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Evolution/Closest Cousins under Uncommon Ancestor

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Question
I have noticed that alligatorids diverged from all other crocodilians 87.1 million years ago and that crocodiles have their most recent common ancestor at 54.5 million years ago.  Since crocodilians are the closest group to birds, do these dates indicate that alligatorids are genetically (or even cousin-wise) more closely related to birds than the rest of the crocodilians are, please?

Thank you.

Answer
Dear Robert,

The last common ancestor of crocodilians and birds existed long before the alligator lineage diverged from the other crocodilians.  So neither group is more closely related to birds than the other.  They share a more recent common ancestor with each other than either does with birds.

There's a nice cladogram here that shows the evolutionary relationships of the various Archosauriform lineages that I think will help you visualize it:

http://en.wikipedia.org/wiki/Crurotarsi


Hope that helps.

Dana

Evolution

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Dana Krempels

Expertise

I can answer questions about evolutionary mechanisms and theory, including genetic drift, mutation, natural selection, etc. I also can clear up misconceptions about evolution as it's sometimes talked about by those not well-versed in the subject (e.g., some politicians and many religious fundamentalists).

Experience

I have a Ph.D. in Biology, and presently teach Evolution and Biodiversity, Genetics, Botany, and Zoology at the University of Miami.

Organizations
House Rabbit Society Beta Beta Beta Biological Honor Society

Publications
Exotic DVM Magazine (veterinary journal)

Education/Credentials
B.S. in Biology B.A. in English Ph.D. in Biology

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