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--- mammals [2023/07/12 04:44] – zookeeper
+++ mammals [2023/10/03 05:21] (current) – [I. MAMMAL DIVERSIFICATION] zookeeper
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 ====== MAMMALS ======
- {{:waemammals.png?nolink&500|}}
 By classical Linnaean classification, Mammals belong to class 'Mammalia'. Modern, phylogenetic classification too seems to put mammals in their own place in the tree of life, with the earliest mammals appearing some 250 million years ago. Mammal diversity increased much after the extinction of dinosaurs, some 66 million years ago, allowing mammals to become larger in size, and take a variety of forms. Mammals share several characteristics, in that they have a kind of layer of hair, are warm-blooded, and produce milk.
 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. {{ :waemammalcollage.png?nolink&400}}
 [{{ :chimpnourish.png?nolink&200|//The act of nourishing the young with milk is an instrumental characteristic throughout the entirety of mammal diversity, and in fact the word 'mammal' derives from the Latin 'mamma', meaning 'breast'. Some mammals, such as the platypus, do not have teats, and instead sweat out the milk.//}}]
-====== I. MAMMAL DIVERSIFICATION ======
+====== MAMMAL DIVERSIFICATION ======
 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.