Chapter Eight: Leaving the Water
Chapter 8: Images for lectures
Notes and updates
The Earliest (Fossil) Land Floras
Complex early (Silurian) vascular plants.
THE EVOLUTION OF LEAVES This refers to a 2004 paper by Osborne et al. in Proceedings of the National Academy of Sciences. They propose a theory for a 50 million year "delay" in evolving leaves which I suspect is faulty. So I have to tell you why I think that, and what the "real story" might be.
Late Silurian and Early Devonian Plants
And the closest algal relative of land plants is.... Charales! NSF press release, December 14, 2001. I almost hate to mention it, but that is what I was taught as an undergraduate fifty years ago...
The Rhynie Chert
Later Devonian Plants
Devonian Plant Ecology: the first trees and forests
The First Land Animals
The oldest land animal, from the Devonian of Scotland is not surprisingly, a millipede. It's not surprising because millipedes eat decaying plant material. BBC News OnLine, January 2004.
A spider from the Rhynie Chert.
Reconstruction of a Rhynie spider
The earliest insect: and apparently it had wings. BBC News OnLine, February 11, 2004. This is important. If it is true (and the specimen looks very poor to me in the photographs), then insects with wings were present in the Rhynie Chert. The specimen itself doesn't have wings. It consists only of a pair of jaws, but the structure of those jaws is found only in winged insects today. In turn, that implies that the first terrestrial insects were early, perhaps even Silurian: and that they had wings. The paper is in Nature, which doesn't place its papers on the Web.
P. 102. Osteolepiforms
P. 106. Air Breathing
I spend some time talking about the evolution of "bubble breathing". Here is an example of a specialised form of that, in mudskippers:
Tiktaalik has its own Web site with links
The First Tetrapods
Which creature would we call the first tetrapod? I (and many others) would choose the first tetrapod: the animal that had evolved feet rather than fins. It is becoming clear that toes (digits, to be anatomically precise) were a new structure in evolutionary terms, added on to bones that were present in the fins of earlier fishes.
Jenny Clack writing about Ichthyostega.
The unique ear of Ichthyostega. A September 2003 paper from Jenny Clack and colleagues. A large air-filled pocket in the skull of this very early tetrapod probably amplified any underwater sound reaching it, then transmitted the signals through a long thin stapes bone to the inner ear. No other tetrapod has anything quite like it, and that means Ichthyostega cannot be the direct ancestor of other tetrapods. Nature doesn't do universal access to its content. Clack, J. A., et al. 2003. A uniquely specialized ear in a very early tetrapod. Nature 425: 65-69.
New reconstruction of Ichthyostega, August 2005. This is from an all-star cast, but was published in Nature, so there is no free Web access.
National Geographic News.
2004. A humerus from a very early tetrapod. The rest of the animal is not there, but the humerus is enough to show that it was capable of powerful "push-ups". I find it delicious that none of the authors or commentators has a clue why. Re-read the section on Basking, and you'll see immediately that this is just another clue about the importance of basking to a set of fairly large-bodied cold-blooded predators living in shallow water.
References for Chapter 8
Page last updated April 7, 2013.
All links checked March 16, 2013.
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