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Last Update: 09/27/2023 04:16 AM
Current Deck: Comp Anat Exam 2::Comp Anat Exam 2 Lecture 7
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Commit #19068
Discuss jaw evolution (include the origin of jaws)
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Commit #19068
Start w hypothetical jawless ancestor (ex. amphioxus) with the arches supporting a filter feeding apparatus or gills
first few arches modified through evolution to become jaws (first few modified and can then grasp things, this is good bc it opens up feeding niches for them), there's still no teeth present here
bc the animals with these new arches modified to be able to grasp survived and reproduced well with the new feeding niches, muscle size supporting arches got bigger and bigger quickly
after this matures, now the fish can modify scales to create something to grab with on the jaws (teeth)
Origin of jaws
visceral arches supporting gills
two main ideas behind what happened to the first two arches in the hypothetical jawless ancestor
1. Serial- first arches go away and reduce metabolic costs bc they are not used (lose pre, form mandibular and hyoid arch from branchial arches)
2. Composite- first arch is a composite of the first few arches fusing together with mandibular arch when that and the hyoid arch form) this is probably more likely
The Palatoquadrate and meckel's cartilage form the premaxilla, maxilla, and dentary in both
first few arches modified through evolution to become jaws (first few modified and can then grasp things, this is good bc it opens up feeding niches for them), there's still no teeth present here
bc the animals with these new arches modified to be able to grasp survived and reproduced well with the new feeding niches, muscle size supporting arches got bigger and bigger quickly
after this matures, now the fish can modify scales to create something to grab with on the jaws (teeth)
Origin of jaws
visceral arches supporting gills
two main ideas behind what happened to the first two arches in the hypothetical jawless ancestor
1. Serial- first arches go away and reduce metabolic costs bc they are not used (lose pre, form mandibular and hyoid arch from branchial arches)
2. Composite- first arch is a composite of the first few arches fusing together with mandibular arch when that and the hyoid arch form) this is probably more likely
The Palatoquadrate and meckel's cartilage form the premaxilla, maxilla, and dentary in both