evolution of jaw of human

1. EVOLUTION OF
Presented by:-
Kumar Adarsh
Preceptor:-
Dr.Piush kumar

2.  Introduction
 Theories of evolution
 Evolution of life forms in different era
 Jaw evolution in marine life
 Jaw evolution in chordates
 Common trait of vertebrate embryo
 Evolution of Temporomandibular joint
 Eolution of jaw muscles
 Jaw evolution in mammals
 Jaw evolution in human
 Genetic Evidence of Evolution
 Jaw suspension
 References

3. DEFINITION OF EVOLUTION
 “A process of orderly & gradual change or development” Taber’s Medical
Dictionary
 “A continuous process of change from one state, condition or form to another “
Stedman’s Medical Dictionary
 “ A developmental process in which an organ or organism becomes more &
complex by differentiation of its parts; a continuous & progressive change
according to certain laws & by means of resident forces “Dorland Medical
Dictionary

4. • Evolution is a continuous process of change from
one form to another.
• According to theory of evolution or origin of
species,all present forms of life have been
derived from earlier simple forms.
• As time progressed, there were changes seen in the inherited
characteristics of these species in order to adapt to the ever
changing environment , basically to survive on the earth
Darwin, Charles- “On the Origin of Species”

5. Darwin’s Theory.
Darwin has defined evolution as “descent with
modification”
 When members of a population die, they are replaced
by the progeny of parents better adapted to survive
and reproduce in the enviourment in which natural
selection takes place.
Past-Apes Present-Humans Future-Mutants.?
Darwin, Charles- “On the Origin of Species”

6. Lamarck’s Theory of Evolution
 The idea that an
organism can pass
on characteristics
that is acquired
during its lifetime to
its offspring.
Lamarck said
“Individuals lose
characteristics they do
not require (DISUSE)
And develop
characteristics that are
useful(USE)
Ref: Invertebrate zoology and paleontology

7. Era Period Age (millions of
years ago)
Life forms
precambrian Archaean 4,500-550 First single-celled
organisms
Paleozoic cambrian 550-505 First trilobites
ordovician 505-438 jawless fish
silurian 438-408 sharks, bony fish
devonian 408-360 tetrapods,
ammonites,
placoderms
carboniferous 360-286 First reptiles,
amphibians
Permian 286-248 Synapsids

8. Era Period Age (million
years)
Life forms
Mesozoi
c
Triassic 248-213 First turtles, lizards, dinosaurs,
mammals
Jurassic 213-145 First squids, frogs, birds,
salamanders
Cretaceous 145-65 snakes, modern fish
Cenozoi
c
Tertiary
epoch)
65-55.5 Diversification of mammals
Eocene epoch 55.5-33.7 First marine and large terrestrial
animals, horses, whales, monkeys
Oligocene epoch 33.7-23.8 Apes,anthropoids
Miocene epoch 23.8-5.3 First hominids
Pliocene epoch 5.3-1.8 First australopithecines

9.  Accoding to Prof.William Patten jaws of vertebrates were
eventually derived by the specialisation of certain parts of
the locomotor appendages of trilobites (Eurypterid in
Palaeozoic era)
 However later study did not found any indication of close
genetic relationship between eurypterids and earliest known
chordates.

10. Cranial neural crest cells
from dorsal neural tube
Trigeminal
Trabecular/Dorsal
primordium/maxillary
condensation
Ventral
primordium/mandibular
condensation
Hyoid/preotic
Common branchial/postotic
palatoquadrate/maxillary
cartilage.
meckel’s/mandibular
cartilage.
trabecular cartilage of
the neurocranium and
forms part of the
frontonasal process
Ref:-Cerny R. et al. Developmental origins and evolution of jaws: new interpretation of Maxillary and
mandibular ;Developmental Biology :276 (2004) ;225–236

12. Amphioxus & lamprey
 Invertebrates use ciliated motion to
move food.
 The ancestors of the vertebrates were
“food-sifter”and lived upon minute
living particles,which were drawn into
the mouth probably at first by the
action of cilia.
 This is the stage preserved in the still
existing amphioxus & in the larval
ammocoetes form of the lamprey.

13. Cyclostomata
 Cyclostomata is a group of chordates that
comprises the living jawless fishes: the lampreys
and hagfishes.
 Both groups have round mouths that lack jaws but
have retractable horny teeth.
 The name Cyclostomata means“round mouths”.
 Their mouths cannot close due to the lack of a jaw,
so they have to constantly cycle water through the
mouth.

14. ostracoderms
 Unlike earlier chordates ostracoderms used gills exclusively
for respiration.
 Ostracoderms had separate pharyngeal gill pouches along the side of
the head, which were permanently open with no
protective operculum.
 Ostracoderms used their muscular pharynx to create a suction that
pulled small and slow moving prey into their mouths.
 The floor of the mouth could be moved up and down.
 In certain Ostracoderms;like Tremataspis the slit like mouth was
bordered by exoskeletal plates

15.  In Pteraspis,the head-shield showed that already there was
a functional mandible,a stout exoskeletal plate,which
opposed a maxillary area on the roof of the mouth.Behind
the mandible there were several smaller plates which were
presumably connected by a flexible integument.
 In all these forms the jaws showed a marked contrast
between the ventral and the dorsal side.

16. Simple skull plate suspended over bony gill
arches that functioned as gill supports.
Arches of cartilage supported the soft gills.
Over time two gill arches disappeared and
the third collaped and swung
forward,enclosing the mouth and forming
upper and lower jawbones.
Fourth gill arch shifted
forward,supporting the jaw.its gill slit
formed a spiracle-an opening behind
the eye through which water is drawn

17. Gnathostomes(pisces)
 From an evolutionary standpoint, fishes were the first animals
to develop bony jaws.
 The evolution of jaws allowed gnathostomes to become
effective predators and probably accounted for much of their
subsequent success (Mallatt,1996).
 The classical view is that jaws evolved via modifications of
ancient gill arch cartilages (viscerocranial elements),but little is
known about the underlying mechanisms .

18. shark
 In the sharks the underlying oralo-branchial arches became enlarged
 Recent discoveries by Dr. D. M. S. Watson and others indicate that
modern sharks have probably lost the primitive bony dermal jaw
plates and have greatly enlarged and specialized the inner or gill arch
jaws.
 The upper bony plate (corresponding to the maxilla) was fixed and
toothless.
 The lower or mandibular plate bore a series of vertical rows of small
teeth arranged along the upper margin

19. Life form jaw
lobe-finned fish,
ganoid and teleost
(Devonian period)
both the upper and lower jaws were of complex type.
consisting of an inner core corresponding respectively with the
cartilage in the lower and the palatoquadrate in the upper, covered by
number of bony plates
amphibia the lower jaw is compound and it articulates with the quadrate bone of
the skull
(quadrate-articular joint )
primitive amphibian,
stem reptile
the dentary and the maxilla increase greatly in size
mammal-like reptiles progressive postero-dorsal enlargement of the ascending ramus of the
dentary bone;its lower corner came near to the squamosal bone of the
temporal region. It was only prevented from forming a contact with
element by a cushion, bursa or meniscus, derived from the temporalis
muscle in which it was embedded
higher mammal-like
reptiles
there was begun a movement to emancipate the jaw muscles proper
from their hyoid and branchial companions, enlarged dentary & has
coronoid process
earlier adult mammals the dentary has become the sole bone of each half of the lower jaw
the premaxilla and maxilla together form the entire subocular surface
the face
man deepening and antero-posterior shortening of these elements

21. Reptile Mammal
Squamosal Squamosal part of temporal bone
Quadrate Incus
Articular Malleus
Angular Tympanic plate
Supra angular Anteior process of malleus
Dentary Mandible

22. Shark(chlamydoselachus)
Lobe finned ganoid (polypterus)
Primitive amphibian (eryops)
Primitive mammal like reptile (scymnognathus)
Advanced mammal like reptile
(cynognathus)
Primitive marsupial (opossum)
Primitive Eocene primate
(notharctus)
chimpanzee
Modern man
Jaw muscle
arose as
specialized
gill-arch
muscle
Increased
jaw
muscle
moveme
nt
Mammals-
• Increased muscle movement
• Old fulcrum at back of
compound joint diminished
• New joint established
between ascending ramus
of dentary plate & the
squamosal plate
• X-V type of jaw musculature
• Temporalis & masseter
muscle cross each other like
an “X”
• Dentary bone/mandible
slung between masseter &
internal pterygoid muscle
forming V-shaped pterygo-
masseteric sling

23. In the first category; Jaws specialized for
shearing (lion),
 condyle is cylindrical and rotates in a
matching groove between the articular
tubercle and the post glenoid tubercle.
 vertical shearing movements - the carnivore.
 Coronoid – large
 Condyle encircled in fossa
 Disc present
 Masseter +temporalis –well developed
Parallel evolution which occurred in T.M.J. within the class of mammals produced
differences in form and function as jaws became specialized for shearing (Lion), grinding
(cow), grasping (for porpoise) cutting and chewing (man).

24. The second type, specialized for grinding;
 Unmatched contours on the condyle and
temporal bone
 Condyle cannot fit into the mandibular fossa
but, instead, contacts both the articular tubercle
and the post glenoid tubercle.
 Ascending ramus increased height
 Condyle oval
 No articular eminence
 Disc & capsule present
 Masseter + temporalis well dev
 Lat pterygoid
 Lateral movements prominent
Evolutio
n

25. The third most dramatic functional modification
in the mammalian temporomandibular joint is
seen in the porpoise.
 The jaws are elongated the teeth are shaped
like needles
 condyle of the mandible is dissected
posteriorly.
 Under developed muscles of mastication
 uses the jaws only for temporarily holding its
food prior to swallowing without biting or
chewing.

26.  The human TMJ is characterized
by its versatility for it appears to
be a compromise of the other
four types.
 The mandibular condyle is free
for both, hinge and sliding
movements
 The dentition is specialized for
both biting and chewing

27. Australopithecus Africanus (3-3.5 million years ago)
Dental features are intermediate between those of apes & modern
human
Australopithecus Robustus (2.0-1.0 million years ago)
Lower jaw is very large
High degree of prognathisim is present
Australopithecus Bosiei (2.3-1.2 million years ago)
Face – long & broad
Facial & zygomatic portions of maxilla are large
Homo Habilis (1.9 – 1.8 million years ago)
• Dental reduction
• orthognathy

28. Homo Erectus
• 1.8my – 300,000 years ago
• Size of the posterior teeth are decreased & anterior were larger than modern
humans
Homo Neanderthals (150,000 – 30,000 years ago)
Dentition as a whole is placed forward relative to the skull
vault
Homo Sapiens
• Orthognathic face
• Teeth progressively reduced in size, concurrently with the reduction in
masticatory apparatus.

29.  MYH16 (myosine heavy chain) gene over the years
became a pseudogene, lead to decrease in the size of
jaw musculature & increase in brain size.
 According to Stedman et al a frameshift mutation in
gene encoding for myosin heavy chain in masticatory
muscle led to marked reduction in size of muscle fibre
and subsequently to jaw bones.
 It caused narrower jaws, smaller teeth and space for the
3rd molar became less. 3rd molar is almost vestigeal now
on account of the MYH-16
 Mutation accounts for the graceful human jaw, in
contrast to apes protruding facial ridges.
 Because Hox genes have marked inhibitory effects on
jaw formation ,it has been proposed that the origin of
jaws was facilitated by a loss of Hox(homebox
transcription factor) expression from the first pharyngeal
arch
Ref:Stedman et al.Myosin gene mutation correlates with anatomical
changes in the human lineage

30. 1)AUTODIASTYLIC
• The jaws are attached to the
cranium by anterior and
posterior ligaments.
• Hyoid arch remains
completely free or
independent and does not
support the jaws.
• Eg:gnathostomes and
acanthodians
JAW SUSPENSION

31. 2)AMPHISTYLIC
• The quadrate or the basal and otic
processes of upper jaw(mandibular arch)
are attached by ligaments to
chondrocranium.
• the upper end of hyomandibula(hyoid
arch) is also attached to chondrocranium,
while the two jaws are suspended from its
other end.
• this arrangment makes double
suspension(amphi=both+styly=bracing)
since both the first and second arches
participate in binding the jaws against the
chondrocranium.
• Eg:primitive shark.

32. 3)HYOSTYLIC
• Upper jaw (palatoquqdrate) is loosely attached by anterior
ethmopalatine ligament and posteror spiracular ligament to
cranium.
• both the jaws are suspended from the hyomandibular,the upper end
of which fits into auditory region of the skull . since only hyoid
arch binds the two jaws against cranium ,this jaw suspension is
termed as hyostylic
• it provides the jaws a wider movement and helps in swallowing
larger preys
• Eg:elasmobranch,bony fishes.

33. 4)AUTOSTYLIC
• hyomandibular becomes modified into columella or stapes of
middle ear for transmitting sound waves.
• the upper jaw is completely fused by its processes to the bony
skull
• the lower jaw is suspended from the upper jaw.
• thus support from the hyomandibular is not needed,so it enters
the middle ear as columella or stapes.
• Eg:bony fishes,tetrapoda.

34. Autostylic jaw suspension is divided into 3 subtypes
a)HOLOSTYLIC
• upper jaw is firmly fused with skull
• lower jaw suspended from it.
• hyoid arch is complete ,independent and not attached to skull;
• Eg:chimaeras
b)MONIMOSTYLIC
• many tetrapods
• hyomandibular forms columella
• articular articulates with quadrate.
• However ,the quadrate remains immovably attached with skull.
c)STREPTOSTYLIC
• Quadrate is loosely attached and is movable
• Eg:reptiles (lizzard,snakes)and birds.

35. 5)CRANIOSTYLIC
• characteristic of mammals
• upper jaw fuses throughout its length with cranium
• hyomandibular forms the ear ossicles malleus and
incus
• dentary of lower jaw and squamosal of skull provide
the articulation between jaws.

36.  Evolution of dental occlusion form fish to man – W.K. Gregory – Angle Orthodontics – Vol
11 No. 3
 Stone age man’s occlusion – Am J Orth 1959; 40; 298
 Anthropology and orthodontics – AO vol.67(1);1997,73 – 77
 Cerny R. et al. Developmental origins and evolution of jaws: new interpretation of
Maxillary and mandibular ;Developmental Biology :276 (2004) ;225–236
 Stedman et al.Myosin gene mutation correlates with anatomical changes in the human
lineage
 Emes Y ,Aybar B,Yalcin S. On The Evolution of Human Jaws and Teeth: A Review