What is the difference between a porcupine and a rat?

The porcupine and the echidna are two very different animals. * Echidnas are monotremes (egg-laying mammals) and porcupines are placental mammals, and belong to the rodent family. * Echidnas are found in Australia and Papua New Guinea but porcupines are found in North America and Africa. * Porcupine quills are used more as active defence, whereas the echidna spines do not do a great deal of damage but certainly deter would-be predators. * There are around two dozen species of porcupine, but only two species of echidna. * Porcupines vary in size, with some species ranging between 80 and 115cm in length (including the tail); echidnas average between 30 and 50cm in length. Porcupines may weigh 5-16kg, but echidnas weigh 2-5kg, with those in the south being heavier than northern echidnas. * Some varieties of porcupine have quills 30cm long, but echidnas' spines average 5cm long. * Porcupines have quite long tails; echidnas have short, stubby, hairless tails. * Porcupines eat seeds, fruit, leaves, grasses, dandelions, bark, buds, twigs and aquatic plants; echidnas live almost exclusively on termites and ants. * Porcupines can climb trees, but echidnas are strictly ground-dwelling animals.