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Akidolestes cifellii
Temporal range: Early Cretaceous, 122 Ma
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Symmetrodonta
Family: Spalacotheriidae
Genus: Akidolestes
Li & Luo, 2006
Type species
Akidolestes cifellii
Li & Luo, 2006

Akidolestes cifellii is an extinct mammal which dates to the early Cretaceous period, 124.6 million years ago. It is part of the Yixian Formation in Liaoning, China. The description is based on a nearly complete skeleton, partially complete skull, and an impression. It is notable in that it displays characteristics of monotremes but appears to be more related to modern therian mammals.

Akidolestes has no modern relatives. It is an early offshoot of mammal related to therians (the subclass containing marsupials and placentals). It clearly belongs within a group of theriiform mammals known as the Spalacotherioidea. Unlike other members of this superfamily, however, Akidolestes has some very prototherian features.

Cervical ribs are present, a condition previously known only from monotremes and basal mammals such as Repenomamus and Fruitafossor. Akidolestes is also monotreme-like in the shape of its pubis, and in aspects of hindlimb posture. Overall, however, other aspects of the appendicular skeleton, dental characters, and cranial characters strongly suggest that Akidolestes falls well within the Spalacotherioidea and does represent an early branch of theriiform mammal. Luo and Li suggest that these primitive characters were reacquired in this group as a result of either convergence or through a modification of a developmental pathway to a prior state.

The genus name, Akidolestes, is derived from akido, Greek for point, and lestes, Greek for thief. Akido- refers to the pointed snout and -lestes is a common suffix for fossil mammals. The specific epithet, cifelli, is in honor of Richard L. Cifelli, a prominent researcher in prehistoric mammals.


  • Li, Gang; Luo, Zhe-Xi (2006). "A Cretaceous symmetrodont therian with some monotreme-like postcranial features". Nature. 439 (7073): 195–200. doi:10.1038/nature04168. PMID 16407951. 

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