Editing Probainognathus (section)

== Description==
''Probainognathus'' was a small cynodont, the apparent body size of which is inconsistent across sources, ranging from being about the size of a rat, to the size of a small dog.<ref name="Romer1970"/><ref name="Bone clones">{{cite web |title=Cynodont - ''Probainognathus jenseni'' Skull |url=https://boneclones.com/product/cynodont-probainognathus-jenseni-skull-CD-01 |url-status=live |archive-url=https://web.archive.org/web/20240828151939/https://boneclones.com/product/cynodont-probainognathus-jenseni-skull-CD-01 |archive-date=August 28, 2024 |website=Bone Clones, Inc. - Osteological Reproductions}}</ref><ref name="Wayback">{{cite web |title=Triassic Cynodonts; Cynognathidae, Probainognathidae and 'Allies', an Internet Directory |url=https://home.arcor.de/ktdykes/cynoga.htm |url-status=dead |archive-url=https://web.archive.org/web/20161005003204/https://home.arcor.de/ktdykes/.suspend.shtml |archive-date=October 5, 2016 |website=Home.arcor}}</ref>

=== Teeth and diet ===
[[File:Probainognathus jenseni teeth.jpg|thumb|right|Dentition of ''Probainognathus jenseni'']]
The diet of ''Probainognathus'' is thought to have been [[carnivorous]] or [[insectivorous]], which can be extrapolated from its teeth.<ref name="Romer1970"/><ref name="Martinelli2016" /> The teeth included dully-tipped, partially developed canines, postcanines, four upper incisors that were positioned vertically, and three lower [[incisors]] that leaned slightly forward.<ref name="Sciencepress">{{cite journal |author=Soares, Marina Bento, Fernando Abdala, Cristina Bertoni-Machado |year=2011 |title=A Sectorial Toothed Cynodont (Therapsida) from the Triassic Santa Cruz Do Sul Fauna, Santa Maria Formation, Southern Brazil |url=https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/g2011n2a4.pdf |journal=Geodiversitas |volume=33 |issue=2 |page=265-278 |doi=10.5252/g2011n2a4 |s2cid=129635627}}</ref> The [[cheek teeth]] were slender from the sides, but were lengthened anteroposteriorly, with several cusps along the row.<ref name="Romer1970"/>

=== Brain ===
Based on an endocranial cast of ''Probainognathus'', several details have been extrapolated about its brain. ''Probainognathus''’ cerebral hemispheres were elongated, it had established olfactory bulbs, and a significant cerebellum and flocculi.<ref name="Quiroga">{{cite journal |last1=Quiroga |first1=JC |title=The brain of the mammal-like reptile Probainognathus jenseni (Therapsida, Cynodontia). A correlative paleo-neoneurological approach to the neocortex at the reptile-mammal transition |journal=Journal für Hirnforschung |date=1980 |volume=21 |issue=3 |pages=299–336 |pmid=7419907 }}</ref> These were among other, less pronounced, structures such as anterior colliculi.<ref name="Quiroga"/> Because of these features, it has been suggested that ''Probainognathus''’ brain had well-developed visual, auditory, motor, and body sensory systems. And, as a whole, the brain of ''Probainognathus'' indicates that it was in the process of developing endothermy.<ref name="Quiroga"/>

=== Skull ===
[[File:Probainognathus Skull in Palatal View.jpg|thumb|Illustration of the skull in palatal view]]

The snout of ''Probainognathus'' extended beyond the [[premaxillary]] processes, and was very thin. The apparent fragility of this structure has led to it being broken off several specimens, and has led to an increased difficulty in studying it.<ref name="Romer1970"/> There are several features that have been identified, however. The suborbital arch and the [[zygomatic arch]] were both shaped relatively sharply, and there was an extension of the squamosal posteriorly on the zygomatic arch. ''Probainognathus'' had a long [[secondary palate]] as it stretched all the way to the posterior end of the tooth row.<ref name="Romer1970"/> The secondary palate was formed largely by the palatine, and it was somewhat narrow. This narrowing of the [[palate]] allowed for the conservation of space to be able to fit the back, lower postcanine teeth. Moreover, the [[vomer]] stretched posteriorly to the secondary palate, and significant [[pterygoid bone|pterygoid]] flanges were present, as well.<ref name="Romer1970"/>

The skull of ''Probainognathus'' was on average around {{Convert|7|cm|in}} in length, and lacked the [[pineal foramen]].<ref name="Romer1970"/> The skull was broad in proportion to its length, the face was short and narrow, but its zygomatic region was relatively large, seemingly for jaw muscle attachment.<ref name="Romer1970"/> The skull also possessed a double occipital condyle, which is a typical mammalian feature.<ref name="Colbert1991">Colbert, E., & Morales, Michael. (1991). Evolution of the vertebrates : A history of the backboned animals through time (4th ed.). New York: Wiley-Liss.</ref> In comparison to close relatives, such as ''[[Chiniquodon]]'', the [[braincase]] of ''Probainognathus'' was broader in the [[Parietal bone|parietal]] region, and the occipital region of the skull was deeper. Likewise, the parietals had more depth, the [[occipital]] crest was higher, and the orbits were proportionately larger relative to the rest of its head. The [[sagittal crest]] was also lengthened posteriorly, and split into the occipital crests. This led to a straighter posterior margin, and a more concave occiput in ''Probainognathus''.<ref name="Romer1970"/>

=== 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>