This document presents a comparative account of jaw suspension in vertebrates, detailing various attachment methods of jaws to the skull across different species. It outlines five main types of jaw suspension: autodiastylic, amphistylic, hyostylic, autostylic, and craniostylic, along with their characteristics and examples. The evolution of jaws is discussed, emphasizing the transition in feeding methods and the significance of jaw structure for predation in vertebrates.

1. COMPARATIVE ACCOUNT OF JAW
SUSPENSION
BY-POOJA PRAVIN KAMBLE
M.SC PART-1

2. PSZO101:NONCHORDATES,CHORDATES AND THEIR
PHYLOGENY
UNIT4:COMPARATIVE VERTEBRATE
OSTEOLOGY-1
4.2:COMPARATIVE ACCOUNT OF JAW
SUSPENSION

3. SYNOPSIS
INTRODUCTION
EXPLANATION
DEFINATION
CONCLUSION
REFRENCES

4. INTRODUCTION OF JAW
 Each
of the upper and lower bony structure
in vertebrates forming the framework of the
mouth and containing the teeth.
.


5. EXPLANATION OF
JAW SUSPENSION
Jaw suspension means attachment of the lower jaw with
upper jaw or skull for efficient bitting and chewing .
There are different ways in which these attachments are attained
depending upon the modification in visceral arches .

7. Evolution of jaw
The prevertebrates had a ciliary pump therefore they were depended on the
suspended matter in sea water .In larger fish (agnathan) the ciliary pump
became 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 agnathan to gnathostomes involved switch in feeding method
.therefore they became raptorial feeders.so 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

9. DEFINATION
The method by which the upper and lower
jaws are suspended or attached from the
chondrocranium is known as suspension

10. 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

11. 2)AMPHISTYLIC
The quadrate or the basal and otic processes of upper
jaw(mandibular arch) are attached by ligaments to
chondrocranium.similarly,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.

12. 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 suspensionis
teremed as hyostylic it provides the jaws a wider movement and helps
in swallowing larger preys
Eg:elasmobranch,bony fishes.

13. 4)AUTOSTYLIC
This condition occurs when hyomandibular does not participate but
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 and 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.

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

15. 5)CRANIOSTYLIC
This type of jaw suspension is characteristic of mammals
and some consider it as a modification of autostylic
suspension .upper jaw fuses throughout its length with
cranium and hyomandibular forms the ear ossicles
malleus and incus consequently two dermal bones
,dentary of lower jaw and squamosal of skull provide the
articulation between jaws.

16. COMPARATIVE ACCOUNT OF JAW
SUSPENSION
1)In agnathans the jaw suspension is in paleostylic stage in
which none of the arches attach themselves directly to the
skull.
2)In ganathostomes and acanthodians jaw suspension is
autodiastylic in which jaws are attached 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 suspension is amphistylic in
which the quadrate or the basal and otic processes of upper
jaw (mandibular arch) are attached by ligaments to
chondrocranium.similarly the upper end of hyomandibula is
also attached to chondrocranium.

17. 4)In modern sharks and all bony fishes the type of jaw suspension is
hyostylic,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 two jaws against cranium
it is called hyostylic jaw
5)In most tetrapods 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 attached
to the skull; this is holostylic type of jaw suspension.

18. 7)In many tetrapods monimostylic jaw suspension is seen
ie.hyomandibular forms columella and articlar articulates with
quadrates.however the quadrate remains immovably attached
with skull.
8)In some reptiles(lizard,snakes)ann birds the type of jaw
suspension is streptostylic ie.quadrate is loosely attached 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 articular and quadrate also become
modified into ear ossicles malleus and incus

19. 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;
_active predation became a common lifestyle in subsequent
vertebrates.

20. REFERENCES:VERTEBRATES-KENNETH V.KARDONG
CHORDATE ZOOLOGY-E.L.JORDAN AND
P.S.VERMA

21. THANK YOU

23. CONCLUSION
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-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;
_active predation became a common lifestyle in subsequent vertebrates.
_After studying jaw suspension it can be concluded that branchial arches
phylogenetically gave rise to jaw.
_From serial theory theory we came to know that first or perhaps second branchial
arch gave rise to hyoid arch and rest to the branchial arches.
_-But Jarvik concluded about the composite theory according to him the
mandibular arch of gnathostomes is formed by the fusion of premandibular
arch.The palatoquadrate forms the epibranchial arch of premandibula,the meckels
cartilage is formed from an expanded ceratobranchial arch,and the hyoid arch is
formed from the epibranchial,hypobranchial and ceratobranchial arches of the
primitive gill arches.
-so study of oesteology became vital for studying jaw suspension.