Why life on Earth first got big

June 25, 2018, University of Cambridge
Ediacaran fossils at Mistaken Point, Newfoundland. Credit: Emily Mitchell

Some of the earliest complex organisms on Earth—possibly some of the earliest animals to exist—got big not to compete for food, but to spread their offspring as far as possible.

The research, led by the University of Cambridge, found that the most successful organisms living in the oceans more than half a billion years ago were the ones that were able to 'throw' their offspring the farthest, thereby colonising their surroundings. The results are reported in the journal Nature Ecology and Evolution.

Prior to the Ediacaran period, between 635 and 541 million years ago, life forms were microscopic in size, but during the Ediacaran, large, complex organisms first appeared, some of which—such as a type of organism known as rangeomorphs—grew as tall as two metres. These organisms were some of the first on Earth, and although they look like ferns, they may have been some of the first animals to exist—although it's difficult for scientists to be entirely sure. Ediacaran organisms do not appear to have mouths, organs or means of moving, so they are thought to have absorbed nutrients from the water around them.

As Ediacaran organisms got taller, their body shapes diversified, and some developed stem-like structures to support their height.

In modern environments, such as forests, there is intense competition between organisms for resources such as light, so taller trees and plants have an obvious advantage over their shorter neighbours. "We wanted to know whether there were similar drivers for organisms during the Ediacaran period," said Dr. Emily Mitchell of Cambridge's Department of Earth Sciences, the paper's lead author. "Did life on Earth get big as a result of competition?"

Mitchell and her co-author Dr. Charlotte Kenchington from Memorial University of Newfoundland in Canada examined fossils from Mistaken Point in south-eastern Newfoundland, one of the richest sites of Ediacaran fossils in the world.

Artist's impression of rangeomorphs, fern-like organisms that lived during the Ediacaran Period. Credit: Charlotte Kenchington

Earlier research hypothesised that increased size was driven by the competition for nutrients at different water depths. However, the current work shows that the Ediacaran oceans were more like an all-you-can-eat buffet.

"The oceans at the time were very rich in nutrients, so there wasn't much competition for resources, and predators did not yet exist," said Mitchell, who is a Henslow Research Fellow at Murray Edwards College. "So there must have been another reason why got so big during this period."

Since Ediacaran organisms were not mobile and were preserved where they lived, it's possible to analyse whole populations from the fossil record. Using spatial analysis techniques, Mitchell and Kenchington found that there was no correlation between height and competition for food. Different types of organisms did not occupy different parts of the water column to avoid competing for resources—a process known as tiering.

"If they were competing for food, then we would expect to find that the organisms with stems were highly tiered," said Kenchington. "But we found the opposite: the organisms without stems were actually more tiered than those with stems, so the stems probably served another function."

According to the researchers, one likely function of stems would be to enable the greater dispersion of offspring, which rangeomorphs produced by expelling small propagules. The tallest organisms were surrounded by the largest clusters of offspring, suggesting that the benefit of height was not more food, but a greater chance of colonising an area.

"While taller organisms would have been in faster-flowing water, the lack of tiering within these communities shows that their height didn't give them any distinct advantages in terms of nutrient uptake," said Mitchell. "Instead, reproduction appears to have been the main reason that life on Earth got big when it did."

Despite their success, rangeomorphs and other Ediacaran disappeared at the beginning of the Cambrian period about 540 million years ago, a period of rapid evolutionary development when most major animal groups first appear in the .

Explore further: Big, shape-shifting animals from the dawn of time

More information: Emily G. Mitchell et al, The utility of height for the Ediacaran organisms of Mistaken Point, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0591-6

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17 comments

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TeeSquared
3 / 5 (6) Jun 26, 2018
"life forms were microscopic in size, but during the Ediacaran, large, complex organisms first appeared,"

They just appeared?
Anonym642864
1 / 5 (1) Jun 27, 2018
To my mind taller organism i.e plant grew as the land started coming near equator. As we all know that equator has maximum sunlight and maximum rain so trees were longer. As per as Dinosaur is concerned they are to my mind a conjugate of birds and reptiles.
Da Schneib
3 / 5 (6) Jun 27, 2018
They just appeared?
It's that, you know, evolution by natural selection thingie. You might have heard of it somewhere before. Search your memory.

Back on topic, it's not all that surprising that reproduction strategies shaped life by providing the main natural selector in terms of reproduction. Predation gets all the attention, but there's no point in getting more to eat if you can't turn it into more progeny.
TeeSquared
2.4 / 5 (7) Jun 27, 2018
Back on topic, it's not all that surprising that reproduction strategies shaped life by providing the main natural selector in terms of reproduction.


Why would an organism change to a reproduction system? Which came first, male or female?
torbjorn_b_g_larsson
2.6 / 5 (5) Jul 02, 2018
Notably rangeomorphs disappeared when most extant animal groups evolved - those had larvae for dispersal.

@TeeSquared: They appeared in the fossil record due to taphonomy (preservation conditions)), they and their ancestors were still soft but the Ediacaran geology was unique in preserving such species.

Rangeomorphs may have reproduced by cloning: no larvae. As for sex evolution, still an open area, the consensus model for body plan animals (i.e. having evolved a Hox box) is that "both sexes", i.e. hermaphrodites, evolve first. Then usually females mating with herms, later males and lastly herms disappearing, for reasons of sex differentiation (ova vs sperm). Sex is easy to evolve, so it seems to have happened in about this generic progression over and over independently. Australian sea snails are reevolving sex, say.

Unicellular life forms evolve sexes differently, and can have any number of them.
PTTG
3.7 / 5 (3) Jul 02, 2018
TeeSquared, since you're obviously trying to push creationism, you tell me:

If a loving god that wanted his creation to know his majesty created the universe, why would he place deceptive fossils? Is he attempting to lead his creation to disbelief? Or is there a nemesis that is more powerful than the creator?
Whydening Gyre
2 / 5 (4) Jul 02, 2018
Back on topic, it's not all that surprising that reproduction strategies shaped life by providing the main natural selector in terms of reproduction.


Why would an organism change to a reproduction system? Which came first, male or female?

Reproduction is not just male and female. It comes in a variety of forms..
Da Schneib
3 / 5 (6) Jul 02, 2018

Why would an organism change to a reproduction system?
I don't even know what this sentence means. For starters, anything that can't reproduce can't exist for more than one generation.

To examine the premises of this question, you might as well ask how Saint Bernards evolved from chihuahuas in one generation. It's idiotic.
humy
3.7 / 5 (3) Jul 03, 2018
Why would an organism change to a reproduction system? Which came first, male or female?

yes, it's a great mystery whether male bacteria or female bacteria came first.
...
No, asexual organism evolved first.
Then, like the strawberry plant can reproduce both by sexual and asexual means, some organism evolved to reproduce both by sexual and asexual means from those purely asexual organism. Then later some of those later organisms evolved to loose their ability to evolve asexually and thus only evolve sexually.
FredJose
1 / 5 (3) Jul 03, 2018
It's that, you know, evolution by natural selection thingie.

, like the strawberry plant can reproduce both by sexual and asexual means, some organism evolved to reproduce both by sexual and asexual means from those purely asexual organism.

Sex is easy to evolve, so it seems to have happened in about this generic progression over and over independently. Australian sea snails are reevolving sex, say


All these statement simply underline just how non-scientific and nonsensical the evolutionary scenario generating scheme really is. Nobody can directly and specifically answer the question so they resort to all kinds of completely vacuous guesswork scenarios.

Never mind that they cannot show how it could happen in a step-by-step fashion and that that path can actually be retraced and repeated.

Life cannot start spontaneously all by itself. Neither can self-replication. Let alone the highly complex systematic process of impregnation, gestation and birth.
SCVGoodToGo
4 / 5 (4) Jul 03, 2018
Fred, we can explain it to you, but we can't understand it for you.
Da Schneib
3.4 / 5 (5) Jul 03, 2018
@FreddyJoe doesn't have a very good imagination, doesn't know how science works, and expects all the answers handed to it on a silver platter.

The world doesn't work like that. It certainly doesn't work like a book by drunken stone age sheep herders about a super magic daddy who gives you pie in the sky when you die says it does.
SCVGoodToGo
3.7 / 5 (3) Jul 03, 2018
@DS I've often wondered how much of the Bibble was originally induced by neurosyphilis (them herders get lonely at night). This does not include all the botched translations and rewritings over the centuries, like the Bibble according to Jimmy.
Da Schneib
3.4 / 5 (5) Jul 03, 2018
I wanna see the part in the Babble where it says how to build a refrigerator. Or make a vaccine.
SCVGoodToGo
4 / 5 (4) Jul 03, 2018
Refrigeration came between Genesis and Exodus, but when the exodus happened the fridge was too heavy so it was left behind. There was no U-Haul yet in those days.
Whydening Gyre
2.3 / 5 (3) Jul 04, 2018
...
Life cannot start spontaneously all by itself.

And it doesn't. It requires a plethora of conditions at a particular moment in time. (EG - heat, motion, pressure, the right combination of elements, etc.). Which, more often then not, a random process. A complex system all it's own...
Neither can self-replication.

It's not really life until it CAN self replicate, is it...
Let alone the highly complex systematic process of impregnation, gestation and birth.

What makes it complicated is that you usually have to buy dinners and develop a "relationship", first...
Whydening Gyre
2.3 / 5 (3) Jul 05, 2018
Fred,
Here's a vid on the mechanic of evolution (a mechanical system in and of itself) that might help you in your quest -
https://www.youtu...RN0KihOU

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