Which was the most recent common ancestor between mammals and birds?

Form a rapid google research I could not find good answers. This site seems to imply it was at least 250 milions of years ago. This scientific article mentions 600 milion years but the sentence is a little unclear.

up vote 3 down vote accepted

You can check it easily in the timetree website: http://www.timetree.org/

Put a mammalian species as taxon 1 (Homo sapiens) and a bird as taxon2 (Gallus gallus) in the first pair of boxes and hit run.

You will see a compilation of studies, with their references, with different calculations about the time when the last common ancestor of both species lived. A median and a mean are also provided.

In this case the values are Median Time: 320 MYA Estimated Time: 312 MYA CI: (297 - 326 MYA)

  • Useful tool for the timing! Any Idea about which one is so far the recognized MRCA? – have fun Dec 15 '17 at 16:18

The Most Recent Common Ancestor (MRCA) of birds and mammals was the first amniotes.

Fossil record

The latest known fossil of amniotes are 312 million years old (Bentou and Donoghue, 2007).

Genetic data

From EOL, using data from The Paleobiology Database, the first amniote is in between 314.6 and 323.2 million years old. Those results are a little bit older than the latest known fossil which very much makes sense.

The (apparent) contradiction in the sources you found

This site seems to imply it was at least 250 milions of years ago.

They actually say 250 to 320 millions years. This broad estimates match the above studies and data.

This scientific article mentions 600 milion years but the sentence is a little unclear.

It is actually a news feature published by a science writer (former neuroscientist according to her twitter account), not a researcher. She indeed made the claim (Even so, 600 million years of evolution and radically different brain architectures separate birds from humans.). There is no reference for the claim and based on above evidences, it appears at first to be a mistake. It is not impossible though that she considered the evolutionary time in both branches in her statement but that would be very unusual If two lineages diverged $t$ years ago, then they both evolved for $t$ years and it could arguably be said that they are separate by $2 t$ years of evolution. If this is what she meant, then the claim is correct but quite misleading.

  • 1
    Scientists do not use the convention of measuring time on both branches, between endpoints, although maximum likelihood methods of estimating nucleotide states do measure both branches. So 600 million years is an error. Also, the first terrestrial ecosystems were little more than some plants surviving on the seashore, about 450 million years ago. The Earth was an inhospitable place with nothing to eat (Misof et al., 2014); no way could amniotes precede plant life. The first tetrapods were much later, which preceded the first amniotes. – Karl Kjer Dec 14 '17 at 17:34
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    Also, the "first" amniote was not the MRCA of birds and mammals, as it is most likely that amniotes survived for a time, and diversified before branching off into synapsids and diapsids. – Karl Kjer Dec 14 '17 at 17:37

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