The Triassic eucynodont Candelariodon barberenai revisited and the early diversity of stem prozostrodontians

Abstract

Ladinian-early Carnian) of south Brazil, is redescribed. Candelariodon was originally classified as Eucynodontia incertae sedis and our analysis recovered this taxon deeply nested within Probainognathia, as the sister taxon of Potheriodon plus Prozostrodontia. The lower postcanine dentition of Candelariodon has several apomorphies shared with Prozostrodon, Santacruzgnathus, Brasilodon/Brasilitherium, and some basal mammaliaforms (Morganucodon, Megazostrodon), such as a lingual cingulum with discrete cusps e and g and two distinct morphologies in the tooth row. The reinterpretation of Candelariodon as a probainognatian cynodont more derived than Probainognathus and the rich Brazilian fossil record document an important adaptive radiation of non-mammaliaform prozostrodontians and closely related forms prior to the origin of the mammaliaform clade.

Disconnecting bones within the jaw‐otic network modules underlies mammalian middle ear evolution

“…In fact, the only mandibular feature to classify Kayentatherium in S1 is its reversion to the reptilian quadrate‐articular jaw joint (Sues, ), trait of focus of many discussions about the origin of mammals (Carroll, , pp. 388–392; Luo, ; Bonaparte et al., ; Liu & Olsen, ; Martinelli et al., ; Bonaparte & Crompton, ).…”

“…To map the evolution of modularity patterns on the phylogeny, we assembled a tree for the 43 taxa studied, following consensus phylogenies for the Synapsida crown group (Rubidge & Sidor, ; Sidor, ), basal synapsids (Spindler, ; Brocklehurst et al., ), non‐mammalian therapsids (Fröbisch & Reisz, ; Huttenlocker et al., ; Kammerer, , , ; Huttenlocker & Smith, ), non‐mammalian cynodonts (Martinelli & Soares, ; Martinelli et al., ) and mammals (Luo, ; O'Leary et al., ; Bi et al., ; Benton et al., ; Han et al., ). We built the phylogenetic tree using R packages ape (Paradis et al., ), phytools (Revell, ), paleotree (Bapst, ) and strap (Bell & Lloyd, ), using the time data reported in the Paleobiology Database (Peters & McClennen, ), Fossil Calibration Database (Ksepka et al., ) and the International Chronostratigraphic Chart (v2017/02) of the International Commission on Stratigraphy (Cohen et al., ) for calibration (see for more details about the building of the phylogenetic tree).…”

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

“…Probainognathian cynodonts, the clade which include the crown Mammalia (e.g., [22–23]), have an extremely conspicuous fossil record in South America, represented by chiniquodontids (e.g., Chiniquodon theotonicus , Aleodon cromptoni ), ecteniniids (e.g., Ecteninion lunensis , Trucidocynodon riograndensis ), probainognathids ( Probainognathus jenseni , Bonacynodon schultzi ), ictidosaurians (e.g., Riograndia guaibensis plus tritheledontids) and other prozostrodontians (e.g., Prozostrodon brasiliensis , Therioherpeton cargnini , Brasilodon quadrangularis ). Although the relevant phylogenetic position of Brasilodon quadrangularis as sister taxon of Mammaliaformes (e.g., [5, 7, 24–26]), many aspects of its postcranial anatomy remain unclear. Some postcranial elements were briefly described and/or mentioned by Bonaparte et al [5, 27], but in-depth studies were never developed.…”

Dinossauromorfos triássicos do sul do Brasil e padrões biogeográficos da irradiação dos dinossauros

“…In general aspect, MCN-PV 10202 and MCN-PV 10203 resemble more Brasilitherium riograndensis and Brasilodon quadrangularis than any other known probainognathians from South America (e.g., Bonaparte and Barberena, 2001;Martinelli et al 2017a, b). They differ from the postcanine teeth of Alemoatherium huebneri because these lack a mesiolabial accessory cusp, their lingual cusps and cingulum are much less developed and cusp "d" is slightly smaller and lower positioned than cusp "b" (Martinelli et al 2017a).…”

“…riograndensis and Brasilo. quadrangularis (Bonaparte et al 2003(Bonaparte et al , 2005Martinelli et al 2017a, b). Accordingly, although MCN-PV 10202 and MCN-PV 10203 clearly represent derived prozostrodontians closely related to the "brasilodontids" from the Riograndia AZ, the differences in their dentition better indicate a new, still poorly sampled taxon, the biostratigraphical significance of which it is still unknown.…”