Updated July 11, 2022
with new data on Notostylops.
This used to be big news,
when a taxon no longer nested in a traditional clade and moved to another. But with the breakup of the Notoungulata, this has become commonplace for former members of this clade and I expect the trend to continue.
in the large reptile tree (LRT) Notostylops murinis (Ameghino 1897, Riggs and Patterson 1935; 75cm in estimated length; Eocene; FMNH-P13319) nests with the Vombatus, the extant wombat (Fig. 2). In Notostylops, the anterior incisors were enlarged, but the anterior jaws narrowed, so the incisors became close together, like those of rodents. The mandible itself was more robust. No canines were present. Five molars were present.
Of course all this is
based in the literature, not firsthand observation of the pertinent specimens. I encourage others to test these taxa to confirm these hypothetical interrelationships.
I became aware of Notostylops
after reading Billet (2010), who wrote: “Intriguing similarities are also detected in the anterior dentition of Pyrotherium and the Casamayoran notoungulate Notostylops. These resemblances suggest a unique relationship between Pyrotheria and Notoungulata, specifically between Pyrotheria and Notostylops.” The LRT confirms that relationship. Both are derived marsupials.
Ameghino F 1897. Mamiferos Cretaceos de la Argentina – Boletin Instituto Geografico Argentino 18:406-521.
Billet G. 2010. New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates. Journal of Mammal Evolution. 17:21-59.
Riggs ES and Patterson B 1935. Description of some notoungulates from the Casamayor (“Notostylops) beds of Patagonia. Proceedings of the American Philosophical Socity 75(2):163-215.