The American badger, Taxidea taxus, is a mustelid carnivoran with a boldly patterned face and a reputation for ferocity. Its scientific name means "like a badger," in reference to its similarity of appearance with the Eurasian badger, Meles meles. The name "badger" probably refers to the "badges" or brownish-black patches of fur on its cheeks. The snout and crown of the head are also black. The facial markings also include a white throat and base of the ears, and a white stripe that extends from behind the nose, over the head, and onto the shoulders. The stripe often extends down to the rump in southwestern Taxidea. |
|
Taxidea is a relatively large mustelid, weighing up to 12 kg (26.5 lbs), with a head and body length range of 42-72 cm (16.5 -28 in). Its tail is relatively short, only 10-15 cm (4-6 in). It is equipped with long foreclaws and powerful front legs for a fossorial (digging) lifestyle. Taxidea excavates burrows for dens and to capture prey. The primary prey of Taxidea are rodents and other small vertebrates. The sense of hearing is acute in Taxidea, as indicated by the inflated and septate tympanic bullae of the skull.
The skull of Taxidea is wedge-shaped, the occiput triangular in outline. The rostrum is short and equipped with large upper and lower canines. The powerful jaws and complex teeth of Taxidea are well-suited for processing prey. Taxidea's dental formula is: I 3/3; C 1/1; P 3/3; M 1/2. The P4 has a medial shelf and a hypocone. Transverse rows of cusps on the M1 are distinctive, yet exhibit some variation within the genus. The m1 has a well-developed trigonid and a talonid with a central hypoconid and entoconid.
The genus Taxidea first appeared in North America about 6 million years ago. The fossil remains of at least two individual Taxidea were recovered from Yepómera, Chihuahua, Mexico, and are the oldest known to date. During the Pleistocene, the range of Taxidea extended north into Alaska and as far east as Maryland and Pennsylvania. Today Taxidea ranges from the western United States, southern British Columbia and northern Alberta, eastward into Ohio. Its southern distribution includes Baja California and northern and central Mexico.
DATA ACQUISITION:
The skull of Taxidea taxus was scanned with the Ultra-High Resolution Image Intensifier System (microfocal X-ray source) at The University of Texas High-Resolution X-Ray CT Facility in Austin, Texas. Dr. Matthew Colbert performed the scan on 13 September 1999. The skull was scanned in air, held in position within a clear plastic cylinder. An empty mount wedge was used in the calibration of the scanner. Scanning parameters were to 0.16 mA and 150 kV energy potential. To reduce beam-hardening artifacts in the output images, an aluminum filter was used to diminish lower energy X-rays. The source-object distance (distance between x-ray source and skull) was 147 mm. The skull was positioned occiput-down and scanned in the coronal (YZ) plane at 190% offset from horizontal with 1800 views, two samples per view. The skull was scanned in 3-slice mode. The field of reconstruction was 76 mm.
The slice images produced by X-ray CT are two-dimensional images of the skull in the coronal plane from snout to occiput. Each slice has a width of 0.2531 mm and the interslice spacing is 0.253 mm The scan data were exported onto a CD-ROM as both 8 bit and 16 bit TIFF formatted images in the coronal plane.
DATA PROCESSING:
I completed the initial inspection and processing of the CT images on a Power Macintosh G3 (Mac OS 8.6) computer that was equipped with 512 megabytes of RAM and 700 megabytes of virtual memory. To assess the content of the dataset I imported the 8 bit dataset within NIH Image 1.62b17/ppc (allocating 500 MB of RAM) and created a "stack" of images that I saved as a "quick and dirty" movie file. Utilizing QuickTime MoviePlayer, I viewed the series of images to determine appropriate cropping dimensions and to select images to make brightness and contrast level adjustments for the 16 bit dataset. The 16 bit images have greater resolution than the 8 bit images. By working with the 16 bit images and then dropping them to 8 bit, I improve the 8 bit output and thus have more control of the digital information.
Once I identified a set of images on which I would test the contrast levels, I opened the 16 bit dataset and duplicated those slices. I opened the selected images in Adobe Photoshop 4.01 and opened the adjust levels dialog box, and confirmed the preview box was checked. I made the first adjustment pass (input levels of 0, 1.00, 15) to spread out the histogram (the image initially appears black because the histogram is compressed within the black end of the spectrum). During the second adjustment pass, I specifically looked for tonal contrasts between thin bones and air, contacts between bones, and structures within the complex auditory region. Generally one has to "compromise" to obtain an image that provides as much information as possible. The final input settings were 30, 1.21, 215. I set the white output levels to 0, 239 - which leaves room for the colored labels that I add further along in the image processing for the CD-ROM.
Within Photoshop I batch-processed the 16 bit data via an action command that opens each image, adjusts the levels to my specifications, converts the 16 bit image to an 8 bit image, saves it, and closes the file. After adjusting and converting the 16 bit images, I cropped excessive black background from the images. Cropping allows one to work with a stack of images that when resliced, does not create stacks in the horizontal and sagittal planes with numerous black slices fore and aft.
To create slices in the horizontal and sagittal planes, the coronal dataset is "resliced". The interslice distance in pixels/mm is required by NIH Image to reslice the coronal stack in the horizontal (XY) and sagittal (XZ) planes. The interslice distance is calculated by dividing the image resolution (512 pixels) by the field of reconstruction (76 mm) and then multiplying that quotient (6.74 pixels/mm) by the interslice spacing (0.253 mm). The interslice distance is 1.70 mm.
Within NIH Image I loaded the Stacks Macros to manipulate the stacks and set the Clipboard buffer size to 600K to work with my processed images. To create a stack in the horizontal plane, I selected reslice "horizontally" from the Special Menu to reslice the coronal stack. I selected reslice "vertically" to create a stack in the sagittal plane. To complete the processing, I rotated the sagittal and horizontal stacks to position the rostrum of the skull to the viewer's left. The slices in each stack were saved as files after deleting extra black slices.
I duplicated one set of images from each slice plane and subsequently reduced the image size for display on the Digital Morphology Group Website. Within Photoshop I set the resolution at 72 dpi and a maximum width of 320 pixels. To ease navigation through the slice planes, each image has a number in the upper left-hand corner. To number the images I opened File Buddy 5.01 and renamed the coronal files sequentially 000-495, sagittal files 000-198, and horizontal files 000-144. I then launched NIH Image and opened all the files. I loaded the Number images macro and selected Special >Number Images. The file-name number was automatically added to each slice.
Once all the images were numbered, I selected windows to stack and then saved the slices as files. I saved the images as TIFF files for import into QuickTime MoviePlayer Pro 3.0. I created a movie from each set of images.
Literature
Drescher, A. B. 1939. A new Pliocene badger from Mexico. Bulletin of the Southern California Academy of Sciences 38:57-62.
Hall, E. R. 1927. The muscular anatomy of the American badger (Taxidea taxus). University of California Publications in Zoology 30:205-219.
Lindzey, F. G. 1982. Badger. Pp.653-663 In: Wild mammals of North America: biology, management, and economics (Chapman, J. A. and G. A. Feldhamer, eds.). 1147 pp.
Long, C. A. 1965. Functional aspects of jaw-articulation in the North American badger, with comments on adaptiveness of tooth wear. Transactions of the Kansas Academy of Science 68(1):156-162.
Long, C. A. 1965. Comparison of juvenile skulls of the mustelid genera Taxidea and Meles, with comments on the subfamily Taxidiinae Pocock. The American Midland Naturalist 74:225-232.
Long, C. A. 1972. Taxonomic revision of the North American badger, Taxidea taxus. Journal of Mammalogy 53:725-759.
Long, C. A. 1971. Taxidea taxus. Mammalian Species 26:1-4.
Long, C. A. 1975. Growth and development of the teeth and skull of the wild North American badger, Taxidea taxus. Transactions of the Kansas Academy of Science 77(2):106-120.
Nowak, R. M. 1999. Taxidea taxus. Walker's mammal species of the world. 6th edition. The Johns Hopkins University Press, Baltimore, Maryland. Volume 1:731-732.
Owen, P. R. 2000. Phylogenetic relationships among American badgers (Taxidiinae) and the evolution of the badger ecomorph. Unpublished Ph.D. dissertation, The University of Texas at Austin, 322 pp. + CD-ROM.
Owen, P. R. 2001. Description of a new genus and species of American badger (Taxidiinae) utilizing high-resolution X-ray computed tomography. Journal of Vertebrate Paleontology 21(Suppl.3):86A.
Pavlinov, I. A. 1995. Contribution to variation and homology of crown pattern of the upper molar in Taxidea taxus (Mammalia: Mustelidae). Acta Theriologica 40(4):439-442.
Pocock, R. I. 1920. On the external and cranial characters of the European badger (Meles) and of the American badger (Taxidea). Proceedings of the Zoological Society of London 1920(29):423-435.
Pocock, R. I. 1925. The external characters of an American badger (Taxidea taxus) and an American mink (Mustela vison), recently exhibited in the Society's Gardens. Proceedings of the Zoological Society of London 1921:473-486.
Quaife, L. R. 1978. The form and function of the North American badger (Taxidea taxus) in relation to its fossorial way of life. M.Sc. thesis, University of Calgary, 197 pp.
Shufeldt, R. W. 1922. Remarkable changes in the skull of an American badger (Taxidea taxus) due to advanced age. Journal of Mammalogy 3:173-175.
Stock, C. 1948. Restos de tejón (Taxidea), Pliocénico del occidente de Chihuahua. Boletín de la Sociedad Geológica Mexicana 13:69-76.
Waterhouse, G. R. 1838. On the skull and dentition of the American badger (Meles labradoria). Proceedings of the Zoological Society of London 1838(6):153-154.
Links
The brain of Taxidea taxus (Comparative Mammalian Brain Collections website)
Taxidea taxus on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Steve Jackson's Brockwatch Badger Pages (Information on the world's extant badgers)
Museum of Vertebrate Zoology, UC Berkeley (Home of the scanned Taxidea skull)
 )
