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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 ...
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]
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 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.
When the upper and lower dental formulae are the same, some texts write the formula without a fraction (in this case, 2.1.2.3), on the implicit assumption that the reader will realise it must apply to both upper and lower quadrants. This is seen, for example, throughout The Cambridge Dictionary of Human Biology and Evolution.
Thecodontia is a paraphyletic group, and its usage as a taxonomic category has been rejected under modern cladistic systems. The name Archosauriformes is intended as a monophyletic replacement compatible with modern taxonomy.
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]
In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. [2] [3] Human dentition is heterodont and diphyodont as an example. [4] In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms.