4 ms·

Isn't it possible to compare dna between marsupials, mammals and monotremes and figure out which is 'earlier'? The paper described depends entirely on fossils

Isn't it possible to compare dna between marsupials, mammals and monotremes and figure out which is 'earlier'? The paper described depends entirely on fossils which is good but not a smoking gun.

masklinn 4y ago
Sure is, that's the principle of a (time-scaled) phylogenetic tree. But it does not tell you anything about where they came from.
adrian_b 4y ago
Marsupials and placentals are more closely related than any of them is related to monotremes. This is what has been determined from the DNA comparison. Neither marsupials nor placentals are "earlier", they both have a common ancestor. This paper is about that common ancestor, more precisely about the continent where it lived, which now appears to have been Gondwana, in contradiction with earlier suppositions. Gondwana is the former union of Africa, South America, Antarctica, Australia, Madagascar and India. The evolution of mammals has been influenced much more by the breaking and fusion of the continents than the evolution of other animals, because for mammals travel across seas was much less likely to be successful.
- hinkley 4y ago
  I assume you mean compared to birds? Ferns, wasps and slugs don’t like ocean voyages much, either. Coconuts are adapted to them (and yet the Polynesians had to bring them along to many places they now exist).
  - JoeAltmaier 4y ago
    After hurricanes, frequently giant rafts of detritus can travel across the ocean. These sometimes have all sorts of life on them. It is conceivable that would include all of those creatures?
  - dotancohen 4y ago
    > Ferns, wasps and slugs don’t like ocean voyages much, either. Coconuts are adapted to them Are you suggesting that coconuts are migratory?
    - hinkley 4y ago
      Oh but they are. They just don’t migrate to central England.
    - kuhewa 4y ago
      Migration is a recurring movement behaviour or pattern, coconuts don't do that. You are probably thinking of dispersal, which is movement that results in gene flow, e.g. into a new place, permanently. That certainly occurs but it seems likely it isn't all that common, coconuts really only needed to disperse as far as the next coral atoll or island, which tends to be as far as a planktonic coral larvae can disperse. Really remote islands probably had coconuts introduced relatively recently by early settlers. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3936586/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3936586/
      - dotancohen 4y ago
        A swallow could grip it by the husk. Will you tell your lord and master that Arthur from the Court of Camelot is here?

Isn't it possible to compare dna between marsupials, mammals and monotremes and figure out which is 'earlier'? The paper described depends entirely on fossils which is good but not a smoking gun.

masklinn 4y ago

Sure is, that's the principle of a (time-scaled) phylogenetic tree. But it does not tell you anything about where they came from.

adrian_b 4y ago

Marsupials and placentals are more closely related than any of them is related to monotremes. This is what has been determined from the DNA comparison. Neither marsupials nor placentals are "earlier", they both have a common ancestor. This paper is about that common ancestor, more precisely about the continent where it lived, which now appears to have been Gondwana, in contradiction with earlier suppositions. Gondwana is the former union of Africa, South America, Antarctica, Australia, Madagascar and India. The evolution of mammals has been influenced much more by the breaking and fusion of the continents than the evolution of other animals, because for mammals travel across seas was much less likely to be successful.

hinkley 4y ago
I assume you mean compared to birds? Ferns, wasps and slugs don’t like ocean voyages much, either. Coconuts are adapted to them (and yet the Polynesians had to bring them along to many places they now exist).
- JoeAltmaier 4y ago
  After hurricanes, frequently giant rafts of detritus can travel across the ocean. These sometimes have all sorts of life on them. It is conceivable that would include all of those creatures?
- dotancohen 4y ago
  > Ferns, wasps and slugs don’t like ocean voyages much, either. Coconuts are adapted to them Are you suggesting that coconuts are migratory?
  - hinkley 4y ago
    Oh but they are. They just don’t migrate to central England.
  - kuhewa 4y ago
    Migration is a recurring movement behaviour or pattern, coconuts don't do that. You are probably thinking of dispersal, which is movement that results in gene flow, e.g. into a new place, permanently. That certainly occurs but it seems likely it isn't all that common, coconuts really only needed to disperse as far as the next coral atoll or island, which tends to be as far as a planktonic coral larvae can disperse. Really remote islands probably had coconuts introduced relatively recently by early settlers. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3936586/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3936586/
    - dotancohen 4y ago
      A swallow could grip it by the husk. Will you tell your lord and master that Arthur from the Court of Camelot is here?