Jaw suspension

Zoology ppt on jaw suspension

1. P R E S E N T A T I O N JAW SUS PEN S ION SUBMITTED TO – DR. RASHMI TRIPATHI MA’M ON SUBMITTED BY – SURBHI YADAV BSC BIOSCIENCE 4 TH SEMESTER

2. SYNOPSIS INTRODUCTION EXPLAINATION DEFINATION CONCLUSION REFERENCES

3. introduction The JAW is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term Lizbeth or "Lizbeth's Jawline" is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals.

4. Arthropods Fig.The mandibles of a bull ant 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 (such as pedipalps) are modified legs.

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. FISHES 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 dozens of bones involved .

8. Amphibians , reptiles and birds 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 degree of cranial kinesis, which allows the snake to swallow large prey items .

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 carbonate .

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 .

14. 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

15. 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 the trigeminal. JAW ORIGIN HYPOTHESIS :- 1.

16. 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.

17. 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 .

18. 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.

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

20. 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 acanthodians ) AUTODIASTYLIC

21. AUTODIASTYLIC CHONDOCRANIUM ORBIT POSTERIOR LIGAMENT OTIC PROCESS ANTERIOR LIGAMENT BASAL PROCESS PALATOQUARATE MECKELS CARTILAGE HYOID ARCH GILL CLEFT HYOMANDIBULAR

22. Jaw of early bony fishes

23. 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 and hexanchus. AMPHISTYLIC

24. JAWS of some primitive sharks like heptanchus and hexanchus

25. Amphistylic suspension (early chondricthyans acanthodians and early bony fishes)

26. 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

27. JAW OF BONY FISH

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

29. 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 lower jaw. Autostylic

30. JAWS OF A LUNG FISH

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

32. 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

33. 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-

34. 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 -

35. 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 :-

36. COMPARATIVE ACCOUNT OF JAW SUSUPENSION :- In agnathans the jaw suspension is in paleostylic stage in which none of the arches attatch themselves directly to the skull. 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 . 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 chondocranium.

37. 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

38. 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 articular and quadrate also become modified into ear ossicles malleus and incus

39. 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.

40. 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.

41. 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

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