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Types of planar joints. 1. butt joint. 2. joint with Type-A interdigitations. 3. stepped joint. 4. joint with Type-B interdigitations. 5. scarf joint. 6. joint with Type-C interdigitations. 7. horizonal or transverse slot joint. 8. lap joint (Weishampel 1984). 9. raised scarf joint. 10. recessed scarf joint ('basal shelf' of Kathe 1995). 11. vertical slot joint. 12. asymmetrical horizontal slot joint with a tab and pocket. 13. scarfed tongue in groove. 14. stepped tongue in groove joint. 15. bird's mouth joint. 16. bear's mouth joint. Unbroken line represents external seam whereas dashed line represents portions of internal interface.
Source publication
The anatomy of the extant lepidosaur Sphenodon (New Zealand tuatara) has been extensively examined by palaeontologists and comparative anatomists because of its phylogenetic status as the only living member of the Rhynchocephalia. It is also of interest because of its sophisticated feeding apparatus and a prooral (anteriorly directed) mode of shear...
Contexts in source publication
Context 1
... joints can exhibit a variety of different constructions, and three main categories are rec- ognised: butt joints, scarf joints and interdigitated joints. Butt joints (Figure 2.1), where bones meet at a flat wall perpendicular, or near perpendicular, to the outer surface of the bones (Moss 1957;Bolt and Wassersug 1975;Weishampel 1984;Busbey 1995) are also sometimes termed vertical wall in Kathe (1995), flat in Bolt and Wassersug (1975), end-to-end in Moss (1957) and Wagemans et al. (1988). Scarf joints (Figure 2.5) involve a partial overlap between two bones (Weishampel 1984;Busbey 1995) and may also be referred to as bev- elled (Moss 1957;Kathe 1995Kathe , 1999), overlapping (Moss 1957), shelved ( Kathe 1995Kathe , 1999) or squamous (Moss 1957;Bolt and Wassersug 1975) Weishampel 1984). ...
Context 2
... joints (Figure 2.1), where bones meet at a flat wall perpendicular, or near perpendicular, to the outer surface of the bones (Moss 1957;Bolt and Wassersug 1975;Weishampel 1984;Busbey 1995) are also sometimes termed vertical wall in Kathe (1995), flat in Bolt and Wassersug (1975), end-to-end in Moss (1957) and Wagemans et al. (1988). Scarf joints (Figure 2.5) involve a partial overlap between two bones (Weishampel 1984;Busbey 1995) and may also be referred to as bev- elled (Moss 1957;Kathe 1995Kathe , 1999), overlapping (Moss 1957), shelved ( Kathe 1995Kathe , 1999) or squamous (Moss 1957;Bolt and Wassersug 1975) Weishampel 1984). ...
Context 3
... tion in the degree and type of facet texture (e.g., gutters and striations or more conspicuous ridges, grooves and fluting) blur the boundaries between these three different joint categories. Moreover, bones do not always overlap in a simple slope-like fashion (Figure 2.5), the interface may be a stepped joint (Figure 2.10) or the overlapping bone may extend a tongue into an evenly recessed groove on the other bone (Figure 2.13-14). Kathe (1995) recognised the problem of using only three categories and expanded their number, for exam- ple dividing scarf joints into 'shelf', 'basal shelf' and 'steep bevel' joints. ...
Context 4
... tion in the degree and type of facet texture (e.g., gutters and striations or more conspicuous ridges, grooves and fluting) blur the boundaries between these three different joint categories. Moreover, bones do not always overlap in a simple slope-like fashion (Figure 2.5), the interface may be a stepped joint (Figure 2.10) or the overlapping bone may extend a tongue into an evenly recessed groove on the other bone (Figure 2.13-14). ...
Context 5
... referred to the sloping fac- ets of scarf joints as 'shelves', but the term 'shelf' is here considered more useful for describing rectan- gular planar projections of bone. Therefore, 'recessed scarf' is used here instead (Figure 2.10, 'butt-lap' of Daza et al. 2008). ...
Context 6
... joints also show a variety of forms depending on the number and shape of interdigitations, their depth from the cranial surface • Type-C (Figure 2.6): spine-like projections overlapping in three planes, essentially a combination of Type A and Type B. Type-A may be thought of as an exaggerated form of a slot contact (Figure 2.7). Similarly, Type- C interdigitations were described as "hypertrophied plug contacts" by Clack (2002). ...
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... Sphenodon the anterior end of the maxilla loosely overlaps the lateral process of the premax- illa below the naris, with a 'recessed scarf' joint ( Figure 2.10). In dorsal view, the seam runs poster- omedially from near the anterolateral corner of the external naris. ...
Context 8
... premaxilla overlaps the anterior process of the nasal in a 'recessed scarf' joint ( Figure 2.10) in which the anterior end of the nasal process slots into a 'pocket' in the back of the premaxilla (at least in DGPC1). In dorsal view, the nasal processes of the paired premaxillae appear to be pinched between the nasals with seams that run postero- medially from the dorsal margin of the naris toward the midline. ...
Context 9
... internal structure of the joint is complex (e.g., LDUCZ x343, YPM 11419, DGPC1, AUP 11883). First, the anterior process of the nasal, which extends beneath the premaxilla, is tri- angular and directed anterolaterally, so the hidden anterior processes of the nasals do not meet along the midline but diverge (Figures 11, 12, 13). Sec- ond, the facet on the nasal is sunk or recessed as in a 'recessed scarf' joint. ...
Context 10
... the anterior tip of the pointed nasal process fits into a pocket in the posteroventral sur- face of the premaxilla (Figures 10.4, 12.4, 12.5). Hence, the nasal has both dorsal and ventral fac- ets for the premaxilla (Figure 12.2, 12.7). The pos- terior wall of the pocket is fairly low, and the interior contains five pits that are probably related to nutri- ent supply (Figure 12.4). ...
Context 11
... the nasal has both dorsal and ventral fac- ets for the premaxilla (Figure 12.2, 12.7). The pos- terior wall of the pocket is fairly low, and the interior contains five pits that are probably related to nutri- ent supply (Figure 12.4). ...
Context 12
... the ventral surface of the process the three gutters are separated by a shallow groove and a concavity. The largest and most lateral of the gutters ( Figure 12.1, 12.2) corresponds to a tuber- cle on the ventral surface of the premaxilla above the pocket (Figures 10.2, 10.4, 12.5, 12.6). ...
Context 13
... the ventral surface of the process the three gutters are separated by a shallow groove and a concavity. The largest and most lateral of the gutters ( Figure 12.1, 12.2) corresponds to a tuber- cle on the ventral surface of the premaxilla above the pocket (Figures 10.2, 10.4, 12.5, 12.6). The two smaller gutters on the nasal also interlock with ridges inside the pocket of the premaxilla. ...
Context 14
... prefrontal's lateral facet has anteroventrally directed striations, and one of these ends in a foramen. Similarly orientated, but less obvious, striations are visible on the facet of the maxilla ( Figure 20). These internal striations paral- lel the anteroventrally directed grooves that can sometimes be seen on the external surface of the facial process of the maxilla. ...
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... internal striations paral- lel the anteroventrally directed grooves that can sometimes be seen on the external surface of the facial process of the maxilla. The ventral margin of the lateral facet (prefrontal) is dentate ( Figures 17.1, 21.1), bearing planar triangular projections which fit into corresponding depressions and recesses on the medial surface of the maxilla (Fig- ures 20, 21.1). The posterodorsal margin of the prefrontal facet is a deep wall which abuts and may occasionally overlap the dorsal margin of the max- illa very slightly. ...
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... internal striations paral- lel the anteroventrally directed grooves that can sometimes be seen on the external surface of the facial process of the maxilla. The ventral margin of the lateral facet (prefrontal) is dentate ( Figures 17.1, 21.1), bearing planar triangular projections which fit into corresponding depressions and recesses on the medial surface of the maxilla (Fig- ures 20, 21.1). The posterodorsal margin of the prefrontal facet is a deep wall which abuts and may occasionally overlap the dorsal margin of the max- illa very slightly. ...
Context 17
... external seam may also appear "slightly interdigitated" (sensu Herring 1972, figure 1). In cross-section the joint most closely resembles a 'stepped joint' (Figure 2.3) but the seam's morphology and facet texture in some individuals also indicates some subtle Type-B inter- digitation. This joint would prevent the facial pro- cess of the maxilla from rotating medially and would also restrict any posterodorsal movement. ...
Context 18
... posterior maxilla-prefrontal joint involves the posteroventral process of the prefrontal, which is associated with the maxilla-palatine and prefron- tal-palatine joints ( Figure 21). The ventrolateral edge of this process sits in a short groove on the dorsal surface of the maxilla just behind the facial process. ...
Context 19
... ventrolateral edge of this process sits in a short groove on the dorsal surface of the maxilla just behind the facial process. The surface of the groove is not smooth in DGPC1 but bears two tubercles and two foramina ( Figure 21.2). The groove is bounded medially by a small ridge ( Figure 22). ...
Context 20
... surface of the groove is not smooth in DGPC1 but bears two tubercles and two foramina ( Figure 21.2). The groove is bounded medially by a small ridge ( Figure 22). The fit is not tight and so may involve substantial soft tissue. ...
Context 21
... posterior surface of the conjoined premax- illae, cleaned of soft tissue, bears little evidence of its relationship with the vomers (e.g., DGPC1, DGPC2), and no facet is visible. The anterior end of each vomer bifurcates into two prongs but can be separated from the premaxilla by a notable dis- tance (occasionally equal to the width of the vom- erine anterior process e.g., NMNZ RE0385) ( Figure 23.1). However, as seen in uncleaned skulls (e.g., LDUCZ x343, LDUCZ x1176) and CT data (YPM 9192), the posterior surfaces of the pre- maxillae and anterior tips of the vomers are con- nected by a thick sheet of soft tissue (Figure 23.2). ...
Context 22
... anterior end of each vomer bifurcates into two prongs but can be separated from the premaxilla by a notable dis- tance (occasionally equal to the width of the vom- erine anterior process e.g., NMNZ RE0385) ( Figure 23.1). However, as seen in uncleaned skulls (e.g., LDUCZ x343, LDUCZ x1176) and CT data (YPM 9192), the posterior surfaces of the pre- maxillae and anterior tips of the vomers are con- nected by a thick sheet of soft tissue (Figure 23.2). This observation demonstrates the problems asso- ciated with inferring soft tissue from fossils. ...
Context 23
... anterior tongue-like edge of the palatine overlaps the posterodorsal surface of the vomer ( Figure 24). The facet on the vomer is scarfed with the slope directed anteromedially (Figures 25, 26). ...
Context 24
... anterior tongue-like edge of the palatine overlaps the posterodorsal surface of the vomer ( Figure 24). The facet on the vomer is scarfed with the slope directed anteromedially (Figures 25, 26). The amount of overlap depends on the vomer's posterior extent (which can be seen in ventral view). ...
Context 25
... disarticu- lated material shows that, at least in some cases, it can be more complex. In specimen AIM LH0617, a small anteromedial shelf from the left vomer slots into a groove in the right vomer, centrally the medial edge of the left is overlapped slightly by the medial edge of the right, and posteriorly the medial edge of the right is overlapped by the left ( Figure 25). In the central portion of the joint the medial margins of the vomers are dorsoventrally expanded, increasing the contact area between them. ...
Context 26
... Sphenodon the palatine has two lateral pro- cesses separated by a foramen for the maxillary division of the trigeminal nerve (cranial nerve 5) and associated blood vessels. This foramen is marked "mf" in figure 3.2). Both of these processes are involved in the joint with the maxilla (Figures 20, 28, 29). ...
Context 27
... foramen is marked "mf" in figure 3.2). Both of these processes are involved in the joint with the maxilla (Figures 20, 28, 29). ...
Context 28
... upper maxilla-palatine joint is a loose butt contact with some very weak vertical Type-B inter- digitation. In lateral view (disarticulated) the upper process of the palatine is rectangular and fluted, in DGPC1 this comprises five or six ridges which are directed posteroventrally in the anterior part and anteroventrally in the posterior part ( Figure 28). Two grooves in this fluting probably relate to the presence of foramina. ...
Context 29
... grooves in this fluting probably relate to the presence of foramina. The corresponding facet on the maxilla for the upper lateral process of the pal- atine bears subtle anteroventrally directed stria- tions ( Figure 22). These striations are not obviously reflected on the palatine's maxillary facet. ...
Context 30
... lower maxilla-palatine joint is primarily a loose butt joint. The lower lateral process of the palatine stems from a point above the anterior half of the palatine tooth row (Figure 29). It expands anterolaterally and posteriorly to form a large pro- cess with an anterolaterally facing ovoid facet. ...
Context 31
... long axis of the cavity is directed anteromedially but it is asymmetrical with a greater lateral compo- nent. At the posterior end of the concavity the lat- eral wall flexes medially and then laterally thus producing a longitudinal ridge ( Figure 20) that slots into a wide groove along the lateral surface of the jugal (Figure 31). The ridge and groove are less pronounced in LDUCZ x1176 than in DGPC1 (Fig- ure 32). ...
Context 32
... the posterior end of the concavity the lat- eral wall flexes medially and then laterally thus producing a longitudinal ridge ( Figure 20) that slots into a wide groove along the lateral surface of the jugal (Figure 31). The ridge and groove are less pronounced in LDUCZ x1176 than in DGPC1 (Fig- ure 32). Posteriorly this ridge has a rugose surface with convoluted striae and gutters directed antero- dorsally, anteriorly and anteroventrally. ...
Context 33
... the ridge is more sharply defined (at least in DGPC1) and shelf-like. Above it, anteriorly, there are three distinct slits (elongate foramina) ( Figure 20). In dorsal view the base of the maxillary con- cavity can be seen to possess small gutters that are generally orientated anteromedially, particularly on the lateral side ( Figure 30). ...
Context 34
... joint primarily involves the anteromedial edge of the jugal abutting against the posterodor- sal edge of the lower lateral palatine process (Fig- ures 28, 32). In addition the tip of the jugal extends anteriorly beyond the maxillary foramen contacting the upper lateral palatine process (e.g., DGPC1, LDUCZ x723, LDUCZ x343 and possibly LDUCZ x1176) for a relatively short distance. ...
Context 35
... joint is essentially a perpendicular butt contact resisting medial movement of the jugal and lateral movement of the palatine. However, in DGPC1 (Figures 32.2, 34) the facet on the jugal is slightly concave and, as reflected in the seam, the posterior end of the joint is notched so that the jugal hooks behind the palatine (Figure 32). This arrangement of the bones would restrict posterior movement of the palatine and anterior movements of the jugal as well as some mediolateral move- ments. ...
Context 36
... joint is essentially a perpendicular butt contact resisting medial movement of the jugal and lateral movement of the palatine. However, in DGPC1 (Figures 32.2, 34) the facet on the jugal is slightly concave and, as reflected in the seam, the posterior end of the joint is notched so that the jugal hooks behind the palatine (Figure 32). This arrangement of the bones would restrict posterior movement of the palatine and anterior movements of the jugal as well as some mediolateral move- ments. ...
Context 37
... arrangement of the bones would restrict posterior movement of the palatine and anterior movements of the jugal as well as some mediolateral move- ments. Apart from the upper facet of the palatine, which bears two vertical ridges, the facets involved lack obvious sculpture ( Figure 28). ...
Context 38
... joint can be divided into three parts. The anterior part involves the palatine overlapping the anterior processes of the pterygoid with a shallow scarf joint (Figures 2.5, 35) so that both palatines meet in the midline on the dorsal surface of the pal- ate (e.g., DGPC2; Sharrell 1966). However, the tips of the pterygoids remain exposed anteriorly (Jones et al. 2009, figure 3.2). ...
Context 39
... anterior part involves the palatine overlapping the anterior processes of the pterygoid with a shallow scarf joint (Figures 2.5, 35) so that both palatines meet in the midline on the dorsal surface of the pal- ate (e.g., DGPC2; Sharrell 1966). However, the tips of the pterygoids remain exposed anteriorly (Jones et al. 2009, figure 3.2). The central part of this joint involves the mediolateral edge of the pala- tine overlapping the lateral edge of the pterygoid but contact is generally minimal (Figure 35) and may even be lost entirely leaving an elongate fon- tanelle (e.g., LDUCZ x036 left side). ...
Context 40
... Sphenodon the paired pterygoids are con- nected anteriorly along a midline seam which is less than half the total length of the bones ( Figure 24.1). In ventral view the seam tends to exhibit low amplitude and long wavelength meandering (e.g., LDUCZ x036). ...
Context 41
... medial view of a disarticulated ptery- goid reveals long slots and flanges that are antero- dorsally inclined from the long axis ( Figure 38). These slots and flanges interlock as in Type-A interdigitation (Figure 2.2) but because the bones are relatively thin, contact seems small relative to the overall size of the bones. Therefore, despite being very distinct the joint is not necessarily strong. ...
Context 42
... despite being very distinct the joint is not necessarily strong. The meandering of the external seams cor- responds to some Type-B interdigitation ( Figure 2.4) but it is very subtle by comparison to the obvi- ous Type-A interdigitation. ...
Context 43
... small slivers of the ectopterygoid (laterally) and pterygoid (medially) are held between the two posterior projections of the pala- tine (Figures 35, 37). Only the tips of the posterior palatine projections are involved leaving a space between the bases (Figure 24.2 figure 3). In specimen DGPC1 contact between the ectopterygoid and palatine is less certain but may have occurred indirectly through soft tissue related to the pterygoid-palatine joint. ...
Context 44
... expanded lateral process of the ectopter- ygoid sits on the dorsal surface of the maxilla above the posterior end of the tooth row ( Figures 20, 30). In dorsal view the seam travels posterome- dially from the edge of the jugal. ...
Context 45
... naso-frontal seam generally runs poster- olaterally from the midline to the junction with the prefrontal (e.g., Jones and Lappin 2009, figure 4; , figure 2). There is some varia- tion in the exact shape of this seam as it may be nearly straight (e.g., BMNH 1844.102911; ...
Context 46
... posterolateral ends of the nasals overlap the anterolateral processes of the frontals with a scarfed tongue-in-groove joint (Figures 2.13, 41, 42, 43, 44). In the disarticulated DGPC1 the medial portions of the bones are not available for study but the structure has been observed in other speci- mens (e.g., BMNH.K). ...
Context 47
... the disarticulated DGPC1 the medial portions of the bones are not available for study but the structure has been observed in other speci- mens (e.g., BMNH.K). The contact is particularly extensive along the junction with the prefrontal but diminishes medially (Figures 42, 44). Of 42 skulls examined, a notable midline fontanelle was pres- ent between the nasals and frontals in nine (21.4%: specimens AMPC 1, BMNH 1844.102911, ...
Context 48
... anterolateral nasal facet on the frontal is generally scarfed, but it is also concave across its width so that the joint resembles a tongue-in- groove joint (Figures 42, 43, 44). Correspondingly the posterior process of the nasal is scarfed and convex across its width ( Figure 13.1, 41). ...
Context 49
... the gutters there are also two large foramina. Other disarticulated nasals (e.g., BMNH.K, YPM 11419) possess a much smoother facet surface (Figure 41.2). This joint would resist dorsal or anterior move- ments of the frontal and ventral or posterior move- ments of the nasal. ...
Context 50
... lateral view the seam travels posteroventrally before folding back anteroventrally in a "V' shape. The frontal-prefrontal joint has two components, an anterior part and a posterior part (Figures 42, 44, 45, 46, 47). In the anterior part, the anterolateral process of the frontal fits inside a deep 'V'-shaped slot in the medial surface of the prefrontal posterior process (Figures 42, 44, 45, 46.3-4). ...
Context 51
... frontal-prefrontal joint has two components, an anterior part and a posterior part (Figures 42, 44, 45, 46, 47). In the anterior part, the anterolateral process of the frontal fits inside a deep 'V'-shaped slot in the medial surface of the prefrontal posterior process (Figures 42, 44, 45, 46.3-4). In the poste- rior part, the posterior process of the prefrontal inserts into a deep cavity in the anterolateral sur- face of the frontal bone (Figures 45, 46.1-2, 47, 48). ...
Context 52
... the anterior part, the anterolateral process of the frontal fits inside a deep 'V'-shaped slot in the medial surface of the prefrontal posterior process (Figures 42, 44, 45, 46.3-4). In the poste- rior part, the posterior process of the prefrontal inserts into a deep cavity in the anterolateral sur- face of the frontal bone (Figures 45, 46.1-2, 47, 48). Longitudinal ridges can be found dorsally in both parts of this joint (Figures 43.1, 43.3, 45.1). ...
Context 53
... joint primarily involves the medial surface of the postfrontal slotting into the lateral surface of the frontal (Figures 47, 48, 49, 50, 51, 52, 53, 54) but it can be divided into three sections. In the anterior section, the anterior process of the post- frontal (Figures 51, 52.2) inserts into a deep slot in the frontal (Figures 43, 47, 48, 49, 54). This slot exhibits gutters and ridges running along its axis (Figures 43, 48). ...
Context 54
... slot exhibits gutters and ridges running along its axis (Figures 43, 48). In the central and largest section the frontal sits in a deep concavity on the postfron- tal (Figure 52.2), and some specimens possess a small shelf on the frontal that enters the postfrontal (BMNH K) (Figure 42). The posterior section is related to the anterior joints of the parietal. ...
Context 55
... slot exhibits gutters and ridges running along its axis (Figures 43, 48). In the central and largest section the frontal sits in a deep concavity on the postfron- tal (Figure 52.2), and some specimens possess a small shelf on the frontal that enters the postfrontal (BMNH K) (Figure 42). The posterior section is related to the anterior joints of the parietal. ...
Context 56
... this cranial joint suture is some- times referred to as the coronal suture, reflecting human terminology (e.g., Moss 1954Moss , 1957Markens and Oudhof 1980;Opperman 2000).The joint is complex and is associated with the medial joints of the postfrontal. Primarily this joint involves an alternating overlap; laterally the frontal overlaps the parietal but medially the parietal overlaps the frontal (Figures 42, 43, 44, 48, 49, 50, 53, 54, 55, 56, 57, 58, 59). ...
Context 57
... two pro- cesses are separated by an oblique slot ( Figure 43.5) that may be smaller in juvenile frontals (e.g., LDUCZ x1176). Occasionally the posteriormost medial edge of the frontal is exposed dorsally (e.g., NMNZ RE0382) but otherwise the overlapping fac- ets of both bones are scarfed, and therefore this resembles the 'birds-mouth' joint found in wood joinery (Figure 2.15; Graubner 1992). On its own, In hatchlings the adjoining medial portions of the frontals and parietals have not fully ossified, resulting in a fronto-parietal fontanelle (Howes and Swinnerton 1901;Rieppel 1992). ...
Context 58
... is the largest joint of the parietal and overall involves the posterior end of the postfrontal overlapping the anterolateral part of the parietal (Figures 42, 44, 47, 48, 49, 50, 51, 52, 53, 56, 57, 58, 59). In dorsal view the seam runs posteromedi- ally from the junction with the frontal for a short dis- tance, occasionally reaching the anterior edge of the parietal crest at a point level with the posterior end of the parietal foramen (Figure 50). ...
Context 59
... internal part of the joint can be divided into a dorsal part and a ventral part. The dorsal part consists of a tongue-in-groove joint where the tongue-shaped medial process of the postorbital (Figures 60, 61) sits in a concavity on the postfron- tal (Figures 2.13, 42, 52, 62). The ventral part of this joint consists of a triple vertical slot joint, with two slots in the postorbital (Figures 2.11, 60, 61) and one in the postfrontal (Figures 51, 52, 53). ...
Context 60
... dorsal part consists of a tongue-in-groove joint where the tongue-shaped medial process of the postorbital (Figures 60, 61) sits in a concavity on the postfron- tal (Figures 2.13, 42, 52, 62). The ventral part of this joint consists of a triple vertical slot joint, with two slots in the postorbital (Figures 2.11, 60, 61) and one in the postfrontal (Figures 51, 52, 53). The latter slot is here referred to as the postfrontal cleft. ...
Context 61
... dorsal part consists of a tongue-in-groove joint where the tongue-shaped medial process of the postorbital (Figures 60, 61) sits in a concavity on the postfron- tal (Figures 2.13, 42, 52, 62). The ventral part of this joint consists of a triple vertical slot joint, with two slots in the postorbital (Figures 2.11, 60, 61) and one in the postfrontal (Figures 51, 52, 53). The latter slot is here referred to as the postfrontal cleft. ...
Context 62
... latter slot is here referred to as the postfrontal cleft. Its exact position can vary, and it may be absent altogether (e.g., Figure 42, BMNH.K, AIM LH 833) but it is usually found at the base of the postfrontal concavity with a long axis parallel to that of the upper postorbital bar. This cleft accepts a narrow bital. ...
Context 63
... 34.3, 62) and provides a shallow depression that accommodates the postorbital. In the upper portion of the joint the jugal expands dorsally alongside the medial sur- face of the postorbital (Figures 62, 63). In the juve- nile LDUCZ x1176, the tip of the jugal dorsal process tapers rather than being "squared-off" as in the adult Sphenodon examined (Figures 32.2, 34). ...
Context 64
... the upper portion of the joint the jugal expands dorsally alongside the medial sur- face of the postorbital (Figures 62, 63). In the juve- nile LDUCZ x1176, the tip of the jugal dorsal process tapers rather than being "squared-off" as in the adult Sphenodon examined (Figures 32.2, 34). In DGPC1, the articulation surface bears sub- tle striations aligned with its long axis (Figure 31). ...
Context 65
... joint has addi- tional features in some larger individuals and so may change with ontogeny. The features include interlocking pegs anteroventrally (e.g., DGPC1) so that the joint as a whole can resemble an asym- metrical 'birds mouth joint' (Figure 2.15; Graubner 1998). Furthermore in DGPC1, at least, the facet on the quadratojugal bears a slight ridge that fits into a groove on the jugal. ...
Context 66
... tip of the thin squamosal anterior process ends in two to four triangular points (two in LDUCZ x723, YPM 11419, LDUCZ x343; three in DGPC1, LDUCZ x036; four in LDUCZ x1176) which lie in a depression on the postorbital (Figure 63). Posteri- orly, the tip of the postorbital sits against a recess in the squamosal bone (Figure 2.13). The extent of the recess varies; being very shallow in some specimens, e.g., LDUCZ x1176 ( Figure 64.1); or deep with edges that envelop the posteriorly taper- ing postorbital, e.g., DGPC1 (Figure 65). ...
Context 67
... opposing facet on the quadratojugal is rough but matching grooves are not obvious (Figure 64). More posteriorly, near the posterior part of the quadratojugal-jugal joint, the lateral edge of the quadratojugal expands dorsally (Figure 64.2). At this point the dorsal surface of the quadratojugal is concave (Figure 67). ...
Context 68
... posteriormost and largest of these slot joints involves the dorsal tip of the quadrate which is an expanded bun-like process with an anteromedially directed long axis (Figures 64, 68, 69). This 'bun' is held in a large concavity in the squamosal (Figures 68) between two ventral extensions (Howes and Swinnerton 1901): a robust posteromedial process (or lappet) which extends ventrally from the dorsal process and a longer thinner process which extends anteromedially from the squamosal ventral process and is associated with the squamosa- pterygoid joint (Figure 69.2). The second slot joint involves the thinner process and extends anteriorly into a slightly sigmoid groove on the crest of the quadrate wing (Figure 68.2). ...
Context 69
... 'bun' is held in a large concavity in the squamosal (Figures 68) between two ventral extensions (Howes and Swinnerton 1901): a robust posteromedial process (or lappet) which extends ventrally from the dorsal process and a longer thinner process which extends anteromedially from the squamosal ventral process and is associated with the squamosa- pterygoid joint (Figure 69.2). The second slot joint involves the thinner process and extends anteriorly into a slightly sigmoid groove on the crest of the quadrate wing (Figure 68.2). The groove itself is contiguous with the rough posterior portion of the quadrate-squamosal joint. ...
Context 70
... ventral process of the squamosal in hatchling Sphenodon is comparable to that of adults, bearing medial and lateral extensions to hold the quadratojugal. There also seems to be a pocket for the head of the quadrate (Rieppel 1992, figure 2). However, there is no apparent postero- medial lappet as found in juvenile specimens (LDUCZ x1176). ...
Context 71
... previously observed (e.g., Robinson 1973), the quadrate of Sphenodon is firmly joined to the pterygoid. Primarily, the joint involves the lat- eral surface of the pterygoid posterolateral process and the medial surface of the quadrate anterome- dial process (Figures 69, 70, 71, 72). However, there are two features of note. ...
Context 72
... there are two features of note. Firstly, the ventral edge of the pterygoid wing slots into a gutter that runs laterally along the base of the quadrate wing ( Figure 69, 72); secondly, the posterodorsal tip of the pterygoid wing abuts the main body of the quadrate and is related to the squamosal-pterygoid joint (Figures 67, 'G' in Figure 68.3). In posterior view the seam has a long sigmoid shape ( Jones et al. 2009). ...
Context 73
... Sphenodon this connection is fused ven- trally but a faint seam may be visible dorsolaterally above the quadratojugal foramen (e.g., DGPC1, LDUCZ x036) (Figure 72). In hatchlings the bones are not fused (Howes and Swinnerton 1901;Rieppel, 1992). ...
Context 74
... (1973) incorrectly thought the epip- terygoid of Sphenodon overlapped the quadrate. In actuality, the posterior end of the epipterygoid base sits against the pterygoid abutting the anterior edge of the quadrate (Figures 70, 71, 72, 73; Appendix 2). From the junction with the pterygoid base of the quadrate-pterygoid wing, in anterolat- eral view, the seam travels anterodorsally, posteri- orly, dorsally and finally anterodorsally again. ...
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... it may be more complicated than this, as work on sheep skulls ( Thomason et al. 2001) found that cranial architecture corresponded to working side compression but not overall strain magni- tudes. Nevertheless, the arrangement of bony ridges and internal facet ornament allows the con- struction of a "hypothesis of compressive stress trajectories" (HCST, Figure 82) that can be tested by comparison to cranial joint structure and Finite Element Analysis. The lines of hypothesised stress are often located along the (thickened) edges of bones rather than running through the exact cen- tre. ...
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... system potentially allows opposing stresses from different regions to be transmitted toward each other as they are reduced and absorbed by the intervening hard and soft tissues (Buckland-Wright 1978). The prefrontal in Spheno- don should, for example, be important in re-direct- ing dorsally directed forces from the palate and maxilla to the skull roof ( Figure 82). Similarly, the ectopterygoid is positioned to transmit forces between the marginal tooth rows and the centre of the pterygoid (Figure 82.3). ...
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... prefrontal in Spheno- don should, for example, be important in re-direct- ing dorsally directed forces from the palate and maxilla to the skull roof ( Figure 82). Similarly, the ectopterygoid is positioned to transmit forces between the marginal tooth rows and the centre of the pterygoid (Figure 82.3). Forces from the jaw joint radiate along five different pathways from a point on the quadrate-quadratojugal (Figure 82.1 and 82.4). ...
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... the ectopterygoid is positioned to transmit forces between the marginal tooth rows and the centre of the pterygoid (Figure 82.3). Forces from the jaw joint radiate along five different pathways from a point on the quadrate-quadratojugal (Figure 82.1 and 82.4). ...
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... behaviour will generate dorsally directed forces within the premaxilla relative to the rest of the skull, resulting in dorsal shear in the premaxilla-nasal joints and ventral tension in the premaxilla-vom- erine and premaxilla-maxilla joints (Taylor 1992;Preuschoft and Witzel 2002;Rafferty et al. 2003). The premaxilla-nasal joint will resist excessive pos- terodorsal slippage of the premaxilla (Figures 12, 13) whereas the extensive soft tissue between the base of the premaxilla and its neighbouring bones (vomer, maxilla) may permit some limited separa- tion. This location of flexibility may also be impor- tant during prooral jaw movement when the premaxillary chisel tooth is contacted by the lower jaw. ...
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... anterior maxilla will be loaded when Sphenodon uses its caniniform teeth ( Figure 5.1), with compressive forces being directed up the anterior edge of the facial process (Figure 82.1) into the nasal and prefrontal. The rather box-like or tubular cross-section of the rostrum at this level is shaped to resist both bending and torsional stress (Preuschoft and Witzel 2002;Rafferty et al. 2003), aided by soft tissue in the large overlaps between the prefrontal, nasal and maxilla. ...
Context 81
... bending of the parietal will be resisted by its dorsoventral expansion. The HCST suggests that compressive forces in the skull roof will converge between the orbits and in front of the upper temporal fenestrae (Figure 82). Significantly, this is where some of the most heavily interlocked joints are located ( Figure 77, e.g., frontal-prefrontal, frontal-postfrontal, pos- torbital-postfrontal). ...
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... frontal-parietal joint is rela- tively narrow in Sphenodon but the interlocking structure maintains a rigid connection, resisting both dorsoventral bending forces and mediolateral torsional forces. It is reinforced laterally by the large spanning postfrontals (Figure 77.2). The interfrontal joint may act as a 'keystone' (Figure 79) to the arches of the orbits with forces travelling posteriorly up the postorbital bars ( Figure 82) and being directed transversely against each other in another arch meeting around the postfrontal-pari- etal-frontal suture ( Figure 82). ...
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... is reinforced laterally by the large spanning postfrontals (Figure 77.2). The interfrontal joint may act as a 'keystone' (Figure 79) to the arches of the orbits with forces travelling posteriorly up the postorbital bars ( Figure 82) and being directed transversely against each other in another arch meeting around the postfrontal-pari- etal-frontal suture ( Figure 82). ...
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... is reinforced laterally by the large spanning postfrontals (Figure 77.2). The interfrontal joint may act as a 'keystone' (Figure 79) to the arches of the orbits with forces travelling posteriorly up the postorbital bars ( Figure 82) and being directed transversely against each other in another arch meeting around the postfrontal-pari- etal-frontal suture ( Figure 82). ...
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... as in other amniotes, the con- vex "arch" formed by the postorbital bars would resist the downward pull of the adductor muscles (Frazzetta 1968), aided by the tight fit of the postor- bital-postfrontal joint and, further ventrally, by the tall medial process of the jugal which is positioned to brace the postorbital (Figure 79). The long over- lapping postorbital-squamosal joints in the upper temporal bars (Figure 62) should allow the small adjustive movements necessary to reduce torsion and shearing in this part of the skull. Similarly, as the plane of the jugal-postorbital joint is almost par- allel to the orbital margin, the intrasutural collagen fibres should be orientated perpendicular to resist posterodorsally directed forces from the upper jaw ( Figure 82). ...
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... long over- lapping postorbital-squamosal joints in the upper temporal bars (Figure 62) should allow the small adjustive movements necessary to reduce torsion and shearing in this part of the skull. Similarly, as the plane of the jugal-postorbital joint is almost par- allel to the orbital margin, the intrasutural collagen fibres should be orientated perpendicular to resist posterodorsally directed forces from the upper jaw ( Figure 82). The parietal-squamosal joint alterna- tively resists the anteroventral pull of the m. ...
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... near vertical facet surfaces permit inter- sutural soft tissue to be orientated so as to prevent excessive shear or torsion between the lower tem- poral bar and squamosal-quadratojugal. The joint between the squamosal and quadrate-quadratoju- gal is roughly parallel to the jaw joint ( Figure 77) and is probably important for transmitting forces from the jaw joint to neighbouring parts of the skull (Figure 82). The lateral part of the interlocking quadrate-squamosal joint appears already well established in hatchlings (Rieppel 1992) but the medial lappet that supports the quadrate in adults does not. ...
Context 88
... vaulting may help to dissi- pate dorsally directed forces from the teeth in a manner analogous to the effects of a 'flying but- tress' (Busbey 1995). Perhaps correspondingly the palatal bone thickenings in Sphenodon (and by inference compressive stresses) converge toward the midline of the palate (Figure 82.3). The vomer, for example, although apparently thin, is reinforced by medial and lateral thickenings. ...
Similar publications
Numerous vertebrates exhibit cranial kinesis, or movement between bones of the skull and mandible other than at the jaw joint. Many kinetic species possess a particular suite of features to accomplish this movement, including flexible cranial joints and protractor musculature. Whereas the musculoskeletal anatomy of these kinetic systems is well und...
Citations
... Menaker et al. (1997) correlated the absence of the foramen with a potential nocturnality in Euparkeria. The foramen, however, is clearly visible in the extant mostly nocturnal tuatara (Jones et al. 2011;Cree 2014). ...
... The tuatara also has a frontonasal fontanelle (Jones et al. 2011). It appears to be related to its unique functional feeding morphology. ...
... nasal and prefrontal) and posterior (incl. frontal) functional snout modules in tuatara, which might support a rather loose connection of the skull roof in this area (sensu Werneburg and Abel (2022)), perhaps also related to some degree of mesokinetic mobility (at least in the juveniles, see Rieppel (1992); Jones et al. (2011); Yaryhin and Werneburg (2019); Zhang et al. (2022)). ...
Using four extinct land vertebrate species as examples, I discuss ontogenetic strategies as well as the potential influence of bite- and other external forces on the formation of the land vertebrate skull. In principle, areas under biomechanical stress are strongly ossified, whereas regions with little or no stress show only weak or no ossification. In this regard, all plates, arcades and openings of the skull – even in that of the multi-fenestrated dinosaurs – can be explained. I trace the changes in feeding mode and body posture at the transition from semi-aquatic to fully terrestrial tetrapods and discuss changes in the position of bite points. Through evolution, an increasing bite force is argued to have a crucial influence on the formation of new skull openings, such as the supratemporal and the antorbital fenestrae in archosaurs, by changing the direction of stress flows in the skull. The conquest of land was also associated with the appearance of novel types of behaviour such as inter- and intraspecific combats. Horns and other cranial weapons were formed repeatedly, which are shown to alter skull construction when receiving external forces. Changes in the skull biomechanics are associated with body posture and postcranial skeletal anatomy. Additionally, vice versa, the neck muscles are shown to have an important impact on the differentiation of the tetrapod skull. Finally, a new hypothesis is provided for the evolution of the temporal openings, based on biomechanical considerations. I argue that the synapsid (infrafenestral) morphotype was ancestral to amniotes related to a strong anterior bite in the mouth. Along the reptilian lineage – such as in many parareptiles, captorhinids and turtles – temporal fenestration was repeatedly closed by stiffening the temporal region in response to external forces. In addition, I argue that the upper temporal opening evolved first and that the diapsid (bifenestral) morphotype is secondary. The “triapsid” morphotype in ceratopsid dinosaurs is shown to be related to concentrated forces on the animal’s neck frill.
... A24 describe a longitudinal sulcus that marks the dorsal border of the secondary bone lip in the labial side of the maxilla. However, if the fragment is interpreted as part of the jaw, this abrupt border is the dorsal limit of the Meckelian groove, which is marked by a sinusoidal border of bone, as is common in the posterior region of the Meckelian groove in Sphenodon and in the mid to posterior region in Kawasphenodon (Jones et al. 2011;. ...
... A24 describe the wear facets of the teeth on the side they consider lingual, but fail to mention that the opposite side is also straight and heavily worn. In both our and their interpretations the small tooth is posterior to the large one, but this is not owned to a successional-additional relation or to an alternate series, but to the smaller size of the recently erupted teeth compared to the central, bigger teeth of the jaw, as observed in both Sphenodon and Kawasphenodon (Jones et al. 2011;. ...
... The ´well-separated´ teeth are considered as autapomorphic of MPM-PV-23097 by A24, since they indicate it differs in that aspect with the ´more imbricate´ teeth in Sphenodon. However, the condition in MPM-PV-23097 is exactly the expected for the mid region of the lower jaw in Sphenodon (Jones et al. 2011), as in Tika giacchinoi and some materials of Kawasphenodon expectatus (Apesteguía et al. , 2021. Further, this feature varies along the toothline and ontogeny in Sphenodon itself (Jones et al. 2011) and related taxa (e.g. ...
Agnolín et al. (2024) (Hereafter A24) report on a Late Cretaceous lepidosaur assemblage from southern Patagonia. The fossils described by A24 are noteworthy as they extend the record of lepidosaurs from southern Patagonia and as such deserve a detailed study. However, we find several issues in the descriptions and consider most of their taxonomic assignments to be unsupported by the data, which in turn makes their faunistic interpretations to be seriously flawed. Here, we would like to comment on some of the major inconsistencies and misstatements that we have found in the work of A24 in order to prevent wrong faunal lists and biogeographic considerations.
... The specimen is publicly available. The osteological description in this manuscript follows the nomenclature and orientation proposed by Evans (2008) and Jones et al. (2011) for the skull, Hoffstetter and Gasc (1969) for the axial skeleton, and Russell and Bauer (2008) for the appendicular skeleton. The ontogenetic status of SNSB-BSPG 2018 I 179 is evaluated based on information previously published for ontogeny in rhynchocephalians (i.e., Evans, 2008;Hoffstetter & Gasc, 1969;Jones, 2008;Simões et al., 2022). ...
... The interfrontal articulation margin is straight. Anteriorly, the anterior end of the frontal widens but is incomplete, and ventrally bears a large medial the facet for the nasal and a smaller lateral facet for the prefrontal (similar but not identical to Sphenodon Gray, 1831: Jones et al., 2011. Anteriorly, the nasal and prefrontal facets appear contiguous (Figure 3a). ...
... Thus, the postorbital is a triradiated bone that articulates to the frontal and parietal dorsomedially, the jugal ventrally, and the squamosal posterodorsally (Figure 3e,f). The anteromedial (lateral in Jones et al., 2011) process is wide, expanding both antero-and posteriorly toward its medial end. The shortest process of the postorbital is the ventral one, which is triangular in outline and rapidly tapers ventrally. ...
Late Jurassic rhynchocephalians from the Solnhofen Archipelago have been known for almost two centuries. The number of specimens and taxa is constantly increasing, but little is known about the ontogeny of these animals. The well‐documented marine taxon Pleurosaurus is one of such cases. With over 15 described (and many more undescribed) specimens, there were no unambiguous juveniles so far. Some authors have argued that Acrosaurus, another common component of the Solnhofen Archipelago herpetofauna, might represent an early ontogenetic stage of Pleurosaurus, but the lack of proper descriptions for this taxon makes this assignment tentative, at best. Here, we describe the first unambiguous post‐hatchling juvenile of Pleurosaurus and tentatively attribute it to Pleurosaurus cf. P. ginsburgi. The new specimen comes from the Lower Tithonian of the Mörnsheim Formation, Germany. This specimen is small, disarticulated, and incomplete, but preserves several of its craniomandibular bones and presacral vertebrae. It shares with Pleurosaurus a set of diagnostic features, such as an elongated and triangular skull, a low anterior flange in its dentition, and an elongated axial skeleton. It can be identified as a juvenile due to the presence of an unworn dentition, well‐spaced posteriormost dentary teeth, a large gap between the last teeth and the coronoid process of the dentary, and poorly ossified vertebrae with unfused neural arches. Acrosaurus shares many anatomical features with both this specimen and Pleurosaurus, which could indicate that the two genera are indeed synonyms. The early ontogenetic stage inferred for the new Pleurosaurus specimen argues for an even earlier ontogenetic placement for specimens referred to Acrosaurus, the latter possibly pertaining to hatchlings.
... The posterior margin between the tabs forms an interdigitated joint with the parietal (Figures 1b and 4l,m). Lateral to the tab, the suture forms a bear's mouth joint (sensu Jones et al., 2011) where the parietal slightly overlaps the frontal medially, and the posterolateral process of the frontal overlaps the anterolateral corner of the parietal (Figure 1b). The frontoparietal joint is clasped by the posteromedial and posterior processes of the postfrontal (Figures 1b and 2a). ...
... The maxillary process is wide, short, and stout ( Figure 8l). There is a raised scarf articulation (sensu Jones et al., 2011) between the maxillary process of the palatine and the maxillary palatal shelf. The anterior border of the palatine contacts the prefrontal lamina of the frontal dorsally and the prefrontal laterally. ...
The rough teiid or water cork lizard (Echinosaura horrida) is a small reptile from Colombia and Ecuador placed in a genus that contains eight species and well‐known phylogenetic relationships. Here we provide a detailed description and illustrations, bone by bone, of its skull, while we discussed its intraspecific variation by comparing high‐resolution computed tomography data from two specimens and the variation within the genus by including previously published data from Echinosaura fischerorum. This allowed to propose putative diagnostic character states for Echinosaura horrida and synapomorphies for Echinosaura. In addition, our discussion includes broader comparisons of new character transformations of the jugal, vomer, orbitosphenoid, and hyoid. These characters are important for diagnosing clades at different levels of the Gymnophthalmoidea phylogeny.
... Several aspects of skull biomechanics are just being explored, including the influence of cranial sutures, cranial kinesis, and the cartilaginous skull (Jones et al., 2020(Jones et al., , 2017Natchev et al. 2016) on force distribution. The tuatara is one of the best-researched species in this regard (Curtis et al., 2010Jones et al., 2011;Jones & Lappin, 2009) making comparisons to other, less studied reptilian taxa rather complicated. ...
The complex constructions of land vertebrate skulls have inspired a number of functional analyses. In the present study, we provide a basic view on skull biomechanics and offer a framework for more general observations using advanced modeling approaches in the future. We concentrate our discussion on the cranial openings in the temporal skull region and work out two major, feeding-related factors that largely influence the shape of the skull. We argue that (1) the place where the most forceful biting is conducted as well as (2) the handling of resisting food (sideward movements) constitute the formation and shaping of either one or two temporal arcades surrounding these openings. Diversity in temporal skull anatomy among amniotes can be explained by specific modulations of these factors with different amounts of acting forces which inevitably lead to deposition or reduction of bone material. For example, forceful anterior bite favors an infratemporal bar, whereas forceful posterior bite favors formation of an upper temporal arcade. Transverse forces (inertia and resistance of seized objects) as well as neck posture also influence the shaping of the temporal region. Considering their individual skull morphotypes, we finally provide hypotheses on the feeding adaptation in a variety of major tetrapod groups. We did not consider ligaments, internal bone structure, or cranial kinesis in our considerations. Involving those in quantitative tests of our hypotheses, such as finite synthesis analyses (FESA), will provide a comprehensive picture on cranial mechanics and evolution in the future.
... Likewise, the postorbital disappears, among other taxa, towards the origins of mammals, birds, lissamphibians, as well as various squamates (Jollie, 1957;Kemp, 1984;Carroll, 2007;Evans, 2008). The postfrontal is absent in the majority of extant tetrapods but still present in tuatara and some squamates (Evans, 2008;Jones et al., 2011). The intertemporal is present only in Paleozoic taxa (e.g., Panchen, 1964;Klembara et al., 2006Klembara et al., , 2014Rawson et al., 2021) but absent in amniotes and lissamphibians. ...
The diversity and evolution of the temporal skull region is a classical text book example of comparative anatomy. In the earliest land vertebrates this region was, in most cases, completely covered by an armor of dermal bones. This armor has been successively reduced over time, leading most famously to the evolution of temporal fenestrae and marginal excavations. Such temporal openings are widespread in extant Tetrapoda, but especially their great diversity within Amniota (mammals and reptiles, including birds) inspired many early studies on the potential phylogenetic and evolutionary implications of temporal openings. In the early 20th century, this led to various researchers naming new taxa that were mainly defined by their temporal morphology, with Anapsida, Synapsida, Diapsida, and Euryapsida being the most known. Most of these taxa are not considered to represent natural groupings anymore; instead, new fossil findings and analyses confirmed that similar types of temporal openings independently evolved several times within, as well as outside of Amniota. Thus, the main focus of temporal region research has been on their functional morphology. The forces generated by the external jaw adductors hereby seem to play an essential role, but additionally the impact of neck mechanics, skull shape, developmental biology, and others are being discussed. In this short review, we summarize the research history and the current state of art to inspire a more integrative morphofunctional and evolutionary discussion of this widely-known character complex in research and education.
... It bears two triangular teeth. The maxilla forms a lingual shelf, which posteriorly bears an elliptical facet for contact with the ectopterygoid, based on comparison with Sphenodon punctatus (Jones et al., 2011). Posteriorly, the maxilla has an extensive surface for the reception of the jugal. ...
Skeletal remains of a small lepidosaurian reptile from the Middle Triassic (Ladinian: Longobardian) Erfurt Formation, exposed in a commercial limestone quarry near Vellberg (Germany), represent the oldest rhynchocephalian known to date. The new taxon, Wirtembergia hauboldae , is diagnosed by the following combination of features: Premaxilla with four teeth, first being largest and decreasing in size from first to fourth. Jugal with tiny, spur‐like posterior process. Lateral surface of dentary strongly convex dorsoventrally for much of length of bone, bearing distinct longitudinal ridge and sculpturing in large specimens. Coronoid eminence of dentary low, subrectangular, and with dorsoventrally concave lateral surface in larger specimens. Dentition with pleurodont anterior and acrodont posterior teeth. Posterior (=additional) teeth with (in side view) triangular, at mid‐crown level labiolingually somewhat flattened crowns, and with oval bases. Phylogenetic analysis recovered the new rhynchocephalian as the earliest‐diverging member of its clade known to date.
... Although the ontogeny of S. punctatus is somewhat known (Dendy, 1899;Howes & Swinnerton, 1901;Jones, 2008;Jones et al., 2011;Rieppel, 1992;Robinson, 1976), the development of its brain cavity is poorly studied (but see Dendy, 1911 for brief discussions for the early life stages of the species). Throughout development, the volume of the endocast of S. punctatus increases linearly with skull size, but its shape varies considerably: it becomes narrower, longer, and less dorsoventrally curved. ...
Understanding the origins of the vertebrate brain is fundamental for uncovering evolutionary patterns in neuroanatomy. Regarding extinct species, the anatomy of the brain and other soft tissues housed in endocranial spaces can be approximated by casts of these cavities (endocasts). The neuroanatomical knowledge of Rhynchocephalia, a reptilian clade exceptionally diverse in the early Mesozoic, is restricted to the brain of its only living relative, Sphenodon punctatus, and unknown for fossil species. Here, we describe the endocast and the reptilian encephalization quotient (REQ) of the Triassic rhynchocephalian Clevosaurus brasiliensis and compare it with an ontogenetic series of S. punctatus. To better understand the informative potential of endocasts in Rhynchocephalia, we also examine the brain-endocast relationship in S. punctatus. We found that the brain occupies 30% of its cavity, but the latter recovers the general shape and length of the brain. The REQ of C. brasiliensis (0.27) is much lower than S. punctatus (0.84-1.16), with the tuatara being close to the mean for non-avian reptiles. The endocast of S. punctatus is dorsoventrally flexed and becomes more elongated throughout ontogeny. The endocast of C. brasiliensis is mostly unflexed and tubular, possibly representing a more plesiomorphic anatomy in relation to S. punctatus. Given the small size of C. brasiliensis, the main differences may result from allometric and heterochronic phenomena, consistent with suggestions that S. punctatus shows peramorphic anatomy compared to Mesozoic rhynchocephalians. Our results highlight a previously undocumented anatomical diversity among rhynchocephalians and provide a framework for future neuroanatomical comparisons among lepidosaurs.
... The braincase anatomy and neural soft tissues of Sphenodon punctatus had been largely explored, indicating a relatively modest pallial specialization for this taxon (e.g., Gisi 1808; Dendy 1909Dendy , 1910O'Donoghue 1920;Christensen 1927;Platel 1976Platel , 1989Bruce 2009;Jones et al. 2011; among many others). Although not described, illustrations of the brain anatomy were made by Dendy (1909) accompanying his work on intracranial vascular descriptions and re-drawn by Diaz and Trainor (2019). ...
Braincase descriptions of lepidosaurian clades (Rhynchocephalia and Squamata) are scarce, and paleoneurological studies are even scarcer when compared to other reptiles. Regarding paleoneurology sensu stricto, so far mosasauroids and snakes (the latter by means of a single published study) remain the better known lepidosaur groups. Further comparisons among extinct and living lepidosaurs – along with their evolutive history starting in the early Triassic– are not possible due to the lack of neuroanatomical information in most families. Here we provide a revision of the published literature on endocranial anatomy and paleoneurology in Lepidosauria, including an overview of the comparative braincase and neuroanatomy of living representatives of the clade. We hope that this information will have an impact on future studies in the field of comparative neuroanatomy in both living and extinct species. Micro-CT and diceCT data are currently facilitating neuroanatomical comparisons among living species, preparing the background for a potential rise of paleoneurological studies of non-marine extinct lepidosaurs.
... On the contrary, in our study, the location doesn't change, but with the development of age, it becomes less visible as a result of the ossification process. On the other hand; De Pollack (1996) stated that increased bone growth at suture margins is linked to cranial suture fusion (craniosynostosis) and added that Jones et al. (2011) recorded that there are over 100 sutural joints in the skull. The suture has been intensively investigated as a model system for skeletal development, according to the report by Di Ieva et al. (2013). ...
Objective:
The sutures are associated with anatomical and physiological differences in skull camels. There is a deficiency in the information regarding the anatomy of dromedary camels, especially on fibrous joints (sutures) of the camels' skull.
Aim:
The goal of this work was to give a detailed gross anatomical and radiographic description of the sutures in the camels' skull. This description may be of great importance for veterinarians to differentiate between the suture and the fracture of the head in the radiographic photos.
Methods:
The current study was conducted on 10 skulls of the young (Howar) dromedary camel at 4-10 months old. The skulls were prepared by using the boiling and maceration techniques. The gross and radiographic photos of the sutures were taken using a digital camera and Siemens mobile full-wave X-ray machine (Siemens Medical Solutions, Erlangen, Germany).
Results:
The skull is made up of nineteen bones -6 single and 13 paired-the majority of which are joined by joints termed as sutures. The sutures of the camel skulls were viewed in dorsal, ventral, lateral-vertical, and inside directions. They were of four types which are the coronal, serrate, plane, and squamosal sutures in different positions of the skull.
Conclusion:
The current study showed that the fibrous joints of camel skulls (sutures) were similar to those of other domestic animals. This information is critical for supporting veterinarians to differentiate sutures from fractures that may have happened in the skull of the dromedary camel using radiological pictures.
