Quantifying the cribriform plate: influences of allometry, function, and phylogeny in Carnivora.

The small, perforated bony cup of the anterior cranial fossa called the cribriform plate (CP) is perhaps the best-preserved remnant of olfactory anatomy in fossil mammal skulls. The CP and its myriad foramina record the passage of peripheral olfactory nerves from nasal cavity to olfactory bulb. Previous work has suggested that CP surface area reflects aspects of olfactory capacity (as inferred from habitat and observed behavior) in mammals. To further explore the utility of CP as a proxy for olfactory function, we designed novel, nondestructive digital methods to quantify CP morphology from dry skulls. Using CT scans and 3-D imaging software, we quantified CP features from 42 species of Carnivora, a group that represents a wide spectrum of ecologies and sensory demands. Two metrics, CP surface area (CPSA) and cumulative CP foramina area (FXSA), scaled to skull length with negative allometry, and differed between aquatic and terrestrial species, with the former having reduced areas. Number of foramina (NF) was not correlated with skull length but tended to be greater in caniforms than feliforms. Both CPSA and FXSA are well correlated with ethmoturbinal surface area, a known osteological correlate of olfactory function. This suggests that CPSA and FXSA are useful proxies for olfactory ability, especially when studying fossils or skulls in which turbinals are not preserved. Total area of CP foramina (FXSA), an exacting measure of olfactory nerve endocasts, is tightly correlated with CPSA. Because of this, it may be desirable to use CPSA alone as a proxy given that it is easier to measure than FXSA.