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February 24, 2007

Ancient Amphibians

Fossilized Frogs.. Ancient Amphibians... Ribbiting Run-in With Resin... Jurassic Jumpers... Well, not really Jurassic period, but the more recent the Paleogene period, which was about 125 million years younger than the Jurassic period.

Regardless, there's been a great discovery of a fully intact tree frog encased in amber. Some people are talking about trying to follow Michael Crichton and extract its DNA, but its unclear whether or not the collector will allow this to happen.

A miner from Mexico's Chiapas state has made the find of a lifetime—a tiny tree frog preserved in amber that could be 25 million years old

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The block of amber, or fossilized tree resin, encasing the 0.4-inch (1-centimeter) frog

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The specimen appears to belong to the genus Craugastor

More At: National Geographic: Ancient Tree Frog Found Encased in Amber

I couldn't find much on Craugastors, other than its a group of frogs from Central America, many of which are critically endangered or extinct. I did find an article that talked about the origin of the Craugastors. The group of Craugastors, which contains over 100 frog species, is monophyletic. This means that the group all had a common ancestor. That ancestor (mommy of of all Craugastor species) looks to have appeared in northern Central America from South American in the early Paleocene epoch, which was about 56-66 million years ago.

Half the time I was finding that Craugastor was a subgenus and then a genus. What appears to have happened is that these frogs were originally lumped into a larger genus called Eleutherodactylus, but once the common ancestor was found, the Craugastor group was extracted from this larger genus and elevated to its own genus.

Still, taxonomy is slippery stuff, scientists do not always agree on how to classify organisms. The original methods involved only what could be observed. Then came DNA and other more intimate methods of determining how species have evolved.

Here's an example of what I mean... some groups like Craugastor are formed (or re-formed) because genetics supports their cohesiveness as a group at the genus level. However there is another genus that seems to have split from Eleutherodactylus but the primary reason for the grouping is all frogs in the group supposedly lack vomerine teeth. Now here we have a physical characteristic for classification that does not necessarily make for a cohesive group from a genetic perspective. We might infer that this group is going to be closer (family-tree wise) to other reptiles and amphibians that do not have vomerine teeth, like geckos. Still, this is just a visual observation and it is possible that the species both evolved seperately to not have the teeth or to have the teeth, as it may be.

Still don't see why physical characteristics might not be the best way to indicate closely related animals? Let's assume that someone decided to put all green lizards together as evolutionarily similar, assuming that their color was their primary distinguishing trait for grouping. Unless other factors are considered, a green lizard on the other side of the world or in a very remote location would likely be put in the same group, even though it might be very hard to see how they could possibly come from a shared ancestor from so far away. Now consider that perhaps the actual distinguishing trait on these groups of lizards is that a set of closely related lizards learned to blend in with their surroundings, not just be green. You might find that a lizard living in a green environment and another living in an orange, rocky environment just down the way are more closely related evolutionarily than the group of green lizards.

Posted by sorsha at February 24, 2007 11:42 PM