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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 mammalian jaw joint is composed of different skull bones, including the dentary (the lower jaw bone which carries the teeth) and the squamosal (another small skull bone). In mammals, the quadrate and articular bones have evolved into the incus and malleus bones in the middle ear. [20] [21]
Early mammals and possibly their eucynodontian ancestors had epipubic bones, which serve to hold the pouch in modern marsupials (in both sexes). 170-120 Ma Juramaia sinensis. Evolution of live birth , with early therians probably having pouches for keeping their undeveloped young like in modern marsupials.
Evolution of mammalian auditory ossicles – Middle ear bones evolved from jaw bones; Evolution of nervous systems – Origin and subsequent variation and development of neurons and neural tissues and organs; Evolution of snake venom – Origin and diversification of snake venom through geologic time
The three small bones in the middle ear of mammals including humans, the malleus, incus, and stapes, are today used to transmit sound from the eardrum to the inner ear. The malleus and incus develop in the embryo from structures that form jaw bones (the quadrate and the articular) in lizards, and in fossils of lizard-like ancestors of mammals.
Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine (TGF-β, IGF) signalling. Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. [1]
In all tetrapods the cartilage partially ossifies (changes to bone) at the rear end of the jaw and becomes the articular bone, which forms part of the jaw joint in all tetrapods except mammals. [1] In some extinct mammal groups like eutriconodonts, Meckel's cartilage still connected otherwise entirely modern ear bones to the jaw. [2]
A mammal (from Latin mamma 'breast') [1] is a vertebrate animal of the class Mammalia (/ m ə ˈ m eɪ l i. ə /).Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones.