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Devonian - Icthyostega: An Early Tetrapod

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  • Neal Robbins
            Ichthyostega was a tetrapod creature of the late Devonian. Gunnar Save-Soderberg named Ichthyostega in 1932. Fossils of it have been found in
    Message 1 of 1 , Dec 1, 2008
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          Ichthyostega was a tetrapod creature of the late Devonian. Gunnar Save-Soderberg named Ichthyostega in 1932. Fossils of it have been found in Greenland. They date to the Famennian age (375 - 359 million years ago). Ichthyostega had seven toes on each of its feet. The habitats of Ichthyostega must have included streams, rivers, lakes, and ponds. Although Ichthyostega was mainly aquatic, it was capable of moving on land. Ichthyostega was about 1.5 m. (4 feet) long.
          This excerpt of Palaeos Vertebrates lists some physical characteristics of Ichthyostega:
       
      dermal skull: snout large & rounded; skull roof flat; unpaired medial rostral
       
          This except says:
       
      branchial: propercular present [R+03]; deeply grooved gill bars for functional gills [C1+3].
       
          This excerpt says:
       
      occiput: posttemporal fenestra absent [R+03] [2]; basioccipital was long and notochordal [R+03], with no occipital condyle
       
          H. Blom wrote an article titled Taxonomic revision of the Late Devonian tetrapod Ichthyostega from East Greenland. It was published in January, 2005 in Palaeontology, Volume 48, Number 1, pp. 111-134. This excerpt from the abstract says:
       
      Two morphologically distinct assemblages of the Late Devonian tetrapod Ichthyostega from East Greenland are described on the basis of a large collection of skulls and postcranial elements. Skull specimens collected on Gauss Halvo show that the assemblage from the lower Aina Dal Formation has proportionally narrower skulls and finer skull roofs than the assemblage from the higher Britta Dal Formation.
       
          This excerpt says:
       
      From the original description of seven taxa, three species are recognized and related to the assemblages from Gauss Halvo. I. stensioei is comparable with the Aina Dal Formation assemblage while I. eigill and I. watsoni are valid specimens found in the Britta Dal Formation. Ichthyostegopsis wimani is not a valid genus or species and may be regarded as a juvenile I. eigilli. This example of species-level variability is the earliest known from the fossil record of early tetrapods.
         
          Neal Robbins
       
      P.S. The taxonomy of Ichthyostega is:
       
      Kingdom: Animalia
      Phylum: Chordata
      Class: Tetrapoda
      Order: Ichthyostegalia
      Family: Ichthyostegidae
      Genus: Ichthyostega
      The species are:
       
      Ichthyostega stensioi
      I. eigilli
      I. watsoni
       
       

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