Episode 31 – The Ediacaran Biota

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Before the Cambrian Explosion, there was … a lot of weird squishy organisms. The Ediacaran, the subject of this episode, was a period just before the Cambrian. During this time we see the rise of a very odd and interesting group of organisms known as the Ediacaran Biota.

In the news
New findings show the last pterosaurs were more diverse than expected.
Early reptiles show signs of being able to lose their tails like some modern lizards.
Spider evolution in Hawaii has been remarkably consistent.
Interesting difference found between the limb bone lengths of crocodiles and alligators.

The Ediacaran: An Alien World

The Ediacaran Period (635-543 million years ago) marks the end of the Proterozoic Eon and is the only time period of the Precambrian that has fossils of complex multicellular life. Previously it had been thought that the Cambrian marked the origination of such organisms on Earth during the Cambrian Explosion. In fact, this line of thinking led to the fossils of the Ediacaran Biota being misidentified, misdated, or disregarded altogether for some time. This group of life has always been difficult to interpret because they show very few recognizable features of known groups of life.

Pictured below are some examples of these odd beings:

Cyclomedusa_cropped
Cyclomedusa, similar to Aspidella, which was the first Ediacaran fossil ever discovered. Image by Verisimilus at Wikimedia.
Charnia
Charnia, the first of the biota correctly dated to the Precambrian. Image by Smith609 at Wikimedia.
1200px-DickinsoniaCostata
Dickinsonia, one of the few of the Ediacaran Biota that shows signs of being able to move due the tracks that have been found in association with these fossils. Image by Verisimilus at Wikimedia.
Spriggina_Floundensi_4
Spriggina has features similar to annelid worms and could even have been a very early predator. Image by Merikanto~commonswiki.

What are they?

Debate continues as to how these strange fossils are related to other organisms. It has been suggested that they may be similar (or related) to early animals, protists, lichens, and more. They may be very early cousins of known groups, or they could be one or more separate branches of complex life altogether. One popular hypothesis is that they are relatives of the Cnidaria (corals and jellies), due to similar body structures – see below – but strong answers elude us.

Ptilosarcus_gurneyi_California
Sea pens are filter feeding cnidarians that strongly resemble the frond-like Charnia. But research so far shows no relation. Image by Toby Hudson at Wikimedia.
Dendrogramma_enigmatica_sp._nov.,_holotype
Dendrogramma is a recently discovered sphinophore, a group within Cnidaria, that has also been hesitantly connected with the Ediacaran Biota. From Just et al. at Wikimedia.

The mysteries surrounding this odd collection of ancient fossils are mostly still unanswered. If you’d like to learn more about what we know – and are still trying to figure out –  please feel free to follow these links to overviews and recent research.
The Burgess Shale: Enigmatic Ediacarans
Digging up the Precambrian—fossil burrows show early origins of animal behavior
Two Explosive Evolutionary Events Shaped Early History of Multicellular Life
Narbonne 2005. The Ediacara Biota: Neoproterozoic Origin of Animals and Their Ecosystems

Some have even suggested that perhaps this assemblage of organisms shouldn’t be considered a related group at all.
MacGabhann 2014. There is no such thing as the ‘Ediacara Biota’

One More Thing…

In case anyone was wondering about those limb segment terms we mentioned during the news: here they are (precise usage may vary).

Limb_Segments
David was right!

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2 thoughts on “Episode 31 – The Ediacaran Biota

  1. David Landis April 2, 2018 / 6:35 pm

    Could you do an episode on the confusing array of Permian reptiles / synapsids / therapsids / thecodonts / pelycosaurs, etc. It becomes so confusing as to their lineage, which came first…!

    Like

    • commondescentpc April 3, 2018 / 9:45 am

      Good suggestion, David! We’ll add that idea to our list.

      We might even have to devote multiple episodes to working through the whole array of Permian vertebrates!

      Like

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