[MM] Kuehneotherium praecursoris
’Symmetrodontans’
DESCRIBER Kermack, Kermack & Mussett, 1968
TIME Triassic Late Jurassic Early
Norian Rhaetian Hettangian Sinemurian
CLASS Mammalia
ORDER Incertae Sedis
FAMILY Kuehneotheriidae
FOSSILSITE Dutchy and Pant Quarries, Pontalum, Ewenny, Wales, Britain
INFO
Kuehneotherium praecursoris (Kermack, Kermack & Mussett, 1968) > Kuehneotherium sp.
Type species by monotype.
Gill, P. (2006) Kuehneotherium: Enigmatic stem mammal from the Mesozoic fissures of South Wales. JVP 26(3) Abstracts pp.67-68
The Late Triassic- Early Jurassic Kuehneotherium is one of the earliest known mammals but, in spite of its importance to mammalian phylogeny, it has not previously been fully described due to the fragmentary nature of the material. The largest collections are from fissure deposits in South Wales, comprising approximately 1,000 isolated teeth and jaws.
The dentition of Kuehneotherium praecursoris is reconstructed, with representative teeth for each locus. The lower dental formula is 5? 1. 6. 6. and the upper formula is assumed to be similar. There is unexpected taxonomic diversity in the Welsh fissure samples and two new species are proposed. Kuehneotherium is fully diphyodont, with differentiated premolars and molars and a consistent alveolar row. There is evidence that this had been only recently established, including a suppressed third replacement wave and continuum of form between the deciduous premolars and mesial molars.
Initial uncertainty in reconstructing the dentition centred on a number of small plesiomorphic molars, some of which are similar to the teeth of a derived cynodont, with less crown triangulation and incompletely divided roots. These teeth are the postcanines of a different kuehneotheriid and in one fissure there is continuity of form between them and Kuehneotherium.
Conservatism in the form of the dentary but wide variation in molar crown triangulation suggests that the latter may have evolved more than once. The molar occlusion is reinterpreted to argue that effective shearing occurs without crown remodelling. The wear seen on the more plesiomorphic kuehneotheriid molars is compared with that on molars of Kuehneotherium suggests that improvements in shearing efficiency may have driven selection for divided roots and a less bulbous crown.
A cladistic analysis places Kuehneotherium within the mammalian crown group which would support to the possibility that both the molar cusp triangulation and the separation of the middle ear from the dentary are homoplastic.