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In tetrapods with a quadratojugal bone, it often forms a portion of the jaw joint. Developmentally, the quadratojugal bone is a dermal bone in the temporal series, forming the original braincase. The squamosal and quadratojugal bones together form the cheek region [4] and may provide muscular attachments for facial muscles. [5]
The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper part of the jaw joint. The lower jaw articulates at the articular bone, located at the rear end of the ...
The posterior end of the lower jaw bones contains a quadrate bone, allowing jaw extension. The anterior tips of the lower jaw bones are joined by a flexible ligament allowing them to bow outwards, increasing the mouth gape. [74] [75] The Pacific tree frog and the Baja California chorus frog are some of the only frog species that make a "ribbit ...
A quadratojugal bone, which in modern birds is fused to the jugal, is preserved in Pterygornis. [30] The presence of these primitive features of the skull would have rendered the Enantiornithes capable of only limited cranial kinesis (the ability to move the jaw independent of the cranium). [31]
The tuatara and some extinct rhynchocephalians have a more rigid skull with a complete lower temporal bar closing the lower temporal fenestra formed by the fusion of the jugal and quadrate/quadratojugal bones, similar to the condition found in primitive diapsids. However early rhynchocephalians and lepidosauromorphs had an open lower temporal ...
Jugal bone labelled Ju, in pale green, at centre left. The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
These extended margins of thinned bone are called supratemporal fossae. Synapsids, including mammals, have one temporal fenestra, which is ventrally bordered by a zygomatic arch composed of the jugal and squamosal bones. This single temporal fenestra is homologous to the infratemporal fenestra, as displayed most clearly by early synapsids. [2]
A correspondingly large intervomerine fontanelle is found on the palate. The quadratojugal is expanded, and in Acanthostomatops and Zatrachys, bears discrete spiky projections. The quadratojugal also obscures the quadrate in dorsal profile. Dasyceps and Zatrachys are only confidently known from cranial material.