Just what did you call me?
What do horses, tigers, humans, and bats have in common?
It turns out that all of these animals have a small “hearing” bone in their ears called the stapes bone.
On a recent trip to the Museum of Natural History in New York City my son, upon taking a quick sly scan of a display poster on evolutionary traits, had the audacity to call me an epithere. Before jumping to conclusions (and thereby acknowledging I had no idea what my precocious son was even remotely talking about) I decided to investigate. In my travels through the museum I learned some cool facts about how early mammals developed.
Fact 1: Ages ago, in some mammals, the main artery for the brain went through the stapes.
Fact 2: Hearing bones developed from parts of the jaw bone that “migrated” over millions of years to a more posterior position.
Amazingly, when humans develop as embryos there is a stage where the brain is actually fed by a stapedial artery. As the human embryo continues to develop in the womb this stapedial artery regresses and the carotid artery takes over.
Fact 3: Epitherians (A-HA!) comprise all the eutherian mammals except the Xenarthra. They are primarily characterized by having a stirrup-shaped stapes in the middle ear, which allows for passage of a blood vessel.