Like other heterostracan fishes, Pteraspis had a protective armored plating covering the front of its body. Though lacking fins other than its lobed tail, it is thought to have been a good swimmer thanks to stiff, wing-like protrusions derived from the armoured plates over its gills. This, along with the horn-like rostrum, made Pteraspis very stre...
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http://en.wikipedia.org/wiki/Pteraspis
genus of extinct jawless fishlike vertebrates found as fossils in Early Devonian rocks (those 387 to 408 million years old) in North America and ... [1 related articles]
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http://www.britannica.com/eb/a-z/p/128
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