Chapter Eight: Leaving the Water

UPDATES

• PAGE 100 UPDATE: 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.

• TIKTAALIK, a tetrapod-like fish from the Late Devonian of the Canadian Arctic. . Tiktaalik was published by Daeschler et al. 2006 in Nature. Neil Shubin wrote a fine essay on the discovery and its implications, so I don't need to condense and rewrite that until it's time to meld it into the next edition. See Chapter 8 references for these papers. The Tiktaalik web site at the University of Chicago

WEB SITES

Being a Paleobotanist Can be Tough

The Earliest (Fossil) Land Floras

The earliest land plants had probably formed associations with fungi. Very many plants today have fungi living attached to their roots. The association allows the plant better uptake of water and nutrients from the soil. The earliest land plants did not have true roots, but living liverworts (probably descended from the earliest land plants) have fungal associates on their underground rhizomes.

This comment is not just theoretical. In 2000, a group of paleontologists reported the discovery of fungal fossils from the Ordovician of Wisconsin. Though the fungi were not associated with plant fossils, they were identifiable as a group of fungi that are still living, and are always associated today with plant roots. Reported in Science by Redecker et al.: see the references for this Chapter at the bottom of this page.

Complex early (Silurian) vascular plants.

• Press release, June 7, 2002.
• University of North Carolina magazine
• Abstract of the paper

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 forty years ago...
• Silurian plants and plant spores
• Cooksonia.

The Rhynie Chert

• The Rhynie Chert Beds of Scotland contain a beautifully preserved Middle Devonian peat bog. The University of Münster maintains a Web page on the Rhynie Chert:
  • Discovery of the Rhynie Chert and the research on it over the years.
  • Beautifully preserved fungi have been discovered in and on plants in the Devonian.
  • Reconstruction of Aglaophyton
  • Reconstruction of Rhynia.
  • Asteroxylon was a Rhynie plant with the beginnings of leaves: it was an early lycopod.
• Rhyniophytes include all the earliest vascular plants, for example, Pertica quadrifaria: Maine's State Fossil, 390 Ma.

Trimerophytes

• from the UC Berkeley Museum of Paleontology
• Devonian Sphenophyta were trees while today their descendants are horsetails
• Devonian lycopods were trees over 35 m tall while today their descendants are club mosses

Later Devonian Plants

• Devonian plants

Devonian Plant Ecology: the first trees and forests

• How stomata allow plants to become trees.. Article by Carl Zimmer, 2000.
• Archaeopteris, the first abundant and widespread tree.
  • Press release on the new research. The research was published in Nature, which hardly ever puts its papers on the Web.
  • Kenneth Chang article. Ken originally wrote it for ABC News, which doesn't archive its stories for long enough...
  • Press release
  • The tree that changed the world, a short 1999 article.
  • Feature on Archaeopteris from the Canadian Geological Survey.

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.
• Arthropleurids.
• Eoarthropleura: more than you wanted to know, probably!
• 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

• Short snappy story about respiration in mudskippers, part of a whole Web site devoted to mudskippers
• the paper about mudskipper breathing
• Article from Natural History, September 2002, on mudskipper biology

Tiktaalik

The First Tetrapods

• In 1998 a rhizodont lobefin, not closely related to the ancestors of amphibians, was shown to have independently evolved finger-like structures in its fins: From Nature news.
• Elginerpeton, from the Palaeos Web site. Toby White explains pungently how the available post-cranial material may not allow detailed reconstruction.
• 1993 reconstruction of Elginerpeton by Ahlberg.
• A very early tetrapod from China. National Geographic News, December 18, 2002. Sinostega. The paper is in Nature.
• Jenny Clack writing about Acanthostega. References complete to 1998.
• A 1995 article by Carl Zimmer in Discover, about Jenny Clack and Acanthostega.
• and I can't resist this one: A PBS interview with Jenny Clack, the "Diva of the Devonian" (!) .

Ichthyostega

• The Palaeos site explains how Erik Jarvik held up research on Ichthyostega for 50 years
• Jenny Clack writing about Ichthyostega. References complete to 1998.
• 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.
  • Here is the abstract
  • Commentary in Science by Erik Stokstad
• 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.
  • Excellent Weblog from the Pharyngula site, with new images.

April 1, 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. I will soon prepare a mini-essay to meld this new material to go along with the analog with living crocodiles and with the clues from nitrogen loss that basking was likely a feature of the lives of the earliest tetrapods.
The paper is in Science, so it won't be generally available on the Web for a few months. Shubin, N. H., et al. 2004. The early evolution of the tetrapod humerus. Science 304, 90-93, and comment from Jenny Clack, pp. 57-58.

• National Geographic News
• NSF press release
• BBC News OnLine

The reference list for Chapter 8, 4th Edition, with associated Web links

Page last updated June 18, 2007.

All links checked October 2, 2005.

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