Thought on dinosaur diversity...and how do you post a PDF?
Ok. Raup states that "Quite likely, no more than fifty dinosaur species lived at any one time." This statement is interesting in terms of speciation rates, but also in the extinction rate of dinosaurs. There are 540 named species of dinosaurs and it is estimated that that number may grow to 900 spp. That being the case, one of very low species diversity, then what was the big deal of the extinction of the dinosaurs?? Who really cares if at the K/T boundary 50 dinosaur species went extinct?
This statement vexes me because that low level of species diversity seems amazingly low for a group of organisms that lived~ 160 m.y. That means since the first incipient dinosaur walked around to the K/T boundary dinosaurs had a "speciation rate" of 3.35 x 10-6 species per m.y. That seems rather low.
Looking at extant reptiles which have been around ~359 m.y. have ~8350 sp (many more to be named). Their "speciation rate" is around 2.32 x 10-4 species per m.y.
Birds, which can be considered feathered dinosaurs have ~10,000 sp. and have been in their current form for about 146 m.y. Their speciation rate is around 6.849 x 10-5 species per million years.
Finally, trilobites has ~15000 species and were extant for ~325 m.y. Their "speciation rate" was about 4.615 x 10-5.
These rates are relative and in no way reflect phylogeny (branch lengths may expound rapid diversification etc) and I'm using the # species/million years as a proxy. But, I find it amazing dinosaurs could have lived as long as they did if there were only 50 species around at any one time.
Dinosaurs are interesting to look at in this perspective because they gave rise to modern reptiles and birds. How could so few species gave lead to the modern radiation of two clades that have >18,000 species combined!
This is just a thought, but I think to look at extinction it is important to think about diversification and speciation rates. I'm open for any critiques on this train of thought, or you can tell me to shut up!
And can someone please let me know how to post a PDF. I have the giant snake paper.
cheers.
Thanks for sending out the snake paper! Wow! I still think that would make a great scary movie!!!!
ReplyDeleteThis is a really good point. I can't imagine there being a vertebrate lineage that low in diversity surviving for any length of time, really. Maybe Raup is using a very strict definition of "dinosaur" here?
ReplyDeleteAlso, this relates back to a point we discussed last spring, which was that only the largest species of dinosaur may have been discovered so far - smaller species would be overlooked, especially since many dinosaurs had hollow bones like birds.
We were discussing the following dinosaur paper that week, if anyone wants to check it out:
Gillooly, James, Andrew Allen, and Eric Charnov, 2006. "Dinosaur Fossils Predict Body Temperatures", PLoS Biology 4:1467-1469
Good point Mason. I think this relates largely to taphonomy and where most work has been done. It seems implausible to me that the terrestrial biota was so depauperate. I'm guessing that the diversity was much greater. Keep in mind that there are large areas of the world where fossils either weren't preserved or where folks haven't looked for them.
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