Teeth are the dermal derivatives of integument They are developed as a result of calcification in the mucous membrane of the l cavity. Along with the ridge of the two jaws, the teeth are arranged in a row. The teeth are present in almost all the mammals except in a few mammals In whale, the teeth are fused into plates and lost in the adult stage of Ant eaters. But in Echidna (spiny ant eater) the teeth are absent even in the embryo.
Structure of tooth: Each typical mammalian tooth is placed in the socket over the jaw bone. It is distinguished into three main pads.
1) Root - It is the basal part embedded in the bony socket.
2) Neck - it is the part above the root enclosed by the gum
3) Crown - It is the upper part beyond the surface of the gum.
The toot is separated from the socket by a vascular pridontal membrane. The vertical section tooth consists of the following parts.
I) Pulp cavity: The entire tooth encloses a central pulp cavity surrounded by a layer of odontoblast cells filled with soft pulp. It is made up of connective tissue, blood vessels and nerve fibers.
II) Dentin: A substance chemically similar to bone- dentine forms the major part of the tooth. But the dentine is permeated by numerous thin canaliculi.
III) Enamel: It is present over the de in the crown and neck regions of the tooth. It is hardest and contains only traces of living matter.
IV) Cement: It surrounds the denting of the root portion of the tooth. It is bony in nature,
The next topic is Mammalian dentition characters
The first post of this blog, on vole incisors, was a kind of response to Mike Taylor’s SV-POW! post on squirrel incisors, so I didn’t really introduce either myself or the blog. So here we go.
In this blog, , inspired by science, palaeontology and evolution blogs such as SV-POW!, What’s In John’s Freezer, The Bite Stuff, Tetrapod Zoology and others, I’m aiming to present scientifically interesting and aesthetically pleasing pictures of tetrapod teeth on a semi-regular basis.
Because I find them fascinating and intriguing, and much of my scientific research is based around them, but also because they can be visually arresting and, in the literal sense of the word, awesome.
Teeth are funny. In many living animals, they are hidden away in the mouth by parts of the skull and/or a covering of soft or hard tissue. They become visible only when the mouth opens during feeding, communication, or even yawning. However, once an animal has died and we can look at the skull without any soft tissue (skin, hair etc.) covering it, teeth often become startlingly obviously a major part of that animal, even if they are often fairly small relative to the total size of the animal.
As an example, above is a picture of a living Eurasian lynx Lynx lynx (by David Castor), and below a skull and jaw of the same species that I am studying at the moment from the Finnish Museum of Natural History. The teeth of the lynx are pretty arresting. As a carnivore and member of the Felidae (cats and their relatives), its teeth are used for both capturing prey and slicing meat. The enlarged canines help with prey capture, and the relatively few but enormous (compared to skull size) premolars and molars have long, sharp cutting edges that work like scissors as the upper and lower teeth move during chewing to cut up meat.
The genus Lynx (including the North American Bobcat and Canadian lynx)is unusual even among felids in having an especially reduced tooth count. It has only two premolar teeth and one molar tooth in the lower jaw, and just one premolar and one molar in the upper jaw (plus occasionally a tiny, vestigial second molar). This allows each of these post-canine teeth to be especially large relative to the skull, and for a reasonable gap or diastema between the canine and post-canine teeth.
These two modifications are both presumably for better capturing, killing, and eating of live prey. Three of the four lynx species, including the bobcat, mostly eat small and medium mammals like rabbits, hares, and rodents. The slightly larger Eurasian lynx tends to eat a larger proportion of large mammals, like reindeer, moose, red deer or roe deer, than smaller mammals. (And topically – see the recent report here on Tetrapod Zoology of a wild living lynx shot and killed in England in 1903, unusual because lynx and other big cats have been extinct in the UK for centuries…).
But back to where we were – teeth as a major and important part of an animal. As the above picture and text should make clear, teeth that are hidden from view during much of an animals day to day life are vitally important in obtaining and processing food. Because not all food items are like the soft but slightly fibrous meat eaten by the lynx, different types of teeth are needed by animals that eat different foods. This was noted as long ago as in Greek times, with Aristotle in ‘On the Parts of Animals’noting that the major use of teeth was in reducing food, but that different shaped teeth served different dietary needs. Much of the variation in tooth shape, the ‘endless forms most beautiful and most wonderful’ (Darwin 1859 in ‘On the Origin of Species…’ – he wasn’t talking specifically about teeth, but I think it’s appropriate), are to do with the different diets and requirements for breaking down food that different animals have. The the link between tooth shape and diet will probably be a theme running through the blog. Some other functions do modify tooth shape, though, including sensing, grooming, use as an offensive or defensive weapon etc, and tooth shape or composition can respond to changes in environment too. I plan to cover some or all of these subjects in further blog posts.
Aristotle on left, Darwin on right
So, though not always visible, teeth can be an important part of an animals body. The huge diversity and variation of their shapes can be linked to various functions, though principally diet. That’s enough reason for me to be interested in studying and researching them on their own. However, a second reason for my interest in teeth is that in the fossil record, and particularly the mammalian fossil record, it’s frequently the hard, mineralised teeth that are the only parts of animals to survive the process of fossilisation. This means that it is often teeth that provide much of the data available to evolutionary biologists and palaeontologists. A high proportion of the information allowing identification of species in the fossil record and the tracing of their evolutionary histories is obtained from differences in tooth shape, especially for mammals.
This was recognised by the great French 19th century scientist Georges Cuvier, who, in comparing the teeth and bones of living animals to those of fossils, helped establish the subjects of comparative anatomy and palaeontology. Cuvier said that simply by looking at the teeth, the whole system of digestive organs appropriate for the type of food consumed could be figured out. He also believed that, through the use of comparative anatomy, a single tooth fossil or bone fragment could be used to recreate extinct animals. His ability to identify species from a single bone or especially tooth was legendary!
A third important reason for my interest in teeth is that the genetic and molecular contributions to tooth shape are increasingly well understood. Teeth have been used as a model system for studying how an organ grows or develops, and what the short term genetic and long term evolutionary forces controlling this development are and have been.
Figuring out the links between all of these different aspects (tooth shape, diet, evolution, genetics, growth and development, and more) interests a number of scientists around the world. They can be from many different specialities – geology, palaeontology, evolutionary biology, developmental biology, environmental sciences etc., but all concentrating on teeth. I hope to explore many of these areas of research in this blog.
In summary – welcome to Tetrapod Teeth and Tales, a blog showing awesome pictures of teeth and talking about some of the science being carried out on them, on a semi-irregular basis.
Who am I?
I’m Ian Corfe, a British palaeontologist and evolutionary biologist with a Ph.D, currently working as a postdoctoral researcher in an Evolutionary and Developmental Biology (EvoDevo) lab in Helsinki, Finland. See the ‘about’ button for more.
What’s a tetrapod?
The short answer is a vertebrate with four limbs and digits at the end of these (so arms and legs, fingers and toes in humans). The slightly longer answer is in the linked ‘about’ section of the blog, or over there on the right somewhere, or possibly up the top (I need to figure out how to control the position of these links!). The even longer version is in a link from the about page.
The actual answer is that the precise definition of the group “Tetrapoda’ is still up for grabs, or ‘under intense discussion and debate’ in scientific speak. I don’t have a horse in this particular race, though the ‘winner’ if one emerges will affect the names I can can call some of my favourite extinct animals, the ‘nearly mammals’ and ‘earliest mammals’ from around 200 million years ago. (Hopefully more on these in the blog soon).
What’s a tooth?
The short answer is a mineralised part of a vertebrate’s body found in the mouth, and usually but not exclusively used for eating. (A vertebrate is an animal with a backbone). The longer answer, including the components of teeth, the locations of teeth, the growth of teeth, the shape of teeth, the use of teeth, and the origin of teeth, I hope to answer as the blog grows.