Link to thisTheory. Sense 1: A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.
Theory, Sense 2: A hypothesis proposed as an explanation; hence, a mere hypothesis, speculation, conjecture; an idea or set of ideas about something; an individual view or notion.
In his book The Greatest Show on Earth, Richard Dawkins says in regard to the theory of evolution that the "scientists are using Sense I. while the creationists are - perhaps mischievously, perhaps sincerely - opting for Sense 2.". Dawkins simply switches the category of evolutionary theory, without justification, from the "unobserved" theoretical sense 2, to the "observable" experimental science sense 1, which relates to theories that can be tested, repeated and publicly verified by the Empirical & Scientific Method.
The sense 1 definition of "Theory" clearly states that it relates to "a hypothesis that has been confirmed or established by "observation or experiment,...something known or observed." The defining words being "established by observation or experiment" and "known and observed."
Never in all of recorded history has anyone ever "observed" any life-form evolve into a life-form of a different kind. Moreover, it will never ever be possible to establish evolutionary theory as a scientific fact using the empirical scientific method, and for good reason. Darwin's Theory of evolution is based on "unobserved" and "unrepeatable" past events believed to have happened over a vast span of time, ensuring there could never be any observers. This makes it impossible for Darwin's evolutionary theory to ever be established by the scientific method, as evolution cannot be tested, repeated, or verified by experiment or observation. Meaning, that in terms of the scientific method, Darwinism must forever remain an "unverifiable" hypothesis, and never anything more.
This places Darwin's Theory of Evolution firmly in Theory, Sense 2: A hypothesis proposed as an explanation; hence, a mere hypothesis, speculation, conjecture; an idea or set of ideas about something; an individual view or notion.
Reply | Report Abuse | Link to thisBecause evolutionary theory can never be established by the scientific method, Darwinism appeals entirely to "explanatory power". And thus amounts to 'science' by "explanations" and "assumptions.", rather that experiment or observation. Being based entirely on subjective presuppositions, interpretations, inferences, conjecture, predictions, and often sheer speculation. There is no possible way of ever empirically establishing whether evolution happened one way, and not another way, or even whether it happened at all.
Christianity has never been challenged by "methodological" naturalism or operational science. Indeed, it was the Christian worldview that provided the climate for scientific thought and the Empirical & Scientific Method, on which modern science is based. The pioneers of modern science were largely theists, who were ever mindful of the "tentative" nature of science, and the limits of "finite" human knowledge and understanding.
Christianity's greatest challenge has come from a scientific establishment seduced by "metaphysical" or "philosophical" naturalism, grounded in materialism and atheism. This is the unverified, and unverifiable, belief that ALL REALITY can, and must, be exclusively explained by natural events and material processes alone, to the exclusion of all transcendent realities, particularly God. In this quest for the Theory of Everything, hypothetical "mind experiments" and theoretical "assumptions" regarding unobserved and unrepeatable past events are now the order of the day. None-the-less, Christianity will survive the universal onslaught of this scientism also.
Furthermore, all of science is founded on realities for which there is absolutely no naturalistic answer, including the origin of the universe, life and consciousness, and the ultimate nature of the energy and matter.
Since the placenta is soft tissue, how do they know this particular animal was a placental. How do they know it descended from a marsupial line instead of developed from an animal whose egg hatched inside its own body as does a shark or any other type of live bearing animal.
Reply | Report Abuse | Link to thisDid the baby spend time in a moist uterus but without a placenta. Is there such an animal alive today?
How did the placenta develop?
That little critter had ancestors. It will be interesting to find them.
Yours are well written and intelligent comments. Thank you. You might also add that the consensus of any group does not make their common theory a fact.
Reply | Report Abuse | Link to thisOn the other hand, this particular little critter looks kind of cute up there in the family 'tree'.
I have no idea why people think evolution has never been witnessed. Its being witnessed constantly, when a bacteria becomes spontaneously resistant to an antibiotic for example.
Reply | Report Abuse | Link to thisAnd for the record, evolution is not when a life-form evolves into another one. We are not pokemons.