Snake and eel bodies are elongated, slender and flexible in all three dimensions. This striking body plan has evolved many times independently in the more than 500 million years of vertebrate animals history. Based on the current state of knowledge, the extreme elongation of the body axis occurred in one of two ways: either through the elongation of the individual vertebrae of the vertebral column, which thus became longer, or through the development of additional vertebrae and associated muscle segments.
A team of paleontologists from the University of Zurich headed by Professor Marcelo Sánchez-Villagra now reveal that a third, previously unknown mechanism of axial skeleton elongation characterized the early evolution of fishes, as shown by an exceptionally preserved form. Unlike other known fish with elongate bodies, the vertebral column of Saurichthys curionii does not have one vertebral arch per myomeric segment, but two, which is unique. This resulted in an elongation of the body and gave it an overall elongate appearance. "This evolutionary pattern for body elongation is new," explains Erin Maxwell, a postdoc from Sánchez-Villagra's group. "Previously, we only knew about an increase in the number of vertebrae and muscle segments or the elongation of the individual vertebrae."
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