Friday, March 23, 2007

The imaginings of children

Comedy may be about timing, but humour is about juxtaposition. I came across this on the New Yorker's website:

The Wisdom of Children, by Simon Rich

A Conversation at the Grownup Table, as Imagined at the Kids’ Table

MOM: Pass the wine, please. I want to become crazy.
GRANDMOTHER: Did you see the politics? It made me angry.
DAD: Me, too. When it was over, I had sex.
UNCLE: I’m having sex right now.
DAD: We all are…

Tuesday, March 20, 2007

Not another gliding reptile...

I haven't got hold of the paper yet, but PNAS is supposed to be carrying a contribution by Xu Xing and colleagues that describes a new lizard from the Early Cretaceous of Liaoning China. (Cue groans of 'oh no, not another spectacular fossil from China'). It's not just the preservation that is spectacular this time, but the splayed ribs supporting a skin membrane that look remarkably like wings. In fact that is their most likely function - not true flapping wings, but something that could be held open enabling the animal to glide.

For once though, China hasn't got there first. This is now the fourth group of reptiles to have independently evolved the same peculiar trait.

We have to go all the way back to the Late Permian, some 260 million years ago, for our first example. Back then it was Coelurosauravus and Weigeltisaurus from Germany and Madagascar respectively. United together in the family Coelurosauravidae it is assumed that these two taxa had a common ancestor in which the splayed-ribs-as-support-for-gliding-membrane adaptation first evolved, but these strange creatures disappeared almost as soon as they had arrived.

Only 40 millions years or so later (in the Late Triassic) it happened again. Icarosaurus and Kuehneosaurus from the US and Europe did pretty much the same thing - evolved this bizarre trait, spread out across the globe, then disappeared.
Another 60 million years later and we have Xianglong zhaoi, our brand new rib-splayed glider. Unlike it's predecessors Xianglong is a true lizard and yet it is not closely related enough to the living Draco (our fourth rib-glider; see movie) to share a gliding ancestor. We could be forgiven for thinking that there must be something about reptilian skin that stops them from making the (presumably) much simpler shortcut to a gliding membrane - just stretching some skin between the forelimbs and hindlimbs, as flying squirrels do. Only that's not true.

At the same time as Icarosaurus and Kuhneosaurus were taking in the Late Triassic air in what would become modern day Russia a creature called Sharovipteryx had made an appearence. Undoubtedly reptilian, although beyond that it's relationships are unclear, Sharovipteryx had developed not just a membrane between the two pairs of limbs, but another between the legs and tail and even one between the neck and arms. Overall this made a triangular-shaped membrane that is unique in nature. Although some authors have suggested Sharovipteryx may be the ancestral pterosaur it is more likely another oddball that disappeared as soon as it had arrived.

There are a number of mysteries here. Why did so many lineages go down the gliding route the 'hard way'? Why did none of the groups possessing this odd trait persist for for more than a few million years? Why do we have so many fossils of a group of animals that have such a low preservation potential?

Any ideas?

Friday, March 16, 2007

Where is evolution fastest?

An incontrovertable fact of life is that species diversity is highest in the tropics and hence it has long been thought that rates of evolution are also highest there. Just last year this was put to the test by Shane Wright and colleagues from the University of Auckland in a paper published in PNAS last May. They examined rates of molecular evolution and showed that tropical plants did indeed seem to be evolving at a faster rate than species from the same genus found in temperate latitudes. Their preferred explanation was elevated rates of mutagenesis.

However, today in Science the whole notion of evolution being higher in the tropics was cast into doubt. Jason Weir and Dolph Schluter at the University of British Columbia took a different approach to examining speciation rates. They took sister-pairs (two species who are more closely related to each other than anything else) of birds and mammals and plotted out the time of divergence against the probable latitude of their common ancestor. Although most of the taxa had shared ancestors at low (tropical latitudes) those with a recent ancestor were concentrated at higher latitudes. When they fitted their data to a birth-death model using maximum likelihood they show a linear relationship between latitude and speciation rate (lineages per million years).

So, who's right? As a student of both evolutionary tempo and biogeography I find such links between the two interesting. Leaving the issue of taxa choice (plants versus birds/mammals) aside, I think it is crucial to point out that the two sets of authors are looking at two fundamentally different questions. Wright et al. were interested in the rate of molecular (DNA) change whereas Wier and Schluter were only examining the frequency of speciation (when one lineage splits into two). These two phenomena aren't necessarily interlinked. In fact Wright and colleagues even stated that, "greater rates of speciation in the tropics do not cause higher rates of molecular evolution."

Perhaps the most interesting conclusion from today's announcement is that tropical diversity was built up over an extended period, suggesting that it is the environmental stability of this region that has led to the huge build-up in species.

Thursday, March 15, 2007

The world gets a new cat

It is very rare to find new species of living mammals and rarer still a top predator like a big cat, but in the news this morning it was reported that clouded leopards from Borneo and Sumatra are genetically distinct enough from their mainland cousins to be considered a separate species. Although this is yet to be published in a scientific journal (where a formal name will be attached to it) there is a video!

This is yet another example of how technology has changed the way we recognise species. It was DNA that told us the clouded leopard should be split in two, but now that has happened we are noticing subtle differences between the 'halves.' For example the new species has smaller 'clouds' and different patterns on the pelage that gives these cats their name. The Borneo/Sumatra species also has the largest canines of any big cat.

Andrew Kitchener of the National Museums of Scotland is quoted as saying "it's incredible that no-one has ever noticed these differences." Indeed, I looked up the clouded leopard in Kitchener's 1991 book The Natural History of the WIld Cats, where he states:

"The clouded leopard is an animal of tropical forests , being found at altitudes of up to 2,500 metres. In Borneo, however, it was found to be mostly terrestrial."

Back then it was only considered as a subspecies under the name diardi, and perhaps the recent divergence date (of one million years) is enough to forgive us for not noticing sooner. In any case this is a welcome new addition to our "entangled bank" and another neat example of evolution in action.

Wednesday, March 14, 2007

Ten wierd things about me

1) I write my eights as two circles.
2) I have a burning desire to know Lemar's thoughts on mixed herbs.
3) I get emotional everytime I watch the climax to Brassed Off.
4) I think 'Endless Love' by Luther Vandross and Mariah Carey is one of the greatest songs ever recorded.
5) I collect my favourite quotes in a little book.
6) I have a pet lungfish.
7) When I was little I thought Harrison Ford was two people (Harris and Ford).
8) I also thought that all the superheroes and cartoon characters were once real, but like dinosaurs became extinct.
9) Before I wanted to be a palaeontologist I wanted to be a fighter pilot.
10) ...erm.

About Me

My photo
Currently I am founding member, president elect and entire membership of SWEMP (the Society of Wonky-Eyed Macroevolutionary Palaeobiologists). In my spare time I get paid to do research on very dead organisms and think about the really big questions in life, such as: What is the ultimate nature of reality? Why is there no room for free will in science? and What are the implications of having a wardrobe that consists entirely of hotpants?