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a.1.(Anat.) Of or pertaining to the quadrate and jugal bones.
Quadratojugal bone
(Anat.) a bone at the base of the lower jaw in many animals.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
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The quadratojugal bears a cluster of long, slender, posterolaterally projecting bony spines.
Aside from its smaller size, the skull is distinguished from other specimens of Hypsognathus fenneri from the Newark Supergroup in having relatively small quadratojugal 'horns, a proportionately shorter snout, and more open cranial sutures, all of which suggest that it is a juvenile.
Among the fossils identified were several fragmentary cranial bones: frontal, parietal, right postorbital, left squamosal, right prefrontal, left quadrate, left jugal, left quadratojugal, left lacrimal and several undetermined fragments; left mandible and a fragment of the right, and one isolated tooth; and postcranial bones: 2 paravertebral osteoderms from the nuchal region, 16 paravertebral osteoderms from the trunk region, 22 ventral osteoderms and 16 appendicular osteoderms; 3 cervical and 7 dorsal vertebrae; 2 cervical and 6 thoracic ribs; left coracoid, left and right ulnae, left and right radii, left and fragmentary right ulnare, left radiale, 4 metacarpals and 1 phalanx.
Most of the left quadratojugal has been preserved (Fig.
1979) in all but Chelus; a vomer is present and usually separating the palatines; a splenial bone is present; a post parieto-squamosal arch is present (except Chelodina) and the quadratojugal is absent.
The otic region of the skull is composed of the squamosal, quadrate, and quadratojugal. The quadratojugal lacks a dorsal process and is not C-shaped (Fig.
a, angular; art, articular; bo, basioccipital; d, dentary; ect, ectopterygoid; f, frontal; j, jugal; l, lacrimal; mcg, meckelian groove; mx, maxilla; n, nasal; op, opisthotic; p, parietal; pal, palatine; pf, postfrontal; pmx, premaxilla; po, postorbital; pp, postparietal; pro, prootic; prf, prefrontal; pbs, parabasisphenoid; pt, pterygoid; q, quadrate, qj, quadratojugal; so, supraoccipital; sp, splenial; sq, squamosal; st, supratemporal; sa, surangular; ta, tabular; v, vomer
Maxillary with a high and well developed pars facialis anterior to orbit; pars facialis with two or three serrations at mid-length; pars facialis articulating dorsomedially only with neopalatines; pars palatina small throughout its length; maxillary firmly articulating with quadratojugal posteriorly and to pterygoid medially.