Structure of the nasal region of non-mammalian cynodonts and mammaliaforms: Speculations on the evolution of mammalian endothermy

Novel Endocranial Data on the Early Therocephalian Lycosuchus vanderrieti Underpin High Character Variability in Early Theriodont Evolution

“…These ridges probably would have stretched along the entire ventral surface of the nasals, although this cannot be seen in this specimen due to damage (Figure 9). These ridges may have served as attachment points for cartilaginous nasal turbinals, as has been described for several therapsids in recent years (e.g., Kemp, 1979;Hillenius, 1994;Crompton et al, 2015Crompton et al, , 2017Bendel et al, 2018;Pusch et al, 2019). In therocephalians in particular, cartilaginous turbinals attaching to the nasals have been proposed for the basal taxon Glanosuchus macrops (Hillenius, 1994;van den Heever, 1994), akidnognathids (Sigurdsen, 2006), and for the baurioid Tetracynodon darti (Sigurdsen et al, 2012).…”

“…In the context of mammalian origins, these novel endocranial data have been instrumental in elucidating patterns of brain and ear evolution, facial innervation, and the evolution of endothermy in non-mammalian therapsids (e.g., Rodrigues et al, 2013Rodrigues et al, , 2014Crompton et al, 2015Crompton et al, , 2017Laaß, 2015aLaaß, ,b, 2016Benoit et al, 2016aBenoit et al, ,b, 2017aBenoit et al, ,b,c, 2018Benoit et al, , 2019Araújo et al, 2017Araújo et al, , 2018Bendel et al, 2018;Pusch et al, 2019). As the therapsid clade ancestral to (and including) modern mammals, Cynodontia has been the primary focus for CTassisted morphological studies in Synapsida (e.g., Rowe et al, 1993;Rodrigues et al, 2013Rodrigues et al, , 2014Crompton et al, 2015Crompton et al, , 2017Benoit et al, 2016aBenoit et al, , 2019Pavanatto et al, 2019;Pusch et al, 2019). By contrast, Therocephalia, generally considered the sister-group of Cynodontia (e.g., Hopson and Barghusen, 1986;Hopson, 1991;Huttenlocker, 2009;Huttenlocker and Sidor, 2016;Huttenlocker and Smith, 2017; but see Abdala, 2007;Botha et al, 2007), has received little study.…”

Virtual reconstruction of cranial endocasts of traversodontid cynodonts (Eucynodontia: Gomphodontia) from the upper Triassic of Southern Brazil

“…As expected, the general endocast morphology of S. niemeyerorum (CAPPA/UFSM 0227) and E. riograndensis (CAPPA/UFSM 0030 and 0227) is closer to that observed in “reptilian” endocasts than in mammaliaforms and mammals. The poorly ossified orbitosphenoid and a large interorbital vacuity are also observed in Massetognathus pascuali , Exaeretodon argentinus , and Chiniquodon , although in the latter taxon, the orbitosphenoid is ossified (Benoit, Jasinoski, Fernandez, & Abdala, ; Crompton, Owerkowicz, Bhullar, & Musinsky, ; Kemp, ). According to Benoit, Jasinoski, et al (2017), in the traversodontids Massetognathus and Exaeretodon , as in other analyzed Gomphodontia, the orbitosphenoid is a fragile cancellous bone.…”

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

“…Histology finally indicates multiple occurrences of fibrolamellar bone from the early Permian to the Triassic and in various taxa [Botha-Brink et al, 2012;Shelton and Sanders, 2017]. It is nevertheless generally accepted that endothermy originated late in NMT history or even in the earliest mammaliaforms, at a time when fur, mammary glands, the typical mammalian jaw joint, a long secondary palate, and a bone histology similar to that of modern mammals were acquired [Rowe et al, 2011;Ruf et al, 2014;Owerkowicz et al, 2015;Benoit et al 2016a, c;Crompton et al, 2017b]. Before true endothermy appeared, it was probably preceded by an intermediate type of body thermoregulation that characterised NMT only [Roth et al, 1986;Benoit et al 2016a].…”