Appearance and Anatomy of the Giant Otter

The information below comes from Duplaix (1980), Chanin (1985), Harris (1968), Otternet and personal observation; the pictures are taken from my original photographs of William and Anja at the Chestnut Centre.


Anja, the Giant Otter Giant otters are big - as long as a man and as heavy as an Alsatian Dog. In shape, they are more sea lion-like than other otters, with short, velvety fur, globular heads, long bodies, short legs and big, flipper-like paws.


Sex Total Length Tail Weight
Male 1.5 - 1.8m
(59 - 71")
0.5 - 0.7m
(20 - 28")
26 - 32kg
(58 - 70lb)
Female 1.5 - 1.7m
(59 - 67")
0.5 - 0.7m
(20 - 28")
22 - 26kg
(48 - 58lb)

Head and Teeth

Note the hairy nose, 

slit-like nostrils, large round eyes, plentiful whiskers, 

thick lips and globular head The globular, slightly flattened head, with blunt, sloping muzzle, and large, round, dark eyes give the Giant Otter a rather pug-like appearance. The nose pad (rhinarium) is hairy, with two slit-like nostrils, rounded when open, but closed by flaps of skin when underwater - the nasal cavity has very well developed scroll bones, denoting an excellent sense of smell. The eyes have huge sphincter muscles to aid focussing, and can bulge visibly (there is a good photograph of this on page 64 of Bright (2000). Like most other placental mammals, Giant Otters do not see red light - they view the world on a blue/green scale, where some shades of blue and green are indistinguishable from grey. The ear pinnae are small, round, and set well back on the head; they are also closed under water. It is likely that while hearing is well developed, sound location is inexact as the pinnae are almost immovable. The lips are thick and muscular.

The head has numerous long, strong, thick whiskers - mystical (moustache), superciliary (eyebrow) and gular (throat). These are richly supplied with nerve endings, leading to an enlarged coronal gyrus in the brain i.e. compared to paw-using otters such as Amblonyx cinereus, more of their brain is given over to analysing whisker input.

The teeth are large and strong, powered by massive cheek muscles, resulting in both the globular, cat-like head and a very powerful bite. The dental formula is

I 3/3 C 1/1 P 4/3 M = 36
but the premolars are rather variable in that some individuals lack one or more of them, leading, perhaps, to the putative division of the species into P. brasiliensis brasiliensis and P. b. paranensis. The molars are wide, giving crushing as well as slicing capability. The incisors are tiny, and used for grooming.


Note the narrow shoulders, wide hips, and thick, strong tail.  Also note the large hind paws. The neck is thick and muscular, and in males can be as thick as the head. The body is long and low, with a broad, muscular pelvis and narrow shoulders. Giant Otters are slender, and their ribs show noticeably through their thin fur. Carrying extra fat would not be useful in a tropical climate.

The lungs are particularly large, with a large tidal volume, resulting in the absorption of more oxygen from each breath than other mammals, which helps when swimming underwater ( Frankfurt Zoological Society Giant Otter Project).

They possess two sub-caudal anal scent glands which open inside the anus, and secrete a dark brown, musky, viscous liquid; these can be contracted voluntarily or as a reflex upon sudden alarm.


The tail is very thickly muscular at the base, then flattened dorsoventrally, with a noticeable bilateral flange for the last two-thirds, like a sword blade. The tail tip is rounded. The tail fur is particularly short.

Legs and Paws

Strong, large paws with thick webbing The forelegs are short and stout, being heavily muscled. The forepaws are large, naked below, with strong toes and claws, thickly webbed to the fingertips, and when fanned out, are almost circular. The hind paws are very large, like clown boots! All otters are plantigrade, i.e. they place their feet flat on the ground. This is particularly noticeable with Giant Otters, especially on a muddy surface when they are in a hurry - they slap along almost like sea lions.


Example of Markings The fur is very short, with guard hairs only 8mm (5/18"), and under fur 4mm (3/16") long. It is very dense - water never reaches the skin - and is very soft and velvety. It ranges in colour from fawn through reddish brown to deep chocolate brown, appearing darker and shiny when wet. The lips, chin, throat and chest are spotted and splashed with lighter markings, from creamy white to yellow-buff, with sharply defined edges. These markings vary from a few spots to a bib, and are unique to each otter; researchers use these markings to identify particular animals.

Giant Otter