Abstract

Seven species of the family Istiophoridae and Xiphias gladiu6 were identified using only features of their rostrum. In the Istiophoridae, two rostral regions were emphasized, one-fourth and one·half the distance between the distal tip and the orbital margin of the lateral ethmoid bone. Characters studied in each region were the depth and width of rostrum and height, width, and position of nutrient canals (as seen in cross-section). Characters studied without reference to region were the distribution of denticles on both dorsal and ventral surfaces of the bilI and position of the prenasal bone. In the Xiphiidae, the only characters studied were the depth and width of the rostrum at the level of the dermethmoid bone and the presence and placement of central chambers as seen in radiographs. A total of 32 characters were analyzed as ratios using both multivariate and univariate statistics. The rostrum of X. gladius was separated from the Istiophoridae by its flat shape, Tetrapturus angwtirostris from all other istiophorids by its widely separated nutrient canals, and the complex of T. audax/T. pfluegeri/Makaira nigricans/M. indica from the complex of lstiophorus platypterus/T. albidus by having a smaller area of denticles on the dorsal surface. Tetrapturus pfluegeri was separated from T. audux, M. nigricans, and M. indica by having a longer denticle-free midline on the ventral surface of the rostrum. Tetrapturus audux was separated from M. nigricans and M. indica by the location of its nutrient canals. The complexes of Makaira nigricand/M. indica and I. platypterus/T. albidus were each separated using multivariate discriminant analysis. We show the study has application in identifying rostral fragments found as fossils and impaled in animate and inanimate objects such as marine turtles and wooden ships and should have application wherever rostral fragments are found.

Disciplines

Biology

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URL: http://digitalcommons.calpoly.edu/bio_fac/16