Was Dickinsonia One of the Earliest Multicellular Animals?

  • Thread starter BillTre
  • Start date
  • Tags
    Animals
In summary, the Ediacaran Period is characterized by the first macro scale fossils that were not thought to be bacterial mats. These fossils are of unusual morphology (strange looking), casting uncertainty on what exactly they are: plant, animal, fungus, colonial bacteria. The Ediacaran was followed by the Cambrian period where the number and variety of obviously animal body plans increased rapidly. At this time, the body plans of many of the animals found today were established. The identity and relationships of the Ediacaran fossils are still a matter of some discussion. Now, additional strong evidence identifying one of the Ediacaran animals, Dickinsonia, as an animal, based on "fossil" cholesterol
  • #1
BillTre
Science Advisor
Gold Member
2,495
9,811
Multicellular animals (metazoans) are thought (based upon molecular divergence data between metazoanas and chanoflagellates) to have initially evolved about 720 MYA, at beginning of the Cryogenian (720-635 MYA). These first pre-metazoans are assumed to have started out very small with no hard parts (including no cell walls) and therefore did not preserve well as fossils.
During this period, the first components of the metazoan system of development (working from a single fertilized egg to a clone of cells that reproducibly shape themselves into a functional adult form, in order to reproduce) that generates the adult body plans were established.

Metazoans are thought to have separated from Chanoflagelates (eucayrotic single celled flagellated metazoan precursors) during the Cryogenian (720-635 MYA).
Near microscopic fossils, often interpreted as embryos, have been found at the beginning or the Ediacaran.
The Ediacaran Period (635-541 MYA) is characterized by the first macro scale fossils that were not thought to be bacterial mats. These fossils are of unusual morphology (strange looking), casting uncertainty on what exactly they are: plant, animal, fungus, colonial bacteria.
The Ediacaran was followed by the Cambrian period where the number and variety of obviously animal body plans increased rapidly. At this time, the body plans of many of the animals found today were established.

The identity and relationships of the Ediacaran fossils are still a matter of some discussion.
Now, additional strong evidence identifying one of the Ediacaran animals, Dickinsonia, as an animal, based on "fossil" cholesterol associated with an organic layer of the fossil animal. Cholesterol is only produced by animals, not plants, fungi, bacteria, or algae.

Dickinsonia is one of the most likely of the Ediacaran fossils to be an animal, based on apparent trace fossils (like footprints), showing its movement and feeding behavior (see areas in a bacterial mat that were fed upon below). The cholesterol findings provide additional strong support for this this being an animal.
Dickinsonia may be a fossil member of the obscure Placozoan phylum. Placozoa are among the most primitive of multicellular animals. They have been variously located either above or below Sponges, Cnidarians (hydra, coral, sea anemone), and Ctenophores (comb jellies).

Considering all that, Dickinsonia seems to be something like this to:
  • two or maybe three tissue layers (Endoderm, ectoderm, (maybe mesoderm)). (Placozoa only have two tissue layers)
  • has a front to back body axis (therefore expect something like a Hox code for ID positions along this axis)
  • looks bilaterally symmetrical (goes with having a front and back axis combined with a top and bottom axis)
  • may have slithered along on cilia (like Placozoa).
  • Eat things (bacterial or algae cells?) it settles upon, then moves on. Probably no predators, for a while.
https://www.physicsforums.com/attachments/231018
Yorgia-with-the-feeding-traces-Epibaion-waggoneris-isp-nov-reconstruction-by-the copy.jpg
 

Attachments

  • Yorgia-with-the-feeding-traces-Epibaion-waggoneris-isp-nov-reconstruction-by-the copy.jpg
    Yorgia-with-the-feeding-traces-Epibaion-waggoneris-isp-nov-reconstruction-by-the copy.jpg
    92.9 KB · Views: 701
  • Like
Likes pinball1970, NTL2009, jim mcnamara and 3 others
Biology news on Phys.org
  • #2
The same approach (chemical indicator of some group of organisms) used in the Dickinsonia case has now been used with sponges, but at much earlier (older) dates.
The Dickinsonia case was from about 635-541 MYA, in the Ediacaran.
The chemical indicative of spongeness, was found in rocks from 660-635 million years ago (Cryogenian, an world wide ice age time before the Ediacaran (first animal fossils)).

The popular versions (Here and here.) I have read were not clear, its not clear to me where exactly they got the samples from.
The actual publication in Nature is behind a paywall.
If it were from some specific fossil remains, like in the Dickinsonia case (which had negative controls), then the fossil and the chemical are pretty specifically tied together.

They were talking about widespread existence of sponges, but very small sponges that would not leave fossils well.
This indicates (to me) they detected the chemical but did not have obvious fossils.
In that case, this approach provides another line of evidence concerning earlier origins of the animal lineage than are indicated by the fossil record.
Molecular studies often place the divergence of the animal lineage separated from their choanoflagelate progenitors at similar Cryogenian times.
This is usually attributed to the fossil record's poor ability to preserve un-skeletonized animals combined with the assumption that the first multicellular animals.

Sponges are often considered the most primitive of the metazoans (animals).
They have no nerve cells, are completely immobile, and have a very simple body plan.
They are like a choanoflagellate (assumed ancestor) embedded in a simple structure (the rest of the sponge) to make better flow for its filter feeding activities.
Geologically they have the oldest fossils thought to be metazoan (animals).
An important cell in the sponge, the choanocyte, is very similar to the choanoflagelates that are considered to be the group that animals evolved from.
 
  • Like
Likes pinball1970

Related to Was Dickinsonia One of the Earliest Multicellular Animals?

What is the earliest animal on record?

The earliest animal on record is a microscopic sea sponge called Otavia antiqua, which lived in what is now Namibia approximately 760 million years ago.

How did the earliest animals evolve?

The evolution of the earliest animals is still a topic of debate among scientists. Some believe that they evolved from single-celled organisms through natural selection and genetic mutations, while others propose that they may have originated from a symbiotic relationship between multiple organisms.

What evidence supports the existence of the earliest animals?

The main evidence for the existence of the earliest animals is fossil records. Fossils of Otavia antiqua and other early animal species have been found in sedimentary rocks and provide insight into their physical characteristics and behavior. Additionally, molecular studies of modern animals have revealed similarities to early animal ancestors.

What role did the earliest animals play in shaping Earth's ecosystems?

The earliest animals played a crucial role in shaping Earth's ecosystems by introducing new forms of predation and competition. They also contributed to the cycling of nutrients and the development of complex food webs, which allowed for more diverse and advanced life forms to evolve.

What can we learn from studying the earliest animals?

Studying the earliest animals can provide insights into the origins and evolution of life on Earth. It can also help us understand the environmental conditions of the past and how they have changed over time. Additionally, studying these ancient creatures can inform our understanding of modern ecosystems and how they may respond to future changes.

Similar threads

Replies
1
Views
1K
Replies
1
Views
2K
  • Other Physics Topics
2
Replies
48
Views
8K
Replies
4
Views
3K
  • General Discussion
Replies
4
Views
3K
Back
Top