Apse = Arch


Photo by Caroline Nye Stevens at the Field Museum

Doing some reading on tuatara, as one does when preparing a zoology lecture later in the semester (OMG, CHORDATES!!! It took only 14 weeks of learning about worms and worm-shaped non-worms to get here!), and I came across this:


Overall, not bad. Written fairly clearly and hits all the main points. My one issue with it is that the author does not define “apse” correctly. I’d put that in the comments section, if it hadn’t been closed long ago. Apse means “arch”, although in architecture it refers to a recessed shallow hole in the wall, not unlike a niche. However, the apse is formed with an arch, and that is what apse means in biology. A diapsid skull is a skull with two arches that form the “holes” in the skull (actually called “fenestrae”). Diapsid wouldn’t even really make sense if you thought “apse” meant “hole”, because there are three fenestrae in the diapsid skull; the orbital, the superior temporal fenestra, and the inferior temporal fenestra.

The real reason I’m involved in this is because some innocent, well-meaning student had to ask what nitty -gritty details distinguished the tuatara (the only members of Order Sphenodontia) from the lizards of Order Squamata. I had a feeling it was something esoteric about the skull, but didn’t have that answer on the tip of my brain. So tomorrow I can say with confidence that the big differences are jaw mobility (tuatara have less) and hemipenes (tuatara must go in for the cloacal kiss that birds are famous for).


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