mammals
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| Most mammals, placentals, give live birth, though a smaller number, the marsupials, grow their young in a pouch until they grow larger, and more defined. For where egg-laying mammals, monotremes, were once common, they have greatly diminished, in that the single species of platypus and four species of echidna of Australia remain the only living Monotremes. {{ : | Most mammals, placentals, give live birth, though a smaller number, the marsupials, grow their young in a pouch until they grow larger, and more defined. For where egg-laying mammals, monotremes, were once common, they have greatly diminished, in that the single species of platypus and four species of echidna of Australia remain the only living Monotremes. {{ : | ||
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| The first mammals are thought to have appeared some 180 million years ago, in a time when reptiles were dominant of the land, and the dinosaurs were growing in size. Such mammals vaguely resembled today’s rodents, though they were still not far diverged from their synapsid ancestors. A long-standing notion is that primitive mammals would have been supressed by the dinosaurs of their time, with the reptiles dominant of the land. Whilst this is reasonable to some extent, it’s possible that larger mammals would have easily thrived amongst the dinosaurs – even feeding upon smaller dinosaurs and mammals. Alongside the non-avian dinosaurs, a great number of mammals too were destroyed by the extinction at the end of the Cretaceous, allowing a lineage of smaller mammal, the Therians, to succeed them. Today, mammals are the most successful of any land-based vertebrate, with over 6,000 different species, themselves belonging to over 100 different families. | The first mammals are thought to have appeared some 180 million years ago, in a time when reptiles were dominant of the land, and the dinosaurs were growing in size. Such mammals vaguely resembled today’s rodents, though they were still not far diverged from their synapsid ancestors. A long-standing notion is that primitive mammals would have been supressed by the dinosaurs of their time, with the reptiles dominant of the land. Whilst this is reasonable to some extent, it’s possible that larger mammals would have easily thrived amongst the dinosaurs – even feeding upon smaller dinosaurs and mammals. Alongside the non-avian dinosaurs, a great number of mammals too were destroyed by the extinction at the end of the Cretaceous, allowing a lineage of smaller mammal, the Therians, to succeed them. Today, mammals are the most successful of any land-based vertebrate, with over 6,000 different species, themselves belonging to over 100 different families. | ||
| Over time, several ‘fathers’ of these families would diversify themselves across the continents, and some mammals would also specialise in an aquatic life-style – all whales and dolphins today are derived from land-based ancestors, which would have taken to the water to get to a then-underlooked food-source. | Over time, several ‘fathers’ of these families would diversify themselves across the continents, and some mammals would also specialise in an aquatic life-style – all whales and dolphins today are derived from land-based ancestors, which would have taken to the water to get to a then-underlooked food-source. | ||
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