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Anuran postnasal wall homology: an experimental extirpation study
1Museum of Comparative Zoology, Harvard University, Cambridge, Massachussetts, USA.
Journal of Morphology
|December 5, 1998
Summary
Removing the nasal placode in frog embryos did not affect larval skull development. However, in adult frogs, it altered nasal capsule structures and nerve pathways, supporting traditional vertebrate skull homologies.
Area of Science:
- Developmental biology
- Comparative anatomy
- Vertebrate paleontology
Background:
- Understanding the evolutionary relationships of cranial structures in amphibians is crucial for vertebrate paleontology.
- Previous research has proposed various homologies for the ethmoidal attachment of the palatoquadrate in anurans and urodeles.
Purpose of the Study:
- To investigate the role of the nasal placode in the development of the amphibian chondrocranium.
- To test proposed homologies for the ethmoidal attachment of the palatoquadrate in anurans and urodeles through experimental manipulation.
Main Methods:
- Unilateral extirpation of the nasal placode in Gosner stage 18-20 embryos of three frog species (Rana sylvatica, R. palustris, R. pipiens).
- Observation and comparison of chondrocranial structures in larval and metamorphosed stages.
- Analysis of the path of the medial nasal branch of the deep ophthalmic nerve.
Main Results:
- Absence of the nasal sac did not significantly impact larval chondrocranial structure formation.
- In metamorphosed frogs, only the lamina orbitonasalis and inferior prenasal process remained on the operated side.
- The medial nasal nerve coursed over the lamina orbitonasalis, bypassing the typical orbitonasal foramen.
Conclusions:
- The nasal placode is essential for the complete development of nasal capsule structures in adult anurans.
- Experimental results support the established homology between the anuran lamina orbitonasalis and the antorbital process found in urodeles and other vertebrates.