Welcome to Zoology World

balindrakumar033@gmail.com   25/11/2017,Saturday

WELCOME TO ZOOLOGY WORLD

The science or study of animal life. Together with botany, the study of plant life, it forms the science of biology. Zoology is such a vast subject that most zoologists specialize or focus on the study of particular organisms or taxonomic groups. tion of animals.

Teeth is a living structure

Teeth

Teeth is a living structure.On the basis of embryonic origin,teeth in vertebrates are of following types-

(i) Horny/ectodermal/ epidermal/false teeth:

The teeth which develops only from ectodermal.Examples-Cyclostomes,tadpole larva of frog,prototherian mammals etc.

(ii)True teeth:

The teeth which develops from both ectoderm and mesoderm .examples-Fishes,amphibians, reptiles,eutherian mammals etc.

Differentiation of teeth

Morphologically,teeth can be distinguished as homodont or heterodont.

(i)Homodont:

When all the teeth are structurally and functionally similar ,than it is called Homodont.ex- Vertebrates except metatherian and eutherian mammals etc.

(ii)Heterodont:

When the teeth are different in structure and functions than, it is called Heterodont.ex- Metatherian and eutherian mammals.

(a)Incisors:

These are the front teeth borne by the premaxillae in upper jaw and tips of dentaries in lower jaw.They are single-rooted monocuspid and long,curved and sharp-edged.They are adapted for cutting or cropping and biting.

(b) Canines:

There is one pointed canine in each maxillary of upper jaw and each dentary of lower jaw next to the incisors.They are meant for piercing,tearing and offence and defence.They are single rooted and monocuspid.

(c) Premolars:

They have one root(only in upper fist PM two roots)and two cusps(bicuspid). They are meant for crushing,grinding and chewing.

(d) Molars:

They have more then two roots(upper molars have three roots and lower molars have two roots) and 4 cuspid.

Teeth is a living structure

Attachment of teeth

On the basis of attachment of teeth at their bases with the jaw bones,teeth can be differentiated into-

(i)Acrodont:

Teeth are attached to the free surface or summit of the jaw bone,as in a shark or frog. Such teeth are apt to break off easily but are replaced.

(ii)Pleurodont:

In this condition,common in urodeles and lizards,teeth are attached to the inner side of jaw bone by their base as well as one side.

(iii)Thecodont:

Such teeth are characteristic of mammals.Teeth have well developed roots implanted in deep individual pits or sockets called aveoli or theca,in the jaw bone.These type of teeth also present in crocodilians,fossil toothed bird(Archeaeopteryx).

Succession of teeth

According to their replacement(succession),teeth can be divided into 3 categories: polyphyodont,diphyodont and monophyodont.

(i)Polyphyodont:

In lower vertebrates,teeth can be replaced on indefinite number of times durign life.eg-Fishes, amphibia,reptilia.

(ii)Diphyodont:

In most mammals teeth develop during life in two successive sets,a condition known as diphyodont.Teeth of the first set are known as deciduous teeth or milk teeth or lacteal teeth. whereas the second set is called permanent teeth.

(iii)Monophyodont:

In some mammals such as platypus, marsupials,moles,sirenians, toothed whale etc. only one set of teeth develops known as monophyodont condition.

Types of cheek teeth