Panarthropoda

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Parent taxa:
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ECDYSOZOA
Taxonomy Phylogeny 
Protostomia
`--Ecdysozoa
   |--Scalidophora
   |?--Protoconodonta†
   |   `--Chaetognatha
   |--+--Nematomorpha
   |  `--Nematoda
   `--o--Lobopoda 
      `--+--Tardigrada
         `--+--Anomalocarida
            `--Arthropoda

Ecdysozoa topics: Fossil Record | Characteristics | Ecology and Lifestyle | References | Links




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Contents

[edit] Introduction

Panarthropods include true arthropods and their soft-bodied relatives, the tardigrades and onychophorans. These share a number of unique features (apomorphies), such as "cuticle of a-chitin which is molted regularly, appendages with chitinous claws, and mixocoel with metanephridia and ostiate heart (absent in tardigrades); several characters, such as the structure of the brain, indicate that arthropods and tardigrades are sister groups." Nielsen, "The Phylogenetic position of the Arthropoda"

During the Cambrian period, Panarthropods were much more diverse than today. There were several different lineages of lobopods and proto-arthropods, including large carnivorous swimming forms like Anomalocaris and Kerygmachela, as well as smaller crawling types.

Whilst true arthropods, tardigrades and onychophorans are highly differentiated in form today, such was not always the case. During the Early Cambrian, many transitional forms co-existed, and exciting new discoveries have come to light. Of particular interest is the afore-mentioned Kerygmachela, which provides a link between the lobopods, anomalocarids and arthropods. Another new anomalocarid-like taxon, Pambdelurion , indicates that the biramous arthropods actually arose from within the anomalocaridids. Budd, "Stem-group arthropods from the Lower Cambrian Sirius Passet fauna of North Greenland

After dominating the oceans for many millions of years, the big protoarthropods died out with the end-Cambrian extinction, their place as super-predators being taken by cephalopod mollusks during the Ordovician.


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[edit] References

  • Claus Nielsen (1997). Animal Evolution: Interrelationships of the Living Phyla. Oxford University Press. ISBN 0-19-850682-1.

[edit] Links

[edit] Credits

Palaeos com MAK020503; Links checked ATW050113

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