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''Jeholodens'' was a primitive mammal belonging to the order 
It is suspected to be a nocturnal 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
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 ...
, and which lived in present-day China during the Middle Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
about 125 million years ago.
Only one specimen has been formally described. This specimen (the holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
) consists of a virtually complete articulated skull and skeleton, it shared its corporal characteristics with most other Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
mammals; it was a long-tailed, nocturnal tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...
(with prehensile fingers and toes) which hunted insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s, its food, during the night.
It is suspected to be a nocturnal 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 theria
Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes.
...
ns like opossums
Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered North A ...
. 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
Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose nu ...
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