teeth and jaws Flashcards
what are some of the functions that teeth and jaws fulfil
1) Respiration (buccal pumping) => fish and amphibians use jaws to pass water over gills or lungs
2) Communication => talking, vocal calls
3) Thermoregulation
4) Parental care => picking up offspring
5) Grooming
6) Fighting
7) Feeding
how are teeth and jaws vital to evolutionary biologists
they are hard structures so fossilise well and show a fossil record
= they are often very characteristic with sterotypic features which can be diagnostic of a species membership
= therefore they can be important for undertsanding the evolution of tetrapods
outline the evolution of early teeth
= First evolved 200 million years before tetrapod’s even emerged and seen in primitive agnathans
= they evolved from modified scales which have migrated to the mouth and harderned, become shar p etc
outline the evolution of early jaws
= developed 20 million years after teeth evoloved and 100 million years before tetrapods emerged
= clade -> gnathostomes (jawed mouth)
how did early jaws evolve
The agnathan clade (no jaw) had 9 pharyngeal arches
compared to the gnathostomes which have 7 due to two of the 9 arches forming the jaw
= evoloved from modified pharyngeal arches
how and why do fish jaws differ from tetrapod
fish jaws tend to be adapted for sucking prey into the mouth with many fish having a second set of pharyngeal jaws further back in the mouth
= THIS ALLOWS SUCTION FEEDING
terrestrial species have to overtake prey and bit down on them with jaws as suction feeding is ineffective on land = this comes with its own challenges
why is suction feeding less effective on land than in water
air is much less viscous than water- water ‘sticks’ to prey where as air does not, air also effects a smaller surface area
what happened to jaws to allow feeding on land
major simplification of jaw structure= fish which suction feed have dozens of bones in their jaw compared to terrestrial tetrapod’s which have 2 = mandible (lower jaw) and maxilla (upper jaw)
compare the jaw anatomy of a mammal with that of a reptile
reptiles = quadrate articular joint
mammals= dentrary squamosal
=> much stiffer but slower in mammals which means less mechaniscal advantage
outline the relation between teeth,jaws and endothermy
mammals and birds have to increase the number of calories they consume to meet the energetic demands of endothermy
this is facilitated by a distinctive chewing system which causes fragmentation of food, increasing its SA for enzymes to act allowing a more complete assimilation of stored energy
what are the muscles involved in mastication (chewing)
1) temporalis = muscle which brings the lower jaw upwards
2) masseter = pulls the jaw left and right for grinding
3) pterygoideus = pills lower molars around
outline how muscles used for mastication differ between carnivores and herbivores
Carnivores = large temporalis as smaller masseter muscles as less grinding action needed to the breakdown of meat
herbivore = small temoralis and large masseter as consumption of more plant material which needs increased grinding for breakdown
outline how buccinator muscles (cheek ) differ between carnivores and herbivores
herbivore= well develop and keeps food in whilst chewing
carnivore = more U shaped so that gape can open wide to catch prey
what comprises the basic tooth structure
1) crown which is made up of
- Enamel
- Dentin
2) Root which is made up of
- cementum
- pulp
outline the evolution of mammalian teeth
teeth and food are locked into an arms race e.g. as prey adapt such as become more slipy, teeth must adapt to catch the prey easily
= differention of teeth into different function units (heterodonts) allows for this compared to homodonts (all teeth are the same) like in most other verterbrates
outline the roles of different teeth seen in heterodonts
= incisors - for cutting
= canines - for piercing
= premolar - transition teeth
= molars - for grinding
= carnassials - modified molars for shearing
what is meant by the dental formula
how many of each specialised tooth can be used to diagnose the type of species e.g.
Humans = 2:1:2:3/ 2:1:2:3
2 inscors
1 canine
2 premolars
3 molars
this is the same on upper and lower jaw
outline other innovations which occured during the evolution of mammalian teeth other than heterodonty
= reduction (in general) to two or less generations of teeth comapred to other spp whcih have continous cycles e.g sharks
= polyphodont- continous succesion of teeth through life such as fish
= diphydont- replacement of milk teeth by permanent - most mammals
= monophyodont - single set of teeth retained entire life e.f. whales
outline the differences in structure between thecodont, pleurodont and acrodont teeth
T= anchored throughly in gums
P= semi supported in gums
A= sits on top of gums
what are the evolutionary inovations in mammalian teeth
1) heterodont= differentiated into functional units
2) Diphyodont = replaced once in a life time
3) Thecodont = teeth set in sockets
if mammals and birds have to increase the number of calories they consume for endothermy and a distinctive chewing system is used in mammals, what is the solution in birds?
Avian beaks
= modified jaws
outline the components of an avian beak
1) maxilla = upper jaw
2) manible = lower jaw
3) rhamphotheca = thin keratinised layer of epidermis which grows continously
4)external nerves
5) tomina = cutting edge
what is beak morphology linked with
feeding ecology e.g. Darwins finches
