A nearly complete skull discovered in Arizona decades ago has provided paleontologists with their clearest insight into Adelphyllus cansensis, a mysterious feline species that roamed North America over 5 million years ago. This animal represents an early branch of the saber-toothed cat lineage.

Adelphyllus cansensis is an early feline of the order Machairodontia, inhabiting North America approximately 7 to 5 million years ago.

The species was first described in 1934, based on a jaw fragment discovered in Kansas.

Since then, additional fossils were suspected to belong to Adelphyllus cansensis, but the anatomy remained poorly understood until now.

Paleontologists Narimane Chater and Z. Jack Tseng from the University of California, Berkeley stated, “Felids of the order Machairodontia, such as Adelphyllus cansensis, were approximately the size of modern pumas and were originally described from late Hemphirian (late Miocene) deposits at the Edson Quarry, Kansas.”

“The holotype consists of the left and right maxilla bones with nearly complete dentition.”

“Since then, additional materials have been referenced for this species.”

“In 1983, paleontologists identified postcranial remains from fauna in the Wikiup area (Mojave County, Arizona), housed at the American Museum of Natural History, yet did not describe the complete fossil set from the area, which included a nearly complete skull with canine teeth and jaw fragments.”

In their recent study, Chater and Tseng thoroughly examined the material from the American Museum of Natural History.

The specimen includes a nearly complete skull, adjacent jaw fragments, and an isolated upper canine tooth.

According to their findings, the skull belonged to a feline about the size of a cougar but displayed several traits indicative of later saber-toothed predators.

The upper canines were flat and serrated, but significantly less pronounced than those of well-known saber-toothed species like Smilodon.

“The upper canine teeth of the ancestral species of saber-tooths were short; Adelphyllus cansensis confirms our theory that once these hypercarnivores began evolving longer fangs, they could not revert to shorter forms,” the researchers explained.

The animal’s narrow snout closely resembles that of Metailurus, the earliest saber-toothed cat known from Eurasia, although its rounded skull outline is more akin to that of Yoshi, another primitive saber-toothed genus.

However, Adelphyllus cansensis differs from them with its exceptionally thin cheekbones and distinct dental features.

“We’ve never encountered a lineage where long upper canine teeth developed and then reverted to a less specialized form. Once a group forms, their adaptations accelerate and lead to extinction,” Dr. Chater noted.

“Saber-toothed carnivores exemplify a macroevolutionary ratchet, where specialized forms evolve for efficiency. When environmental changes make these adaptations less effective, extinction becomes more likely.”

This analysis also highlights numerous taxonomic issues, with some fossils previously assigned to Shudaelrus now being categorized under Adelphyllus cansensis, a comprehensive group of primitive felid fossils.

“Shudaellus is regarded as a genus of average-sized Miocene felines, previously dubbed the ‘trash can genus,'” the scientists remarked.

The research findings contribute to a broader understanding of the origin and early diversification of saber-toothed cats.

During the late Miocene, carnivores migrated between Eurasia and North America via the Bering Land Bridge.

The authors propose that Adelphyllus cansensis suggests a separate migration of primitive saber-toothed cats into North America, distinct from the dispersal of early felids.

“While we have not fully determined the timing and number of dispersal events in the North American fossil record, our review indicates that the Adelphyllus cansensis skull material exhibits an intermediate morphology between Yoshi and Metailurus,” they concluded. “This suggests a placement near the base of macrodontid diversification.”

The team’s paper has been published in the Journal of Vertebrate Paleontology.

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Narimane Chatter & Z. Jack Tseng. New material of Adelphyllus cansensis shedding light on the cranial anatomy of early-diverging felids of the order Machairodontales. Journal of Vertebrate Paleontology, published online June 19, 2026. doi: 10.1080/02724634.2026.2667939