text: Image copyright Cambridge University Image caption Artist’s reconstruction of Saccorhytus coronarius, based on the original fossil finds. The actual creature was probably no more than a millimetre in size 
   
   Researchers have discovered the earliest known ancestor of humans - along with a vast range of other species. 
   
   They say that fossilised traces of the 540-million-year-old creature are "exquisitely well preserved". 
   
   The microscopic sea animal is the earliest known step on the evolutionary path that led to fish and - eventually - to humans. 
   
   Details of the discovery from central China appear in Nature journal. 
   
   The research team says that Saccorhytus is the most primitive example of a category of animals called "deuterostomes" which are common ancestors of a broad range of species, including vertebrates (backboned animals). 
   
   Saccorhytus was about a millimetre in size, and is thought to have lived between grains of sand on the sea bed. 
   
   Image copyright Jian Han, Northwest University, China Image caption Saccorhytus was also covered with a thin, relatively flexible skin and muscles. It probably moved around by wriggling 
   
   The researchers were unable to find any evidence that the animal had an anus, which suggests that it consumed food and excreted from the same orifice. 
   
   The study was carried out by an international team of researchers, from the UK, China and Germany. Among them was Prof Simon Conway Morris, from the University of Cambridge. 
   
   He told BBC News: "To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail was jaw-dropping. 
   
   "We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. All deuterostomes had a common ancestor, and we think that is what we are looking at here." 
   
   Degan Shu, from Northwest University in Xi'An, Shaanxi Province, where the fossils were found, said: "Saccorhytus now gives us remarkable insights into the very first stages of the evolution of a group that led to the fish, and ultimately, to us." 
   
   Until now, the deuterostome groups discovered were from between 510 to 520 million years ago. These had already begun to diversify into not just the vertebrates, the group to which we and our ancestors belong and animals such as starfish and sea urchins. 
   
   Because they looked so different from one another, it was difficult for the scientists to determine what an earlier, common ancestor might have looked like. 
   
   The study suggests that its body was symmetrical, which is a characteristic inherited by many of its evolutionary descendants, including humans. 
   
   Saccorhytus was also covered with a thin, relatively flexible skin and muscles, leading the researchers to conclude that it moved by contracting its muscles and got around by wriggling. 
   
   The researchers say that its most striking feature is its large mouth, relative to the rest of its body. They say that it probably ate by engulfing food particles, or even other creatures. 
   
   Also interesting are the conical structures on its body. These, the scientists suggest, might have allowed the water that it swallowed to escape and so might have been a very early version of gills. 
   
   Follow Pallab on Twitter ||||| Researchers have identified traces of what they believe is the earliest known prehistoric ancestor of humans – a microscopic, bag-like sea creature, which lived about 540 million years ago. 
   
   Named Saccorhytus, after the sack-like features created by its elliptical body and large mouth, the species is new to science and was identified from microfossils found in China. It is thought to be the most primitive example of a so-called “deuterostome” – a broad biological category that encompasses a number of sub-groups, including the vertebrates. 
   
   If the conclusions of the study, published in the journal Nature, are correct, then Saccorhytus was the common ancestor of a huge range of species, and the earliest step yet discovered on the evolutionary path that eventually led to humans, hundreds of millions of years later. 
   
   Modern humans are, however, unlikely to perceive much by way of a family resemblance. Saccorhytus was about a millimetre in size, and probably lived between grains of sand on the seabed. Its features were spectacularly preserved in the fossil record – and intriguingly, the researchers were unable to find any evidence that the animal had an anus. 
   
   The study was carried out by an international team of academics, including researchers from the University of Cambridge in the UK and Northwest University in Xi’an China, with support from other colleagues at institutions in China and Germany. 
   
   Simon Conway Morris, Professor of Evolutionary Palaeobiology and a Fellow of St John’s College, University of Cambridge, said: “We think that as an early deuterostome this may represent the primitive beginnings of a very diverse range of species, including ourselves. To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail is jaw-dropping. All deuterostomes had a common ancestor, and we think that is what we are looking at here.” 
   
   Degan Shu, from Northwest University, added: “Our team has notched up some important discoveries in the past, including the earliest fish and a remarkable variety of other early deuterostomes. Saccorhytus now gives us remarkable insights into the very first stages of the evolution of a group that led to the fish, and ultimately, to us.” 
   
   Most other early deuterostome groups are from about 510 to 520 million years ago, when they had already begun to diversify into not just the vertebrates, but the sea squirts, echinoderms (animals such as starfish and sea urchins) and hemichordates (a group including things like acorn worms). This level of diversity has made it extremely difficult to work out what an earlier, common ancestor might have looked like. 
   
   The Saccorhytus microfossils were found in Shaanxi Province, in central China, and pre-date all other known deuterostomes. By isolating the fossils from the surrounding rock, and then studying them both under an electron microscope and using a CT scan, the team were able to build up a picture of how Saccorhytus might have looked and lived. This revealed features and characteristics consistent with current assumptions about primitive deuterostomes. 
   
   Dr Jian Han, of Northwest University, said: “We had to process enormous volumes of limestone – about three tonnes – to get to the fossils, but a steady stream of new finds allowed us to tackle some key questions: was this a very early echinoderm, or something even more primitive? The latter now seems to be the correct answer.” 
   
   In the early Cambrian period, the region would have been a shallow sea. Saccorhytus was so small that it probably lived in between individual grains of sediment on the sea bed. 
   
   The study suggests that its body was bilaterally symmetrical – a characteristic inherited by many of its descendants, including humans – and was covered with a thin, relatively flexible skin. This in turn suggests that it had some sort of musculature, leading the researchers to conclude that it could have made contractile movements, and got around by wriggling. 
   
   Perhaps its most striking feature, however, was its rather primitive means of eating food and then dispensing with the resulting waste. Saccorhytus had a large mouth, relative to the rest of its body, and probably ate by engulfing food particles, or even other creatures. 
   
   A crucial observation are small conical structures on its body. These may have allowed the water that it swallowed to escape and so were perhaps the evolutionary precursor of the gills we now see in fish. But the researchers were unable to find any evidence that the creature had an anus. “If that was the case, then any waste material would simply have been taken out back through the mouth, which from our perspective sounds rather unappealing,” Conway Morris said. 
   
   The findings also provide evidence in support of a theory explaining the long-standing mismatch between fossil evidence of prehistoric life, and the record provided by biomolecular data, known as the “molecular clock”. 
   
   Technically, it is possible to estimate roughly when species diverged by looking at differences in their genetic information. In principle, the longer two groups have evolved separately, the greater the biomolecular difference between them should be, and there are reasons to think this process is more or less clock-like. 
   
   Unfortunately, before a point corresponding roughly to the time at which Saccorhytus was wriggling in the mud, there are scarcely any fossils available to match the molecular clock’s predictions. Some researchers have theorised that this is because before a certain point, many of the creatures they are searching for were simply too small to leave much of a fossil record. The microscopic scale of Saccorhytus, combined with the fact that it is probably the most primitive deuterostome yet discovered, appears to back this up. 
   
   The findings are published in Nature. Reference: Jian Han, Simon Conway Morris, Qiang Ou, Degan Shu and Hai Huang. Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China). DOI: 10.1038/nature21072. 
   
   Inset image: Photographs of the fossils show the spectacularly detailed levels of preservation which allowed researchers to identify and study the creature. Credit: Jian Han. ||||| A scanning election microscope (SEM) took this detailed image of the deuterostome with the extra-large mouth. 
   
   A speck-size creature without an anus is the oldest known prehistoric ancestor of humans, a new study finds. 
   
   Researchers found the remains of the 540-million-year-old critter — a bag-like sea organism — in central China. The creature is so novel, it has its own family (Saccorhytidae), as well as its own genus and species (Saccorhytus coronaries), named for its wrinkled, sac-like body. ("Saccus" means "sac" in Latin, and "rhytis" means "wrinkle" in Greek.) 
   
   S. coronaries, with its oval body and large mouth, is likely a deuterostome, a group that includes all vertebrates, including humans, and some invertebrates, such as starfish. [7 Theories on the Origin of Life] 
   
   "We think that as an early deuterostome, this may represent the primitive beginnings of a very diverse range of species, including ourselves," Simon Conway Morris, a professor of evolutionary palaeobiology at the University of Cambridge, said in a statement. "To the naked eye, the fossils we studied look like tiny black grains, but under the microscope the level of detail is jaw-dropping." 
   
   At first glance, however, S. coronaries does not appear to have much in common with modern humans. It was about a millimeter (0.04 inches) long, and likely lived between grains of sand on the seafloor during the early Cambrian period. 
   
   While the mouth onS. coronaries was large for its teensy body, the creature doesn't appear to have an anus. [See Images of the Bag-Like Animal & Other Cambrian Creatures] 
   
   "If that was the case, then any waste material would simply have been taken out back through the mouth, which from our perspective sounds rather unappealing," Conway Morris said. 
   
   Other deuterostome groups are known from about 510 million to 520 million years ago, a time when they had already started to evolve into vertebrates, as well as sea squirts, echinoderms (starfish and sea urchins) and hemichordates (a group that includes acorn worms). 
   
   However, these incredibly diverse animals made it hard for scientists to figure out what the common deuterostome ancestor would have looked like, the researchers said. 
   
   The newfound microfossils answered that question, they said. The researchers used an electron microscope and a computed tomography (CT) scan to construct an image of S. coronaries. 
   
   "We had to process enormous volumes of limestone — about 3 tonnes [3 tons] — to get to the fossils, but a steady stream of new finds allowed us to tackle some key questions: Was this a very early echinoderm or something even more primitive?" study co-researcher Jian Han, a paleontologist at Northwest University in China, said in the statement. "The latter now seems to be the correct answer." 
   
   The analysis indicated that S. coronaries had a bilaterally symmetrical body, a characteristic it passed down to its descendants, including humans. It was also covered with a thin, flexible skin, suggesting it had muscles of some kind that could perhaps help it wriggle around in the water and engulf food with its large mouth, the researchers said. 
   
   Small, conical structures encircling its mouth may have allowed water it swallowed to escape from its body. Perhaps these structures were the precursor of gill slits, the researchers said. 
   
   An artist's interpretation of Saccorhytus coronaries, which measured about a millimeter in size. Credit: S Conway Morris/Jian Han 
   
   Now that researchers know that deuterostomes existed 540 million years ago, they can try to match the timing to estimates from biomolecular data, known as the "molecular clock." 
   
   Theoretically, researchers can determine when two species diverged by quantifying the genetic differences between them. If two groups are distantly related, for instance, they should have extremely different genomes, the researchers said. 
   
   However, there are few fossils from S. coronaries' time, making it difficult to match the molecular clocks of other animals to this one, the researchers said. This may be because animals before deuterostomes were simply too miniscule to leave fossils behind, they said. 
   
   The findings were published online today (Jan. 30) in the journal Nature. 
   
   In another paper, researchers reported on the discovery of another type of tiny animal fossil from the late Cambrian. These creatures, called loriciferans, measured about 0.01 inches (0.3 mm) and, like S. coronaries, lived between grains of sand, the researchers said in a study published online today in the journal Nature Ecology and Evolution. 
   
   The newly identified species, Eolorica deadwoodensis, discovered in western Canada, shows when multicellular animals began living in areas once inhabited by single-celled organisms, the researchers said. 
   
   Original article on Live Science.
target: – Our very primitive beginnings look to have been very primitive indeed. It turns out the earliest known ancestor of humans was a sea creature a millimeter in size that likely lacked an anus. In a study published in Nature on Monday, scientists named Saccorhytus coronaries as a 540 million-year-old member—at that age the oldest one—of a category of animals called deuterostomes. The BBC explains deuterostomes gave rise to vertebrates. "All deuterostomes had a common ancestor, and we think that is what we are looking at here," researcher Simon Conway Morris tells the BBC. As for what they're looking at, "the bag-like body bears a prominent mouth and associated folds," the researchers write. Live Science reports the deuterostome groups scientists have previously discovered were at most 520 million years old, and had begun evolving into vertebrates, echinoderms (ie, starfish), and hemichordates (acorn worms). That left scientists stumped as to what a common ancestor would have looked like. Now they say they know. "We had to process enormous volumes of limestone—about [3 tons]—to get to the fossils, but a steady stream of new finds allowed us to" answer that question, says co-author Jian Han of the find, made in China. Two other details, from a Cambridge press release: The minuscule creature is thought to have lived between grains of sand on the sea bed, and it featured small conical structures that the water it ingested may have exited through "and so were perhaps the evolutionary precursor of the gills we now see in fish." (Scientists have found Earth's oldest civilization.)