Disconnecting bones within the jaw-otic network modules underlies mammalian middle ear evolution

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Paleontology

Background:

• Mammalian middle ear ossicles evolved from the jaw articulation of synapsid ancestors.
• This evolutionary event is reconstructed through fossil records and developmental studies.
• Homologies exist between early synapsid jaw bones and mammalian middle ear ossicles.

Purpose of the Study:

• To investigate the anatomical changes during the evolution of mammalian middle ear bones.
• To analyze the role of mandibular bone disconnection in this evolutionary process.
• To identify anatomical modules and evolutionary stages in jaw-to-ear bone transformation.

Main Methods:

• Anatomical network analysis of the jaw-otic complex.
• Comparison across 43 synapsid taxa.
• Examination of functional exaptation aspects like muscle increase and bone separation.

Main Results:

• The disconnection of mandibular bones was crucial for mammalian middle ear evolution.
• This disconnection altered skull anatomical modularity and enabled new functions.
• Three types of anatomical modules evolved through five stages, with Meckel's cartilage ossification/degradation being key.

Conclusions:

• Mandibular bone disconnection significantly impacted skull evolution and middle ear development.
• The transformation of jawbones into middle ear ossicles involved distinct evolutionary stages and modular changes.
• Ontogenetic changes in Meckel's cartilage are central to the shift in anatomical modularity during mammalian evolution.