The olfactory bulb endocast as a proxy for mammalian olfaction

Area of Science:

• Paleontology
• Neuroscience
• Genomics

Background:

• Olfaction is vital for tetrapod survival and reproduction.
• Comparative olfactory studies often use anatomical proxies like olfactory bulb endocasts, especially for extinct species.
• The correlation between olfactory bulb size and gene counts is not fully understood.

Purpose of the Study:

• To investigate the relationship between olfactory bulb endocast volume and chemoreceptor gene numbers in mammals.
• To determine if olfactory bulb size can predict olfactory capabilities in extinct mammals.

Main Methods:

• Analyzed brain endocasts from all mammalian orders.
• Correlated absolute (absOB) and relative (relatOB) olfactory bulb volumes with intact chemoreceptor gene counts.
• Estimated olfactory receptor (OR) gene numbers for taxa lacking genomic data and extinct mammals.

Main Results:

• No significant correlation was found between absolute olfactory bulb volume (absOB) and genomic proxies.
• A significant positive correlation exists between relative olfactory bulb volume (relatOB) and the total number of intact chemoreceptor genes (CombChemo), mainly driven by OR genes.
• Successfully estimated OR numbers for understudied and extinct mammalian groups.

Conclusions:

• Relative olfactory bulb volume (relatOB) serves as a reliable proxy for inferring mammalian olfactory capabilities.
• This method provides a new avenue for studying sensory evolution and paleoecology in extinct mammals.
• The findings link anatomical and genomic data to reconstruct sensory abilities of ancient life.