Boreosphenida

Right upper molar of Kielantherium gobiensis in (a) occlusal, (b) anterior and (c) labial views, from Lopatin & Averianov (2006).

Belongs within: Trechnotheria.
Contains: Metatheria, Eutheria.

The Boreosphenida is the clade uniting modern marsupials and placentals with their immediate fossil relatives sharing ancestrally tribosphenic molars (with three cusps).

Synapomorphies (from Rougier et al. 1998): Protocone small with distinct trigon basin (inferred from talonid); lower molar talonid with multicuspidated basin.

<==Boreosphenida
    |  i. s.: Tribactonodon VG09
    |         Kermackia FP99
    |--Kielantherium gobiensis LC07, WR07
    `--+--Aegialodon LC07
       |--Potamolestes RWN98
       `--+--Slaughteria RWN98
          `--+--Pappotherium FP99
             `--Theria [Creophaga, Deltatheridia, Deltatheridioidea, Insectivora, Palaeoryctoidea, Sarcobora] WR07
                  |  i. s.: Chronozoon DeVis 1883 LA02
                  |           `--*C. australe DeVis 1883 LA02
                  |         Mixodectidae S35
                  |           |--Mixodectes S35
                  |           `--Eudaemonema Simpson 1935 S35
                  |                `--*E. cuspidata Simpson 1935 S35
                  |         Vulpavoides Matthes 1952 V66
                  |         Ziphacodon Marsh 1872 (n. d.) V66
                  |         Aethechinus algirus JP84
                  |         Miothen Cope 1873 M60
                  |           |--*M. crassigenus Cope 1873 M60
                  |           `--M. gracile Cope 1873 M60
                  |--Metatheria WR07
                  `--Eutheria WR07

*Type species of generic name indicated

REFERENCES

[FP99] Flynn, J. J., J. M. Parrish, B. Rakotosamimanana, W. F. Simpson & A. R. Wyss. 1999. A Middle Jurassic mammal from Madagascar. Nature 401: 57-60.

[JP84] Jolicoeur, P., P. Pirlot, G. Baron & H. Stephan. 1984. Brain structure and correlation patterns in Insectivora, Chiroptera, and Primates. Systematic Zoology 33 (1): 14-29.

[LA02] Long, J., M. Archer, T. Flannery & S. Hand. 2002. Prehistoric Mammals of Australia and New Guinea: One Hundred Million Years of Evolution. University of New South Wales Press: Sydney.

Lopatin, A. V., & A. O. Averianov. 2006. An aegialodontid upper molar and the evolution of mammal dentition. Science 313: 1092.

[LC07] Luo, Z.-X., P. Chen, G. Li & M. Chen. 2007. A new eutriconodont mammal and evolutionary development in early mammals. Nature 446: 288-293.

[M60] McKenna, M. C. 1960. The Geolabidinae: a new subfamily of early Cenozoic erinaceoid insectivores. University of California Publications in Geological Sciences 37 (2): 131-164.

[RWN98] Rougier, G. W., J. R. Wible & M. J. Novacek. 1998. Implications of Deltatheridium specimens for early marsupial history. Nature 396: 459-463.

[S35] Simpson, G. G. 1935. New Paleocene mammals from the Fort Union of Montana. Proceedings of the United States National Museum 83 (2981): 221-244.

[V66] Van Valen, L. 1966. Deltatheridia, a new order of mammals. Bulletin of the American Museum of Natural History 132 (1): 1-126.

[VG09] Vullo, R., E. Gheerbrant, C. De Muizon & D. Néraudeau. 2009. The oldest modern therian mammal from Europe and its bearing on stem marsupial paleobiogeography. Proceedings of the National Academy of Sciences of the USA 106 (47): 19910-19915.

[WR07] Wible, J. R., G. W. Rougier, M. J. Novacek & R. J. Asher. 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature 447: 1003-1006.