Giant Otter Shrew

Jul 4

Amphioctopus marginatus

The giant otter shrew is named for its resemblance to both an otter and a shrew, despite not actually being either. It hunts nocturnally in forest pools and streams, swimming with a laterally flattened tail, like that of a fish or crocodile — an unusual swimming method among mammals.

Otter? Shrew? No…

"This semi-aquatic mammal, with insulated dark fur, lives in forested wetlands where rivers and pools are plentiful. Its burrows line the banks of the waterway. An adept swimmer, it dives beneath the surface, using its sensitive whiskers to find and capture crustaceans, frogs and fish."

Such a passage could equally be describing a giant otter ¹ from the rivers of the Amazon Rainforest or a tiny water shrew from the streams of Europe and North America. However, there is also an animal from Central Africa that bears the name and nature of both otter and shrew, but is actually neither.

The giant otter shrew looks about how you'd expect based on its name; like a large shrew, shaped vaguely like an otter. In size — its head and body measuring around 30 cm (12 in) long — the giant otter shrew falls somewhere between a shrew and an otter. Like a giant otter's, its shape is long and lithe and the fur on its back is dark brown, while its belly is cream-coloured. But its feet are small, clawed, and unwebbed, like those of a water shrew. Its face is set with beady black eyes and nostril flaps that close when diving, and its snout is lengthy (water-shrew-like), but somewhat wide (otter-like). The giant otter shrew's tail is its most interesting feature — unique among aquatic mammals ² — it is long broad, and flat, but instead of being compressed horizontally (like that of the giant otter, and other aquatic mammals such as dolphins and manatees), it is flattened laterally, so that the otter shrew swims with side-to-side sways of its tail, like a fish or crocodile.

Waterside Hunter

A giant otter shrew using its laterally flattened tail to swim like a little, furry crocodilian.

As it swims, the giant otter shrew resembles an odd, furry crocodilian. Its forelimbs lie prone against its sides, while flaps of skin hold its hind limbs tight against its body. Its limbs aren't used in swimming — it relies entirely on its powerful tail to propel it after aquatic prey. But, unlike a crocodile, the giant otter shrew is an active predator. It hunts alone at night, patrolling a territory of around 800 metres (half a mile). In the dark, its already tiny, weak eyes become all but useless. Instead, it uses its copious bristly whiskers to feel for prey as it dives beneath the black surface of forest pools and streams. Each dive happens in a flash, lasting only a few seconds, in which the otter shrew can find its prey and attack it with sharp bites and clawed forepaws, before dragging it onto the bank to consume it. Fish are deconstructed into edible parts while frogs are ingested head first. It stops often to fastidiously groom itself and once it reaches the end of its territory, it treks back upstream and dives in once more to hunt with the current.

The otter shrew also stalks the waterside for prey, using its strong sense of smell to find food in the dark. Its movements are less graceful on land than in the water. Nonetheless, it can still conquer armoured foes; pinning crabs with its front paws or flipping them over to expose their undersides — although it's careful to avoid crabs larger than 7 cm (2.8 in) across. Hidden piles of faeces line the riverbanks like signposts, indicating the edges of giant otter shrew territories. As the otter shrew hunts, it often stops to sniff at these dropping, checking up on the status of its neighbours. After a night of hunting, with a belly full of fish, frogs, and crustaceans, the giant otter shrew returns to its waterside burrow, hidden in a crevice along the riverbank. Dry leaves line the inside and the otter shrew settles in for a restful sleep.

What Exactly Is It?

A painting of a giant otter shrew — photos of this animal are few and far between due to its elusive nature.

If the giant otter shrew isn't an otter or a shrew, what exactly is it?
Well, it's an otter shrew — a member of the family Potamogalidae with two other otter shrew species: the Nimba otter shrew and the Ruwenzori otter shrew. The giant otter shrew is the sole member of its genus, while its two cousins — who are also known as 'dwarf otter shrews' because they are about half the size of the giant otter shrew — are sister species in the same genus.

But this scarcely seems like a satisfactory answer. In the broader picture, the closest relative of otter shrews are the tenrecs; an enigmatic family (Tenrecidae) of about 30 species from Africa — mostly found on Madagascar — some of which resemble hedgehogs, with their many hard short spines, while others are more shrew-like, betraying their relatedness to otter shrews.

One step up on the taxonomic ladder is the order Afrosoricida. This order of odd African mammals is a case study in convergent evolution (in which two unrelated animals evolve the same traits due to similar environmental pressures). The order contains the otter shrews, which look and act like otters and shrews but are unrelated to either ³, the tenrecs, which look and act like shrews and hedgehogs, but are unrelated to either, and the golden moles, which look and act like true moles from North America, Europe, and Asia, and marsupial moles from Australia, but are unrelated either. All three of these Afrosoricida groups evolved their traits individually in Africa, separated long ago from their look-alikes on the mammalian family tree.

This phylogenetic tree¹ presents the giant otter shrews placement among the broader mammalian class. The three highlighted groups belong to the superorder of mammals known as **Afrotheria** — mammals of African origin.
The otter shrews belong in the green section (the order Afrosoricida). They were once placed in the family Tenrecidae, but are now usually considered to be in their own family (Potamogalidae, not featured on the tree), most closely related to the tenrecs.

A giant otter (*Pteronura brasiliensis*); the largest living otter species.

¹ Reaching lengths of up to 1.8 metres (6 ft) and a weight of 34 kg (75 lbs), the giant otter is the largest extant otter species and the largest living mustelid (the family that includes otters, weasels, ferrets, martens, badgers, and wolverines). It is a South American river dweller, gliding through the waterways of the Amazon, Orinoco, and La Plata at speeds of 14 km/h (8.7 mph) — almost twice as fast as the human record. Unfortunately, this apex river predator is also endangered due to hunting for fur and habitat degradation/destruction.

A comparison of a dugong (on the left) of which there is one species, and a manatee (on the right) of which there are three.

² The tails of almost all aquatic and semi-aquatic mammals are horizontally flattened; used to propel them through the water with an up-and-down motion, akin to the arching spinal movements of a land mammal as it gallops, rather than the side-to-side swivel of a crawling lizard or salamander. You see this most clearly in the fully aquatic bunch, which includes the cetaceans (whales, dolphins, and porpoises), whose tails branch into two elegantly curving flukes, and sirenians or "sea cows" (dugongs, who have similar tails to cetaceans, and manatees, who sport broad paddle-like tails). Some semi-aquatic mammals also sport very flat horizontal tails, such as the oblong paddle tails of beavers and platypuses. Others, like most otters, also have horizontally flat tails, but they are longer and less conspicuous.

For some semi-aquatic mammals, this horizontal tail rule is obviously non-applicable — such is the case with polar bears, capybaras, and hippos — for their tails could do little in the way of propulsion. Others, like some swimming rodents and shrews, have tails that are more or less long, tapering cylinders.

Pinnipeds (seals, sea lions, and walruses) present an odd case for aquatic mammals. Their tails are small and almost unnoticeable, tucked between their hind legs, which themselves are very short but have very long toes covered in extensive webbing, creating effective flippers. Depending on the species, pinnipeds either use their front flippers to propel them or their back flippers — paddling in a side-to-side motion, rather than the typical mammalian up-and-down. Even though it isn't strictly their tails that they're using, in their swimming technique, they are more similar to the movements of fish with their vertical tails and side-to-side sway.

³ I say "unrelated" for shorthand convenience. Being mammals, they are related, just distantly so. If I was being accurate to the extreme, as far as is known, all life on Earth is related — branches and twigs growing from the trunk of our shared family tree — so saying any Earthly (known) animal is unrelated to another would be incorrect.

**Where Does It Live?**
⛰️ Rainforests; usually in wet environments, such as near rivers, springs, and swamps.

📍 Central Africa; from Nigeria to Zambia.

‘Least Concern’ as of 28 February, 2015.

IUCN

Size // Small
Length // 30 cm (12 in) head and body, 26 cm (10 in) tail
Weight // Less than 400 grams (0.9 lbs)
Activity: Nocturnal 🌙
Lifestyle: Solitary 👤
Lifespan: 2 - 3 years, up to 5 years
Diet: Carnivore
Favorite Food: Fish, frogs, and crabs 🐟
Class: Mammalia
Order: Afrosoricida
Family: Potamogalidae
Genus: Potamogale
Species: P. velox

The closest living relatives to the giant otter shrew are two species of 'dwarf otter shrew' in the same family (Potamogalidae). Together, they are most closely related to the tenrecs; a group of small hedgehog and shrew-like mammals from Africa (mostly Madagascar).

The giant otter shrew is solitary. It patrols a 500 to 1,000-metre (1,640 - 3,280 ft) stretch of waterside territory, marked with piles of faeces.

It is nocturnal, hunting both in water and on land, using its strong sense of smell and whiskers to find its prey: fish, crabs, water insects, and frogs.

It prefers to move downstream when hunting, swimming with the current. When it reaches the end of its territory, it typically exits the water and walks back upstream along the bank.

The giant otter shrew's burrow is located near the water where it hunts and usually has an underwater entrance. It shelters in this burrow, lined with leaves on the inside, during the day.