This article says it's only the third confirmed hybrid between species in the family Delphinidae in the wild. That surprised me, but I looked up my own work on this, and it may be right, as I see this:
Robin Baird wrote in 1998 that a fetus recovered from the corpse of a
Dall’s porpoise (Phocoenoides dalli) proved to have an unusual father: a harbor
porpoise (Phocoena phocoena). Baird
found this particularly intriguing because there are several other reports of
unusually pigmented cetaceans with the general size and form of Dall’s
porpoises. Although Dall’s porpoises are
notably variable in their pigmentation, Baird suggests some of these cases are due to ongoing
hybridization with harbor porpoises. Another intergeneric hybrid, this one
between the long-beaked dolphin (Delphinus capensis) and the dusky dolphin
(Lagenorhynchus obscurus) was nabbed off Peru.
In 2001, an apparent hybrid between a dusky dolphin and a southern
right whale dolphin, Lissodeplhis peronii, was photographed among a school of
duskies. This very unusual-looking
animal was about seven feet long, larger than normal for a dusky. It sported a solid black upper body and was
completely white underneath, lacking the intermediate shades normally present
on a dusky’s body. On the other hand (or
flipper), it had black pectoral fins, whereas the right whale dolphin’s are
white, and it had a small triangular dorsal fin. Right whale dolphins have no dorsal fin at
all.
Finally, three odd-looking dolphins which washed up on an Irish beach
in 1933 were identified by one expert as hybrids between the bottlenosed
dolphin and Risso's dolphin. While the
match between these two species was proven viable by the incident from
captivity described above, not all cetologists accept the hybrid interpretation
in this case.
A few of the sources I used:
Baird, Robin, et. al., 1998. “An
intergeneric hybrid in the family Phocoenidae,” Abstract, posted to MARMAM@UVM.UVIC.CA mailing list, March 12. Baird, Robin.
1997. Personal communication,
March 28. Carwardine, Mark. 1995.
Whales, Dolphins, and Porpoises.
London: Dorling Kindersley.
Ellis, Richard. 2000. Personal communication, March 10. Ellis, Richard. 1989.
Dolphins and Porpoises. New York:
Alfred A. Knopf.
Naish, Darren.
2001. Personal communication,
September 28