When and how did mammals evolve?

Question

Did dinosaurs and mammals have a common ancestor somewhere down the evolutionary chain?

Answer 1

Absolutely!

Dinosaurs and mammals would have shared a common reptilian ancestor at some point during the paleozoic era. Mammals are evolved from so-called synapsid reptiles which existed before the dinosaurs had evolved. Synapsid reptiles evolved in the late carboniferous period of the paleozoic era, about 300 million years ago.

Dinosaurs came about in what we call the mesozoic era. Their ancestors, and those of mammals, existed during the palaeozoic era. The diapsid reptiles - the ancestors of dinosaurs and of most living reptiles are also believed to have evolved around the same time as synapsids - in the late carboniferous.

So you can probably assume the common ancestor of the two groups lived during the early carboniferous around 360 million years ago, even though dinosaurs and mammals themselves did not evolve until a little over 200 million years ago.

There were four different main groups of mammals - multituberculates, monotremes (such as the echidna and platypus), marsupials and placentals. The last 3 are still in existence and it is believed from genetic evidence that all of these groups evolved BEFORE the dinosaurs went extinct (although they all remained as small shrew-like animals).

Answer 2

Every living creature had a common ancestor somewhere down, as far as science knows ;)
The most recent common ancestor of dinosaurs and mammals (which is, in fact, the mrca. of ALL living amniotes (reptiles, mammals and birds in Linnaean classification) could have lived somewhere in the Carboniferous, somewhat over 300 million years ago. The amniote lineage split as early as the late Carboniferous (look for the Joggins fossilsite in some reliable source), and since then, the "reptile" and the "mammal" branches evolved separately.

Mammals are the only remaining side-branch of the synapsids (often called "mammal-like reptiles", even though they were no reptiles at all!), which were the dominant terrestrial vertebrates of the Permian period (a very popular early Permian example is the sail-backed Dimetrodon, which is actually quite close to the ancestors of advanced synapsids and mammals).
During the later Permian, advanced synapsids (therapsids) diversified, and somewhere in the late Triassic(? not sure about this), cynodont therapsids gave rise to the earliest mammals. Cynodonts themselves, especially the more derived ones, are very similar to mammals (they developed a mammal-like jaw, strongly differentiated teeth, a more upright stance, probably a diaphragm, supposedly hair as well... etc, I'm not the best source for details)

There are three main living groups of synapsids (making up Mammalia), the monotremes, the marsupials (Metatheria) and the placentals (Eutheria). Monotremes split off earliest (early Jurassic?), while the two other groups could have separated somewhere in the early Cretaceous or late Jurassic, but you'd better ask an expert on this :)

Answer 3

Amniotes were the last common ancestors, although the fossils from the period are a bit murky on the developmental chronology.

the amniotes split into several groups including the ancestors of modern reptiles birds and dinosaurs, the archosaurs, which developed from the earlier diapsid reptiles, and the synapsid group which is almost entirely extinct with the exception of mammals.

Tetrapods to diapsids and synaptids. Diapsids to archaeosaurs, synapsids to therapsids. Arhcaosaurs to dinosaurs. Therapsids to mammals.

Yes, that's incredibly oversimplified, but it includes the major names that you can punch into your browser to get more info on.

Answer 4

According to the discovery channel mammals evolved from reptiles. Dinosaurs also came from reptiles.

Answer 5

"If mammals stepped forward from Therapsids (mammal-like reptiles) then what approximately Dinosaurs?" From very dinosaur-like, archosaur reptiles. "i'm attempting extremely confusing to comprehend this whether it extremely is extremely confusing." The confusion is totally widely used. This concern isn't effortless, and the unfamiliar names may be confusing to preserve. "So in fact Dinosaurs at the instant are not Therapsids and are not Synapsids yet are extremely Diapsids?" properly suited. "Please i actually extremely extremely wanna comprehend this" attempt to be satisfied with sluggish progression, and be arranged to prefer lots staying power. do not assume to comprehend this interior some weeks, months of years. as quickly as you have grasped that therapsids are synapsids and not in all probability reptiles in any respect, then you definately will discover you will possibly be at a loss for words by using therapsid cynodonts extremely. after which you watch for getting at a loss for words by using cynodont eucynodonts, mammaliformes, crown-team mammals, boreosphenidans... Confusion is a classic characteristic for this territory.

Answer 6

Wow, it makes me so sad that people are so lost...Nothing evolved. Even if you dont believe in God, common sense should tell you that... they say this evolved this many million years ago and then this and so on meanwhile no one is smart enough to realize that if we actually did evolve we'd still be doing it...which were not! Do youself a favor, there is this AMAZING dvd called Intelligent Design- Unlocking the Mysteries of Life. It actually PROVES Darwin's theory of evolution false... and before you say no it doesnt... watch it-

Answer 7

all life, whether mammal, reptile or even bacteria share a common ancestor - though it's probably some form of amino acid ;)

Answer 8

I think you're confused. The Universe including dinosaurs, mammals, and man were all created by God. There's no evidence that any species evolved from another.

Answer 9

in australia but the world was a completely differnt shape then and it was already during the last dinosaur age.The first mamals and dinosaurs lived at the same time

Answer 10

Yes, they would have done, but quite a distant one.