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''Jeholodens'' was a primitive 
It is suspected to be a
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
belonging to the order Eutriconodonta
Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...
, and which lived in present-day China during the Middle Cretaceous about 125 million years ago.
Only one specimen has been formally described. This specimen (the holotype) consists of a virtually complete articulated skull and skeleton, it shared its corporal characteristics with most other Mesozoic mammals; it was a long-tailed, nocturnal tetrapod (with prehensile fingers and toes) which hunted insects, its food, during the night.
It is suspected to be a nocturnal
Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Nocturnal creatures generally have highly developed sens ...
creature because it had very large eyes which were roughly 5 mm across. This would have allowed it to have better night vision for catching insects. It is notable for its relatively derived forelimb morphology, having shoulder blades and other pectoral girdle elements comparable to those of modern therians like opossums. It also had grasping hands. By contrast, however, the hindlimbs retained primitive characters, suggesting a sprawling stance.
Recent studies show that it was specialised to an arboreal lifestyle, possessing prehensile hands.Meng Chen, Gregory Philip Wilson, A multivariate approach to infer locomotor modes in Mesozoic mammals, Article in Paleobiology 41(02) · February 2015
References
Eutriconodonts Cretaceous mammals Mesozoic mammals of Asia Fossil taxa described in 1999 Yixian fauna Taxa named by Qiang Ji (paleontologist) Taxa named by Zhe-Xi Luo Taxa named by Shu-An Ji Prehistoric mammal genera {{cretaceous-mammal-stub