Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Natural History of the Pig (Sus scrofa)

Author: Lazaro Gonzales, Jr.

Classification:
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Suidae
Subfamily: Suinae
Genus: Sus
Species: S. scrofa

Common name: Pig

Evolution and Phylogeny:

Artiodactyls are first seen in the Eocene as rabbit-sized animals known as dichobunids. A split in dichobunids by late middle Eocene created two new members, the Bunodontia and the Selenodontia. The family Suidae (pigs) is made up of members of Bunodontia within Suiformes which can be traced back to the split in the Eocene [1]. The earliest roots of this family go back to early Oligocene in Europe, Oligocene in Asia, and early Miocene in Africa [2].

Appearance:

Members of the genus Sus (S. scrofa, S. barbatus, S. celebensis, S. verrucosus) can measure 900-1800 millimeters (mm) in head and body length, 550-1100 mm in shoulder height, and weigh 50-350 kilograms (kg). The tail is approximately 300 mm from body to tip [3,4]. The usually smaller females have 6 pairs of mammae [3].

Geography and Habitat:

The pig enjoys a diverse selection of habitat. One common element is vegetation in which the pig and can crawl under. This is done by cutting grass into a pile or a sheet then getting underneath and lifting it onto uncut grass which holds it up. Pigs are also often found enjoying mud [4].

Activity and Behavior:

Although Sus scrofa has an average herd ("sounder") size of 20, herd size seems to vary with region [5]. The female and her litter are the social unit of the group [6]. In areas where people bother them they are particularly active at night.

Locomotion:

Sus scrofa is a quadruped unguligrade. A note of interest in the morphology of artiodactyls is found in the ankle joint. In addition to a dorsal articular surface on the astralagus, a ventral articular surface is also present. An explanation of this unique morphology has yet to be determined. The foot of the pig contains two unfused bones. On each foot the 3rd and 4th digits are hooved and are the only contact points in locomotion [1].

Diet:

Sus has a 3143 dental formula for the upper and lower jaw, giving a total of 44 teeth. Pigs are omnivorous and use their specialized snout to dig through surface soil for food. A specialization of the pig that strengthens its snout is a bone known as the prenasal [4].

Reproduction and Ontogeny:

In reproduction the male has anywhere from 1-8 female partners over the span of a pig's 10 year average life [4]. Male sexual maturity is reached around 8-10 months while females are not ready until around 18 months[3,5,6]. A female pig has a 100-140 day gestation period. During this annual occurrence a litter of 1-12 pups is birthed into a nest. The piglets remain in the nest until they are weaned then leave before the next litter is born. It is uncommon among ungulates to be born and remain in a nest such as the pig does [4].

References:

1. Christine Janis, "Artiodactyla", in AccessScience@McGraw-Hill,
http://www.accessscience.com
/server-java/Arknoid/science/AS/Encyclopedia/0/05/Est_053500_frameset.html, last modified: July 15, 2002.

2. Simpson. 1984. Artiodactyls. In Anderson and Jones (1984), pp. 563-88.

3. Grzimek, B., ed. 1975. Grzimek's animal life encyclopedia. Mammals, I-lV. Van Nostrand Reinhold, New York, vols. 10-13.

4. Nowak, Ronald, "Pigs, Hogs, or Boars", in Walkers's Mammals of the World Online 5.1, http://www.press.jhu.edu/books/walkers_mammals_of_the_world/artiodactyla/artiodactyla.suidae.sus.html, last modified: 1997.

5. Lekagul, B., and J. A. McNeely. 1977. Mammals of Thailand. Sahakarnbhat, Bangkok, li + 758 pp.

6. Fradrich, H. 1974. A comparison of behaviour in the Suidae. In Geist and Walther (1974), pp. 133-43.