The European species are among the earliest known members of the Thaumastocyoninae, a group of aberrant amphicyonids showcasing hypercarnivorous adations, but are only known from fragmentary remains.

However, Ginsburg disagreed with this assignment, and erected the genus Ysengrinia in 1965, with Y. gerandiana, previously referred to Pseudocyon, serving as its type species.

The following year, he also moved the species Amphicyon tolosanus and Pseudocyon depereti to Ysengrinia, an arrangement generally followed by later authors, although Bonis (1973) suggested that Y. gerandiana might be synonymous with Y.

[3] However, newer studies have recognized the distinct anatomical differences between this taxon and the type species Y. gerandiana, resulting in the creation of the separate genus Namibiocyon for the amphicyonid from Arrisdrift.

[5][6] Heizmann and Kordikova erected the tribe Ysengrini in 2000, in which they included not only Ysengrinia, but also Crassidia and Amphiyconopsis, and which they considered to be in an intermediary position between the Amphicyoninae and Thaumastocyoninae.

The authors also point out that Y. americana has notable differences in the upper dentition compared to the rest of the genus, and displays a morphotype less adapted to hypercarnivory.

The authors suggest that Y. gerandia and Y. valentiana both belong to the Thaumastocyoninae, while Y. americana may either be the sister taxon of that subfamily, or be more closely related to Amphicyonines.

The first fossils belonging to this species, a palate with nearly complete dentition, an upper canine and a calcaneum, were discovered by H.C. Clifford in 1875, and used as holotype for the description of "Amphicyon" americanus by Wortman in 1901.

It shows transitional features between Peignecyon and Thaumastocyon, though the fragmentary nature of its remains makes concluding the closer relationship of this taxon impossible.

The presence of a deep masseteric fossa bordered by thickened ventral and anterior margins indicates that a considerable force was developed during the occlusion of the carnassials and molars.

Overall, these characteristics indicate that Ysengrinia lacked any cursorial adaptations and was an ambush hunter similar to big cats, relying on short bursts of speed to catch its prey, which was then disposed of with help of its powerful forelimbs and large canines.

[18][19][20] Their emergence is linked to the turnover of Europe's carnivores around MP 26 (~26.5 Ma), that saw the diversification of amphicyonids, and the emergence of the first large members of the family; as well as the Microbunodon event, which took place during MP 28 (24.8-24 Ma), and saw a huge faunal turnover of 40% of the European ungulate fauna within 500k years, correlated with a major arrival of Asian immigrants.

Ysengrinia coexisted with this smaller taxon, the medium-sized amphicyonids Cynelos and Brachycyon, as well as Hyaenodon, which seems to have been less affected by the environmental changes than the carnivorans.

However, despite their apparent adaptations towards more open environments, the late Oligocene ultimately saw the local extinction of hyaenodonts, and the continuing diversification of amphicyonids, indicating that the latter benefitted from the environmental and faunal changes.

[22] In North America, the temnocyonine amphicyonids were the only large-sized carnivorans present during the Oligocene-Miocene boundary, after the local extinction of both nimravids and hyaenodonts.

However, in the earliest Miocene, tectonic activities in Asia led to a dispersal event of Eurasian species into North America that lasted from circa 23 to 15.5 Ma, from the late Arikareean to the Hemingfordian.

[23] Ysengrinia americana, which was considerably larger than even the largest temnocyonines, was among the earliest of these immigrants, first appearing around 23 Ma, alongside another amphicyonid, Cynelos, the chalicothere Moropus, the rhinoceros Menoceras and the ursid Cephalogale.

Most of these belong to either Daphoenodon superbus, or the rarer Delotrochanter oryktes, a temnocyonine showcasing adaptions towards both durophagy and cursoriality, both of which were found in the remnants of their dens.

Ysengrinia, however, is absent from the dens, likely as a result of its large size, and only found at the waterhole, where Moropus, Menoceras and the huge, omnivorous Daeodon are the most common taxa.

[1][32] A partially preserved maxilla and isolated teeth of Ysengrinia, resembling Y. americana, have also been reported from the Xiejahe Fauna of China, which is part of the Shanwang Formation, and dates to circa 18 Ma.