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Thecodont dentition is a morphological arrangement in which the base of the tooth is completely enclosed in a deep socket of bone, as seen in crocodilians, dinosaurs and mammals, and opposed to acrodont and pleurodont dentition seen in squamate reptiles. [1] Notably, this appears to be the ancestral tooth condition in Amniota. [2]
Thecodontia (meaning 'socket-teeth'), now considered an obsolete taxonomic grouping, was formerly used to describe a diverse "order" of early archosaurian reptiles that first appeared in the latest Permian period and flourished until the end of the Triassic period. All of them were built somewhat like crocodiles but with shorter skulls, more ...
This feature is responsible for the name "thecodont" (meaning "socket teeth"), [8] which early paleontologists applied to many Triassic archosaurs. [7] Additionally, non-muscular cheek and lip tissue appear in various forms throughout the clade, with all living archosaurs lacking non-muscular lips, unlike most non-avian saurischian dinosaurs. [ 9 ]
The dashes (-) in the formula are likewise not mathematical operators, but spacers, meaning "to": for instance the human formula is 2.1.2.2-3 2.1.2.2-3 meaning that people may have 2 or 3 molars on each side of each jaw. 'd' denotes deciduous teeth (i.e. milk or baby teeth); lower case also indicates temporary teeth.
The thecodont condition was historically used to define a clade, the Thecodontia, which is now considered paraphyletic and thus obsolete. [7] angular The angular is a dermal bone of the lower jaw. In lateral view, it covers a larger area of the posteroventral region of the jaw, being located behind the dentary and below the surangular.
In contrast, Archosauromorphs possess a parasagittal gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, and a more thecodont dentition. Living lepidosauromorphs have retained an ectothermic (" cold blooded ") metabolism, unlike the ancestral condition in archosauromorphs.
The dentition of Cymbospondylus is generally thecodont, meaning that the tooth roots are deeply cemented into the jawbone. However, not all species share the same robustness in terms of their dental implantation. C. petrinus has a particular form of thecodont dentition, its teeth appearing to be fused at the bottom of the alveoli. [70]
Mosasaurs possessed a thecodont dentiton, meaning that the roots were cemented deeply into the jaw bone. Mosasaurs did not use permanent teeth but instead constantly shed them. Replacement teeth developed within a pit inside the roots of the original tooth called the resorption pit.