Cordichelys, Gaffney & Meylan & Wood & Simons & De Almeida Campos, 2011
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publication ID |
https://doi.org/ 10.1206/350.1 |
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persistent identifier |
https://treatment.plazi.org/id/C95DDC2B-FFFA-5EFC-FE9D-A73F9ED2D484 |
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treatment provided by |
Felipe |
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scientific name |
Cordichelys |
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Cordichelys Figures 52–55 View Fig View Fig View Fig View Fig
The skull of Cordichelys YPM 7457 is particularly well preserved and complete, which makes it convenient to include wider comparisons with other Stereogenyini . The reader should make use of this section as an introduction to Stereogenyini skull morphology in general.
PREFRONTAL
Preservation: The prefrontals in YPM 7457 (formerly YPM 6205) lack the anterior edges on both sides, and small portions near the maxilla contacts.
Contacts: As in the other subtribe Stereogenyina , the contacts are with the other prefrontal on the midline, the maxilla anteroventrolaterally, and the frontal posteriorly.
Structures: Cordichelys has a shallow interorbital depression, wider and less defined than in Podocnemis , that appears to be restricted to this taxon. The interorbital distance in Cordichelys is relatively broad, significantly different from Podocnemis and agreeing with the other Stereogenyini . The dorsal edges of the orbits are raised in Cordichelys and this produces the apparent depression rather than a well-defined groove as in Podocnemis .
FRONTAL
Preservation: Both frontals in YPM 7457 are complete.
Contacts: The contacts are with the other frontal on the midline, the prefrontal anteriorly, the postorbital posterolaterally, and the parietal posteriorly, as in the other subtribe Stereogenyina . These general relations of the frontal are found in all Stereogenyini and most pelomedusids, but the frontal of Bairdemys venezuelensis is particularly similar in shape to the frontal in Latentemys . The interorbital distance is slightly greater in Cordichelys than it is in Shweboemys , but the distance is nearly the same in Bairdemys venezuelensis and Latentemys .
Structures: Cordichelys is slightly convex between the orbits, but it is not curved to the degree seen in Bairdemys venezuelensis . In lateral view the prefrontal and frontal of Bairdemys are dorsally convex, curving anteroventrally from the fronto-parietal suture. In all other members of the Stereogenyini the skull roof is nearly flat in profile. Among Podocnemidinae only Podocnemis approaches the degree of curvature in Bairdemys venezuelensis but does not reach it.
The ventral surface of the frontal in Cordichelys and other Stereogenyini is dominated by a thick and well-developed parasagittal septum orbitotemporale separating the fossa orbitalis laterally from the sulcus olfactorius medially. The septum is lowest anteriorly where it is a continuation of the ridge on the ventral surface of the prefrontal that separates the fossa orbitalis and the fossa nasalis. The ridge on the frontal thickens and deepens posteriorly where it contacts the processus inferior parietalis posteromedially and the posterior wall of the fossa orbitalis posterolaterally. The structure of this region in Stereogenyini differs from other pelomedusoides.
In turtles generally, a view into the front part of the cavum cranii shows a pair of parasagittal walls ending anteriorly in the fissure ethmoidalis. Each wall, the processus inferior parietalis, is formed dorsally by the parietal primarily and by the frontal to a varying extent and ventrally by the pterygoid ( Gaffney, 1979). In all pleurodires the processus trochlearis pterygoidei forms a buttress with the palatine and jugal, so that there is a separate postorbital wall, the septum orbitotemporale ( Gaffney et al., 2006). Cryptodires lack this structure and usually are open behind the orbit. In pleurodires the connection between the processus trochlearis pterygoidei and the septum orbitotemporale
7457. [F. Ippolito, del.]
is variably developed, being shortest in chelids ( Gaffney, 1979: fig. 55) and largest in podocnemidines ( Gaffney, 1979: fig. 54). In pelomedusoides this connection forms a parasagittal wall, lateral to the processus inferior parietalis, with a tunnellike space between them. This space, the sulcus palatinopterygoideus ( Gaffney et al., 2006), is filled by the pars rostromedialis of the M. pterygoideus ( Schumacher, 1973: figs. 9 and 11). In the podocnemidines generally and the Stereogenyini in particular, the wall is extensive and thick, involving the palatine and frontal bones and being thicker and more extensive than the braincase wall itself, which is the processus inferior parietalis. In Stereogenyini when looking into the front part of the cavum cranii, a structure that appears to be the fissure ethmoidalis is visible. However, this structure is not the fissure; rather, it is the anteromedially expanded septum orbitotemporale that connects with the processus trochlearis pterygoidei. The fissure ethmoidalis is present but it is posterior to the septum orbitotemporale. The anterior edge of the septum orbitotemporale is formed by the frontal dorsally and the palatine ventrally. More posteriorly it is formed by the pterygoid ventrally and the parietal dorsally (fig. 55C).
The orientation of the orbital rim varies among the subtribe Stereogenyina . In Cordichelys the orbit is almost completely vertical with no dorsal component as in Brontochelys and Stereogenys . The orbit in Cordichelys faces anterolaterally, as in most subtribe Stereogenyina .
PARIETAL
Preservation: The left parietal in YPM 7457 is, as far as can be determined, complete. Only a small piece of the posterior edge is missing from the right parietal.
Contacts of dorsal plate: The parietal in Cordichelys contacts the parietal on the midline, the frontal anteriorly, the postorbital laterally, and the quadratojugal posterolaterally, as in the other subtribe Stereogenyina in which the temporal roof is known. The parietal in Bairdemys differs from that in Cordichelys in having a longer contact with the postorbital, but otherwise they agree closely. Only the frontal and part of the postorbital contact areas are preserved in Brontochelys , Shweboemys , and Latentemys . The free plate of the parietal is missing in all these specimens, but the preserved areas agree with Bairdemys . In Stereogenys (BMNH R.3190) the sutures are not clear, but the bone contacts appear to be the same as in the other Stereogenyini .
Structures of dorsal plate: The complete extent of the temporal roof (parietal and quadratojugal) can be determined only in Cordichelys , Bairdemys venezuelensis , and Stereogenys (BMNH R.3190). In these taxa the temporal roof is relatively extensive and comparable in extent and shape to Peltocephalus among the living podocnemidids. In these genera the temporal roof completely covers and extends posterior to the otic chamber.
Contacts of processus inferior parietalis: This structure is not entirely clear of matrix in YPM 7457, but on the external surface of the right processus inferior parietalis it can be seen that the parietal contacts the palatine anteroventrally and the pterygoid ventrally. The parietal reaches the prootic posteroventrally, and the supraoccipital posteriorly, all as in other podocnemidids.
Structures of processus inferior parietalis: The ventral surface of the parietal in all Stereogenyini has a thick parasagittal, ventral ridge, the processus inferior parietalis, that forms the side wall to the cavum cranii. Although not determinable in Cordichelys , the cavum cranii in Bairdemys , Stereogenys (BMNH R.3191, DPC 4120), and Latentemys , has distinct cerebral expansions. Brontochelys differs from these in having much smaller cerebral expansions as in Podocnemis expansa ; they are indeterminate in the remaining specimens in the Stereogenyini .
The foramen nervi trigemini in YPM 7457 is formed by the parietal anterodorsally, the prootic dorsolaterally, and the pterygoid ventrally.
JUGAL
Preservation: The left jugal in YPM 7457 has a small break on its ventral cheek margin, but is otherwise complete. The right jugal lacks the posterior part of its lateral plate.
Contacts of lateral plate: As in Bairdemys venezuelensis , the jugal in Cordichelys contacts the maxilla anteroventrally, the postorbital dorsally, and the quadratojugal posterodorsally.
Structures of lateral plate: The jugal of Cordichelys forms the posteroventral margin of the orbit. The degree of exposure in the rim is less than in Latentemys and significantly less than in Bairdemys venezuelensis .
The degree of cheek emargination in the subtribe Stereogenyina is determinable only in Bairdemys venezuelensis , B. hartsteini , Cordichelys , and Stereogenys , the cheek bones being mostly missing in Latentemys , Shweboemys , and Brontochelys . Stereogenys has only a very slight emargination, the least of the group. Cordichelys lacks most of the right cheek, but much of the ventral margin of the left cheek is a natural edge indicating an emargination greater than Stereogenys but less than Bairdemys venezuelensis and B. hartsteini .
Contacts and structures of medial process: In the floor of the fossa orbitalis the jugal in Cordichelys contacts the maxilla anteriorly and laterally and the palatine medially. In the posterior view of the septum orbitotemporale, the jugal contacts the postorbital dorsally and the palatine ventrally. In contrast to the other subtribe Stereogenyina , the jugal in Cordichelys does not reach the pterygoid here due to a contact of the postorbital and palatine. The jugal forms part of the septum orbitotemporale as in the other subtribe Stereogenyina and does not enter the triturating surface.
QUADRATOJUGAL
Preservation: In YPM 7457 the left quadratojugal lacks only part of the ventral margin, but enough of the natural edge remains to show the original emargination. The right quadratojugal lacks its entire ventral margin.
Contacts: The quadratojugal in Cordichelys contacts the parietal medially, the quadrate posteroventrally, the squamosal posterodorsally, the postorbital anterodorsally, and the jugal anteroventrally, as in Bairdemys venezuelensis .
Structures: Above and posterior to the quadrate, a thin process of the quadratojugal contacts the squamosal. In these contacts Cordichelys agrees closely with Bairdemys but not with Podocnemis , which has a very small postorbital and lacks a quadratojugalpostorbital contact. As in nearly all other turtles the quadratojugal of Cordichelys has a curved contact with the quadrate paralleling the cavum tympani margin. The quadratojugal and the jugal form most of the edge of the cheek emargination in podocnemidids.
SQUAMOSAL
Preservation: The left squamosal in YPM 7457 is nearly complete, lacking only some abraded area posteriorly. The right squamosal is entirely missing.
Contacts: The squamosal in Cordichelys contacts the quadrate anteriorly and ventrally, the opisthotic medially, and the quadratojugal anterodorsolaterally, as in Bairdemys venezuelensis .
Structures: As in all other turtles the squamosal of Cordichelys lies on the posterodorsal margin of the quadrate. It has a narrow contact with the quadratojugal anteriorly and forms the posterolateral margin of the temporal emargination.
In all turtles the squamosal is the primary bone forming the antrum postoticum, which is a space behind and above the cavum tympani. In pelomedusids ( Pelusios and Pelomedusa ), the antrum postoticum is relatively large, as in nearly all other turtles. But other pelomedusoides have a variably reduced, antrum postoticum. In most podocnemidids the antrum is smaller than in Pelusios but still a distinct space filling the posterior projection of the squamosal. The antrum postoticum is preserved only in Bairdemys , Cordichelys , Latentemys , and Stereogenys among the Stereogenyini . The entire squamosal is absent in Brontochelys and Shweboemys . In Cordichelys and Latentemys the antrum postoticum is a distinct, tubular space, much smaller than the Pelusios condition and somewhat smaller than in Podocnemis . In Bairdemys and Stereogenys , however, the antrum is reduced to a slit, formed primarily by the quadrate internally and enclosed by the cone-shaped squamosal. The slit is orientated dorsolaterally ventromedially, in common with the plane of the widest dimension in Latentemys . Both Bairdemys venezuelensis and B. hartsteini have the collapsed, slitlike antrum postoticum. Many bothremydids also have a small or absent antrum, but in this group the space is either a small canal and not a slit or completely filled with bone.
POSTORBITAL
Preservation: The postorbital in YPM 7457 is present on both sides. The right one is complete; the left one lacks only a small part of the ventral margin.
Contacts of lateral plate: The postorbital in Cordichelys contacts the frontal anteromedially, the jugal ventrally, the quadratojugal posteriorly, and the parietal posteromedially, as in Bairdemys .
Structures of lateral plate: The postorbital forms the posterodorsal orbital margin, as in Bairdemys .
Contacts of medial process: In the anterior surface of the septum orbitotemporale, facing the fossa orbitalis, the postorbital contacts the frontal dorsomedially, the palatine medially, and the jugal ventrally. In the posterior surface of the septum orbitotemporale, facing fossa temporalis, the postorbital contacts the parietal dorsomedially, the pterygoid ventromedially, the jugal ventrolaterally, and the palatine ventrally.
Structures of medial process: The postorbital in Cordichelys as in other subtribe Stereogenyina forms part of the roof and lateral wall of the sulcus palatinopterygoideus and part of both surfaces of the septum orbitotemporale.
PREMAXILLA
Preservation: In YPM 7457 the left premaxilla is preserved completely, the right one is missing much of its anterior and medial parts.
Contacts: The premaxilla in Cordichelys contacts the maxilla posterolaterally and the other premaxilla medially on the midline.
Structures: The premaxilla is an important element in the distinctive triturating surface morphology characteristic of the Stereogenyini . All the members of this group have a secondary palate that is formed primarily from the maxilla and palatine. The premaxilla forms the anteromedial part of the triturating surface and the labial ridge that is the edge of the triturating surface. In Cordichelys the premaxillary surface forms a ventrally opening concavity on the midline, very similar to the one seen in Bairdemys venezuelensis . Shweboemys also has a median premaxillary depression, but it is shallower and smoothly continuous with the posterolateral or maxillary surface of the triturating area. Although the available material of Stereogenys is not well preserved, two specimens, BMNH R.1390 and a cast of CGM 10027 (cast is AMNH 14736), show a premaxillary depression similar to Bairdemys venezuelensis and Cordichelys in being deep and well defined but unique in having a small accessory ridge on the premaxilla. This ridge parallels the labial ridge and is separated from it by a narrow groove; the ridge is entirely limited to the premaxilla and is continuous across the midline.
The premaxilla in the Stereogenyini forms the anterior margin of the palatal cleft (missing in Brontochelys and Latentemys ). The margin is a C-shaped trough, opening posteriorly. In Podocnemis and Dacquemys the maxillae meet behind the premaxillae, but in the other vomerless podocnemidids the premaxillae are free posteriorly as in the Stereogenyini .
The premaxillary portion of the snout shows varying degrees of protrusion or ‘‘pinching’’ among the Stereogenyini . Stereogenys shows the most protruded, with the labial margin of the skull being concave anterolaterally. Bairdemys hartsteini is also pinched and protruded while Shweboemys , Cordichelys , and Latentemys are slightly protruded but not pinched. Brontochelys seems to be lacking a protrusion (although the premaxillae are absent and the anterior part of the skull is broad). Bairdemys venezuelensis lacks pinching and a protrusion.
Wood (1970) characterized ‘‘ Shweboemys ’’ (here Brontochelys ) gaffneyi as having a horizontal midline labial ridge and Shweboemys pilgrimi and ‘‘ Shweboemys ’’ (here Cordichelys ) antiqua as being notched on the midline in anterior view. Unfortunately, the two Asian species are represented by specimens that are broken in this area, but it does seem likely that at least Shweboemys has a premaxillary notch or embayment similar to that seen in Bairdemys hartsteini . Bairdemys venezuelensis lacks a notch. Cordichelys also has an embayment similar to that in Bairdemys hartsteini , and the partially preserved specimens of Stereogenys also seem consistent with a notch. In Latentemys the notch is not determinable. Thus, only Brontochelys and Bairdemys venezuelensis seem to be lacking a premaxillary embayment, but even this is not definitely determinable in Brontochelys . Podocnemis and many other podocnemidids have a midline protrusion or overhanging projection rather than a notch. Mogharemys is missing the premaxillae and lacks this area. However, the basal podocnemidid Lapparentemys has a midline notch and that may be the primitive condition.
Laterally, the premaxilla of Cordichelys is longer and lower than the premaxilla in Bairdemys venezuelensis ; this is presumably related to the shorter and deeper preorbital region of Bairdemys .
Dorsally, the premaxilla forms the ventral and part of the lateral margin of the aperture narium externa. The oval aperture is similar in shape in both Bairdemys and Cordichelys , the Stereogenyini that have the margins best preserved. Stereogenys and Shweboemys are damaged in this area, but show what appear to be broader narial openings. The other taxa are indeterminate.
In Cordichelys and Bairdemys venezuelensis there is a median, anteroposteriorly oriented ridge on the dorsal surface of the premaxilla that begins at the anteroventral margin of the aperture narium externa and rises in height along the floor of the fossa nasalis. There is a similar ridge in Podocnemis .
MAXILLA
Preservation: In YPM 7457 both maxillae are nearly complete; there is some damage around the prefrontal suture.
Contacts of vertical plate: The maxilla of Cordichelys contacts the premaxilla anteromedially, the jugal posterodorsally, and the prefrontal anterodorsally, as in the other subtribe Stereogenyina .
Structures of vertical plate: The width of the facial portion of the skull expressed in the angle of the labial ridge to the midline can be used to differentiate a broader jawed group from a narrower jawed group. In Bairdemys venezuelensis the angle is 45 °, in Cordichelys it is 40 ° and in Latentemys it is 30 °. In Brontochelys , the labial ridge angle is about 60 °. In Shweboemys it is hard to be sure due to damage, but the angle is around 50 ° –55 °. In Stereogenys 50 ° seems to be the most reliable. Mogharemys is too broken along the labial ridge to make a measurement, but the preserved triturating morphology is most similar to the broad jawed Brontochelys . The taxa with labial ridge angles of 50 ° or more might be interpreted as constituting a broad-jawed group and those with labial ridges of 45 ° or less a narrow-jawed group. But the variation of the angles really forms more of a spectrum and the recognition of groups is somewhat arbitrary.
Contacts of horizontal plate: The maxilla in Cordichelys contacts the premaxilla anteromedially, the palatine posteromedially, and the jugal posterolaterally, as in the other subtribe Stereogenyina . As far as can be determined, the maxillae do not meet on the midline in any of the subtribe Stereogenyina .
Structures of horizontal plate: The labial ridge forms the outermost part of the triturating surface. In Bairdemys , Cordichelys , and Latentemys , the labial ridge is relatively deep and narrow. These are in contrast to the labial ridge of Stereogenys , which is lower and thicker. In Brontochelys and Shweboemys the labial ridge is largely worn away, but the preserved parts are more consistent with a low and thick labial ridge.
The Stereogenyini has as its principal synapomorphy, a well-developed secondary palate. Secondary palates occur in a number of other turtles groups, with Osteopygis and Rhetechelys ( Gaffney, 1979) having the most extensive ones. The Stereogenyini , however, differ from all other turtles with secondary palates in having a midline cleft extending from the premaxillae posteriorly to the choanal opening proper. Was this cleft covered with soft tissue in life? Did the cleft provide an opening for air or other material? Did it mean that these turtles were warmblooded?
The maxilla in the Stereogenyini forms the anterolateral part of the palate and the palatine forms the posterior part. The maxilla-palatine suture trends laterally from the midline then curves posterolaterally until it reaches the jugal in the margin of the fenestra temporalis inferior.
In Cordichelys and some other subtribe Stereogenyina , the maxillary part of the triturating surface has a distinct swelling or convexity just lateral to the midline cleft and internal to the labial ridge. This convexity is part of a raised platform that (in ventral view) is stepped above the palatine portion of the palate. The maxilla-palatine suture in Bairdemys intersects part of the convexity, but for the most part it lies close to the demarcation between the anterolateral raised section and the more posterior lower section. Latentemys agrees with Bairdemys venezuelensis and also has a raised convexity. Cordichelys has a similar palatal morphology, but the maxilla-palatine suture runs more anteriorly through part of the convexity. Brontochelys , Shweboemys , and Stereogenys have much flatter, triturating surfaces; there is a gentle curve to the surface, but no raised convexity is present.
PALATINE
Preservation: Both palatines in YPM 7457 are apparently complete. It is possible that a small part of the thin bone on the midline is missing.
Contacts: In ventral view the palatine of Cordichelys contacts the maxilla anterolaterally, the other palatine medially on the midline, and the pterygoid posteriorly. It is possible that there was a basisphenoid contact, but the medial edges of the pterygoids are damaged. On the dorsal surface, the palatine dorsal process contacts the frontal anterodorsally and the parietal dorsally. In the anterior wall of the septum orbitotemporale, the palatine contacts the maxilla anterolaterally, the jugal laterally, the postorbital posterolaterally, and the frontal dorsally.
The figure of ‘‘ Shweboemys ’’ (now Cordichelys ) antiqua in Gaffney (1979: fig. 136) that shows a basisphenoid-palatine contact is incorrect. Although this area is damaged in this specimen, further work has shown that the pterygoids meet in the midline.
Structures: The palatine in the subtribe Stereogenyina has a horizontal plate forming the posterior portion of the secondary palate ventrally, a vertical plate extending dorsally to contact the parietal, and a horizontal plate meeting on the midline to form the primary palate. The presumed primitive condition of the palatine in turtles in general and podocnemidids in particular is a flat, platelike bone forming the roof of the palate, the posterior margin of the apertura narium interna, and a small anterolateral contribution to the triturating surface (posteromedial to the maxilla). This condition can be seen in Euraxemys ( Gaffney et al., 2006) . In the Stereogenyini , the palatine shows two modifications from this primitive condition: a secondary palatal plate ventral to the primary palatal palate and a vertical process extending dorsal to the primary palate and reaching the temporal roofing bones.
The variation in length of the secondary palate is mostly dependent on the palatine length and the degree of palatine participation. Within the Stereogenyini there is a range of variation in length of the secondary palate from Stereogenys , which has the longest secondary palate, to Bairdemys venezuelensis , which has the shortest. Here we use a comparison based on the ratio of total skull length to secondary palate length, as expressed by the length of the midline cleft. These measurements are not exact due to variation in preservation and positions of measurements, but the ratio does seem the most objective way to compare the secondary palate in these skulls. The ratios of secondary palate lengths to skull lengths seem to fall into three categories. Stereogenys is alone with its palate about 40% of the skull length. Cordichelys , Shweboemys , and Brontochelys have palates that are about 30% of skull length, although there is a certain amount of spread, and the two Asian species are not well preserved. Brontochelys completely lacks premaxillae making both measurements only approximate. Bairdemys venezuelensis and Latentemys are in the 20% range, although Latentemys must be considered problematical due to significant missing areas of the palate.
There could be a small foramen palatinum posterius in Cordichelys at the posteriormost end of the secondary palate, just under the fold of bone and not visible in ventral view.
QUADRATE
Preservation: The right quadrate in YPM 7457 is missing, except for the contact area around the prootic and opisthotic, but the left one is nearly complete, lacking some of the condylus mandibularis and some of the ventral edge.
Contacts on lateral surface: In Cordichelys the quadrate contacts the quadratojugal anterodorsally and the squamosal posterodorsally, as in Bairdemys .
Structures on lateral surface: YPM 7457 is one of the few subtribe Stereogenyina skulls to show a complete cheek and its emargination is somewhat less than in Bairdemys venezuelensis . The quadratojugal in Cordichelys is more extensive ventrally, although the ventral edge of the quadrate could be broken and more like that in Bairdemys .
The cavum tympani in Cordichelys is shallower than that in Bairdemys venezuelensis , but both have a closed incisura columellae auris enclosing the eustachian tube as in all the other subtribe Stereogenyina . The eustachian tube sulcus that opens on the posterior surface of the occiput in Cordichelys is open, communicating with the fenestra postotica, in contrast to the closed condition, separating the two structures seen in Bairdemys . There is no fossa precolumellaris. The antrum postoticum in Cordichelys is relatively small compared to pelomedusids, but it is not a narrow slit as seen in Bairdemys venezuelensis .
Contacts on dorsal and anterior surface: As in the other podocnemidids, the quadrate in Cordichelys contacts the prootic anteromedially, the opisthotic posteromedially, and the squamosal posteriorly and posterolaterally.
Structures on dorsal and anterior surface: The foramen stapedio-temporale is in its usual position for podocnemidids, between the quadrate and prootic facing more dorsally than anteriorly.
Contacts on ventral surface: As in Bairdemys , the contacts in Cordichelys are with the pterygoid anteromedially, the basisphenoid medially, the basioccipital posteromedially, and the prootic medially, within the cavum pterygoidei.
Structures on ventral surface: The condylus mandibularis in Cordichelys is in about the same relative position as it is in Bairdemys venezuelensis . The cavum pterygoidei in Cordichelys is also similar in position and extent to that in Bairdemys venezuelensis , except that the ventral opening is in a slightly more horizontal plane in Cordichelys . The quadrate shows on both sides the opening of the cavum cavernosus, formed between the quadrate, pterygoid, and prootic.
Contacts on posterior surface: The quadrate contacts in Cordichelys are with the squamosal dorsolaterally, the opisthotic dorsomedially, and the basioccipital ventromedially.
Structures on posterior surface: The fenestra postotica in Cordichelys is confluent with the sulcus eustachii in contrast to Bairdemys . The left quadrate shows a foramen chorda tympani inferius just below the sulcus eustachii.
PTERYGOID
Preservation: In YPM 7457 the pterygoids are present on both sides and nearly complete. They lack some of the margins of the cavum pterygoidei. Most of the pterygoid flange is broken off on both sides, but a significant portion of its base remains on the right pterygoid.
Contacts on ventral surface: The pterygoid in Cordichelys contacts the palatine anteriorly, the basisphenoid posteromedially, the prootic posteriorly in the cavum pterygoidei, and the quadrate posterolaterally. The possible medial contact of the pterygoids, which would prevent a palatine-basisphenoid contact, is not determinable in YPM 7457 because the thin medial edges of both pterygoids are abraded away, revealing the overlying basisphenoid. As preserved, there is no midline contact of the pterygoids. There is also a median contact of the palatines with the basisphenoid. However, this area is eroded and these contacts seem to be artifacts of preservation. It is most likely that the pterygoids were worn away and that a narrow midline, pterygoid contact separating the palatines from the basisphenoid was present as in Bairdemys .
Structures on ventral surface: The processus trochlearis pterygoidei in Cordichelys lies at a right angle to the midline as in the other subtribe Stereogenyina . The cavum pterygoidei is formed ventrally by the pterygoid as in the other podocnemidids. The base of a well-developed pterygoid flange is present on the ventral surface of the left pterygoid.
Contacts on dorsal surface: In Cordichelys the contacts at the base of the processus trochlearis pterygoidei (the septum orbitotemporale posterior surface) are with the postorbital dorsolaterally, the palatine anteroventrally, and the parietal anterolaterally. Due to the postorbital-palatine contact there is no pterygoid-jugal contact in Cordichelys . The contacts of the crista pterygoidea are not visible internally, but externally they are the usual contacts in pleurodires: the parietal anterodorsally and the prootic posterodorsally.
Structures on dorsal surface: The pterygoid in Cordichelys forms the anteroventral margin of the foramen nervi trigemini, the parietal the anterodorsal margin, and the prootic the posterodorsal margin, as in the other podocnemidids.
SUPRAOCCIPITAL
Preservation: Most of the supraoccipital is present in YPM 7457, but the posterior edge is a broken margin, so its original extent may have been longer as in Bairdemys .
Contacts: The contacts are as in Bairdemys .
Structures: The crista supraoccipitalis in Cordichelys has a relatively wide, horizontal plate, on the ventral edge of the crista, as in Bairdemys .
EXOCCIPITAL
Preservation: Both exoccipitals in YPM 7457 are present and complete except for parts of the condylus occipitalis. Enough bone is present, however, to show that the exoccipitals did make up at least part of the condylus, along with the basioccipital.
Contacts: As in Bairdemys .
Structures: The two foramen nervi hypoglossi are recessed and united in a single opening on the occipital surface, as in most of the other subtribe Stereogenyina except Bairdemys sanchezi . The foramen jugulare posterius is completely closed as in other subtribe Stereogenyina . The condylus occipitalis does not retain any original surface, but the exposed elements indicate that it was made up of the basioccipital as well as the two exoccipitals, as in all other subtribe Stereogenyina . The fenestra postotica is closed, and separated from the sulcus eustachii, also as in Bairdemys .
BASIOCCIPITAL
Preservation: The basioccipital in YPM 7457 is cracked on the midline, but it lacks only part of the condylus occipitalis surface.
Contacts: As in Bairdemys venezuelensis and B. hartsteini .
Structures: As in Bairdemys , except that Cordichelys has a flat, slightly concave ventral surface to the basioccipital; Bairdemys venezuelensis has a convexity on the midline.
PROOTIC
Preservation: Both prootics are preserved intact in YPM 7457.
Contacts: As in Bairdemys venezuelensis and B. hartsteini .
Structures: As in Bairdemys venezuelensis and B. hartsteini .
OPISTHOTIC
Preservation: Both opisthotics are preserved intact in YPM 7457.
Contacts: As in Bairdemys venezuelensis and B. hartsteini .
Structures: As in Bairdemys venezuelensis and B. hartsteini .
BASISPHENOID
Preservation: The basisphenoid in YPM 7457 is complete, but the area of palatine and pterygoid underlying it anteriorly is abraded, exposing areas the basisphenoid that had been covered.
Contacts on ventral surface: The contacts in Cordichelys appear to be the same as in Bairdemys venezuelensis . The anterior contacts of the basisphenoid, whether or not it reached the palatines, however, are unclear due to the breakage of both palatines and pterygoids. The contacts could easily be the same as in Bairdemys venezuelensis , however.
Structures on ventral surface: The basisphenoid in Cordichelys is incompletely clear of matrix inside the cavum pterygoidei, and the foramen posterius canalis carotici interni cannot be seen.
Contacts and structures on dorsal surface: The dorsal surface of YPM 7457 is not visible.
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