Estimates for the volume and mass of most ancestral multicellular organism, and a similar question for alive animals with radial symmetry

please I'm interested in an estimate for the volume and weight, the mass, of (most) ancestral multicellular organisms. Wikipedia has the article Multicellular organism, and my main interest are estimates for ancestral eukaryotic groups (the oldest and simplest of these fossiles) in the International System of Units.

Other question of my interest are the same estimates of volume an mass for alive animals with radial symmetry. I apologize if my question bother some user of the site Biology Stack Exchange, I'm not a biologist. Wikipedia has the article Symmetry in biology, and I clarify that the approximations/estimates are for a typical specimen of the cited in this paragraph: alive animals with radial symmetry.

Question. Please provide estimates for the volume and the mass, of (most) ancestral multicellular organisms, and for the volume and the mass of a typical animal (of our geological epoch) with radial simmetry. Many thanks

I'm motivated to ask these questions after I read the book by Walter Álvarez [1], and inspired in a graphic, the Figure 2.1, that refers the book [2] by John D. Barrow. I know the Spanish editions of these books.

References:

[1] Walter Álvarez, A Most Improbable Journey: A Big History of Our Planet and Ourselves, W. W. Norton & Company, (2016).

[2] John D. Barrow, The Constants of Nature, Jonathan Cape; 1st edition (2002).

• Please if my question isn't suitable for the site add a comment, I can to delete the question in next hours. Jan 24 at 18:03
• Welcome to the Biology Stack Exchange. Please take a tour and visit the help center for more information on what we do here and what makes a good question and answer. Note that we usually ask that the OP make some attempt at answering the question for themselves. We also have a requirement for answers backed with references - which might be a challenge for this question. I would guess multicellular algae, <1 mm across and a few micrograms in mass.
– bob1
Jan 24 at 18:43
• Many thanks for you kind messages. I'm mathematician, I am not able to answer my question, I think that I'm not able to answer the kind of questions that I'm asking in this site Biology Stack Exchange, these are of my invention since I'm curious about from the books that I read @bob1 . I don't know how to search information related to Biology, and I add the encyclopedia Wikipedia as general reference for all users and because my English is bad. If you want, please expand you comment in an answer. Jan 24 at 19:31
• The browser of Google has an answer for "What is the oldest known fossils of multicellular eukaryotes?", but I don't know how to estimate the density and length/volume of a fossil (estimates for the organism corresponding to the fossil, when this organism was alive). I'm agree with the requirements of the site and I add the promise of make more attempt of answering my questions @bob1 Jan 25 at 15:57
• I'll convert this to an answer...
– bob1
Jan 25 at 19:42

So, it looks like it all depends on how you define multicellular - living in mats/biofilms, which are often mixed species, isn't necessarily a multicellular organism, even though it can behave like one, but might be one of the steps along the pathway to being multicellular.

In addition, organisms that live as a group/chain of cells (such as Spirogyra, or many bacterial species which grow in clumps or chains such as Staphylococcus aureus or Streptococcus pyogenes) are not necessarily multicellular organisms.

The earliest I could find that seem to fit the description of Eukaryotic and Multicellular is a report in PLoS Biology entitled: "Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae" (Bengtson et al, 2017). In this paper, they discuss fossils of a couple of thallate multicellular red alga from about 1.6 billion years ago (PalaeoMesoproterozoic).

They state that the structures are:

The 58–175 μm wide Rafatazmia tubes are up to ca. 2 mm in length

and

The thalli are megascopic, ranging from approximately half a millimetre up to well over 3 mm across.

So - pretty small. I don't know how this equates to mass, but I would guess a wet weight (i.e. living state with no additional water) of about 0.5 grams.

Full reference: Bengtson S, Sallstedt T, Belivanova V, Whitehouse M (2017) Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae. PLoS Biol 15(3): e2000735. https://doi.org/10.1371/journal.pbio.2000735

• Thank you very much I will study your post. It looks like one of the most nice posts I've seen on these sites Stack Exchange. The origin of biofilms seems misterious and fascinanting (I didn't know this article of Wikipedia about biofilms). Many thanks for your work (your remarks and bibliography) that will be interesting for your colleagues; next time I try improve my research about the questions that I'm asking, but your work is unbeatable. My main interest was the details that you've provided. Jan 26 at 12:56