It's about one-and-one-tenth times as heavy as a Polar Bear.
In other words, 521 kilograms is 1.01 times the weight of a Polar Bear, and the weight of a Polar Bear is 0.990 times that amount.(Ursus maritimus) (adult, male)
An adult, male polar bear weighs between 352 and 680 kg. Polar bears are so heavily insulated by their 9.9 cm (3.9 in) layer of blubber that they are often difficult to detect using infrared photography sensors.
It's about as heavy as a Grizzly Bear.
(a.k.a. brown bear, a.k.a. silver bear, Ursus arctos horribilis) (Adult, male, coastal area population average)
An adult, male grizzly bear from a coastal area (where food is plentiful) can weigh up to 521 kg. In spite of their tremendous size, grizzly bears can run at speeds of up to 55 kph (34 mph).
It's about three-fourths as heavy as a Cow.
In other words, the weight of a Cow is 1.30 times 521 kilograms.(for Holstein, a.k.a. Holstein Friesian, a.k.a. Friesian, Bos primigenius) (adult, heifer)
A mature Holstein cow (the well-known black-and-white, spotted breed of cow) typically weighs 680 kg. President William Howard Taft (1909 - 1913) kept a Holstein cow named Pauline Wayne on the White House grounds — a gift from a Wisconsin senator and the source of the First Family's milk.
It's about three-tenths as heavy as a Car.
In other words, 521 kilograms is 0.31540 times the weight of a Car, and the weight of a Car is 3.1710 times that amount.(for 2009 Ford Taurus; automatic transmission; curb weight)
A 2009 Ford Taurus weighs 1,652 kg. The first mass-produced car, the Curved Dash Oldsmobile — introduced in 1901 — weighed just 386 kg.
It's about one-fourth as heavy as a Rhinoceros.
In other words, 521 kilograms is 0.250 times the weight of a Rhinoceros, and the weight of a Rhinoceros is 4 times that amount.(for Black rhinoceros, Diceros bicornis) (Adult, male)
An adult black rhinoceros weighs between 1,400 and 2,800 kg. Rhinoceros are extremely aggressive — nearly one of every two males will die as a result of fighting with other rhinoceros.
It's about one-fifth as heavy as a Giraffe.
In other words, 521 kilograms is 0.210 times the weight of a Giraffe, and the weight of a Giraffe is 4.80 times that amount.(Giraffa camelopardalis reticulata) (adult, male)
An adult, male giraffe weighs an average of 2,500 kg. Reaching 5.5 m (18 ft) in height by adulthood, giraffe calves can grow as much as 3 cm (1 in) per day.
It's about one-fifth as heavy as The Tongue of a Blue Whale.
In other words, 521 kilograms is 0.190 times the weight of The Tongue of a Blue Whale, and the weight of The Tongue of a Blue Whale is 5.30 times that amount.(Balaenoptera musculus) (adult)
The tongue of a Blue Whale can weigh up to 2,700 kilograms. Despite their tremendous size, blue whales feed almost exclusively on tiny crustaceans called krill and cannot swallow anything much larger than a beach ball.