CAT Scan-Based Images of the Skeleton of the Asian CatfishCranoglanis(Siluriformes: Cranoglanididae)

Abstract

Figured on the following two pages are 3D models of the bony skeleton of the Asian catfish Cranoglanis bouderius, produced with High Resolution X-ray Com puted Tomography (HRXCT) imaging methods. The scanned specimen is from China, Guangdong Province Guangzhou city, and is deposited at the Academy of Natrual Sciences: ANSP 164978, Standard Length = 125 mm. Additional images and animations of this specimen are publicly available at the CatfishBones website, http:// catfishbone.acnatsci.org/. The specimen was scanned at the High-Resolution X ray CT Facility, The University of Texas, Austin. The scan ning parameters are as follows. A Feinfocus microfocal X-ray source operating at 180 kV and 0.133 mA with no X ray prefiltering. For each slice, 1600 views were taken with two samples per view. The field of image reconstruction was 40 mm, corresponding to a resolution of 39.1 microns per pixel for the 1024 by 1024 pixel slices. The specimen was scanned in multi-slice mode, in which 15 slices were collected simultaneously during a single specimen rota tion resulting in a total of 645 transverse (=coronal) CT slices. The scan was taken along the long axis of the speci men from the tip of the snout to the middle of the dorsal fin base. Visualizations were produced in the commercial software package VG Studio Max?. Although the render ings appear similar to photographs, they represent the den sity differences of the biological materials as reflected in their X-ray opacity. Preparation of the figures utilized still frames captured from digital animations of HRXCT and were prepared using Adobe?Photoshop?CS. The genus Cranoglanis, with three species, is placed in its own family Cranoglanididae. These catfishes are endemic to southern mainland China, Hainan Island and Viet Nam. The relationship of Cranoglanis to other cat fishes has long been uncertain due to its generalized mor phology. Cranoglanis has been variously thought related to Asian Bagridae, Pangasiidae or Schilbidae. However, one morphological study by Diogo et al. (2002) and recent molecular-based phylogenetic studies by Hardman (2005) and Sullivan et al. (2006) indicate a sistergroup relation ship between Cranoglanididae and the North American catfish family Ictaluridae. This discovery confirms the long-standing supposition of close evolutionary relation ship between North American and some Asian catfishes. Lundberg et al. (2007) applied fossil-calibrated molecu lar dating analyses to chart the time course of catfish di versification. They estimated the age of the phylogenet ic split between Cranoglanididae and Ictaluridae to have been roughly 85 million years ago in the Late Cretaceous when the early Bering land bridge between eastern Asian and western North America provided a migration path for biotic exchange.