Animals are divided into herbivores, carnivores, and omnivores according to the types of food they eat, and each has characteristic teeth and eye positions. Their respiratory organs also differ according to their habitats.
Basic Knowledge
Tooth structure:
・Herbivores (cows, horses): incisors (cut grass) and molars (grind food) are well developed. Canines are almost absent.
・Carnivores (lions, wolves): canines (capture prey) and carnassial teeth (tear meat) are sharply developed.
Eye position:
・Herbivores: eyes are on the sides of the face. They have a wide field of vision and can easily detect enemies (but have a narrow range of stereoscopic vision).
・Carnivores: eyes are at the front of the face. They have a wide range of stereoscopic vision and can judge distance (an advantage in hunting).
Respiratory organs:
・Fish: gills (take in dissolved oxygen from water)
・Amphibians: larvae use gills; adults use lungs and skin
・Reptiles, birds, and mammals: lungs
・Insects: tracheae (take in air through spiracles)
Incisors (front teeth; cut objects; well developed in herbivores)
Canines (fangs; capture prey; well developed in carnivores)
Molars (back teeth; grind food; especially well developed in herbivores)
Carnassial teeth (teeth that tear meat; characteristic teeth of carnivores)
Rumination (returning swallowed food to the mouth and chewing it again; cows and sheep)
Stereoscopic vision (vision that judges distance by viewing the same object with both eyes)
Further Study (Background and Significance)
The differences in teeth result from adaptation to food. Plant cell walls (cellulose) are hard and difficult to digest, so herbivores evolved a long digestive tract and symbiosis with microorganisms. Cows have four stomachs, repeatedly grind grass through rumination, and microorganisms in the first stomach break down cellulose.
Meat, on the other hand, is nutritious and easy to digest, so carnivores can have shorter digestive tracts.
The difference in eye position represents the difference in strategies between “those that eat” and “those that are eaten.” A zebra can detect enemies with a field of vision close to 360 degrees, while a lion can accurately judge the distance to prey in front of it—the history of evolution is recorded in body structure.
Humans are omnivores with well-developed incisors, canines, and molars, as well as front-facing eyes capable of stereoscopic vision.
- Herbivores=well-developed incisors and molars, side-facing eyes, long digestive tracts
- Carnivores=well-developed canines and carnassial teeth, front-facing eyes, short digestive tracts
- Cows ruminate with four stomachs→cellulose breakdown
- Fish=gills, adult amphibians=lungs+skin, reptiles, birds, and mammals=lungs, insects=tracheae
- Tracheae take in air through spiracles
- Stereoscopic vision=can judge distance (advantage for carnivores)
- A wide field of vision=advantage for detecting enemies (advantage for herbivores)
Points of Caution (Easily Confused)
① Tooth functions=incisors (cut), canines (pierce), and molars (grind). ② Rumination occurs in cows, sheep, goats, and other animals, but not in horses or rabbits (which use hindgut fermentation). ③ Insects respire through tracheae, not lungs. ④ Gills and tracheae are different. Gills are used in water, while tracheae are used in air.
Practice
- State the difference in eye position between herbivores and carnivores.
- What is it called when an animal such as a cow returns swallowed food to its mouth and chews it?
- Name the respiratory organ of insects.