are groups of mammals
that lived before humans developed writing
. 164 million years ago, in the Jurassic
period, Castorocauda lutrasimilis
, a mammal-like (mammaliaform) animal weighing about 500 grams
(1.1 lb), had a full mammalian pelt, with guard hairs and under fur, webbed feet, and scales on the tail like a modern beaver
, as well as teeth specialized for catching fish.
Later, about 130 million years ago in the Cretaceous, there existed larger mammals, including Repenomamus giganticus and Repenomamus robustus. Fossils up to one meter (3¼ ft) long have been found, with dinosaur remains in their stomach contents.
The lineages of many varieties continued through the Tertiary period where some reached very large sizes. Most of the very large mammals became extinct in the last ice age, but have smaller descendants.
List of prehistoric mammals
Prehistoric mammals include:
Malagasy River Dolphin
North American Camel
North American Lion
North American Llama
Pygmy Polar Bear
Pygmy Giant Panda
Powerful Killer Whale
Repenomamus giganticus and r.robustus
Rinston's Bottlenose Dolphin
Saber-toothed cats Samotherium
Wilmington's Ground Sloth