canine, etc.); for the family, it is suid (as with bovid, canid). Description and behaviour A typical pig has a large head with a long snout that is strengthened by a special prenasal bone and by a disk of cartilage at the tip. The snout is used to dig into the soil to find food and is a very acute sense organ. Each foot has four hoofed toes, with the two larger central toes bearing most of the weight, and the outer two also being used in soft ground. The dental formula of adult pigs is , giving a total of 44 teeth. The rear teeth are adapted for crushing. In the male, the canine teeth form tusks, which grow continuously and are sharpened by constantly being ground against each other. Occasionally, captive mother pigs may savage their own piglets, often if they become severely stressed. Some attacks on newborn piglets are non-fatal. Others may kill the piglets and sometimes, the mother may eat them. An estimated 50% of piglet fatalities are due to the mother attacking, or unintentionally crushing, the newborn pre-weaned animals. Distribution and evolution With around 1 billion individuals alive at any time, the domestic pig is one of the most numerous large mammals on the planet. The ancestor of the domestic pig is the wild boar, which is one of the most numerous and widespread large mammals. Its many subspecies are native to all but the harshest climates of continental Eurasia and its islands and Africa as well, from Ireland and India to Japan and north to Siberia. Long isolated from other pigs on the many islands of Indonesia, Malaysia, and the Philippines, pigs have evolved into many different species, including wild boar, bearded pigs, and warty pigs. Humans have introduced pigs into Australia, North and South America, and numerous islands, either accidentally as escaped domestic pigs which have gone feral, or as wild boar. Habitat and reproduction The wild boar (Sus scrofa) can take advantage of any forage resources. Therefore, they can live in virtually any productive habitat that can provide enough water to sustain large mammals such as pigs. If there is increased foraging of wild boars in certain areas, they can cause a nutritional shortage which can cause the pig population to decrease. If the nutritional state returns to normal, the pig population will most likely rise due to the pigs' naturally increased