Lemurchelys, 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-FF19-5ED4-FEC5-A2059EC6D1E2 |
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treatment provided by |
Felipe |
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scientific name |
Lemurchelys |
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Lemurchelys Figures 67–70 View Fig View Fig View Fig View Fig
This taxon is based on the sole skull, DPC 6425. The skull is generally well preserved but has a thin coating of iron oxide covering some parts. The occiput and left septum orbitotemporale have been abraded and lost some of their original surface. Most of the left otic chamber is missing and the skull roofing elements are also gone.
PREFRONTAL
Preservation: Both prefrontals are preserv- ed and complete in DPC 6425. The anterior margins of both bones are preserved; frequently broken in the subtribe Stereogenyina .
Contacts: The prefrontal in Duke contacts the prefrontal on the midline, the maxilla anteroventrolaterally, and the frontal posteriorly, as in the other subtribe Stereogenyina .
Structures: The dorsal margin of the apertura narium externa is slightly protruding, but not to the extent seen in Bairdemys venezuelensis .
FRONTAL
Preservation: Both frontals are present and complete.
Contacts: The frontal in DPC 6425 contacts the other frontal on the midline, the prefrontal anteriorly, the postorbital posterolaterally, the parietal posteriorly, and the palatine ventrally, as in all other subtribe Stereogenyina .
Structures: The frontal in DPC 6425 forms a relatively small section of the dorsal orbital rim, less than in other subtribe Stereogenyina and much less than in Cordichelys and Brontochelys .
PARIETAL
Preservation: The parietals in DPC 6425 are present only anteromedially, the posterior and lateral portions forming the fossa temporalis covering are broken away.
Contacts and structures of dorsal plate: The parietal in DPC 6425 contacts the other parietal on the midline, the frontal anteriorly, and the postorbital laterally. Other cheek contacts are not preserved. The degree of emargination is unknown.
Contacts and structures of processus inferior parietalis: The area of contact of the processus inferior parietalis and the crista pterygoidea is largely covered by matrix. The pterygoidparietal contact can be seen in places. As in other podocnemidids, the parietal contacts the prootic posteroventrally and the supraoccipital posteriorly. The foramen nervi trigemini is formed by the parietal anterodorsally, the prootic dorsolaterally, and the pterygoid ventrally. The parietal forms part of the roof of the sulcus palatinopterygoideus.
JUGAL
Preservation: Both jugals are present, but the thin cheek plate covering the fossa temporalis is broken away on both sides, so the presence and extent of the cheek emargination is unknown.
Contacts of lateral plate: The preserved portion of the jugal contacts the maxilla anteroventrally and the postorbital dorsally, but the posterior contacts are unknown.
Structures of lateral plate: The jugal in Duke 6425 forms most of the posterior orbital rim, as in Shweboemys and Bairdemys but in contrast to the small portion in Cordichelys . The possibility of a cheek emargination is unknown.
Contacts and structures of medial process: In the floor of the fossa orbitalis, the jugal contacts the maxilla anteriorly and laterally and the palatine medially, as in Latentemys . In the septum orbitotemporale in posterior view, the jugal contacts the postorbital dorsomedially, the palatine ventromedially, the pterygoid posteriorly and the maxilla ventrally, also as in Latememys. There is no contribution to the triturating surface.
QUADRATOJUGAL
The quadratojugal is not preserved in DPC 6425.
SQUAMOSAL
Preservation: Very little of the right squamosal and none of the left are preserved. There are some parts of the quadrate-squamosal suture remaining on the right side, including fragments of the squamosal internal bone.
Contacts and structures: The quadrate anteriorly and some of the opisthotic suture posteromedially remain and are as in Latentemys . The squamosal portion forming the small antrum postoticum is present and can be seen from the anterior opening of the antrum. The external shape of the squamosal is not preserved.
POSTORBITAL
Preservation: The anterior and medial portions of both postorbitals are mostly preserved. On the left side a large hole in the middle of the septum orbitotemporale has removed most of the ventral plate, but the dorsal and ventral sutures remain. The thin, posterior sheets covering the fossa temporalis are gone on both postorbitals.
Contacts of lateral plate: The preserved contacts of the postorbital are with the frontal anteromedially, the jugal ventrally, and the parietal posteromedially.
Structures of lateral plate: The postorbital makes up the posterodorsal part of the orbital rim. The degree of exposure in DPC 6425 is more than in Shweboemys and about the same as in Latentemys and Stereogenys .
Contacts and structures of medial process: The anterior surface of the septum orbitotemporale is obscured by a layer of matrix in the fossa orbitalis on both sides of DPV 6425 and the sutures are not clear. In the posterior surface of the septum orbitotemporale, facing the fossa temporalis, the postorbital contacts the parietal dorsomedially, the pterygoid ventromedially, and the jugal ventrolaterally, as in Latentemys and Brontochelys and in contrast to Shweboemys and Stereogenys in which the dorsal process of the palatine reaches the postorbital. As in the other subtribe Stereogenyina , the postorbital makes up part of the roof and lateral wall of the sulcus palatinopterygoideus and the dorsal portion of the septum orbitotemporale. The fossa orbitalis in DPC 6425 and the other subtribe Stereogenyina has a posterior enlargement, extending well past the orbital rim, and forming a relatively large cavity behind the eye itself.
PREMAXILLA
Preservation: Most subtribe Stereogenyina manage to loose their premaxillae for some reason, but DPC 6425 has both of them complete.
Contacts: The premaxilla contacts the maxilla posterolaterally and the other premaxilla medially on the midline.
Structures on dorsal surface: The premaxilla forms the floor of the fossa nasalis, with DPC 6425 showing the beginning of the choanal division with a posteriorly rising ridge on the midline. The margin of the apertura narium externa is very blunt and there is no sharp division of the fossa nasalis and the external surface of the skull. A foramen praepalatinum can be seen in each premaxilla extending from the dorsal surface to the ventral surface.
Structures on ventral surface: The shape of the premaxilla in DPC 6425 is difficult to compare with that in other subtribe Stereogenyina because most lack the premaxilla. However, DPC 6425 has a slight pinching or protrusion of the anterior snout that is absent in Latentemys , Cordichelys , and Bairdemys venezuelensis , indeterminate (although probably absent) in Brontochelys , and present in Stereogenys and Shweboemys . There is a slight midline concavity not defined posteriorly but sloping dorsally into the apertura narium interna, similar to that seen in Bairdemys venezuelensis . There are no accessory ridges. The foramen praepalatinum lies closer to the posterior edge of the premaxilla than to the anterior edge.
MAXILLA
Preservation: Both maxillae are present and nearly complete. The labial ridges are slightly damaged and the posteroventral margin is broken.
Contacts of vertical plate: The maxilla as preserved contacts the premaxilla anteromedially, the jugal posterodorsally, and the prefrontal anterodorsally.
Structures of vertical plate: The ventral margin of the orbital rim is formed by the maxilla and is a rounded, sloping surface, as in Brontochelys , not a sharp ridge as in all other subtribe Stereogenyina . The apertura narium externa in DPC 6425 is similar in shape to that in Bairdemys venezuelensis . The apertura is damaged or missing in other subtribe Stereogenyina precluding useful comparisons. There is no remnant of possible cheek emargination.
Contacts of horizontal plate: The horizontal plate of the maxilla in DPC 6425 contacts the premaxilla anteromedially, the palatine posteromedially, and the jugal posterolaterally.
Structures of horizontal plate: The triturating surface in DPC 6425 is similar to that in Stereogenys and Shweboemys and different from all other subtribe Stereogenyina , in having parallel medial margins forming the apertura narium interna. However, the length of the secondary palate is shorter in DPC 6425 than in the other two genera. There is a slight convexity on the maxilla in DPC 6425, similar to that in Cordichelys and much smaller than in Bairdemys venezuelensis . The labial ridge is blunt and rounded in DPC 6425, similar to that in Shweboemys but different from the higher, but still blunt, ridge in Stereogenys . The maxilla in DPC 6425 is relatively thick and swollen as in Shweboemys , in contrast to the thin and narrow maxilla of Latentemys and Cordichelys .
VOMER
It can be determined that there is no vomer in DPC 6425.
PALATINE
Preservation: Both palatines are present and complete in DPC 6425.
Contacts: The palatine contacts the maxilla anterolaterally and the pterygoid posteriorly. On the dorsal surface the palatine contacts the processus inferior parietalis. The sutures in the fossa orbitalis are difficult to make out due to matrix, but there is the usual palatinemaxilla anteriorly and the palatine-jugal anterolaterally.
Structures on dorsal surface: DPC 6425 shows the choanal passages extending from the apertura narium externa posteriorly into the cleft-shaped apertura narium interna. The palatine forms the posterior part of this secondary palate and the maxilla forms the anterior part. There is no indication of a foramen palatinum posterius in DPC 6425.
Structures on ventral surface: The palatine is slightly shorter than the maxilla in DPC 6425, in contrast to Shweboemys and Stereogenys , which have palatines that are longer than the maxilla. The palatine surface is slightly concave, as in Latentemys and Cordichelys , not as deep as in Bairdemys venezuelensis .
QUADRATE
Preservation: Only the posterior part of the right quadrate is present in DPC 6425. None of the cheek or skull roof contacts remain.
Contacts on lateral surface: The only remaining contact on the quadrate lateral surface is with the squamosal posterodorsally.
Structures on lateral surface: The posterior part of the cavum tympani is preserved, showing the enclosed incisura columellae auris containing the eustachian tube and stapes. The eustachian tube is not separated by bone from the fenestra postotica in DPC 6425. The antrum postoticum is very small and tubular, as in Stereogenys , not flat as in Bairdemys venezuelensis . The fossa precolumellaris is not preserved.
Contacts on dorsal and anterior surface: The quadrate contacts the prootic anteromedially, the opisthotic posteromedially, and the squamosal posteriorly and posterolaterally.
Structures on dorsal and anterior surface: Although the surfaces of both otic chambers are slightly abraded, the foramen stapedio-temporale is clearly preserved on the right side. It is oriented anterodorsally, as in the other subtribe Stereogenyina in which it is preserved.
Contacts on ventral surface: The quadrate contacts the pterygoid anteromedially, the basisphenoid medially, the basioccipital posteromedially, and the prootic medially, as in the other subtribe Stereogenyina .
Structures on ventral surface: The cavum pterygoidei is formed laterally and dorsally by the quadrate in podocnemidids, and this is the case in DPC 6425. The lateral extent of the cavum, however, is deeper in DPC 6425 than in other subtribe Stereogenyina , being similar in extent to that in Mogharemys . In the roof of the cavum pterygoidei is the opening of the canalis cavernosus, the foramen cavernosum, formed mostly by the prootic but with some quadrate entering into its margin. Just ventromedial to the foramen cavernosum, is a much smaller foramen, the foramen nervi facialis. The full cavum pterygoidei is preserved on the right side of DPC 6425. On the left side the cavum is broken about midway along its length, showing a section of the foramen cavernosum.
Contacts on posterior surface: The posteri- or surface of DPC 6425 is abraded to a varying extent and some of the visible sutures are actually below the original bone level. The quadrate in DPC 6425 contacts the squamosal dorsolaterally, the opisthotic dorsomedially, and the basioccipital ventromedially.
Structures on posterior surface: The fenestra postotica in DPC 6425 is not separated by bone from the sulcus eustachii as in Bairdemys and Latentemys , but is confluent as in Stereogenys . The incisura columellae auris is visible posteriorly and is intact on the right side of DPC 6425; on the left side it is broken revealing its medial shape as an oval tunnel. The presence of the foramen chorda tympani inferius cannot be determined due to abrasion and matrix in DPC 6425.
PTERYGOID
Preservation: The pterygoid is present on both sides of DPC 6425, but they are damaged posteriorly with the floor of the cavum pterygoidei eroded away exposing the interior. The pterygoid flanges are broken away on both sides.
Contacts on ventral surface: The pterygoid in DPC 6425 contacts the palatine anteriorly, the other pterygoid medially, the basisphenoid posteromedially, and the quadrate posterolaterally, as in the other subtribe Stereogenyina .
Structures on ventral surface: The processus trochlearis pterygoidei in DPC 6425 is similar to that in the other subtribe Stereogenyina , it lies at right angles to the midline and has a small concavity at its base on the ventral surface. The cavum pterygoidei is floored by the pterygoid, although in DPC 6425 the floor is mostly eroded away. The presence of a pterygoid flange is revealed by the presence of its base, but its extent is not determinable. There is no sign of a foramen palatinum posterius, and the palatine-pterygoid suture area is well preserved on the left side of DPC 6425, so if one were present it would probably be visible. See Quadrate for cavum pterygoidei description.
Contacts on dorsal surface: The contacts of the pterygoid at the base of the processus trochlearis pterygoidei are with the postorbital dorsolaterally, the jugal anterolaterally, the palatine anteroventrally, and the parietal anterolaterally. The contacts of the crista pterygoidea are unclear due to matrix, but these contacts are visible: the parietal anterodorsally, the prootic posterodorsally, the quadrate posterolaterally, and the palatine anteriorly.
Structures on dorsal surface: The sulcus palatinopterygoideus and its associate septum orbitotemporale are formed in DPC 6425 as in Latentemys , by the postorbital, parietal, pterygoid, and palatine. Also as in the other subtribe Stereogenyina , the foramen nervi trigemini in DPC 6425 is formed by the parietal anterodorsally, the prootic dorsolaterally, and the pterygoid ventrally.
SUPRAOCCIPITAL
Preservation: Only the base of the supraoccipital is preserved in DPC 6425, the crista supraoccipitalis is broken away.
Contacts: As in other subtribe Stereogenyina the supraoccipital in DPC 6425 contacts the parietals dorsally and anteriorly, the prootic anterolaterally, the opisthotic posterolaterally, and the exoccipitals posteroventrally.
Structures: Although most of the structure is broken away, the base of the crista in DPC 6425 is much deeper than in Cordichelys , Stereogenys , and Shweboemys .
EXOCCIPITAL
Preservation: Both exoccipitals are present in DPC 6425, but they are abraded on their posterior surface, showing some of the sutures below the original bone surface.
Contacts: The exoccipital in DPC 6425 contacts the supraoccipital dorsally, the opisthotic laterally, and the basioccipital ventrally.
Structures: Although broken off, the base of the condylus occipitalis shows the typical tripartite structure of two exoccipitals and a median basioccipital. In contrast to all other subtribe Stereogenyina except Bairdemys sanchezi , the foramen nervi hypoglossi are two separate openings not combined into a single recessed opening. It is possible that this is the result of the abrasion and erosion of the occipital surface seen in DPC 6425, but it is the same on both sides and this seems unlikely. The foramen jugulare posterius is closed by bone, which seems to include the opisthotic and basioccipital, although this may be due to damage.
BASIOCCIPITAL
Preservation: The basioccipital in DPC 6425 is mostly present, but its surface is damaged by abrasion. The left lateral edge is broken.
Contacts: The basioccipital contacts the basisphenoid anteriorly, the quadrate laterally, the exoccipitals posterodorsally, and the opisthotic laterally.
Structures: Compared with forms like Latentemys and Cordichelys, DPC 6425 has no distinct tuberculum basioccipitale. However, this area is abraded and it is likely that these were worn away. The basioccipitale of DPC 6425 is sufficiently worn to look more like the very short basioccipitale in Stereogenys and Shweboemys . However, this does not seem to be the case when compared with surrounding elements to get a better idea of its length.
PROOTIC
Preservation: The right prootic in DPC 6425 is complete, the left one lacks some of its lateral edges due to the breakage of the otic chamber at this position.
Contacts: The prootic contacts the parietal dorsomedially, the quadrate laterally, the supraoccipital posterodorsally, the pterygoid ventrally, the basisphenoid ventrally, and the opisthotic posteriorly, as in other podocnemidids.
Structures: The prootic in DPC 6425 is very similar to that bone in the other subtribe Stereogenyina . It has a smooth surface medial to the foramen stapedio-temporale, rather than the raised convexity seen in Cordichelys and Latentemys . The prootic forms part of the foramen cavernosum in the roof of the cavum pterygoidei, and this can be seen in section on the left side of DPC 6425.
OPISTHOTIC
Preservation: The right opisthotic is preserved in DPC 6425, but it is incomplete laterally and its sutures are unclear in some places due to an iron oxide crust.
Contacts: Enough of the contacts can be made out to see that they are as in other podocnemidids: the supraoccipital anteromedially, the prootic anteriorly, the quadrate anterolaterally, the squamosal posterolaterally, and the exoccipital posteromedially.
Structures: The opisthotic forms the lateral wall of the foramen jugulare posterius and the medial wall of the fenestra postotica.
BASISPHENOID
Preservation: The basisphenoid in DPC 6425 is nearly complete. It lacks a small portion of its lateral margin and its contacts with the pterygoids are eroded away along with the flooring of the cavum pterygoidei. Only the ventral surface is visible.
Contacts on ventral surface: The basisphenoid contacts the pterygoids anterolaterally, the basioccipital posteriorly, the prootic dorsolaterally (within the cavum pterygoidei), and the quadrate laterally.
Structures on ventral surface: The basisphenoid shape differs from that in Stereogenys and Shweboemys in being much wider than long as in Brontochelys . The basisphenoid makes up the medial wall of the cavum pterygoidei, although the sutures here are unclear.
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