Belongs within: Cimolodonta.
The Ptilodontoidea are a group of multituberculate mammals known from the Upper Cretaceous to the Eocene of Eurasia and North America, characterised by a very large, arcuate lower rear premolar protruding dorsally above the level of the molars (Kielan-Jaworowska & Hurum 2001).
Characters (from Kielan-Jaworowska & Hurum 2001): Dental formula 2.0.4.2/1.0.2.2; enamel usually microprismatic (gigantoprismatic in Cimolodon); I2 probably single-cusped, I3 placed on margin of premaxilla; lower incisor usually gracile, completely covered with enamel (robust with limited enamel band in Neoliotomus); P4 elongated, shaped as isosceles triangle in lateral view, protruding ventrally over level of anterior premolars and molars; p4 very large, arcuate, strongly protruding dorsally over level of molars; molars with ornamentation of grooves and ridges, cusps tending to coalesce. Snout wide, gently incurved in front of zygomatic arches. Frontals small, pointed posteriorly.
<==Ptilodontoidea
|--Cimolodontidae K-JH01
| |--Anconodon Jepsen 1940 K-JH01
| |--Liotomus Cope 1884 K-JH01
| `--Cimolodon Marsh 1889 K-JH01
| `--C. electus K-JH01
`--+--Neoliotomus Jepsen 1930 K-JH01
`--+--Ptilodontidae [Chirogidae] K-JH01
| |--Kimbetohia Simpson 1936 K-JH01
| |--Prochetodon Jepsen 1940 K-JH01
| |--Baiotomeus Krause 1987 SFY02
| | |--B. douglassi (Simpson 1935) SFY02
| | |--B. lamberti Krause 1987 SFY02
| | `--B. russelli Scott, Fox & Youzwyshyn 2002 SFY02
| `--Ptilodus Cope 1881 SFY02
| |--P. douglassi Simpson 1935 S35b
| |--P. fractus Dorr 1952 SFY02
| |--P. gidleyi Simpson 1935 S35b
| |--P. gnomus Scott, Fox & Youzwyshyn 2002 SFY02
| |--P. kummae Krause 1977 SFY02
| |--P. mediaevus Cope 1881 SFY02
| |--P. montanus Douglass 1908 [incl. P. admirabilis Hay 1930, P. gracilis Gidley 1909 (preoc.)] S35b
| |--P. sinclairi Simpson 1935 S35b
| |--P. trovessartianus S35b
| |--P. tsosiensis Sloan 1981 SFY02
| `--P. wyomingensis D07
`--Neoplagiaulacidae K-JH01
|--Xyronomys Rigby 1980 K-JH01
|--Cernaysia Vianey-Liaud 1986 K-JH01
|--Krauseia Vianey-Liaud 1986 K-JH01
|--Mesodma Jepsen 1940 K-JH01
|--Mimetodon Jepsen 1940 K-JH01
|--Mesodmops Tong & Wang 1994 K-JH01
|--Xanclomys Rigby 1980 K-JH01
|--Neoplagiaulax Lemoine 1882 K-JH01
| `--N. hazeni K-JH01
|--Parectypodus Jepsen 1930 K-JH01
| |--P. jepseni Simpson 1935 S35b
| |--P. laytoni K-JH01
| |--P. simpsoni S35b
| `--P. tardus S35b
`--Ectypodus Matthew & Granger 1921 K-JH01
|--*E. musculus Matthew & Granger 1921 S35a
|--E. cochranensis S35b
|--E. grangeri Simpson 1935 S35b
|--E. russelli Simpson 1935 S35b
|--E. silberlingi Simpson 1935 S35b
`--E. tardus K-JH01
*Type species of generic name indicated
REFERENCES
[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.
[K-JH01] Kielan-Jaworowska, Z., & J. H. Hurum. 2001. Phylogeny and systematics of multituberculate mammals. Palaeontology 44 (3): 389–429.
[SFY02] Scott, C. S., R. C. Fox & G. P. Youzwyshyn. 2002. New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada. Acta Palaeontologica Polonica 47: 691–704.
[S35a] Simpson, G. G. 1935a. The Tiffany fauna, Upper Paleocene. I.—Multituberculata, Marsupialia, Insectivora, and ?Chiroptera. American Museum Novitates 795: 1–19.
[S35b] Simpson, G. G. 1935b. New Paleocene mammals from the Fort Union of Montana. Proceedings of the United States National Museum 83 (2981): 221–244.
