Sexual dimorphism in toothed whales: which are the differences between male and female cetaceans?

odontoceti is a suborder that includes all the cetaceans (whales and dolphins)
with teeth. In general, this group looks to follow the mammalian pattern of
increasing sexual dimorphism with the increasing of body size. For example, the
sperm whale (Physeter macrocephalus)
is the largest toothed whale and the cetacean with a bigger sexual dimorphism
(different characteristics in males and females of the same specie). 

whales present very few secondary sexual characteristics and are not very
evident  – males are bigger than females
and in some families there are differences in the number of teeth and size of
the dorsal fin. Although in most of the
cases is almost impossible to distinguish a male from a female dolphin in wild
, unless there is a clear view of the genital area.  The bottlenose dolphins, the common dolphins,
Atlantic spotted dolphins and Risso’s dolphin are some of the examples. Males
have two slits, the long one is the genital slit and the smaller one is the houses
the anus. In females there is a continuous slit that are both the genital and
anus slit and two mammary slits.


Orca (Orcinus orca) – dorsal fins of males can reach up
to 2 m and in females only 1 m. In females the fin is slightly curved and in
males completely vertical.
Pilot whale (Globiceplala spp.)– males can have a more swollen head
with better defined melon. The dorsal fin in males is strongly hooked and very

Beaked whales (Ziphiidae family)– It is the second biggest group in the cetacean
world and is the more mysterious one. In this group there is 21 species and all
of them are different but in general only in males the tusks come out from the
gums and females and juveniles are toothless. Only in a few species we can see functional
teeth in both sexes.
Sometimes we can also distinguished
a male from a female because of their behaviour. Just like us, cetaceans
present a really strong bond between mother and calf, so when we see a baby is
always associated with a female (no necessary the mother).  In sperm whales, for example, females live in
groups with juveniles (males and females) and calves, adult males live solitary
lives. So, in our tours when we see a baby we know immediately that the individual
associated is a female. 

SHIRIHAI, Hadoram. Whales, Dolphins and Seals: A Field
Guide to the Marine Mammals of the world: Bloomsbury, 2006.

Written by Inês Coelho

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