Evolution of Mammals - Expansion of Ecological Niches in The Mesozoic

Expansion of Ecological Niches in The Mesozoic

There is still some truth in the "small, nocturnal insectivores" stereotype, but recent finds, mainly in China, show that some mammaliaforms and crown group mammals were larger and had a variety of lifestyles. For example:

• Castorocauda, a member of Docodonta which lived in the middle Jurassic about 164 million years, was about 42.5 cm (16.7 in) long, weighed 500–800 g (18–28 oz), had limbs that were adapted for swimming and digging and teeth adapted for eating fish.
• Multituberculates are allotherians that survived for over 125 million years (from mid Jurassic, about 160M years ago, to late Eocene, about 35M years ago) are often called the "rodents of the Mesozoic". As noted above, they may have given birth to tiny live neonates rather than laying eggs.

• Fruitafossor, from the late Jurassic period about 150 million years ago, was about the size of a chipmunk and its teeth, forelimbs and back suggest that it broke open the nest of social insects to prey on them (probably termites, as ants had not yet appeared).
• Volaticotherium, from the boundary the early Cretaceous about 125M years ago, is the earliest-known gliding mammal and had a gliding membrane that stretched out between its limbs, rather like that of a modern flying squirrel. This also suggests it was active mainly during the day.
• Repenomamus, a eutriconodont from the early Cretaceous 130 million years ago, was a stocky, badger-like predator that sometimes preyed on young dinosaurs. Two species have been recognized, one more than 1 m (39 in) long and weighing about 12–14 kg (26–31 lb), the other less than 0.5 m (20 in) long and weighing 4–6 kg (8.8–13 lb).