Dorsal Fin Shape Research Articles

Psettodoidea and pleuronectoidea (Pisces, Heterosomata) : Nielsen, J., 1961. Atlantide Rep. 6: 101–127

The family Delphinidae is one of three extant families (with Phocoenidae and Monodontidae) in the cetacean superfamily Delphinoidea (which also includes two extinct families, Kentriodontidae and Albireonidae). Delphinids likely arose in the mid- to late Miocene (11–12 mya) from kentriodontid-like ancestors and quickly radiated into many different morphological and ecological types. Today the Delphinidae is the most speciose family of marine mammals, with 33–35 recognized extant species arranged into 17–19 genera. At present, there is much uncertainty about the evolutionary relationships among the species of delphinids. Of the many recent classifications that have been proposed, two are depicted here. One represents a more traditional view of dolphin taxonomy, and the other is a revised classification based on various recent molecular and morphological phylogenetic analyses. Delphinids also show wide variation in their external morphology. Only a few species (e.g., Orcinus orca, Globicephala spp.) are dramatically sexually dimorphic, although many others may have subtler dimorphism in body size and shape, coloration, and dorsal fin shape.

Carcharhinus floridanus, the Silky Shark, a Synonym of C. falciformis

Carcharhinus floridanus Bigelow, Schroeder, and Springer, 1943 (holotype a female about 2,300 mm long) and C. falciformis (Bibron 1841) (holotype a 528-mm embryo) represent the size extremes of a single species the name of which should be C. falciformis. This conclusion is based on the study of 65 specimens comprising both sexes and well distributed over the size range of the animal. The physical characters heretofore used to distinguish these nominal species, pectoral fin length, eye diameter, dorsal fin shape, contour of snout, and character of the denticles, all are shown to change gradually with growth from one supposed diagnostic set to the other. C. falciformis is sometimes confused with other carcharhinid sharks and means of distinguishing it from two of these, C. obscurus and Hypoprion signatus, are given.