Evolution

X Rays of Fossil Reveal Hidden Snake Leg



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A new type of 3D X-ray imaging technology has revealed vestigial legs on an snake fossil. This physical evidence confirms that snakes did evolve from reptiles millions of years ago.

The results appear in the February 8th issue of the Journal of Vertebrate Paleontology.

The debate on the origin of snakes had several theories—the two most heated were whether snakes developed on land or the oceans. The new imaging seems to have ended the decades-long debate once and for all.

Snakes developed from land-based reptiles. The interior of the snake's structure appears remarkably like that of modern lizards.

Alexandra Houssaye from the Museum National d'Histoire Naturelle (MNHN) in Paris, France, led the group of researchers that included the Karlsruhe Institute of Technology (KIT), Germany, that provided the imaging instrument, and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where the actual process of the 3D imaging took place.

The important new evidence reveals in the details that the species of snake in the fossil—Eupodophis descouensi—became legless because the appendages developed very slowly or only grew for a very short period of time. The finer details of the 3D imaging shows that the internal, underdeveloped leg is attached to the pelvis and bent at the knee. Curiously, the snake's ankle is comprised of four distinct bones, but has no accompanying foot or toes.

"The revelation of the inner structure of Eupodophis hind limbs enables us to investigate the process of limb regression in snake evolution," Houssaye explained.

A new type of imaging technology—synchrotron laminography—that's specifically designed to investigate big, flat objects was used on the snake fossil. According to physorg.com, the technology "is similar to the computed tomography (CT) technique used in many hospitals, but uses a coherent synchrotron X-ray beam to resolve details a few micrometers in size—some 1000 times smaller than a hospital CT scanner. For the new technique, the fossil is rotated at a tilted angle in a brilliant high-energy X-ray beam, with thousands of two-dimensional images recorded as it makes a full 360-degree turn. From these individual images, a high-resolution, 3-D representation is reconstructed, which shows hidden details like the internal structures of the legs."

This revolutionary leap in the evolution of 3D imaging will enable researchers to study ancient fossil—like the 95-million-year-old fossilized snake discovered in Lebanon—in minute detail.

Co-author of the study, Paul Tafforeau of the ESRF, almost waxes poetic about the benefits of the breakthrough. "Synchrotrons, these enormous machines, allow us to see microscopic details in fossils invisible to any other techniques without damage to these invaluable specimens."

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