Editing Probainognathus (section)

=== Jaw ===
[[File:Probainognathus.jpeg|thumb|Illustration of the skull in lateral view]]

The jaw of ''Probainognathus'' is of particular [[phylogenetic]] importance. Morphologically, the dentary made up most of the lower jaw, and it curved and extended down posteriorly to the area of the articular and jaw articulation.<ref name="Romer1970"/> Correspondingly, in the upper jaw, the squamosal bone became situated next to the quadrate.<ref name="Berkeley">{{cite web |title=Jaws to ears in the ancestors of mammals |url=https://evolution.berkeley.edu/what-are-evograms/jaws-to-ears-in-the-ancestors-of-mammals/ |url-status=live |archive-url=https://web.archive.org/web/20240623213756/https://evolution.berkeley.edu/what-are-evograms/jaws-to-ears-in-the-ancestors-of-mammals/ |archive-date=June 23, 2024 |website=Understanding Evolution (UE)}}</ref> Like some other cynodonts, ''Probainognathus'' possessed a double jaw joint, as indicated by a socket (glenoid) in the [[squamosal bone]]. Romer (1970) interpreted this socket as articulating with the dentary bone of the lower jaw, as seen in modern mammals and early [[mammaliaform]]s like ''[[Morganucodon]]''.<ref name="Romer1970"/> Later studies have reinterpreted the socket as articulating with the [[surangular]], one of the postdentary bones, instead of the dentary.<ref name="Crompton1972">{{cite journal |last1=Crompton |first1=A. W. |last2=Joysey |first2=K. A. |last3=Kemp |first3=T. S. |title=The evolution of the jaw articulation of cynodonts |journal=Studies in Vertebrate Evolution |date=1972 |pages=231–251 |url=https://www.researchgate.net/publication/275345018}}</ref> Once the dentary-squamosal articulation became established, the former bones involved in jaw articulation, the articular and quadrate, could become integrated into the [[inner ear]] as the [[malleus]] and [[incus]], respectively.<ref name="Romer1970"/>  This had not yet happened in the case of ''Probainognathus'', but the reduced size of the quadrate, as well as its loose association with the squamosal and proximity to the stapes indicates the quadrate to incus process was underway.<ref name="Colbert1991"/>

The jaw of ''Probainognathus'' is suggested to have had mammal-like [[soft tissue]] features. The jaw muscles in ''Probainognathus'' are thought to have been positioned farther forward, with the [[masseter]] splitting into two separate muscles: the superficial masseter and the deep masseter.<ref name="Ridley">{{cite web|url=https://www.blackwellpublishing.com/ridley/tutorials/Fossils_and_the_history_of_life25.asp|title=Fossils and the history of life - How did mammals evolve?|website=Blackwell Publishing|archive-url=https://web.archive.org/web/20231007055056/https://www.blackwellpublishing.com/ridley/tutorials/Fossils_and_the_history_of_life25.asp|archive-date=October 7, 2023|url-status=live}}</ref><ref name="Bard">{{cite book|author=Jonathan Bard|year=2016|title=Principles of evolution: System, species, and the history of life|publisher=Garland Science, Taylor & Francis Group|page=92|isbn=9781351854771}}</ref>