Head scan of a Texas Horned Lizard
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Head scan of a Texas Horned Lizard

June 1, 2010
Head scan of a Texas Horned Lizard, part of a series of 3-D head scans showing clear skin and solid bone. The image series was created at the High-Resolution X-ray Computed Tomography Facility (UTCT) at the University of Texas, Austin. The UTCT, a National Science Foundation (NSF)-supported shared multiuser facility, gives researchers a nondestructive technique for visualizing features in the interior of opaque solid objects, and obtain digital information on their 3-D geometries and properties. The scans were taken as part of ongoing research by Wendy Hodges, a biologist at the University of California, Riverside, who is attempting to reconstruct the physical features of the common ancestor of the 13 species of North American horned lizards.

Between 23 and 30 million years ago, the first North American horned lizards branched off from sand lizards, becoming stockier and spinier and evolving their distinctive crowns of horns. A single common ancestor gave rise to the 13 North American species, each developing a unique set of cranial horns and spikes. Researchers are trying to determine what this prehistoric, common ancestor may have looked like and how the horns of these species developed. [Image 4 of 9 related images. See Image 5.]

More about this Image With the assistance of Reuben Reyes, a visualization expert from the Texas Advanced Computing Center (UT-Austin), Wendy Hodges is applying advanced computer analysis and graphics techniques to 3-D data sets acquired through computed tomography (CT). CT reconstruction allows the analyses and comparison of the morphologies of different species of horned lizards. The final goal of the project is the visualization of the evolution of horns in this group of lizards and determining how horn number increased through evolutionary time.

Hodges and Reyes have been applying "morphing" programs and algorithms for computing ancestral states in combination with 3-D morphologies from CT scans to visualize an intermediate form between two horned lizard species. Hodges acquired structural information from preserved horned lizard museum specimens using a high-resolution CT scanner at the NSF-supported University of Texas High-Resolution X-ray Computed Tomography Facility. The scanner is comparable to a conventional medical diagnostic CT device, but was custom-built to have greater resolution and penetrating power and was specifically designed to explore the internal structures of natural objects and materials at macro- and microscopic levels.

Eventually, images of each horned lizard species' head will be created from the CT data using visualization software, to reveal both the external configurations and the internal structures of the specimens. One visualization application depicts the external skin and internal skeleton using a color-mapping scheme that represents the distance from the skin to the bone, giving some of the lizard head reconstructions a polychromatic, "tie-dyed" appearance.

[This research is funded in part by an NSF postdoctoral fellowship in biological informatics award given to Hodges.]

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