Yesterday we looked at the origin of taeniodonts, like Stylinodon. and found it nested with Mustela the mink and Phoca the seal. Other workers (Lillegraven 1969, Rook and Hunter 2013) indicated that Cimolestes (Fig.1, Late Cretaceous) was a suitable ancestor to the taeniodonts. So, let’s look at Cimolestes and compare it to related taxa.
Figure 1. Cimolestes mandible from Lillegraven 1969 compared to a phylogenetically basal eutherian the marsupial without a pouch, Monodelphis, the basal tenrec, Maelestes and Cimolestes. All have a slender mandible without the anterior depth found in Stylinodon, Mustela and Martes in figure 2.
In comparison
Cimolestes is more like the basal marsupials Monodelphis and Maeilestes (Fig. 1) in having a rather slender mandible with incisors anterior to the canines. By contrast, the carnivores Martes, the martin, and Mustela (Fig. 2), and the taeniodonts, Wortmania (Fig. 3) and Stylinodon have a robust mandible, deep anteriorly with canines to the anterior and incisors between them.
Figure 2. Martes, the extant martin, and Mustela, the extant mink or polecat mandibles. Both are deeper in front, more like the taeniodont, Stylinodon. Note the number of teeth varies among these closely related taxa.
Lillegraven 1969 wrote: “A smaller carnivorous species described as new of Cimolestes probably represents a primitive stage in the development of miacids, and subsequently fissiped and pinniped carnivores.” Well, we’re all in the same ballpark and thinking along similar lines. Not sure where Cimolestes nests in the LRT yet. Not much is known of it, other than jaw fragments.
Figure 6. Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.
References
Lillegraven JA 1969. Latest Cretaceous mammals of upper part of Edmonton formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution. Article 50 (Vertebrata 12) The U. of Kansas Paleontological Contributions. 122pp.
Rook DL and Hunter JP 2013. rooting around the eutherian family tree: the origin and relations of the Taeniodonta. Journal of Mammal Evolution. DOI 10.1007/s10914-013-9230-9
The Pterosaur Heresies 
The following paper split Cimolestes in four:
Fox RC. 2015. A revision of the Late Cretaceous–Paleocene eutherian mammal Cimolestes Marsh, 1889. Canadian Journal of Earth Sciences 52(12): 1137–1149. DOI 10.1139/cjes-2015-0113
Specifically, the abstract states that “this paper limits Cimolestes to Cimolestes incisus Marsh and Cimolestes stirtoni Clemens; Cimolestes magnus Clemens and Russell, Cimolestes cerberoides Lillegraven, and Cimolestes propalaeoryctes Lillegraven are reclassified in the new genera Altacreodus, Ambilestes, and Scollardius, respectively. Altacreodus magnus, having a massive shearing dentition, is reconfirmed as showing a relationship to some Tertiary ‘creodonts’ not shared by other species of Lancian cimolestids; Ambilestes cerberoides exhibits a distinctive molar wear pattern that emphasized horizontal grinding, not orthal shear; Scollardius propalaeoryctes, the smallest species in this revision and having hyper-faunivorous molars, was not ancestral to Paleogene Palaeoryctidae, as indicated in part by contradictions in premolar number and morphology.”
There’s no phylogenetic analysis; Cimolestidae is maintained, but its monophyly isn’t tested or otherwise investigated. The discussion includes a warning that the “Cimolestes” included in recent phylogenetic analyses is a chimera.
The one that has been connected to Taeniodonta is Ambilestes, which is from the same formation and age as the much later discovered Schowalteria, the Cretaceous stylinodontid taeniodont.
Altacreodus has been connected to “creodonts”, which is funny because there’s no evidence that Hyaenodontidae and Oxyaenidae are sister-groups or close relatives at all. Ambilestes has been connected to Carnivora, but Fox (2015) provided good reasons to doubt that.
Holy mackerel! Thanks for sharing!