What did mammals evolve from?

Answer 1

Reptiles evolved some 320 million years ago from amniote ancestors, specifically from advanced reptiliomorph labyrinthodons. They were among the first vertebrates to successfully sever their ancestral tie to water, as they developed impermeable skin and a mode of reproduction that did not depend upon a body of water (internal fertilization coupled with the amnion, a semi-permeable membrane that protects the embryo in the egg and allows for an exchange of gases such as oxygen and carbon dioxide, allow the developing animal to breathe).

Answer 2

Mammals evolved from synapsids, and more specifically, from therapsids.

Reptiles started to differentiate (become different) from amphibians around 400 million years ago. Various groups evolved out of these early reptiles including crocodiles, dinosaurs and birds, but most importantly to us a strange group of animals called the Mammal-like Reptiles.

The Mammal-like Reptiles, or Therapsids first appeared about 285 million years ago near the begiining of the Permian which is well before the dinosaurs. They evolved quickly and many different groups arose. They were very successful until about the end of the Permian, about 245 million years ago, when something catastrophic affected the earth and nearly all of the species then living died out. New species evolved rapidly to fill this empty habitat, among them the first dinosaurs and a few million years later the first mammals.

The first mammal may never be known, but the Genus Morganucodon and in particular Morganucodon watsoni, a 2-3 cm (1 inch) long weasel-like animal whose fossils were first found in caves in Wales and around Bristol (UK), but later unearthed in China, India , North America, South Africa and Western Europe is a possible contender. It is believed to have lived between 200 MYA and 210 MYA. However Gondwanadon tapanireported from India on the basis of a single tooth in 1994 may be an earlier contender for the title, with a claimed date of 225 MYA.

These early mammals were small, insectivorous, nocturnal, hairy and warm-blooded. Warm-bloodedness is believed to have first evolved among the cynodonts, a late but successful group of mammal-like reptiles from which the mammals evolved. The cynodonts were the only mammal-like reptiles to survive to the Jurassic, in fact they nearly made it into the Cretaceous, and definitely coexisted with many of the major dinosaurs.

The first true mammals were forced to remain small and relatively "insignificant" because of the domination of the dinosaurs. However, after their extinction mammals were given more room to grow larger and diversify.

Answer 3

Many people find this very hard to believe, but palaeontologists think that the first mammals evolved from mammal-like reptiles, for an example the mammal-like reptile Cynodont evoled into the first mammals Morganucodon and Megazostrodon.

Answer 4

Kingdom Animalia, the animal kingdom