Why are there so few tropical Caudates?

I know there are a few, but compared to the number of tropical Anurans, why so few tropical Caudates?
And why so few caudates in the southern hemisphere?
Am I missing something?

Oh boy...

Remember all of those FAQs on keeping the tank cool?

I think it is a good question, why are most urodela heat sensitive?

It has a large part to do with the ability to spread from the point of radiation. I think the current "point of evolution" for newts occured in asia based on fossil records (Did I remember that correctly?)
Plethodontidae appear to have originated in Eastern North America (guess based on number of species) and have radiated out to appropriate habitats that were available.
One of the items that would limit plethodontid radiation would be anything that limits the ability to exchange gases through the skin, warmer temps are often linked to higher evaporative rates as well as increased metabolic rates increasing the rate of oxygen consumption and CO2 production. If the skin dries out at all the ability to exchange gases becomes compromised.
This is just some supposition to give some people some items to ponder. For all I know its because they have some conserved heat labile protiens that begin to break down at 85F.
Ed

Hi guys, I would point out here that out of the 520 or so known species of caudates in the world, 213 of them belong to the tropical (with a few subtropical members) genera within the tribe Bolitoglossini. That's over 40% of all known species! And more are being described from the tropics every year. So I dunno what the "so few" talk is about

I certainly agree with Ed's comments about why they could be rare in the Southern Hemisphere...haven't had enough time to invade South America yet, can't cross the Sahara, and haven't had any decent land bridges to Australasia.

I'd say bad luck. Basically being of Laurasian origin S.A., Africa, etc. were off limits until places reconnected. Africa has a desert acting as a barrier, and while South America was open for a while the deserts of the South West and Mexico basically cut it off again.

Sorry was typeing it while other post came in so don't mean to be repetative.

While lungless salamanders made it into South America they still are pretty constrained in some ways. I'd say if the North American newts especially Paleotaricha or maybe even Notophthamus had made it further south before the drying of the South West/ Mexico. South America could have had it's own newts.

Sorry was typeing this while other posts came in so don't mean to be repetative.

(Message edited by Brian on February 27, 2004)

Nate - forgive me but those reasons you cite in your last message don't seem to have stopped frogs... How different are the points of origin?

Hi John,
I had to and dig out out my copy of Biology of Amphibians look at the anuran question it looks at if there was several different radiations of anurans, the first mainly with Gondwanaland and a second radiation during the initial break up of Pangea in the early Jurassic. By the late Jurassic period there are different anuran fossils from Europe and the Americas, presuming widespread distribution during the Jurassic period. According to the BOA, caudates however are associated with the middle Jurassic so it appears that they recieved a much later start for distributional colonization.

Ed

Ah, I had a feeling it was something like that. Isn't it widely held now that Caudata and Anura do not share a close common ancestor?

Thanks for filling me in Ed.

(Message edited by john on February 27, 2004)

Aren't a lot of Bolitoglossini cloud forest animals so that the temps are still cool?

I had heard there's still some debate about the Caudata and Anuran relationships.

Yep, several are cloud forest inhabitants.