3 ms·

Would you call single-celled organisms (or anything that came before Dickinsonia) animals?

btilly 8y ago
Yes. See https://www.smithsonianmag.com/smart-news/one-oldest-known-animals-tiny-ancient-sponge-180954523/ https://www.smithsonianmag.com/smart-news/one-oldest-known-a... for a fossil of an arguable animal that at 600 million years predates this one. In fact we have evidence that the sponge/other animals split was one of the early taxonomic splits to happen, so it seems likely to me that Dickinsonia could be an ancestor of every animal EXCEPT sponges. Which may well have naturally developed from colony organisms like Stromatolites. (Which in turn date back over 3 billion years.)
baddox 8y ago
As far as I know, Animalia currently only includes multicellular organisms by definition, but maybe different definitions are used for the distant past.
- a1369209993 8y ago
  I don't know about the definition you're using, but taxonomically speaking there is at least one single-celled organism that's indisputably part of (as in descended from) Animalia: Canis lupus incertae sedis[1][2], a infectious disease that evolved from dogs[3]. (On further wiki-walking, there also appear to be similar diseases evolved from devils, hamsters, and clams[4].) There are also choanoflagellates[5], which might have reverted to single-celled life after a stint as multicellular, or might not, but are in any case more closely related than the opisthokont[6] common ancestor of animals and fungi. (These are rather more relevant to the context of "were there single-celled animal ancestors?". If opisthokonts already formed differentiated clonal colonies, then there was no point in the main [modern normal animals] lineage that was defensibly already animal but not yet multicellular. Apoikozoa[7] allegedly formed colonies, but it's not clear to what extent they were differentiated and/or obligate.) 1: https://en.wikipedia.org/wiki/Canine_transmissible_venereal_tumor https://en.wikipedia.org/wiki/Canine_transmissible_venereal_... 2: https://www.quora.com/Has-a-complex-organism-like-a-dog-ever-evolved-into-a-single-cell-organism/answer/Israel-Ramirez https://www.quora.com/Has-a-complex-organism-like-a-dog-ever... 3: https://sci-hub.se/https://doi.org/10.1016/j.gde.2015.03.005 https://sci-hub.se/https://doi.org/10.1016/j.gde.2015.03.005 4: https://en.wikipedia.org/wiki/Transmissible_cancer https://en.wikipedia.org/wiki/Transmissible_cancer 5: https://en.wikipedia.org/wiki/Choanoflagellata https://en.wikipedia.org/wiki/Choanoflagellata 6: https://en.wikipedia.org/wiki/Opisthokonta https://en.wikipedia.org/wiki/Opisthokonta 7: https://en.wikipedia.org/wiki/Apoikozoa https://en.wikipedia.org/wiki/Apoikozoa

Yes. See https://www.smithsonianmag.com/smart-news/one-oldest-known-animals-tiny-ancient-sponge-180954523/ https://www.smithsonianmag.com/smart-news/one-oldest-known-a... for a fossil of an arguable animal that at 600 million years predates this one. In fact we have evidence that the sponge/other animals split was one of the early taxonomic splits to happen, so it seems likely to me that Dickinsonia could be an ancestor of every animal EXCEPT sponges. Which may well have naturally developed from colony organisms like Stromatolites. (Which in turn date back over 3 billion years.)

baddox 8y ago

As far as I know, Animalia currently only includes multicellular organisms by definition, but maybe different definitions are used for the distant past.

a1369209993 8y ago
I don't know about the definition you're using, but taxonomically speaking there is at least one single-celled organism that's indisputably part of (as in descended from) Animalia: Canis lupus incertae sedis[1][2], a infectious disease that evolved from dogs[3]. (On further wiki-walking, there also appear to be similar diseases evolved from devils, hamsters, and clams[4].) There are also choanoflagellates[5], which might have reverted to single-celled life after a stint as multicellular, or might not, but are in any case more closely related than the opisthokont[6] common ancestor of animals and fungi. (These are rather more relevant to the context of "were there single-celled animal ancestors?". If opisthokonts already formed differentiated clonal colonies, then there was no point in the main [modern normal animals] lineage that was defensibly already animal but not yet multicellular. Apoikozoa[7] allegedly formed colonies, but it's not clear to what extent they were differentiated and/or obligate.) 1: https://en.wikipedia.org/wiki/Canine_transmissible_venereal_tumor https://en.wikipedia.org/wiki/Canine_transmissible_venereal_... 2: https://www.quora.com/Has-a-complex-organism-like-a-dog-ever-evolved-into-a-single-cell-organism/answer/Israel-Ramirez https://www.quora.com/Has-a-complex-organism-like-a-dog-ever... 3: https://sci-hub.se/https://doi.org/10.1016/j.gde.2015.03.005 https://sci-hub.se/https://doi.org/10.1016/j.gde.2015.03.005 4: https://en.wikipedia.org/wiki/Transmissible_cancer https://en.wikipedia.org/wiki/Transmissible_cancer 5: https://en.wikipedia.org/wiki/Choanoflagellata https://en.wikipedia.org/wiki/Choanoflagellata 6: https://en.wikipedia.org/wiki/Opisthokonta https://en.wikipedia.org/wiki/Opisthokonta 7: https://en.wikipedia.org/wiki/Apoikozoa https://en.wikipedia.org/wiki/Apoikozoa