1) Is global diversity a reasonable measure of true biodiversity?
2) How did tetrapods diversify? Did they conquer new niches or expand into new habitats?
3) How did mass extinction events effect community structure?
But even more interestingly, this study has an application to our present situation. We are witnessing a biodiversity crisis right now and it is not clear whether it is simply a part of Earth’s natural cycle or massive impact by human presence (though to be honest I lean towards the latter). Studying past communities helps us understand more about our present situation.
The first part of my research covered the Palaeozoic, from the origin of tetrapods about 375 million years ago to about 250 million years ago. At this time there were no birds, no mammals and no dinosaurs. The landscape was dominated by large amphibians and the first reptiles. Amphibians at the time were not like frogs but more like very large salamanders, and the largest of these superficially resembled crocodiles (For example, see my post of Parotosuchus). This period of time ended with the largest mass extinction event, in Earth’s history, the Permo-Triassic event 251 million years ago, when over 90% of Earth’s species went extinct.
During the 125 million years though, a lot of changes took place. I realize this post has gotten long already so I will continue more next week starting with a look at the first tetrapods, who possessed a strange oddity that we rarely see today and one that has changed our understanding of the evolution of life on land. Can you spot this oddity in the image to the right?Click to view a larger image at http://universe-review.ca/I10-72-Acanthostega.jpg
8 comments:
Sarda, your descriptions of your work are very interesting, especially to someone like me who doesn't work in the field. Thanks for taking the time to describe what you're doing - it looks like very important work.
Next, your link to the enlarged image is broken - it should be:
http://universe-review.ca/I10-72-Acanthostega.jpg
which is the text of the link; the URL behind the link is the one that's a wee bit mangled.
Looking at the full picture, it strikes me that this creature is not pentadactyl (five-fingered). It would make a good pianist, that's for sure, as long as you could give it a tiny waterproof piano and a big brain. And preferably lessons.
My understanding, such as it is, is that early tetrapods have all sorts of differing numbers of digits, but five somehow won the day. I've never heard anything more than conjecture about why five. What's the currennt thinking?
My eyes go blurry trying to count, but your amphibian seems to have seven visible digits on its rear limbs and maybe nine on its forelimbs, which would be a surprise. Has it ever been the case that tetrapods had differing numbers of digits on front and rear limbs? Or do I need new glasses?
Thanks again for keeping such a fascinating blog.
I'll guess that the "strange oddity" found on Acanthostega fossils is the large number of digits, as the John guessed.
The tails are kinda funky. Are these guys marine or freshwater?
"Has it ever been the case that tetrapods had differing numbers of digits on front and rear limbs?"
It is pretty common. Cats and dogs, frogs, tyrannosaurs and whales would be some examples that come immediately to mind.
Ah, I'd thought that they still had vestigial digits that took the total up to five on each limb, and were fundamentally still pentadactyl. Sounds like I'm wrong.
Another nice post Sarda; I started reading Carl Zimmer's At the Water's Edge the other day and I'm amazed at how much we've learned in the past few years.
When you say, "At this time there were no birds, no mammals and no dinosaurs." don't you mean that there are no bird, mammal or dinosaurs known to have been found in these particular layers?
walt, I think she means it literally.
375 M years ago mammals, birds and dinos hadn't evolved yet. They came later on, from some of those first reptiles. I guess the others went on to become turtles, crocodiles and the other modern reptiles, or went extinct.
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