Evolution of Jaws & TMJ

Evolution of Jaws &Evolution of Jaws &
Temporomandibular JointTemporomandibular Joint
www.indiandentalacademy.com

IntroductionIntroduction
 It is a fascinating account of interactionIt is a fascinating account of interaction
between living organisms & their environmentbetween living organisms & their environment
 It is a sequence of reactions & modifications toIt is a sequence of reactions & modifications to
the pressures of external world that resultedthe pressures of external world that resulted
in the chain of evolutionary changes that leadin the chain of evolutionary changes that lead
to humansto humans
 The understanding of evolution & comparativeThe understanding of evolution & comparative
anatomy yields important insights into normalanatomy yields important insights into normal
& potentially abnormal functions in humans& potentially abnormal functions in humans

Five kingdomsFive kingdoms
 AnimaliaAnimalia
 PlantaePlantae
 FungiFungi
 ProtistaProtista
 ProkaryotaProkaryota oror MoneraMonera
H.Sapiens
Homo
hominidae
Primates
Mammalia
chordata
Animalia
eukaryota

 Homosapiens sapiensHomosapiens sapiens
 LatinLatin: "wise human" or "knowing: "wise human" or "knowing
humanhuman
 By Linnaeus in 1758By Linnaeus in 1758

 To trace the evolution we start at the point of history whereTo trace the evolution we start at the point of history where
bones appeared for the first time- vertebratesbones appeared for the first time- vertebrates
 TheThe DevonianDevonian is ais a geologic period and systemgeologic period and system of theof the
PaleozoicPaleozoic era spanning fromera spanning from 416416 ±2.8 to±2.8 to 359.2359.2 ±2.5 million±2.5 million
years agoyears ago
 The Devonian period marks the beginning of extensive landThe Devonian period marks the beginning of extensive land
colonization bycolonization by plantsplants..

 Aquatic jawlessAquatic jawless
fishes( agnatha)fishes( agnatha)
 Similar toSimilar to
contemporarycontemporary
lampreylamprey

 GnathostomataGnathostomata is the group ofis the group of vertebratesvertebrates withwith jawsjaws..

CLASSCLASS
ACANTHODIIACANTHODII
(the(the
acanthodiansacanthodians
or spiny fishes)or spiny fishes)
"Acanthos""Acanthos"
means "spiny".means "spiny".

PlacodermPlacoderm

 Premaxilla is mobile, it can swingPremaxilla is mobile, it can swing
ventrally & protrude.ventrally & protrude.
 Advantages-Advantages-
• large gape relative to jaw sizelarge gape relative to jaw size
• Suction volume is increased & gape isSuction volume is increased & gape is
nearly circularnearly circular
• Increased suction efficiencyIncreased suction efficiency

 Came up from muddy & stagnant pools toCame up from muddy & stagnant pools to
take a gulp of fresh air adjusting density oftake a gulp of fresh air adjusting density of
body with waterbody with water
 The air bladder became vascular &The air bladder became vascular &
honeycombed like a lung – lungfish (Dipnoi)honeycombed like a lung – lungfish (Dipnoi)

 The dentition of lungfish isThe dentition of lungfish is
conspicuously differentconspicuously different
from that of any otherfrom that of any other
vertebratevertebrate group.group.
OdontodesOdontodes on the palateon the palate
and lower jaws develop in aand lower jaws develop in a
series of rows to form aseries of rows to form a
fan-shapedfan-shaped occlusionocclusion
surface. These odontodessurface. These odontodes
then wear to form athen wear to form a
uniform crushing surface.uniform crushing surface.

Air breathing fishAir breathing fish

 OrderOrder
CrossopterygiiCrossopterygii oror
crossopterygians -crossopterygians -
TheThe ancestors of theancestors of the
amphibiansamphibians..
This group isThis group is
considered to beconsidered to be
ancestral to theancestral to the
amphibians because ofamphibians because of
thethe arrangement ofarrangement of
bones in their fins, thebones in their fins, the
pattern of bones ofpattern of bones of
the skull, and thethe skull, and the
structure of their teethstructure of their teeth
Eusthenopteron

 There are many similarities betweenThere are many similarities between
crossopterygian fish and amphibians.crossopterygian fish and amphibians.

IchthyostegaIchthyostega
 "Ichthyo" means "fish" and "stega" means"Ichthyo" means "fish" and "stega" means
"roof" or "cover" (probably referring to the"roof" or "cover" (probably referring to the
bones in the roof of the skullbones in the roof of the skull
 367-362.5 million years ago, and an367-362.5 million years ago, and an
intermediate betweenintermediate between fishfish andand amphibiansamphibians..

The AmphibiansThe Amphibians
 CLASS AMPHIBIACLASS AMPHIBIA
 NameName: "Amphi" means "both" or "double", and: "Amphi" means "both" or "double", and
"bios" means "life". "Amphibios" means living a"bios" means "life". "Amphibios" means living a
double life, referring to living in water and ondouble life, referring to living in water and on
the land.the land.
 Chief characteristics and mode of lifeChief characteristics and mode of life::
Amphibians can live on the land as adults, butAmphibians can live on the land as adults, but
they lay their eggs in water. Young amphibiansthey lay their eggs in water. Young amphibians
live in the water and are fish-like (tadpoles).live in the water and are fish-like (tadpoles).

 DiadectesDiadectes sp.,sp.,
from the Earlyfrom the Early
Permian (280-250Permian (280-250
m.y.) was a land-m.y.) was a land-
dwelling plantdwelling plant
eater.eater.
The skeletalThe skeletal
anatomy isanatomy is
reptilian, but thereptilian, but the
skull resemblesskull resembles
that ofthat of
SeymouriaSeymouria, an, an
amphibianamphibian

The Amniotic EggThe Amniotic Egg
 The next major evolutionary developmentThe next major evolutionary development
in vertebrate history was the ability toin vertebrate history was the ability to
reproduce without returning to water.reproduce without returning to water.
This was accomplished with theThis was accomplished with the amnioticamniotic
eggegg..
 The amniotic egg is the key feature in theThe amniotic egg is the key feature in the
development of thedevelopment of the reptilesreptiles..

The ReptilesThe Reptiles
"reptilis" meaning"reptilis" meaning
"creeping"."creeping".
 In reptiles, the roof ofIn reptiles, the roof of
the mouth is arched,the mouth is arched,
with small openings. Inwith small openings. In
amphibians, it is flatamphibians, it is flat
with large openings.with large openings.

 The articular portionThe articular portion
is the sameis the same
(amphibians) but the(amphibians) but the
length of dentary orlength of dentary or
tooth bearing portiontooth bearing portion
is increased.is increased.

 Various groups of vertebrates can beVarious groups of vertebrates can be
distinguished on the basis of the positiondistinguished on the basis of the position
and number of openings behind the eye onand number of openings behind the eye on
the side of their skulls.the side of their skulls.
 AnapsidaAnapsida (no holes) - amphibians, the(no holes) - amphibians, the
earliest known reptile (earliest known reptile (HylonomusHylonomus), and), and
turtlesturtles

 DiapsidaDiapsida (two holes) - dinosaurs, flying(two holes) - dinosaurs, flying
reptiles, birds, and all groups of living reptilesreptiles, birds, and all groups of living reptiles
except turtlesexcept turtles
 This arrangement allows for the attachment ofThis arrangement allows for the attachment of
larger, stronger jaw muscles, and enables thelarger, stronger jaw muscles, and enables the
jaw to open more widelyjaw to open more widely
 Some diapsids have lost either one holeSome diapsids have lost either one hole
(lizards), or both holes (snakes), or have a(lizards), or both holes (snakes), or have a
heavily restructured skull (modern birds), theyheavily restructured skull (modern birds), they
are stillare still classifiedclassified as diapsids based on theiras diapsids based on their
ancestryancestry

 EuryapsidaEuryapsida (upper hole only) - extinct(upper hole only) - extinct
marine reptiles Examples are:marine reptiles Examples are:
 PlesiosaursPlesiosaurs
 IchthyosaursIchthyosaurs
 PlacodontsPlacodonts

 SynapsidaSynapsida (lower hole only) – eg(lower hole only) – eg
pelycosaurs, therapsids, and mammalspelycosaurs, therapsids, and mammals
 SynapsidsSynapsids ('fused arch'), also known as('fused arch'), also known as
theropsidstheropsids ('beast face'). The non-('beast face'). The non-
mammalian members were traditionallymammalian members were traditionally
described asdescribed as mammal-like reptilesmammal-like reptiles

TherapsidsTherapsids
Therapsids were small to moderate-sizedTherapsids were small to moderate-sized
animals with several mammalian skeletalanimals with several mammalian skeletal
characteristics, such as:characteristics, such as:
 Regulation of body temperatureRegulation of body temperature
 Fewer bones in the skull than the other reptilesFewer bones in the skull than the other reptiles
 Mammal-like structure of the jawMammal-like structure of the jaw
 Differentiated teeth (incisors, canines, andDifferentiated teeth (incisors, canines, and
cheek teeth)cheek teeth)
 Limbs in more direct alignment beneath theLimbs in more direct alignment beneath the
bodybody
 Reduction of ribs in the neck and lumbarReduction of ribs in the neck and lumbar
regions, allowing greater flexibilityregions, allowing greater flexibility

Stages of Tooth evolutionStages of Tooth evolution
 Graphically there are 4 stages of toothGraphically there are 4 stages of tooth
evolution:evolution:
1. Reptilian stage (Haplodont).1. Reptilian stage (Haplodont).
2. Early mammalian stage (triconodont).2. Early mammalian stage (triconodont).
3. Triangular stage (trituburcular molars).3. Triangular stage (trituburcular molars).
4. Quadritubercular molars.4. Quadritubercular molars.

Characteristics of human dentitionCharacteristics of human dentition
Teeth of the vertebrates are characterized dependingTeeth of the vertebrates are characterized depending
upon:upon:
a. a. Mode of attachment .Mode of attachment .
b. b. Number of successive sets.Number of successive sets.
c. Shape of teeth.c. Shape of teeth.
The way teeth are attached to jaws:The way teeth are attached to jaws:
a. Acrodonta. Acrodont
b. Pleurodontb. Pleurodont
c. Thecodontc. Thecodont

Depending on no. ofDepending on no. of successive sets of teeth:successive sets of teeth:
a. Polyphyodonta. Polyphyodont
b. Diphyodontb. Diphyodont
c. Monophyodontc. Monophyodont
According to type or shape of teeth:According to type or shape of teeth:
a. Homodonta. Homodont
b. Heterodontb. Heterodont

 The squamosal-dentary took over all joint
function leaving quadrate and postdentary
Bones able to take over new functions.
 The mammalian middle ear has three
ossicles:
 Stapes
 incus(= quadrate),
 malleus(= articular).
 The angular became the ectotympanic,
which supports the tympanic membrane
(eardrum).

 Primates are defined as mammals with thumbsPrimates are defined as mammals with thumbs
and large toes that oppose the other digits. Theand large toes that oppose the other digits. The
ends of the digits are flattened and have nailsends of the digits are flattened and have nails
rather than claws.rather than claws.
 Fossil evidence has uncovered a very old, veryFossil evidence has uncovered a very old, very
small, warm-blooded creature calledsmall, warm-blooded creature called
megazostrodon.megazostrodon.
Primates (Order)Primates (Order)

It had a sharp snout andIt had a sharp snout and
pointed ears, nursed itspointed ears, nursed its
young, and is the oldestyoung, and is the oldest
known mammal.(200known mammal.(200
million years ago)million years ago)
 It survived the JurassicIt survived the Jurassic
Age of the now-extinctAge of the now-extinct
terrestrial dinosaursterrestrial dinosaurs
1.5-2 cm long &1.5-2 cm long &
weighed 20-30 gmsweighed 20-30 gms
MegazostrodonMegazostrodon

From shrews to humansFrom shrews to humans
 Climbs vertically andClimbs vertically and
scampers along the topsscampers along the tops
of branches.of branches.
 The large toe is flattenedThe large toe is flattened
and has a nail, but theand has a nail, but the
other digits have clawsother digits have claws
 The tree shrew formulaeThe tree shrew formulae
are: upper I-2, C-1, P-3,are: upper I-2, C-1, P-3,
M-3; and lower I-3, C-1,M-3; and lower I-3, C-1,
P-3, M-3.P-3, M-3.
 The teeth are generallyThe teeth are generally
more cone shaped thanmore cone shaped than
those of other primates.those of other primates.

LemurLemur
 The upper lip has a medianThe upper lip has a median
cleftcleft
 The dental formula : I-2, C-The dental formula : I-2, C-
1, P-3, M-3.1, P-3, M-3.
 The two central incisors areThe two central incisors are
separated by a wideseparated by a wide
diastemadiastema
 Laterals, are small andLaterals, are small and
cone shaped. In somecone shaped. In some
lemurs, the upper anteriorslemurs, the upper anteriors
are entirely missing.are entirely missing.

Aye-ayeAye-aye
 A strange lemur genus isA strange lemur genus is
the aye-aye.the aye-aye.
 It lives in cane brakes andIt lives in cane brakes and
bamboo forests where itbamboo forests where it
bores into stalks for juicesbores into stalks for juices
and grubs.and grubs.
 The dental formula is:The dental formula is:
upper I-0, C-1, P-1, M-3upper I-0, C-1, P-1, M-3
and lower I-0, C-1, P-0, M-and lower I-0, C-1, P-0, M-
3.3.
 The upper and lowerThe upper and lower
canines are inclined labiallycanines are inclined labially
and are in contact rightand are in contact right
with left.with left.
 PolyphyodontsPolyphyodonts

TarsierTarsier
 Some believe thatSome believe that
from these manyfrom these many
genera evolved thegenera evolved the
branch leading tobranch leading to
modern great apesmodern great apes
and to man.and to man.
 Dental formula:Dental formula:
upper I-2, C-1, P-3,upper I-2, C-1, P-3,
M-3; and lower I-1,M-3; and lower I-1,
C-1, P-3, M-3.C-1, P-3, M-3.

Old World MonkeysOld World Monkeys
 The dental formula:The dental formula:
upper and lower, I-2,upper and lower, I-2,
C-1, P-2, M-3. This isC-1, P-2, M-3. This is
the same as that forthe same as that for
great apes andgreat apes and
hominids.hominids.

New world monkeysNew world monkeys
 New world monkeys areNew world monkeys are
almost completelyalmost completely
arborealarboreal
 The smallest of livingThe smallest of living
monkeys is themonkeys is the
marmosetmarmoset..
 This new world creatureThis new world creature
has two rather thanhas two rather than
three molars in eachthree molars in each
quadrant.quadrant.
 curved claws on all digitscurved claws on all digits
except for the large toes,except for the large toes,
similar to the tree shrewsimilar to the tree shrew
and the aye-aye.and the aye-aye.

 The dental formulaThe dental formula
for new worldfor new world
monkeys is: uppermonkeys is: upper
and lower I-2, C-1,and lower I-2, C-1,
P-3, M-3.P-3, M-3.

Anthropoid apesAnthropoid apes
 There are four living types of anthropoid apes:There are four living types of anthropoid apes:
gorilla, gibbon, orangutan, and chimpanzee.gorilla, gibbon, orangutan, and chimpanzee.

Hominids (Family)Hominids (Family)
 Subgroup that includesSubgroup that includes
humans & extinct humanhumans & extinct human
like species.like species.
 The earliest knownThe earliest known
hominids :Ardipithecushominids :Ardipithecus
ramidusramidus
 They lived 4.4 millions yearThey lived 4.4 millions year
ago in Africaago in Africa

 NumerousNumerous
Australopithecus evolvedAustralopithecus evolved
during the next 2 millionduring the next 2 million
years agoyears ago
 They had large face,They had large face,
protruding jaw ,smallprotruding jaw ,small
skull & they could walkskull & they could walk
uprightupright

Humans ariseHumans arise
 The firstThe first
member ofmember of
genus Homogenus Homo
was H.habiluswas H.habilus
 They lived inThey lived in
woodlands &woodlands &
they resemblethey resemble
apes & hadapes & had
protrudingprotruding
jaws.jaws.

HOMO ERECTUSHOMO ERECTUS
 They evolved in AfricaThey evolved in Africa
& migrated to Europe& migrated to Europe
& Asia about 1.5& Asia about 1.5
million years agomillion years ago

Homo NeanderthalensisHomo Neanderthalensis
 They were earlyThey were early
humans that lived inhumans that lived in
Europe & near EastEurope & near East
 They possessed bigThey possessed big
but less protrudingbut less protruding
jawsjaws
& they disappeared& they disappeared
when H. sapienswhen H. sapiens
appearedappeared

Homo SapiensHomo Sapiens
 They were the more modern men who evolved 100000 years agoThey were the more modern men who evolved 100000 years ago
 Current data suggests that modern humans evolved primarily in east AfricaCurrent data suggests that modern humans evolved primarily in east Africa
 They had smaller teeth & jaws than H. erectusThey had smaller teeth & jaws than H. erectus
 The facial bones are smaller ,skull is larger & rounded & jaw size further reduced & less protrudingThe facial bones are smaller ,skull is larger & rounded & jaw size further reduced & less protruding

 Homo sapiens, maturing more slowly thanHomo sapiens, maturing more slowly than
other primates, retained many primitiveother primates, retained many primitive
features, which may be why the genus hasfeatures, which may be why the genus has
been successful.been successful.
 Special adaptations are beneficial only so longSpecial adaptations are beneficial only so long
as the conditions to which the adaptation wereas the conditions to which the adaptation were
made remain static.made remain static.
 Climatic and geologic changes throughClimatic and geologic changes through
millions of years reshaped environmentsmillions of years reshaped environments
 Organisms that failed to adapt became extinct.Organisms that failed to adapt became extinct.

ConclusionsConclusions
 The canine, C-1, is the one constant number inThe canine, C-1, is the one constant number in
all the dental formulae of the various primates.all the dental formulae of the various primates.
Even in the strange aye-aye, canines replacedEven in the strange aye-aye, canines replaced
the incisors.the incisors.
 Is it possible that the forward mesial growth ofIs it possible that the forward mesial growth of
the canines in the aye-aye is related to thethe canines in the aye-aye is related to the
palatal impacted canine presented by somepalatal impacted canine presented by some
orthodontic patients?orthodontic patients?
 Tarsiers have coniform incisors. Are they relatedTarsiers have coniform incisors. Are they related
to the pegged lateral incisors we see in someto the pegged lateral incisors we see in some
patients today?patients today?

 Progressive shortening (especially in front)Progressive shortening (especially in front)
& relative widening of the dental arches& relative widening of the dental arches
 The least altered parts are the incisorsThe least altered parts are the incisors
 The canines were reduced in sizeThe canines were reduced in size
 Lower premolar crown was transformedLower premolar crown was transformed
from an obliquely oval to a morefrom an obliquely oval to a more
symmetrical crownsymmetrical crown
 Third molars originally larger than the firstThird molars originally larger than the first
were reduced & often eliminatedwere reduced & often eliminated
 The first lower molars became theThe first lower molars became the
dominant cheek toothdominant cheek tooth

BibliographyBibliography
 Ellis, Harold; Susan Standring; Gray, HenryEllis, Harold; Susan Standring; Gray, Henry
David (2005).David (2005). Gray's anatomy: TheGray's anatomy: The
Anatomical Basis Of Clinical PracticeAnatomical Basis Of Clinical Practice. St. Louis,. St. Louis,
Mo: Elsevier Churchill Livingstone, 38.Mo: Elsevier Churchill Livingstone, 38.
 K.F. Liem, W.E. Bemis, W.F Walker6 & L.K.F. Liem, W.E. Bemis, W.F Walker6 & L.
Grande 2001 Functional Anatomy ofGrande 2001 Functional Anatomy of
Vertebrates;3Vertebrates;3rdrd
Edition, Hard-court,Edition, Hard-court,
PhiladelphiaPhiladelphia
 Fred F. Crutcher ;Anthropology andFred F. Crutcher ;Anthropology and
orthodontics ,1997 No. 1, 73 – 78, Angleorthodontics ,1997 No. 1, 73 – 78, Angle
OrthodonticsOrthodontics
 W. K. Gregory ;The evolution of DentalW. K. Gregory ;The evolution of Dental
Occlusion from Fish to Man 1941,145-172,Occlusion from Fish to Man 1941,145-172,
Angle OrthodonticsAngle Orthodontics

 Ash & Stanley Nelson, Dental Anatomy,Ash & Stanley Nelson, Dental Anatomy,
Physiology & Occlusion, 8Physiology & Occlusion, 8thth
Edition, ElsevierEdition, Elsevier
 Adriana E. Aquino, Scott A. Schaefer,
Amalia M. Miquelarena A New Species ofA New Species of
Hisonotus (Siluriformes,Loricariidae) of theHisonotus (Siluriformes,Loricariidae) of the
Upper Rı´o Uruguay Basin ,AmericanUpper Rı´o Uruguay Basin ,American
Museum Of Natural HistoryMuseum Of Natural History, June 22, 2001
 Westenberg, K. (1999) — From Fins to
Feet. National Geographic, 195, 5:114–
127
 http://www.theodora.comhttp://www.theodora.com
 http://www.wikipidea.comhttp://www.wikipidea.com

Thank youThank you

Evolution of Jaws & TMJ

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (6)

Similar to Evolution of Jaws & TMJ

Similar to Evolution of Jaws & TMJ (20)

More from Indian dental academy

More from Indian dental academy (20)

Recently uploaded

Recently uploaded (20)

Evolution of Jaws & TMJ