Extended Data Fig. 8: Images of jaw joints rendered from CT scans.

Images show jaw joints that are used as the basis for Fig. 4. a, Thrinaxodon (AMNH 5630), exclusive articular–quadrate joint. b, Probainognathus¹¹, articular–quadrate joint with surangular–squamosal contact. Interpretation of the jaw joint of Thrinaxodon and Probainognathus in Fig. 4 also refers to Allin and Hopson²⁵ (Fig. 28.8) and Luo⁷³ (Fig. 3). c, Riograndia⁷ articular–quadrate joint with the dentary–squamosal contact. Interpretation of its jaw joint also refers to Soares et al.⁷⁴, Rodrigues et al.⁷⁵, and Kerber et al.⁷⁶. d, Polistodon (ZDM8601), dentary–jugal joint; its primary joint in Fig. 4 is reconstructed based on tritylodontid specimen (IVPP V14232). e, Dianoconodon²⁸ (IVPP V4257), partial but load-bearing dentary–squamosal jaw joint (PDSJ) with a bulbous dentary condyle and coexisting with a reduced but functional articular–quadrate joint. f, Camurocondylus (IVPP V8685), PDSJ with no expanded dentary condyle; its primary joint in Fig. 4 is reconstructed based on other morganucodontans, including Dianoconodon. g, Feredocodon⁷¹ (IMMNH-PV01925), exclusive dentary–squamosal joint (EDSJ) with postdentary bones remaining long and attached to the dentary but the articular–quadrate joint has completely lost its jaw suspension function. h, Qishou⁷⁷ (JZT-D061), EDSJ for palinal jaw movement. i, Liaoconodon^78,79,80 (IVPP V16051), EDSJ with the ossified Mechel’s cartilage (ONC) bridging the dentary and the detached postdentary bones (middle ear ossicles) in which the anterior processes of the malleus and ectotympanic are long and have substantial overlap with the OMC. j, Origolestes^79,80 (JZD-DB0064), EDSJ with a long OMC that is decoupled from the middle ear ossicles in which the anterior processes of the malleus and ectotympanic are reduced. k, Tachyglossus aculeatus (AMNH teaching specimens, no catalogue number), EDSJ highly specialized and teeth are lost. l, Didelphis (AMNH 137900), EDSJ with medial extension of the dentary condyle, the middle ear ossicles fully suspended at the basicranial region, and a horseshoe shaped ectotympanic. m, Erinaceus (AMNH 57218), EDSJ with the ectotympanic expanded to from the tympanic bulla. All images are original except for b (3D rendering courtesy of Stephan Lautenschlager and DigiMorph.org; https://www.digimorph.org/index.phtml) and c (open-access publication).