Zalambdalestes was a placental mammal

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...

 living during the Upper 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...

 in Mongolia

Mongolia

Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...

. It is one of the oldest examples of a placental mammal known, and would have lived alongside the dinosaurs.

Zalambdalestes was a shrew

Shrew

A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...

-like animal with a long snout, long teeth, a small brain and large eyes. It was about 20 centimetres (7.9 in) long, with a head only 5 centimetres (2 in) long. It had strong front paws and even stronger rear ones, but its claws were not opposable, so it is unlikely to have climbed trees. Its diet was probably composed mainly of insects that it hunted in the forest undergrowth using its sharp, interlocking teeth.