Zoology ppt on jaw suspension

1. PRESENTATION
JAW SUSPENSION
SUBMITTED TO – DR.
RASHMI TRIPATHI
MA’M
ON
SUBMITTED BY –
SURBHI YADAV
BSC BIOSCIENCE
4TH SEMESTER

2. SYNOPSIS
INTRODUCTION
EXPLAINATION
 DEFINATIO
NCONCLUSION
REFERENCES

3. introduction

4.  Arthropods
 In arthropods, the jaws are chitinous and oppose laterally, and may
consist of mandibles or chelicerae . These jaws are often composed
of numerous mouthparts . Their function is fundamentally for food
acquisition, conveyance to the mouth, and/or initial processing
(mastication or chewing). Many mouthparts and associate structures

5.  VERTEBRATES
fig. Jaws of great
white shark
In most vertebrates , the jaws are bony or
cartilaginous and oppose vertically, comprising an upper
jaw and a lower jaw. The vertebrate jaw is derived
from the most anterior two pharyngeal arches
supporting the gills, and usually bears numerous teeth.

6. FIG. Moray eels have two sets of jaws: the oral jaws that capture
prey and the pharyngeal jaws that advance into the mouth and move
prey from the oral jaws to the esophagus for swallowing

7. The vertebrate jaw probably originally evolved in the Silurian period and
appeared in the Placoderm fish which further diversified in the Devonian.
The two most anterior pharyngeal arches are thought to have become the
jaw itself and the hyoid arch, respectively. The hyoid system suspends the
jaw from the braincase of the skull, permitting great mobility of the jaws.
While there is no fossil evidence directly to support this theory, it makes
sense in light of the numbers of pharyngeal arches that are visible in extant
jawed vertebrates (the Gnathostomes), which have seven arches, and
primitive jawless vertebrates (the Agnatha), which have nine.
It is thought that the original selective advantage offered by the jaw was
not related to feeding, but to increased respiration efficiency. The jaws
were used in the buccal pump (observable in modern fish and amphibians)
that pumps water across the gills of fish or air into the lungs in the case of
amphibians. Over evolutionary time the more familiar use of jaws (to
humans), in feeding, was selected for and became a very important function
in vertebrates. Many teleost fish have substantially modified jaws for
suction feeding and jaw protrusion , resulting in highly complex jaws with

8.  Amphibians,reptiles andbirds
 The jaw in tetrapods is substantially simplified compared to
fish. Most of the upper jaw bones (premaxilla, maxilla, jugal,
quadratojugal, and quadrate) have been fused to the
braincase, while the lower jaw bones (dentary, splenial,
angular, surangular, and articular) have been fused together
into a unit called the mandible. The jaw articulates via a hinge
joint between the quadrate and articular. The jaws of
tetrapods exhibit varying degrees of mobility between jaw
bones. Some species have jaw bones completely fused, while
others may have joints allowing for mobility of the dentary,
quadrate, or maxilla. The snake skull shows the greatest

9. REPTILE
AMPHIBIAN
BIRD

10.  In the evolution of the mammalian jaw, two of the bones of
the jaw structure (the articular bone of the lower jaw, and
quadrate ) were reduced in size and incorporated into the
ear , while many others have been fused together . As a
result, mammals show little or no cranial kinesis, and the
mandible is attached to the temporaL bone by the
temporomandibular joints . Temporomandibular joint
dysfunction is a common disorder of these joints,
characterized by pain, clicking and limitation of mandibular
movement.
 MAMMALS :-

11. LION

12.  SEA URCHINS
Sea urchins possess unique jaws which display five-
part symmetry, termed the Aristotle's lantern.
Each unit of the jaw holds a single, perpetually
growing tooth composed of crystalline calcium

13. Meaning of jaw suspension
Jaw suspension means attachment of the
lower jaw with the upper jaw or the skull
for efficient biting and chewing. There
are different ways in which these
attachments are attained depending upon
the modifications in visceral arches in
vertebrates.

15. The pre-vertebrates had an ciliary pump therefore they were
depended on the suspended matter in sea water. In larger fishes
(agnathan) the ciliary pump becomes less effective and was replaced
by muscular pharynx pump. As agnathans were deposit feeders, mud
grobbers that pushed their mouth into loose organic or siltmud and
drew sediment rich organic particles . Then transition from
agnathans to gnathostomes involved switch in feeding method.
Therefore they became raptorial feeders. So the sudden expansion
of pharynx developed to close the mouth to prevent escape of
capture and ingestion. So the jaws develop powered by muscle
action.so the mouth could shut quickly
JAW ORIGIN HYPOTHESIS

16. There was an arch rostral to the one that become the jaws .
it was subsequently lost , and is referred to as premandibular
arch . This is supported by the fact that part of the
trigeminal nerve , the nerve of the jaw arch ,or
MANDIBULAR ARCH, has three major branches . Most
have two branches (one strictly sensory ,other sensory+
motor ). The trigeminal has an additional sensory branch
reaching forward of the other two , and it is generally
thought that this is sensory branch that was “ captured” by
 JAW ORIGIN HYPOTHESIS :- 1.

18.  JAW ORIGIN HYPOTHESIS :- 2.
Some researchers suggest that
there were two premandibular
arches. But , as the arches are long
gone , it is impossible to test.

19. JAW ORIGIN HYPOTHESIS :- 3.
some researchers suggest that not only there
was a premandibular arch , but that there could
have been another . this theory known as
COMPOSITE THEORY suggests that the resulting
Mandibular arch as components of numerous
adjacent arches incorporated .

20. All of these hypotheses , at least one
premandibular arch is suggested . The additional
, many would suggest that the paired trabeculae
of the rostral underside of the braincase are
homologous to premandibular visceral arch
elements.
Immediately caudal to the mandibular arch , the
next arch known as the hyoid arch is also highly
modified , in part to facilitate suspension of the
jaws on the underside of the brain case.

21.  DEFINATION
The method by which the upper and
lower jaws are suspended or attatched
from chondocranium is called
suspension

22. The jaws are attatched by ligaments(anterior
and posterior) to the chondoranium.the hyoid
arch does not support the jaws but remain
completely free as the posterior branchial
arches.the gill cleft in front of the hyoid arch
does not form a spiracle but forms a complete
gill .
e.g.,early bony fishes (gnathostomes and
AUTODIASTYLIC

23. AUTODIASTYLIC
CHONDOCRANIUM
ORBIT
POSTERIOR LIGAMENT
OTIC
PROCESS
ANTERIOR
LIGAMENT
BASAL PROCESS
PALATOQUARAT
E MECKELS
CARTILAGE
HYOID ARCH
GILL
CLEFT
HYOMANDIBULAR

24. Jaw of early bony fishes

25. The upper jaw( mandibular arch) has basal and otic processes
which are attatched by ligaments to the chondoranium . Besides
this , the hyomandibular of the hyoid arch is also attached to
the chondocranium . At the other end both jaws are suspended
from it . thus it is a double suspension in which both the
mandibular and hyoid arches are attached to the chondocranium
. this arrangement makes double suspension since both first and
second arches participate in binding the jaw against
chondocranium .this type of suspensorium is found in
crossopterygii and in some primitive sharks like heptanchus
 AMPHISTYLIC

26. JAWS of some primitive sharks like heptanchus and
hexanchus

28. The upper jaw is (palatoquadrate)is loosely articulated with the
cranium by anterior ethamopalantine ligament and posterior
spiracular ligament.both jaws are suspended from the cranium
and hence,it is called hyostylic.both the jaws are suspended
from the hyomandibular ,the upper end of which fits into the
auditory region of skull.since only hyoid arch binds the two jaws
against cranium ,it provides the jaws a wider movement and
helps in swallowing preys.it is found in most elasmobranchs and
bony fishes,which are able to swallow large preys
 HYLOSTYLIC

29. JAW OF BONY FISH

30. HYOSTYLIC suspension ( most derived
chondrycthyans and bony fishes)
ORBITAL
PROCESS

31. The upper jaw ( platoquadrate) is completely fused by its
processes to the bony skull and the articular of lower jaw is
suspended from the quadrate of the upper jaw . the
hyomandibular do not take part in suspensorium and
modified into columella and stapes of the middle ear . some
authorities use the term autosystylic for autostylic . It is
found in extinct placoderms , chimera , lung fishes and
tetrapods. I.e., amphibians, reptiles and birds . in these , the
quadrate of the upper jaw articulates with the articular of

32. JAWS OF A LUNG FISH

33. PRIMTIVE AUTOSTYLIC SUSPENSION (
IDEALIZATION BASED ON SOME PLACODERMS)

34. The autostylic suspension is divided into three
varieties-
The upper jaw is fused to the skull and the lower jaw is
suspended from it . the hyoid arch is complete and not
attached to the skull, e.g., holocephali ( chimaera)
 A. Holostylic -
JAWS OF Chimaera

35. In many tetrapoda , except mammals ,
hyomandibular forms columella ( middle ear
bone) and the articular of lower jaw
articulates with the quadrate of the upper
jaw . the quadrate becomes an immovable
part of skull
(B). Monimostylic-

36. In lizards, snakes and birds the articulation is between
quadrate and articular , but the quadrate is not firmly fused
with the skull and is movable at both ends . this autostylic
suspension is distinguished as streptoatylic
 (c) Streptostylic -

37. The upper jaw is fused with the cranium in its entire
length . hyomandibular forms the stapes of middle ear
bone . the quadrate and articular also modified into
malleus and incus respectively . thus , squamosal of the
skull and dentary of lower jaw articulate with each
other and both are dermal bones . it is found in
mammals . some consider it as modification of
autostylic type
 5. CranIostylic :-

38.  COMPARATIVE ACCOUNT OF JAW
SUSUPENSION :-
1. In agnathans the jaw suspension is in paleostylic stage in which
none of the arches attatch themselves directly to the skull.
2. In gnathostomes and acanthodians jaw suspension is
autodiastylic in which jaw are attatched to the cranium by
anterior and the posterior ligaments. Hyoid arch remains
completely free and does not support the jaws .
3. In primitive sharks the jaw susupension is amphistylic in which
the quadrate or the basal and otic processes of upper jaw
(mandibular arch) are attatched by ligaments to chondocranium .
Similarly the upper end of hyomandibula is also attatched to

39. 4. In modern sharks and all bony fishes the type of jaw
suspension is hylostylic , in which the upper jaw (
palatoquadrate ) is loosely attached by anterior ligament
to cranium . Both the jaws are suspended from the
hyomandibular . Since only hyoid arch binds the jaws
against cranium it is called hyostylic jaw .
5. In most tetra pods like amphibians , reptiles , and birds
hyomandibular does not participate but becomes modified
into columella or stapes of middle ear for transmitting
sound waves .
6. In most lung fishes upper jaw is firmly fused with skull
and lower jaw suspended from it . Hyoid arch is complete
, independent and not attatched to the skull ; this is
holostylic type of jaw suspension

40. 7. In many tetrapods monimostylic jaw suspension is seen
i.e., hyomandibular forms columella and articular
articulates with quadrate remains immovably attatched to
the skull.
8. In some reptiles ( lizards, snakes ) ann birds the type
jaw suspension is streptostylic i.e., quadrate is loosely
attatched and is movable at both the ends a condition
known as streptostylism .
9. In mammals craniostylic type of jaw suspension is seen
it is modification of the autostylic suspension . Upper jaw
fuses throughout its length with cranium , and
hyomandibular forms the ear , ossicle , stapes , but

41.  CONCLUSION :-
 Development of jaws transition was there in feeding
method.
Due to jaw the mouth could shut quickly with a strong
bite , securing the “inhaled “ prey.
Limits to prey size were also removed.
After studying jaw suspension it can be concluded that
branchial arches phyllogenically gave rise to jaw.
From serial theory we came to know that first or
perhaps second branchial arch gave rise to hyoid arch
and rest to the branchial arches.

42.  But jarvik concluded about the composite
theory according to him the mandibular arch
of gnathostomes is formed by fusion of
premandibular arch . The palatoquadrate
forms the epibranchial arch of premandibula
,the meckels cartilage is formed from an
expanded ceratobranchial arches of the
primitive gill arches.
So the study of osteology become vital for
studying jaw susupension.

43.  REFRENCES
 Internet sites :-
https://www.slideshare.net/poojakamble1609/comparative-account-of-jaw-suspension
 www.encyclopedia.com/science/dictionaries-thesauruses.../hyostylic-jaw-suspension
 www.iaszoology.com/jaw-suspension/
 www.encyclopedia.com/science/dictionaries-thesauruses.../autostylic-jaw-suspension
 https://en.wikipedia.org
 www.sfu.ca/biology/courses/bisc316/intros/lab5.html
Books :-
 chordate zoology by P.S. Verma
Vertebrates by RL Kotpal

45. The end…!!