Scientists take a closer look at Earth's first animals

Evolution is getting a rethink after scientists take a closer look at Earth’s first animals
An Ediacaran fossil from the National Earth Science Museum, Namibia. Credit: J. Hoyal Cuthill

When did animals originate? In research published in the journal Palaeontology, we show that this question is answered by Cambrian period fossils of a frond-like sea creature called Stromatoveris psygmoglena.

The Ediacaran Period lasted from 635 to 542m years ago. This era is key to understanding animal origins because it occurred just before the "Cambrian explosion" of 541m years ago, when many of the animal groups living today first appeared in the fossil record.

Yet when large fossils from the Ediacaran Period were first identified during the 20th century they included unique frond-like forms, which were not quite like any living animal. This prompted one of the greatest debates still raging in evolution. What exactly were these enigmatic fossils, often called the Ediacaran biota?

Linking Ediacaran and Cambrian fossils

By comparing members of the Ediacaran biota to a range of other groups in a computer analysis of evolutionary relationships, we found that Stromatoveris psygmoglena provides a crucial link between the older period and the which appeared in startling number and diversity during the Cambrian period.

Fossils of Stromatoveris psygmoglena are found in only one place in the world: Chengjiang county, China. This region is known for exceptionally well-preserved Cambrian fossils from 518m years ago.

Evolution is getting a rethink after scientists take a closer look at Earth’s first animals
A Cambrian fossil of Stromatoveris from Northwest University, China. Credit: J. Hoyal Cuthill

While the fossil record most often preserves only hard shells or bones, some special sites like Chengjiang preserve the remains of soft-bodied animals, such as Stromatoveris psygmoglena. Originally described in 2006 from eight known specimens, we examined over 200 new fossils of the organism that have since been discovered by researchers from Northwest University, China, and dated to the Cambrian period.

The way in which fossils of the Ediacaran Period were preserved has been another of their mysteries. These fossils often show signs of bending, twisting and tearing, suggesting that they preserve soft-bodied organisms without hard parts. However, there is rarely anything left of the soft tissues themselves.

Instead, they left moulds in the surrounding sediment, a little like a footprint on the beach. In contrast, the newly examined Cambrian fossils of Stromatoveris psygmoglena retain carbon-based tissue, allowing us to see the detailed and internal anatomy of the body itself.

During a research fellowship at the Tokyo Institute of Technology and the University of Cambridge, the new Cambrian period fossils of Stromatoveris psygmoglena were compared to earlier Ediacaran fossils in a computer analysis of anatomy and evolutionary relationships. This was also the first analysis to test the relationships between the Ediacaran biota and a range of other organisms, covering single-celled creatures called protozoans, algae, fungi, and nine types of animals, including Stromatoveris psygmoglena. This analysis used over 80 photographs of individual fossil specimens to compare anatomical features across these groups.

The analysis showed that Stromatoveris psygmoglena and seven key members of the Ediacaran biota share very similar anatomies, including multiple, branched fronds which radiate outwards like seaweed, uniting them all in a new group of early animals called Petalonamae. The name means "Nama Petals" and was chosen to honour biologist Hans Pflug and his work on the Ediacaran biota in Namibia, a reference to the petal-like fronds which, Pflug noted, distinguish these unusual animals.

Evolution is getting a rethink after scientists take a closer look at Earth’s first animals
The front view of a rangeomorph fossil, the oldest of the Ediacaran biota. Credit: Jennifer Hoyal Cuthill, Author provided

Rethinking animal evolution

Uniting these members of the Ediacaran biota and Stromatoveris psygmoglena in a single group of animals has major implications for animal origins. In light of this new evidence, some older ideas on early animal evolution may need to be revised.

Because members of the Ediacaran biota can now be classed as animals, we can date the origin of the animal kingdom to at least the time when these fossils appeared. The oldest members of these groups are known as "rangeomorphs" and appear in the fossil record approximately 571m years ago, in the late Ediacaran Period.

This means that animal species were diversifying well before the Cambrian explosion. It may also mean that the search for animal origins should now focus on the time before this, in the early Ediacaran and even more ancient geological periods. Based on this, animals may have originated much earlier than the traditional reading of the record had suggested.

This study also has key implications for the ecology and eventual extinction of the petalonamids. Many Ediacaran species have not been found in later rocks leading some researchers to think that they were a "failed experiment" in evolution, disappearing by the beginning of the Cambrian. Indeed, this was my own view until I saw the remarkable new fossils of Stromatoveris psygmoglena.

The inclusion of this Cambrian animal among the petalonamids changes the picture of the Ediacaran biota. Stromatoveris psygmoglena shows that the petalonamids were alive and well over 20m years into the Cambrian period and did not go extinct at its outset, as had been thought.

Even more intriguing, more than 200 fossils of Stromatoveris psygmoglena have now been found, despite the fact that it lacked hard parts which are usually most easily preserved. This indicates that this species was an important member of its shallow marine ecosystem rather than a rare or marginal survivor.

This could mean that the petalonamids adapted more successfully to the changes of the Cambrian period than had been thought, or that the Ediacaran period and its animals were less alien and more advanced than previously realised. We can be confident, however, that the animal kingdom we occupy is much older than we once thought.

Explore further

Researchers report the earliest fossil footprints

More information: Jennifer F. Hoyal Cuthill et al. Cambrian petalonamid Stromatoveris phylogenetically links Ediacaran biota to later animals, Palaeontology (2018). DOI: 10.1111/pala.12393
Journal information: Palaeontology

Provided by The Conversation

This article was originally published on The Conversation. Read the original article.The Conversation

Citation: Scientists take a closer look at Earth's first animals (2018, August 10) retrieved 16 October 2019 from
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Aug 10, 2018
Fossils, or "fossils", being present in only one relatively small region of the earth.
That region being fairly close to the "Ring of Fire", certainly subject to everything from earthquakes to volcanoes, especially after half a billion years.
Being subject to the eroding power of rain, also, but not being damaged.
For that matter, having started as impressions in mud or silt, yet not having been erased at all. The article talks about a "footprint on the beach". How long do any of those last? Has anyone actually seen an impression in dirt begin to fossilize? For that matter, has anyone really seen remains halfway between being still wholly biological and completely mineral? In the past few years, they've been trying to tell us they found footprints in a muddy beach from tens of thousands of years ago to "fossil raindrops" from 2 billion years ago! Thee is no reason to accept claims of "fossils" as anything more than untruths.

Aug 10, 2018
There are also ossified brains in living humans. These people are sometimes known as "boneheads". These folks are dead-ends off the main line of Homo sapiens' descent. They cannot accept reality-based science due to a lack of evolution in their cerebral cortex, which limits logic and deductive reasoning.

Fossils are found all over the world, not just near the "Ring of Fire". And no one is likely to ever find a partially mineralized decaying organism as it takes many thousands of years for this process to occur, and it most commonly occurs near or under bodies of water where most fossil hunters cannot look for them, but they are certainly there. Fossils are found embedded in solid rock, thousands of feet down. How did they get there? Long term processes for sure.

Analyze the content of ancient "bones", also known as fossils, and you will find they are made of minerals via a process known as petrification.

Learn about it : https://en.wikipe...ifaction


Aug 10, 2018
"Fossil" footprints are not classic fossils but rather typically made by creatures walking near various geological features, one of which could be an active volcano. The falling ash from a volcano fills the foot prints and preserves them over time, usually as the positive image since the ash is dissolved away, leaving the "footprint on the beach", now preserved in stone. Such "fossils" are extremely rare as they are only formed under very exacting conditions since their initial impressions are very fleeting.

Aug 10, 2018
I'm sure that if I were to point out to the creationist up top that where I live, in the heart of the Great Plains of the US, there are areas of badland outcroppings dating to 80 mya that are so full of marine fossils you can't take a step without crushing some underfoot, that he would pounce upon that fact as "proof" that the Genesis flood occurred and that these shells, giant extinct fish, ichthyosaurs, mosasaurs, plesiosaurs, giant turtles, and shark teeth so plentiful some local families have achieved some fame by using them to construct works of folk art date to a mere 3,000 BC or so.

How strange that so many swimming animals drowned.

Btw, the only ring of fire around here is those wildfires that every year seem to get closer and closer to the towns instead of merely destroying tens of thousands of acres of crops and pasture, and a few hours west, mountain forests from what we call the "Front Range" all the way to California and Washington state.

Aug 11, 2018
Well there was that recent article about Homo Erectus and the speculation that innate "laziness" may have resulted in their extinction.

The creationists are evidence that the primitive hominids are not extinct. Instead their legacy for intellectual laziness is carried on by the religious woo merchants of today.

Aug 11, 2018
Placing religion aside, which today is known to be as erroneous as astrology and homeopathy and certainly should not be discussed on science sites, this is a tremendous advance! It secures the rangeomorphs as animals, place them on the phylogenetic tree and show evidence for a nice progression to Cambrian biota. I read somewhere else that the Petalonamae found in this work was still 0.5 % of biota.

Re the frequent impression fossils and then their absence, the burrow tracks are rare at the time. And the height of the Petalonamae - up to 2m - indicated an absence of free swimming larvae. Their fractal repair (see the paper) indicates reproduction by cloning, which is no surprise in early organisms, and explain the need to reach away from an immobile or poorly mobile steadfast.

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