Akidolestes
Encyclopedia
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 theria
n mammals.
Akidolestes has no modern relatives. It is an early offshoot of mammal related to therians (the subclass containing marsupial
s 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 prototheria
n features.
Cervical rib
s 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 mammal
s.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
which dates to the early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period, 124.6 million years ago. It is part of the Yixian
Yixian
Yixian may refer to:*Yi County, Anhui, in China*Yi County, Hebei, in China*Yi County, Liaoning, in China*Yixian Formation, a geological formation in Liaoning Province*Empress Yixian, Liang Nüying , Chinese empress during the Han Dynasty...
formation in Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. The description is based on a nearly complete skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
, partially complete skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
, and an impression. It is notable in that it displays characteristics of monotremes but appears to be more related to modern theria
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
n mammals.
Akidolestes has no modern relatives. It is an early offshoot of mammal related to therians (the subclass containing marsupial
Marsupial
Marsupials are an infraclass of mammals, characterized by giving birth to relatively undeveloped young. Close to 70% of the 334 extant species occur in Australia, New Guinea, and nearby islands, with the remaining 100 found in the Americas, primarily in South America, but with thirteen in Central...
s and placentals). It clearly belongs within a group of theriiform mammals known as the Spalacotherioidea. Unlike other members of this superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
, however, Akidolestes has some very prototheria
Prototheria
Prototheria is a taxonomic group, or taxon, to which the order Monotremata belongs. It is conventionally ranked as a subclass within the mammals.Most of the animals in this group are extinct...
n features.
Cervical rib
Cervical rib
A cervical rib is a supernumerary rib which arises from the seventh cervical vertebra. It is a congenital abnormality located above the normal first rib. A cervical rib is present in only about 1 in 500 of people; in even rarer cases, an individual may have two cervical ribs...
s are present, a condition previously known only from monotremes and basal mammals such as Repenomamus
Repenomamus
Repenomamus is the largest mammal known from the Cretaceous period of Manchuria, and it is the mammal for which there is the best evidence that it fed on dinosaurs. It is not possible to determine if Repenomamus actively hunted live dinosaurs or scavenged dead dinosaurs.-Paleobiology:Repenomamus...
and Fruitafossor
Fruitafossor
Fruitafossor was a termite-eating mammal endemic to North America during the Late Jurassic epoch , existing for approximately ....
. Akidolestes is also monotreme-like in the shape of its pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
, and in aspects of hindlimb posture. Overall, however, other aspects of the appendicular skeleton
Appendicular skeleton
The Appendicular skeleton is composed of 126 bones in the human body. The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger...
, dental
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
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
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
or through a modification of a developmental pathway to a prior state.
The genus name, Akidolestes, is derived from akido, Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
for point, and lestes, Greek for thief. Akido- refers to the pointed snout
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
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 mammal
Prehistoric mammal
Prehistoric mammals are groups of mammals that lived before humans developed writing. 164 million years ago, in the Jurassic period, Castorocauda lutrasimilis, a mammal-like animal weighing about 500 grams , had a full mammalian pelt, with guard hairs and under fur, webbed feet, and scales on the...
s.