Bag-like sea creature was humans' oldest known ancestor

>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.

>>107025
What? I thought the oldest relative was that rock thing.

>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.

>More information: Jian Han et al, Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China), Nature (2017). DOI: 10.1038/nature21072
>Journal reference: Nature
>Provided by: University of Cambridge

>>107025
I can't tell where this thing begins and ends

My great grandfather was a plastic bag, they're not so distant.

>>107029
trilobytes come after, this thing appears to be hardly after the single cell stage.

>>107025
>oldest known ancestor
What does this term even mean?
Wouldn't our oldest ancestor be the first living creature to exist? Like a really basic amoeba or something?

>>107025
Looks like a final fantasy boss

>he researchers were unable to find any evidence that the animal had an anus.

>>107088
give a hoot. read a book.

only you can prevent stupid questions!

>>107025
Doesn't surprise me, I know a lot of people with similarities to old windbags

Lovecraft was right all along.

>>107088
KNOWN ancestor anon

>>107092

Yeah. Why is that in the article anyway? It seems weird. It'd be like mentioning they didn't find a cock or pussy. Did they expect to find an anus and didn't? I thought most lifeforms that small just excreted it through their skin or right from the cell itself. I thought only complicated lifeforms had a need for mass waste removal requiring one.

>>107092
>>107226
The development of a one way gastrointestinal tract was a pretty big milestone which allowed significant tissue specialisation and therefore organism complexity

Before anuses existed most creatures were about as simple as sea anemones

When the researcher was interviewed they probably mentioned it because it is significant but the interviewer would not have grasped on the implications, just that it was important, so they stuck it in the article

>>107044
I used a plastic bag for a condom one time but she still got pregnant

>>108800
This one is rather small, anon.

>>107088
>know ancestor
It means that it is the oldest one we know about that we actually found. Older lifeforms tend to be smaller which implies that it is difficult to find. That thing is 1mm, I don't even know how they managed to find it so easily in limestone.