evolutionary relationships

[Jennewt]

I have heard it said that amphibians are more closely related to fish than they are to reptiles. I'm trying to verify that this is (or isn't) true, but I'm having difficulty finding the info. The Tree of Life is a wonderful resource, but I can't find a tree that shows the fish, amphibians, and reptiles on the same tree. I'm also interested in finding whether reptiles are closer to amphibians, or to birds.

If anyone has a trustworthy scientific resource that shows the relative evolutionary distances among these groups, please help me out. I'm giving a talk about amphibians in a couple of weeks, so I'm trying to find information that will surprise people.

 

[eldaldo]

You should check out NCBI. It is the real deal for any sort of genetics stuff and it has a sizeable taxonomic database. It has a disclaimer that it is not authoritative, but that is because with all the genetic research going on taxonomy changes every day now.


This link is to the taxonomy browser
http://www.ncbi.nlm.nih.gov/Taxonom...mode=Root&id=1&lvl=3&keep=1&srchmode=1&unlock

and this is to the phylum chordata
(http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=7711)

The database is for people who are looking for genes and proteins, but I imagine that useful information can be gathered from the tree because phylogenetic trees are set up to try and describe the divergence in evolution. And with a little research on the particular branches you can probably find the current accepted opinion on the evolutionary relationships.

You should check the site yourself, but what I gathered from the tree was that Sarcopterygii (lobe-finned fishes) broke off from other bony fishes, and tetrapods (amphibians and amniotes) broke off from them. Amphibians were the first on land so I would say that they are close to fish, but I imagine that reptiles evolved from amphibians back in the day. I would reccomend researching the evolution of amniotes (Now that my curiosity is sparked I probably will to and let you know what I found out). My guess is that modern amphibians are not the ones that reptiles evolved from making modern amphibians direct descendents of fish like the ceolacanths, and reptiles closer to the ancient amphibians they descended from.

Birds are now considered direct descendents of dinosaurs making them obviously very close to reptiles, but asking whether reptiles are closer to birds than amphibians is a more complicated question. (I had to search for Aves on the NCBI tree but found that they are under Sauropsida, Dinosauria, Therapoda)

I hope that this helps. You have helped me so much in the past with my newts I was glad to see an opportunity to try and repay you with my knowledge as a Biology student who happens to be very interested in evolution.

 

[mikebenard]

Hi Jen,

Modern amphibians are more closely related to reptiles and mammals than to fish. Both modern amphibians and reptiles share a more recent common ancestor with each other than either does with fish.

For reptiles, you need to consider crocs, squamates (tuatara, lizards and snakes), and turtles separately.

Crocs and birds are each others closest living relatives.

All amniotes (birds, mammals, turtles, squamates, crocs) are more closely related to one another than any of them are to amphibians.

I can give you references to several books that describe these relationships clearly.

You can visualize these relationships at the tol website if you start here:

http://www.tolweb.org/Gnathostomata/14843

and follow the sacroptergii branch of the tree.

When you get here:

http://www.tolweb.org/Terrestrial_Vertebrates/14952

You will see that all amniotes are more closely related to one another than any are to amphibians.

Best wishes,

Mike

 

[Jennewt]

Thank you both for the thoughtful answers. I think I've got it. Reptiles are indeed closer to birds than they are to amphibians. But amphibians are definitely not closer to fish than to reptiles.