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- 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.
www.britannica.com › animal › mammalMammal - Evolution, Classification, Adaptations | Britannica
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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.
Jan 6, 2021 · The new genomes of both species will enable further insights into therian innovations and the biology and evolution of these extraordinary egg-laying mammals.
- Yang Zhou, Linda Shearwin-Whyatt, Jing Li, Zhenzhen Song, Takashi Hayakawa, David Stevens, Jane C. F...
- 2021
The evidence for evolution. In this article, we'll examine the evidence for evolution on both macro and micro scales. First, we'll look at several types of evidence (including physical and molecular features, geographical information, and fossils) that provide evidence for, and can allow us to reconstruct, macroevolutionary events.
- Yes, they share 'form' during embryonal development. But there is when the evolution of life becomes really interesting. Embryonic stages of all ch...
- you can think for you that a designer is guiding evolution. we will just not speak in terms of a god/creator or something because there is no mater...
- Probably yes. But offspring has to inherit at least some genes from some ancestor.
- Protein structure is crucial evidence in Bioinformatics because based on protein structures we can predict protein functions! It is believed that p...
- Evolution is the explanation for why the various species developed.
- Based on my limited knowledge, DNA sequencing is better evidence for Universal Common Descent (UCD) than fossil evidence. This is mostly because in...
- No, evolution is continuously occurring. If a population is reproducing, it is evolving.
Oct 31, 2023 · The evolution of mammals passed through many stages since the first appearance of their synapsid ancestors in the late Carboniferous period. Mammals are synapsids: they have a single opening in the skull. They are the only living synapsids as earlier forms became extinct by the Jurassic period.
All living mammals today, including us, descend from the one line that survived. During the next 145 million years of evolution, the dominance of dinosaurs ensured that our distant mammalian...
Nov 11, 2020 · “But, based on the current fossil record, early mammals seem to have experienced three distinct diversification events, starting with very early mammals (and mammalian 'cousins', often called mammaliaforms) during the Early or Middle Jurassic, or about 180‐160 million years ago.
