Chapter 7 Part 3 Flashcards
Describe the anatomy of the osteostracan skull
- agnathan
- o The floor of the pharynx could be raised and lowered to actively draw water into the mouth and drive it out through the several branchial pores
Phylogeny of the Vertebrate Skull: Anapsids
- agnathan
- Throat cartilages supported the floor of the buccal cavity
- Might have been part of a pump to draw water into the mouth and then force it across the gills and out through the external branchial pores
Phylogeny of the Vertebrate skull: Heterostracans
- agnathan
- Water flowed through the mouth, over the gills, suspended in branchial pouches, and into a common chamber (branchial duct) before exiting via the external branchial pore
Phylogeny of the vertebrate skull: Gnathostomes(fishies!)
- Placoderms: water exits around dermatocranium
- Acanthodians: more developed gill arches, bony covering, large upper’lower cartilage, small scales so no thick dermal armour on head
How are shark jaws attached to chondrocranium and how do they move?
- flexible ligaments and muscles known as hyostylic suspension; allows movement and flexibility
- when biting, lower jaw drops down and back while upper jaw moves forward and down
- remember no bones, cartilage
What is the suspensorium in primitive bony fishes?
o The mandible rotates on its articulation with the suspensorium(piece making up part of jaw), which in turn is articulated with the opercular bones
o The pectoral girdle remains relatively fixed in position, but the neurocranium rotates on it to lift the head
- Done by Jaw protrusion, suction feeding, linkage system, and pharyngeal jaws altogether
Jaw Protrusion
The premaxilla (upper jaw) can slide forward, while the lower jaw (mandible) drops down and swings forward. This enables the fish to extend their mouth towards their prey, creating a suction effect
Suction feeding
When the fish opens its mouth quickly, water rushes in, carrying prey along with it. This is particularly effective for catching small, fast-moving prey. The rapid expansion of the buccal cavity (mouth) generates a pressure difference that draws water and prey into the mouth.
Linkage system
The jaw movement is facilitated by a series of bones and joints that act like a linkage system. The maxilla and premaxilla are highly mobile and connected by flexible ligaments, allowing for significant movement
Pharygneal jaws
Some teleosts also have a second set of jaws located in the throat (pharynx). These pharyngeal jaws can grasp and process food after it has been captured by the oral jaws. This is particularly seen in species like moray eels.
How did the nasal openings change in the transition to tetrapods?
- Water into ocntact w/special smell receptor, then flush out, in actinopterygians
- Originally led to outside in fishies, now tube inside and kept moist in sarcopterygians and tetrapods; part goes to eye to keep eye moist in socket
Describe structures seen in early tetrapods
Retained many of their rhipidistian skull features, including most of the bones of the dermatocranium and lateral line system
Describe modern amphibians in relation to this chapter in structures
2 types: stegokrotaphic(no opening) and zygokrotaphic(opening)
The splanchnocranium is reduced in amphibians
Suction feedingo In salamanders with gills
in salamanders with gills: the floor of the throat is rapidly expanded and the jaws parted enough so that the pulse of water carrying the intended prey enters
Excess water gulped in with the prey exits at the back of the mouth through the gill slits - a unidirectional flow into the mouth and out the gill slits
In metamorphosed salamanders and in adult frogs, gill slits are absent, so excess water entering the mouth during feeding must reverse its flow to exit via the mouth; bidirectional flow
(expand mouth, drop lower, create vacuum, water rid of body through gill slits)
Which part of the anuran skull is greatly reduced relative to other tetrapods?
splanchocranium
What is cranial kinesis?
Significance of movement of skull bones relative to each other and adddtion to movmeent ath joint of upper and lower jaws
Metakinesis
joint in back for movement; lizards
type of cranial kinesis
Mesokinesis
- type of cranial kinesis
- joint in middle for movement; lizards
Prokinesis
- type of cranial kinesis
- front of jaw moves up and down for movement; snakes
Streptostyly
- type of cranial kinesis
- different parts of skull move; both lizards and snake
Joints within the skull allow the snout to lift upward or bend downward about its mesokinetic articulation with the rest of the braincase - changes the angle of closure of the teeth when the animal grabs its prey
Describe modified skulls of lizards
Modified diapsid skulls (ventral bony border of the lower fenestra is absent); with metakinesis and/or mesokinesis )
Describe modified skull of snakes
modified diapsid skull, Frontal and parietal bones have grown down around the sides of the skull to form most of the walls of the braincase
Joint between compound and bone, dentary; joint can open mouth really wide for food; In vipers, maxilla rotates to extend fangs
Which vertebrates have akinetic skulls?
o Without movment, sphenodon, tuatara
o Akinetic diapsid skull with the dermatocranium dominant in Crocodylians
In birds, how does a neognathous skull differ from a paleogranthous skull?
o Palaeognaths have small and thick pterygoids, short and broad palatines, thick short jugals, broad thin maxillae, a well-developed vomer
o Neognathae have much thinner sturcture, less structure to work with
Describe bird cranial kinesis
The closed, resting position of a bird’s jaw shows that the maxilla and dentary are in contact. The cranium sits on the craniofacial hinge in a neutral position. The articular and the quadrate are also in neutral positions, held in place by the slight pressure of the jugal arch and palatine bones
When the quadrate bone pivots forward, it begins to push on the jugal arch and palatine, lifting the premaxilla and opening the jaw from the craniofacial hinge.
When the bill begins to close again, the actions are reversed: the craniofacial hinge rotates down, the premaxilla and maxilla drop, and the quadrate rotates back.
Which region of the mammal skull is derived from all three components of the vertebrate skull?
temporal region comes from all 3 regions(chondrocranium, splanchocranium, and dermatocranium)
Describe skulls of monotremes
Retain several early synapsid skull features: prefrontal, postfrontal, and pleurosphenoid bones together with unfused occipitals
What are turbinates?
Pockets/swirls within skull that creates cold air insdie the body
