Tuesday, March 20, 2012

The Great Appendage

A new fossil species, Schinderhannes bartelsi, discovered in a German quarry 3 years ago, may provide a clue about the evolution of grasping claws. S. bartelsi was an ancient creature with large, bulging eyes and what scientists call a "great appendage."


What is a great appendage? Great appendages are large, interconnected claw-like appendages that are attached to the heads of "great appendage arthropods," which include anomalocaridids. This group consists of early marine animals from the Cambrian period. Great appendages are highly modified limbs that are thought to help the organism catch prey and manipulate food (i.e., grasping and handling).


Modern arthropods have grasping claws that appear to have evolved from the great appendage. An example is the pedipalps (i.e., pincers) of the scorpion. Also, great appendages are thought to be homologous to antennae of insects and to chelicerae (mouthparts) of Chelicerata such as spiders. Up until the discovery of S. bartelsi, evidence from the fossil record had led scientists to believe that the great-appendage arthropods had all disappeared during the Cambrian period, creating an evolutionary dead end. However, the slate deposit in which the fossil was found dates to 390 million years ago -- which is 100 million years after the group of great-appendage animals were predicted to have been eliminated to extinction.

Thus, the fossil could be a "missing link" in claw evolution and could potentially provide clues as to how extant arthropods are related to their great-appendage ancestors.


Sources:
1. Jaggard, Victoria. "Great Appendage Photo: Fossil Linked to Claw Evolution." National Geographic News. 5 Feb. 2009. National Geographic Society. <http://news.nationalgeographic.com/news/2009/02/090205-great-appendage-picture.html>
2. Kuhl G, Briggs DE, Rust J. A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsruck Slate, Germany. Science. 2009;323(5915): 771-3.

2 comments:

  1. So how were these great appendages useful for "organism to catch prey and manipulate food," before the modern grasping claws emerged? Were they just used as sharp "weapons" or sticks for predation?

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  2. I wonder why the great appendage in these organisms eventually evolved to become grasping claws in modern arthropods. Were environmental conditions changing such that they needed more precision or power to grasp things? Or maybe the great appendage was not as productive as we would think, so something better was bound to evolve.

    -Hayley Hemstreet

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