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Figure 1:In mammals, the quadrate and articular bones are small and part of the middle ear; the lower jaw consists only of dentary bone.. While living mammal species can be identified by the presence of milk-producing mammary glands in the females, other features are required when classifying fossils, because mammary glands and other soft-tissue features are not visible in fossils.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
Tiktaalik, a lobe-finned fish with some anatomical features similar to early tetrapods. It has been suggested to be a transitional species between fish and tetrapods. [81] 365 Ma Acanthostega is one of the earliest vertebrates capable of walking. [82] 363 Ma By the start of the Carboniferous Period, the Earth begins to resemble its present state.
Pteraspidomorphi is an extinct class of early jawless fish. The fossils show extensive shielding of the head. Many had hypocercal tails to generate lift to increase ease of movement through the water for their armoured bodies, which were covered in dermal bone. They also had sucking mouth parts and some species may have lived in fresh water ...
Stone tools found at the Shangchen site in China and dated to 2.12 million years ago are considered the earliest known evidence of hominins outside Africa, surpassing Dmanisi hominins found in Georgia by 300,000 years, although whether these hominins were an early species in the genus Homo or another hominin species is unknown. [37
The first lobe-finned fish, found in the uppermost Silurian (c. 418 Mya), closely resembled spiny sharks, which became extinct at the end of the Paleozoic. In the Early to Middle Devonian (416–385 Mya), while the predatory placoderms dominated the seas, some lobe-finned fish came into freshwater habitats.
Early fish had no jaws. Most went extinct when they were outcompeted by jawed fish (below), but two groups survived: hagfish and lampreys. Hagfish form a class of about 20 species of eel-shaped, slime-producing marine fish. They are the only known living animals that have a skull but no vertebral column. Lampreys form a superclass containing 38 ...
Vernix caseosa, the thin skin found on newborn babies, is also found on seals, beavers, and otters, but not on other primates. Furthermore, human placentophagy seems to have disappeared at a very early point in the human species, as it was practiced by no known culture; placentophagy is common in primates, but not among seals or dolphins ...