A backbone of interlocking vertebrae is a prerequisite for a tetrapod - a vertebrate that lives on land. However, skeletal details are very hard to make out in fossils of the very earliest tetrapods because the specimens are often swathed in rocky matrix. Application of the latest synchrotron microtomography technology to the three best-known early tetrapods - Ichthyostega, Acanthostega and Pederpes - has now overcome that inconvenience. Early tetrapods were presumed to have had 'rhachitomous' vertebrae, with a neural arch and spine above, a single intercentrum front and ventral and paired pleurocentra to the rear and ventral. But the microtomography scans reveal a 'reverse' rhachitomous design, effectively rewriting the 'textbook' view of vertebral column evolution in the first limbed vertebrates.
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