origin of jaws Flashcards
what are the branchial/ visceral arches developed into in gnathostomes?
• From branchial (visceral) arches
○ 1st arch develops into the jaws (palatoquadrate and lower mandible)
○ 2nd arch develops the hyoid apparatus
○ 1st gill slit becomes the spiracle
• Visceral arches form neural crest cells (from the neuroectoderm)
what is the gill tissue derived from?
endoderm
who came up with the origin of jaw theory? what is the theory?
Jon Mallatt’s view - jaws were originally important for gill ventilation, not grasping prey
• He argued the jaw originated from the 1st gill slit - supports ventilation theory
what did the PQ and Meckles cartilage form?
• Mandibular arch
○ Palatoquadrate = upper jaw
Meckel’s cartilage = lower jaw
what is the fate of the pq in bony fishes?
a. Two bones - premaxilla and maxilla ensheath the p.q. (derived from p.q.?)
○ Ossification of palatine and ectopterygoid bones had to occur for this
○ Quadrate bone forms posteriorly after
○ Whole complex fuses with dermatocranium
what is the fate of meckle’s cartilage?
ate of Meckel’s cartilage
○ Articular bones form (posterior)
○ Dentary and angular form rest
• Involved the repositioning of gills
○ Cyclostome pattern different from gnathostome
• Resulted in a paired nasal sac and nostril pattern
what is the adaptive value of jaws?
- Increase strength and mobility of mouth
- Increased suction
- Manipulation of non-food items
benefit of increased strength and mouth mobility?
- Capture and hold prey better
- Can eat larger food items (aided by dentition)
- Can cut, shear, and grind food
benefit of increased suction?
- Aids in holding food
* Aids in increased gill aeration (Mallatt Hypothesis)
benefit of manipulation of non- food items?
- For grasping mates
- For building nests
- For protecting young
- Increased opportunities for mating, parental care, and survival
