|From Introduction to Paleobiology and the Fossil Record, Benton and Harper|
18 September 2013
I was looking up something on Oligokyphus just now and apparently enough people have searched "Oligokyphus dinosaur" that it pops up on Google. We are here to teach, so of course my first response to that is that there needs to be a little more outreach concerning the nature of these enigmatic little devils. First and foremost, Oligokyphus is a Synapsid whereas dinosaurs, and extant reptiles including birds (that is a different discussion altogether as many of us know), are Sauropsids. The important difference here is the skull morphology. Synapsids have what is called a synapsid skull in which the skull is perforated below the squamosal bone by a single temporal fenestra. Sauropsid skulls can be one of three forms: Diapsid, Anapsid, and Euryapsid. Diapsid and Anapsid skulls can still be found today, in birds/lizards and turtles respectively, while the Euryapsid condition was an alternative skull found in extinct Ichthyosaurs and Plesiosaurs. Oligokyphus, as a rather odd mammal-like reptile, has a Synapsid skull while retaining a jaw joint between parts of the lower jaw known as surangular and articular and a quadrate bone in the skull (refer to earlier discussions in the week on mammal vs. reptile jaw articulations). That skull morphology alone excludes Oligokyphus from the dinosaurs, so please pass that along to anyone you hear refer to Oligokyphus as a dinosaur!