Resultado da Busca
Most research concerning the evolution of mammals centers on the shapes of the teeth, the hardest parts of the tetrapod body. Other important research characteristics include the evolution of the middle ear bones , erect limb posture, a bony secondary palate , fur , hair, and warm-bloodedness .
- Overview
- The evolution of the mammalian condition
Mammals were derived in the Triassic Period (about 252 million to 201 million years ago) from members of the reptilian order Therapsida. The therapsids, members of the subclass Synapsida (sometimes called the mammal-like reptiles), generally were unimpressive in relation to other reptiles of their time. Synapsids were present in the Carboniferous Period (about 359 million to 299 million years ago) and are one of the earliest known reptilian groups. They were the dominant reptiles of the Permian Period (299 million to 252 million years ago), and, although they were primarily predaceous in habit, the adaptive radiation included herbivorous species as well. In the Mesozoic Era (about 252 million to 66 million years ago), the most important of the synapsids were the archosaurs, or “ruling reptiles,” and the therapsids were, in general, small active carnivores. Therapsids tended to evolve a specialized heterodont dentition (that is, a set of teeth separated into molars, incisors, and canines) and to improve the mechanics of locomotion by bringing the plane of action of the limbs close to the trunk. A secondary palate was developed, and the temporal musculature, the muscle involved in closing the jaw, was expanded.
The several features that separate modern reptiles from modern mammals doubtless evolved at different rates. Many attributes of mammals are correlated with their highly active habit—for example, efficient double circulation with a completely four-chambered heart, anucleate and biconcave erythrocytes, the diaphragm, and the secondary palate (which separates passages for food and air and allows breathing during mastication or suckling). Hair for insulation is a correlate of endothermy, or warm-bloodedness, the physiological maintenance of individual temperature independent of environmental temperature. Endothermy allows high levels of sustained activity. The unique characteristics of mammals thus would seem to have evolved as a complex interrelated system.
Mammals were derived in the Triassic Period (about 252 million to 201 million years ago) from members of the reptilian order Therapsida. The therapsids, members of the subclass Synapsida (sometimes called the mammal-like reptiles), generally were unimpressive in relation to other reptiles of their time. Synapsids were present in the Carboniferous Period (about 359 million to 299 million years ago) and are one of the earliest known reptilian groups. They were the dominant reptiles of the Permian Period (299 million to 252 million years ago), and, although they were primarily predaceous in habit, the adaptive radiation included herbivorous species as well. In the Mesozoic Era (about 252 million to 66 million years ago), the most important of the synapsids were the archosaurs, or “ruling reptiles,” and the therapsids were, in general, small active carnivores. Therapsids tended to evolve a specialized heterodont dentition (that is, a set of teeth separated into molars, incisors, and canines) and to improve the mechanics of locomotion by bringing the plane of action of the limbs close to the trunk. A secondary palate was developed, and the temporal musculature, the muscle involved in closing the jaw, was expanded.
The several features that separate modern reptiles from modern mammals doubtless evolved at different rates. Many attributes of mammals are correlated with their highly active habit—for example, efficient double circulation with a completely four-chambered heart, anucleate and biconcave erythrocytes, the diaphragm, and the secondary palate (which separates passages for food and air and allows breathing during mastication or suckling). Hair for insulation is a correlate of endothermy, or warm-bloodedness, the physiological maintenance of individual temperature independent of environmental temperature. Endothermy allows high levels of sustained activity. The unique characteristics of mammals thus would seem to have evolved as a complex interrelated system.
18 de ago. de 2020 · Learn how mammals evolved from tiny shrew-like creatures to diverse and adaptable forms after the dinosaurs' extinction. Explore the fossil record, genetic evidence, and modern examples of mammalian diversity and behavior.
- Rick Gore
22 de dez. de 2021 · Here we develop a Bayesian molecular-clock dating approach to estimate a timetree of 4,705 mammal species integrating information from 72 mammal genomes.
23 de out. de 2019 · Learn how ancient mammals evolved a wide variety of adaptations to exploit different habitats and survive the dinosaur era. Discover the latest fossil finds from China and the controversies over mammal origins and diversity.
- John Pickrell
- 2019
30 de dez. de 2021 · In Beasts Before Us, Elsa Panciroli tells the history of synapsid evolution, from their origins at around 300 Ma up to the emergence of the major groups of mammals that we are so familiar with...
11 de nov. de 2020 · Climate change as driver of evolution. Still lacking though was an understanding of what happened during that rapid expansion or the selective forces behind the rapid increase in size and changes in behaviour such as a switch from nocturnal to diurnal living for some species.
