When did the first mammals start to evolve?
- It was only after the dinosaurs went kaput that mammals were able to evolve beyond their tiny, quivering, mouselike forms into the widely specialized species that populate the world today. These popular misconceptions about the mammals of the Mesozoic Era are easy to explain.
Case Studies in Ecology and Evolution DRAFT D. Stratton 2011 1 1 Phylogenetic History: The Evolution of Marine Mammals Think for a moment about marine mammals: seals, walruses, dugongs and whales. Seals and walruses are primarily cold-water species that eat mostly fish and can spend part of their time on land (or ice).
the evolution of the structure of inner ears of mammals. In this article, we intend to show that this is a misleading concept. Although it is a given that the responses of mecha-nosensory organs will depend on the physical properties of their components, the mechanisms of evolution are different from the deterministic nature of physics.
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When did the first mammals start to evolve?
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How did the therapsids contribute to the evolution of mammals?
Jul 25, 2012 · During the transition of mammals to reptiles, therefore, it is supposed that the quadrate and articular (as well as pre-articular) bones became separated from the posterior lower jaw and evolved into the incus and malleus, two of the bones associated with the mammalian ear.
- Jonathan Mclatchie
May 21, 2007 · Also, the two recently evolved marine mammals, the polar bear and sea otter, spend most of their time in the water feeding. This is no great surprise, because a great deal of mammalian evolution has been linked to changes in feeding ecology.
- Mark D. Uhen
- Debunking Popular Misconceptions
- First Mammals
- Lifestyles of First Mammals
- Nuclear Winter's Effect
These popular misconceptions about the mammals of the Mesozoic Era are easy to explain. Scientifically speaking, dinosaurs tended to be very, very big and early mammals tended to be very, very small. With a couple of exceptions, the first mammals were tiny, inoffensive creatures, rarely more than a few inches long and a few ounces in weight, about on a par with modern shrews. Thanks to their low profiles, these hard-to-see critters could feed on insects and small reptiles (which bigger raptors and tyrannosaurs tended to ignore), and they could also scurry up trees or dig into burrows to avoid getting stomped on by larger ornithopods and sauropods.
Before discussing how the first mammals evolved, it's helpful to define what distinguishes mammals from other animals, especially reptiles. Female mammals possess milk-producing mammary glands with which they suckle their young. All mammals have hair or fur during at least some stage of their life cycles, and all are endowed with warm-blooded (endothermic) metabolisms. Regarding the fossil record, paleontologists can distinguish ancestral mammals from ancestral reptiles by the shape of their skull and neck bones, as well as the presence, in mammals, of two small bones in the inner ear (in reptiles, these bones constitute part of the jaw).
The most distinctive thing about the mammals of the Mesozoic Era is how small they were. Although some of their therapsidancestors attained respectable sizes. For example, the late Permian Biarmosuchus was about the size of a large dog. Very few early mammals were larger than mice, for a simple reason: dinosaurs had already become the dominant terrestrial animals on earth. The only ecological niches open to the first mammals entailed a) feeding on plants, insects and small lizards, b) hunting at night (when predatory dinosaurs were less active), and c) living high up in trees or underground, in burrows. Eomaia, from the early Cretaceous period, and Cimolestes, from the late Cretaceous period, were fairly typical in this regard.
Ironically, the same characteristics that helped mammals maintain a low profile during the Mesozoic Era also allowed them to survive the K/T Extinction Event that doomed the dinosaurs. As we now know, that giant meteor impact 65 million years ago produced a kind of "nuclear winter," destroying most of the vegetation that sustained the herbivorous dinosaurs, which themselves sustained the carnivorous dinosaurs that preyed on them. Because of their tiny size, early mammals could survive on much less food, and their fur coats (and warm-bloodedmetabolisms) helped keep them warm in an age of plunging global temperatures.
- Bob Strauss
- Science Writer
Mar 21, 2012 · This is an exciting time to study marine mammal evolution as many of the most important discoveries in this field have been made in the last 10-15 years, and there is no reason to expect that pace ...