Armbruster's wolf (''Canis armbrusteri'' or ''Aenocyon armbrusteri'') is an extinct

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

canine Canine may refer to: Zoology and anatomy * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...

that was endemic to

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

and lived during the

Middle Pleistocene The Chibanian, more widely known as the Middle Pleistocene (its previous informal name), is an Age (geology), age in the international geologic timescale or a Stage (stratigraphy), stage in chronostratigraphy, being a division of the Pleistocen ...

epoch. It is proposed as the ancestor of the

dire wolf The dire wolf (''Aenocyon dirus'' ) is an Extinction, extinct species of Caninae, canine which was native to the Americas during the Late Pleistocene and Early Holocene epochs (125,000–10,000 years ago). The species was named in 1858, four y ...

, one of the most famous prehistoric carnivores in North America, and possibly a member of the same genus ''Aenocyon''.

Taxonomy

''Canis armbrusteri'' was named by James W. Gidley in 1913. It appeared in North America in the

, and is a wolf-like form larger than any ''Canis'' at that time. The first fossils were uncovered at

Cumberland Bone Cave The Cumberland Bone Cave is a fossil-filled cave along the western slope of Wills Mountain on the outskirts of Cumberland, Maryland near Corriganville in Allegany County, Maryland. History and paleontology In 1912 workers excavating a cut for th ...

, Maryland, in an Irvingtonian terrestrial horizon. Fossil distribution is widespread throughout the United States. All specimens are known from around the latest early

Irvingtonian The Irvingtonian North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), spanning from 1.8 million – 250,000 years Before Present, BP.

to the early

Rancholabrean The Rancholabrean North American Land Mammal Age on the geologic timescale is a North American faunal stage in the North American Land Mammal Ages chronology (NALMA),Sanders, A.E., R.E. Weems, and L.B. Albright III (2009) Formalization of the mid- ...

stages (

epoch). In the Middle Pleistocene of North America, wolf species became larger, with some studies concluding that '' C. priscolatrans'' diverged into the large wolf ''C. armbrusteri'' based on tooth specimens. R. A. Martin disagreed, and believed that ''C. armbrusteri'' was '' C. lupus''. However, Ronald M. Nowak proposed instead that ''C. armbrusteri'' was not related to ''C. lupus'', but ''C. priscolatrans'', positing that this then gave rise to ''C. dirus''. Richard H. Tedford, on the other hand, suggested that the South American '' C. gezi'' and '' C. nehringi'' share dental and cranial similarities developed for hypercarnivory, suggesting ''C. armbrusteri'' was the common ancestor of ''C. gezi'', ''C. nehringi'' and ''C. dirus''. Based on morphology from China, the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58X. Wang, R. H. Tedford and R. M. Nowak have all proposed that ''C. dirus'' had evolved from ''C. armbrusteri'', with Nowak stating that there were specimens from Cumberland Cave, Maryland that indicated ''C. armbrusteri'' diverged into ''C. dirus''. The two taxa share a number of characteristics (

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

), suggesting an origin of ''C. dirus'' in the late

around central America in open terrain habitats, with later eastward expansion and displacement of ''C. armbrusteri''. In 2021, researchers sequenced the nuclear DNA (from the cell nucleus) of the

. The sequences indicate the dire wolf to be a highly divergent lineage which last shared a most recent common ancestor with the wolf-like canines 5.7 million years ago, with morphological similarity to the grey wolf being a result of convergent evolution. The study's findings are consistent with the previously proposed taxonomic classification of the dire wolf as genus ''Aenocyon''. The study proposes an early origin of the dire wolf lineage in the Americas, and that this geographic isolation also resulted in reproductive isolation, driving their divergence 5.7 million years ago. Concurrently, Coyotes, dholes, gray wolves, and the extinct ''

Xenocyon ''Xenocyon'' ("strange dog") is an extinct group of canids, either considered a distinct genus or a subgenus of ''Canis''. The group includes ''Canis'' (''Xenocyon'') ''africanus'', ''Canis'' (''Xenocyon'') ''antonii'' and ''Canis'' (''Xenocyon'') ...

'' ostensibly evolved in Eurasia and expanded into North America more recently, during the Late Pleistocene, and did not experience admixture with the dire wolf. This long-term isolation of the dire wolf lineage implies that other American fossil canines, including ''C. armbrusteri'' and '' C. edwardii'', may belong to the same lineage as ''Aenocyon''. Ruiz-Ramoni et al. (2022) proposed that the Armbruster's wolf should be given a new genus name, possibly included within the genus ''Aenocyon'', as it was probably ancestral to the dire wolf and its assignment within the genus ''Canis'' is not well-founded. This was also considered plausible by other authors. In their revision of the Pleistocene assemblage from the

, Eshelman et al. (2025) proposed the new combination of the Armbruster's wolf within the genus ''Aenocyon'' (''A. armbrusteri''), which would expand the earliest known occurrence of this genus up to the

References

{{Taxonbar, from=Q3884275 Extinct wolves Prehistoric canines Pleistocene carnivorans Prehistoric mammals of North America Irvingtonian Fossil taxa described in 1913