Data from: Olfaction written in bone: cribriform plate size parallels olfactory receptor gene repertoires in Mammalia

The evolution of mammalian olfaction is manifested in a remarkable diversity of gene repertoires, neuroanatomy, and skull morphology across living species. Olfactory receptor genes (ORG), which initiate the conversion of odorant molecules into odor perceptions and help an animal resolve the olfactory world, range in number from a mere handful to several thousand genes across species. Within the snout, each of these ORGs is exclusively expressed by a discrete population of olfactory sensory neurons (OSN), suggesting that newly evolved ORGs may be coupled with new OSN populations in the nasal epithelium. Because OSNs axon bundles leave high-fidelity perforations (foramina) in the bone as they traverse the cribriform plate (CP) to reach the brain, we predicted that taxa with larger ORG repertoires would have proportionately expanded footprints in the CP foramina. Previous work found a correlation between ORG number and absolute CP size that disappeared when body size effects were accounted for. Using updated, digital measurement data from high-resolution CT scans and reexamining the relationship between CP and body size, we report a striking linear correlation between relative CP area and number of functional ORGs across species from all mammalian superorders. This correlation suggests strong developmental links in the olfactory pathway between genes, neurons, and skull morphology. Furthermore, because ORG number is linked to olfactory discriminatory function, this correlation supports relative CP size as a viable metric for inferring olfactory capacity across modern and extinct species. By quantifying CP area from a fossil sabertooth cat (Smilodon fatalis) we predicted a likely ORG repertoire for this extinct felid.

哺乳动物嗅觉的演化，体现为现生各物种在基因库、神经解剖结构以及颅骨形态方面的显著多样性。嗅觉受体基因（olfactory receptor genes, ORG）负责将气味分子转化为嗅觉感知，并帮助动物辨识嗅觉环境，不同物种中该类基因的数量从寥寥数个到数千个不等。在鼻腔内，每一个嗅觉受体基因均仅由一群离散的嗅觉感觉神经元（olfactory sensory neurons, OSN）特异性表达，这提示新演化出的嗅觉受体基因，可能与鼻腔上皮中新增的嗅觉感觉神经元种群形成耦合关联。由于嗅觉感觉神经元的轴突束在穿过筛骨板（cribriform plate, CP）抵达大脑的过程中，会在骨骼上留下高保真的穿孔（即筛孔），我们推测拥有更大嗅觉受体基因库的类群，其筛骨板上的筛孔印迹面积也会成比例扩大。此前已有研究发现嗅觉受体基因数量与筛骨板绝对尺寸存在相关性，但在控制体型效应后，该相关性便不复存在。本研究借助高分辨率CT扫描获取的更新版数字化测量数据，重新审视了筛骨板与体型间的关系，结果显示：在所有哺乳动物超目类群中，相对筛骨板面积与功能性嗅觉受体基因数量之间存在显著的线性相关性。该相关性表明，嗅觉通路中基因、神经元与颅骨形态之间存在紧密的发育关联。此外，由于嗅觉受体基因数量与嗅觉辨别功能密切相关，这一相关性也证实，相对筛骨板面积可作为推断现生及灭绝物种嗅觉能力的有效指标。通过对化石物种致命刃齿虎（Smilodon fatalis）的筛骨板面积进行量化分析，我们预测了这一已灭绝猫科动物的潜在嗅觉受体基因库规模。