qm > Organisation > Publications > Memoirs of the Queensland Musuem Contents

Memoirs of the Queensland Museum Article Detail

Memoirs of the Queensland Museum Volume: 39 Part: 2 Year: 1996

Phylogentic status of the Irrawaddy Dolphin Orcaella brevirostris (Owen in Gray) : a cladistic analysis
Author(s): Arnold, P.W. & Heinsohn, G.E.
Pages: 141-204

Examination of Orcaella brevirostris from Queensland has provided new information on colour pattern, external morphometrics, skull morphology, variation in the tympanoperiotic bones and postcranial skeleton. Facial anatomy is described for the first time.

Cladistic analyses, incorporating the new information, investigated the phylogenetic position of Orcaella. Our results provide no support for the separation of beluga and narwhal into two different families (Kasuya, 1973) nor for the proposal that Orcaella and Delphinapterus are closely related (Kasuya, 1973 ; Pilleri et al., 1989). The position of delphinoid families in our cladograms is consistent with previous synoptic classifications (Slijper, 1962, fig. 36 ; Heyning, 1989 ; Barnes, 1990). Our results offer no support for classifications which widely separate delphinids and phocoenids (Shimura & Numachi, 1987 ; Lint et al., 1990 ; Pilleri et al., 1989).

We suggest that Orcaella is a delphinid sensu lato. Comparison of characters in the two nearest outgroups (phocoenids and monodontids) suggest Orcaella (and other 'blunt-headed' genera) represent the most primitive Delphinidae. However, we cannot rule out the alternative that extensive convergence occurred. Extensive neoteny of the skull in Orcaella suggests one means by which the many apparently primitive features could occur.