Four Chambered Hearts

[Matt L.]

I was wondering if birds and mammals developed four chambered hearts independantly or if there was a common ancestor that had one. Birds, as I understand it, follow from crocodilians which have four chambered hearts, but there is no lineage from crocs to mammals. It seems like the common ancestors that birds and mammals share would likely have had a three chambered heart (cotylosaurs).

It seems amazing to me that two lines could develop such an advanced structure independantly - although I wouldn't say it would be impossible. A common ancestor just seems like a more likely scenario although there seems to be no support in the fossil record for that animal.

Interested in your thoughts.

Matt

[kotoreru]

It's possible that complex features can evolve more than once, though, like all palaeontology, nothing is certain.

There is a paper regarding the potential for the mammalian middle ear being evolved twice independently in monotremes and therians - I'll see if I can find the paper. This was previously thought to be a ridiculous notion given the complexity of the structures involved.

There wouldnt be a lineage from crocs to mammals as they quite simply dont follow. Mammals evolved from the synapsid side of early amniotes while reptiles (including those paraphyletic birds) all came from the diapsids. We're talking late Carboniferous/early Permian.

Otherwise, Im really not too in the know about hearts in this context

[Darby]

Endothermy, which probably evolved separately in the groups, almost requires that the pulmonary and somatic loops be separate, which works with a septum in the ventricle. It's most likely convergence, not ancestral.