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About the Species
Gravid adult female Sceloporus occidentalis (Phrynosomatidae) were collected near Pinecrest, California during June and July of 1997. Females were maintained on a mixture of moistened sand and peat moss until egg deposition. Eggs were weighed and placed in small plastic cups filled with a sand/peat mixture and incubated at 27C until hatching. The specimen used in this study hatched on July 31 after 44 days incubation. Live mass was 0.6g. The specimen was euthanized and preserved in formaldehyde within 12 hours of hatching and transferred to 70% ethanol after 96 hours. Injection of preservative was avoided in order to minimize changes in specimen volume and placement of internal structures.
About this Specimen
Before scanning, the specimen was placed in a lidded 35x10 mm plastic petri dish lined with plastic florist's foam saturated with 70% ethanol. A small plastic tube was imbedded vertically into the foam near the specimen to serve as a reference point for calibration of digital measurements. Computed tomography was conducted by Richard Ketcham and Cambria Denison in the fall of 1997 using an image intensifier at 100/.24 KV/mA, a slice width of 0.1mm and a slice increment of 0.08mm. 61 slices were made in the horizontal plane at a source-object distance of 68mm.
Digital Image Processing
Digital files were downloaded to a local FTP serve and transferred to 1 GB removable disk. Raw 8 bit resolution files were stacked and converted to windows using NIH Image vol 1.62ppc. Slices at the top and the bottom of the stack with no portion of the specimen visible were deleted and replaced with black screens.
Grayscale image levels were adjusted to minimize noise in non-specimen regions of each image and to enhance contrast between tissues of different densities. Misaligned slices (49 and 52 in horizontal plane) were aligned to match the orientation of adjacent slices. A black screen was layered over visible portions of the petri dish in each slice which was flattened and converted to TIFF format using a batch function. Slices were then exported to NIH image where they were stacked, calibrated, and rotated to fit window frame. The stack was then resliced in the coronal plane (slice thickness equal to one pixel). Visual artifacts left by the petri dish and florist's foam were edited out using a paintbrush tool loaded with background color. Editing was conducted by reference to adjacent slices. The edited coronal stack was then resliced to generate views in the horizontal and sagittal planes. It is possible that a small amount of error was introduced into the data set during editing (some portions of the specimen may have been removed or not all substrate may have been completely removed). Setting threshold values is an inexact science as is editing by hand. In acknowledgment that future researchers may wish to examine this data set, raw data sets (8 bit and 16 bit resolution) are provided for reference.
Slices were batch processed to a size of 640x400 pixels with a custom color palette in Photoshop. Reslicing in coronal and sagittal planes was conducted in NIH Image.
Stacks of images from all three views were reduced in size (380x330 pixels max) with specimen proportions maintained. Files were converted to Quicktime movie format (256 colors, 180 k/sec, and each slice indexed) with cinepak compression in Graphic Converter.
de Queiroz, K. 1987. Phylogenetic systematics of iguanine lizards: A comparative osteological study. University of California Publications, Vol. 118.
Oelrich, T. 1956. The anatomy of the head of Ctenosaura pectinata (Iguanidae). Miscellaneous Publications of the Museum of Zoology, University of Michigan No. 94.
Wiens, J.J., and Reeder, T.W. 1997. Phylogeny of the spiny lizards (Sceloporus) based on molecular and morphological evidence. Herpetological Monographs No. 11:1-101.
Sceloporus occidentalis natural history
Sceloporus undulatus hyacinthinus (Northern Fence lizard) on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Sceloporus woodi (Florida Scrub Lizard, Scrub Pine Lizard) on The Animal Diversity Web (The University of Michigan Museum of Zoology)
San Diego Natural History Museum fieldguide- Sceloporus occidentalis
Sceloporus occidentalis on Calphotos.