Kinkonychelys sp.
|
publication ID |
https://doi.org/ 10.1206/672.1 |
|
persistent identifier |
https://treatment.plazi.org/id/03C687C2-B26B-2701-FF61-5373516A06A6 |
|
treatment provided by |
Carolina |
|
scientific name |
Kinkonychelys sp. |
| status |
|
SPECIMEN: FMNH PR 2446, left half of braincase (figs. 5–8).
LOCALITY: MAD 05-63 (latitude 16 ° 2 9 58.6 0 S, longitude 46 ° 3 9 39.4 0 E) in the Masiakakoho Study Area (fig. 1). MAD 05-63 lies approximately 4.7 km south-southeast of the village of Masiakakoho and 36.2 km northeast of the type locality of Kinkonychelys rogersi .
HORIZON: Anembalemba Member, Maevarano Formation, Maastrichtian, Upper Cretaceous. FMNH PR 2446 was surfacecollected on red, weathered slopes of the Masorobe Member immediately below the contact between the Masorobe Member and the overlying Anembalemba Member (fig. 1). After examining field relations and the distribution of bone, it was concluded that the specimen most likely eroded prior to discovery from the base of the Anembalemba Member, which at this locality is represented by a massive bed of poorly sorted, clay-rich sandstone (‘‘facies 2’’ of Rogers et al., 2000). Fossils from facies 2 were entombed in massive debris flows during the rainy season ( Rogers, 2005).
DESCRIPTION
Figures 5–8 View Fig View Fig View Fig View Fig
QUADRATE
PRESERVATION: The left quadrate is preserved but lacks most of its lateral margins, retaining the more medial surfaces of the cavum tympani. The medial contacts and structures are present.
CONTACTS ON LATERAL SURFACE: Of these, only a small part of the probable suture with the squamosal is preserved.
STRUCTURES ON LATERAL SURFACE: No information on the temporal or cheek emargination is preserved. However, much of the cavum tympani can be determined. There is a completely closed incisura columellae auris with a eustachian tube separated from the stapes by bone, all diagnostic for bothremydids. As in Kinkonychelys and Kurmademys , the antrum postoticum is large and deep, the fossa precolumellaris is deep and well defined, and there is a remnant of the narrow trough on the ridge extending from the incisura columellae auris to the sulcus eustachii.
CONTACTS ON DORSAL, VENTRAL, POSTERIOR, AND ANTERIOR SURFACES: These quadrate contacts are determinable in FMNH PR
2446: the prootic anteromedially, the opisthotic posteromedially, the pterygoid anteromedially, the basisphenoid medially, the basioccipital posteromedially, and the exoccipital medially. The exoccipital contact is synapomorphic for the Bothremydidae .
STRUCTURES ON DORSAL, VENTRAL, POSTER- IOR, AND ANTERIOR SURFACES: The foramen stapediotemporale (see Prootic) faces dorsally, as in other Kurmademydini . There is a large and well-defined fossa pterygoidea (see Pterygoid) very similar to that in Kinkonychelys (UA 9748). The condylus mandibularis in FMNH PR 2446 is broken off, but its position can be determined as farther anteriorly in comparison to that in Kinkonychelys and more like that in Kurmademys . The fenestra postotica in FMNH PR 2446 is formed laterally, ventrally, and dorsolaterally by the quadrate, with the medial and dorsomedial walls formed by the opisthotic. The fenestra postotica in FMNH PR 2446 is more ovoid and equidimensional, rather than more horizontal as in Kurmademys and Kinkonychelys . There is also a distinct ridge separating the lateral head vein and stapedial artery in the roof of the fenestra.
PTERYGOID
PRESERVATION: The posteriormost portion of the left pterygoid is preserved in FMNH PR 2446.
CONTACTS: The pterygoid fragment contacts the basisphenoid posteromedially, the prootic posterodorsally, and the quadrate posterolaterally. Viewed in the roof of the fossa pterygoidea, the pterygoid contacts the basiphenoid anteriorly, the prootic medially, and the quadrate posteriorly.
STRUCTURES: The fossa pterygoidea (fig. 7) in FMNH PR 2446 is formed by the pterygoid anterolaterally, the basisphenoid medially, the quadrate posterolaterally, and, in a small part of the roof dorsally, the prootic. Other than the exposure of the prootic, the fossa pterygoidea structure and contacts in FMNH PR 2446 are very similar to those in UA 9748. The prootic exposure has contacts with the other three bones: the pterygoid anterolaterally, the basisphenoid medially, and the quadrate posterolaterally. The foramen posterius canalis carotici interni lies at the anteriormost edge of the fossa pterygoidea, as in UA 9748. There is no indication of a foramen nervi vidiani or foramen caroticum laterale in the fossa pterygoidea. Most of the foramen lies in the basisphenoid.
The anteriormost end of the fossa pterygoidea is broken off, so the complete wall of the fossa is not preserved. In the pterygoid part of the break, anterodorsal to the foramen posterius canalis carotici interni, is the upper half of a small foramen, presumed to be the foramen nervi vidiani, which is in this position in the pterygoid of Kurmademys ( Gaffney et al., 2006: fig. 63).
The ventral margin of the foramen nervi trigemini is preserved and formed by the pterygoid anteriorly and prootic posteriorly. The sulcus cavernosus and canalis cavernosus are also preserved. There is no indication of the foramen caroticum laterale on the dorsal surface of the pterygoid.
EXOCCIPITAL
PRESERVATION: All of the left exoccipital is present except for most of the dorsal process forming the foramen magnum.
CONTACTS: The preserved contacts of the exoccipital in FMNH PR 2446 are with the opisthotic laterally, the quadrate ventrolaterally, and the basioccipital ventrally.
STRUCTURES: In FMNH PR 2446 the condylus occipitalis is formed by the exoccipitals only, without contribution from the basioccipital. Although only one exoccipital is preserved, the formation of the condylus occipitalis by the exoccipitals only can still be determined because the limit of the basioccipital is visible anterior to the base of the exoccipital. This condition also occurs in UA 9748 but not in Kurmademys . The foramen nervi hypoglossi in FMNH PR 2446 is paired on both sides and not recessed. The foramen jugulare posterius is formed mostly by the exoccipital, but its lateral wall is formed by the opisthotic.
BASIOCCIPITAL
PRESERVATION: The left half of the basioccipital is preserved. The posterior end of the bone is a sutural surface indicating that it did not enter into the condylus occipitalis.
CONTACTS: The contacts in FMNH PR 2446 are with the basisphenoid anteriorly, the quadrate laterally, and the exoccipitals posterodorsally.
STRUCTURES: The basioccipital in FMNH PR 2446 is slightly longer than in UA 9748. It does not enter the condylus occipitalis. The tuberculum basioccipitale is slightly more pronounced than in UA 9748.
PROOTIC
PRESERVATION: Most of the prootic is present in FMNH PR 2446, but its dorsomedial portion is broken away.
CONTACTS: These contacts remain in FMNH PR 2446: the quadrate laterally, the pterygoid ventrally, the basisphenoid ventromedially, and the opisthotic posteriorly (at least internally, the external surface is damaged).
STRUCTURES: The prootic in FMNH PR 2446 forms the usual structures: the foramen nervi trigemini with the pterygoid and parietal, and the foramen stapediotemporale with the quadrate laterally. As in UA 9748, this foramen faces dorsally, not anteriorly. In the roof of the fossa pterygoidea, the prootic is exposed and forms the anterolateral margin of the foramen nervi facialis, rather than the whole structure as in other Kurmademydini . The basisphenoid forms the medial edge of the foramen nervi facialis with a small spur of the quadrate extending into the foramen posteriorly. Although this condition is unique for FMNH PR 2446, it could be interpreted as similar to that seen in UA 9748, in which the pterygoid and basisphenoid, with a small spur from the quadrate, form the foramen. Both taxa have the basisphenoid and quadrate in the foramen, with the pterygoid covering the remaining exposed part of the prootic in UA 9748.
OPISTHOTIC
PRESERVATION: Much of the left opisthotic remains in FMNH PR 2446, but it lacks its anterior and posterior ends.
CONTACTS: The remaining contacts of the opisthotic of FMNH PR 2446 are with the prootic anteriorly, the quadrate anterolaterally, and the exoccipital posteromedially.
STRUCTURES: The opisthotic forms the wall between the more medial foramen jugulare posterius and the more lateral fenestra postotica.
BASISPHENOID
PRESERVATION: The left half of the basisphenoid is present; it is broken just anterior to the dorsum sellae anteriorly, but its posterolateral portions remain.
CONTACTS ON VENTRAL SURFACE: The basisphenoid contacts are with a small part of the pterygoid anterolaterally, the basioccipital posteriorly, the prootic laterally, and the quadrate laterally.
STRUCTURES ON VENTRAL SURFACE: The foramen posterius canalis carotici interni lies at the anterior end of the fossa pterygoidea, under the overhang formed by the basisphenoid, as seen in UA 9748. The foramen is formed mostly by the basisphenoid with a small part formed by the pterygoid dorsally. The medial half of the fossa pterygoidea is formed by the basisphenoid and it has an overhang for most of its length, very similar to that seen in UA 9748.
CONTACTS ON DORSAL SURFACE: These are the usual bothremydid contacts: the pterygoid anterolaterally, the prootic laterally, and the basioccipital posteriorly.
STRUCTURES ON DORSAL SURFACE: Because FMNH PR 2446 is broken close to the dorsum sellae, very little of the sella turcica and none of the rostrum basisphenoidale remain. The foramen anterius canalis carotici interni is present at the posterolateral corner of what remains of the sella turcica, as in Kinkonychelys rogersi and Kurmademys . The processus clinoideus is broken off, but the foramen nervi abducentis (VI) remains.
DISCUSSION
This specimen is a bothremydid because it has the diagnostic characters of an exoccipitalquadrate contact and a fully enclosed incisura columellae auris. It belongs to the tribe Kurmademydini because it has a deep fossa pterygoidea, a small part of the prootic is exposed on the ventral surface at the junction of basisphenoid, pterygoid, and quadrate (not in UA 9748), a foramen stapediotemporale that faces dorsally, a deep fossa precolumellaris, and a large, wide antrum postoticum. It agrees with UA 9748 in the form of the fossa pterygoidea, which is unique. The fossa has the medial basisphenoid margin overlapping the fossa covering the foramen posterius canalis carotici interni in ventral view. The anterior end of the fossa is deep, not shallow as in Kurmademys , and the foramen nervi facialis has at least the basisphenoid and quadrate in its margin rather than being formed entirely by the prootic. FMNH PR 2446 also agrees with UA 9748 in having the condylus occipitalis formed only by the exoccipitals, but this is a character that has evolved a number of times in turtles, not just in pleurodires.
As can be seen in table 1, UA 9748 ( Kinkonychelys rogersi ) and FMNH PR 2446 ( Kinkonychelys sp. ) differ in the following characters:
(1) UA 9748 has a condylus mandibularis that is relatively more posterior than in FMNH PR 2446.
(2) The foramen jugulare posterius has only the exoccipital in its margin in UA 9748, but the opisthotic also enters it in FMNH PR 2446.
(3) The prootic is exposed ventrally in FMNH PR 2446, but it is covered in UA 9748.
(4) Related to (3), the foramen nervi facialis in FMNH PR 2446 has the prootic in its margin and not the pterygoid, but in UA 9748 it is the pterygoid but not the prootic in the foramen margin.
The overhanging medial edge of the fossa pterygoidea in both specimens and their general similarity argue for close relationship. But the above-listed characters make it likely that FMNH PR 2446 represents a different taxon than UA 9748. We recognize this affinity by placing both in the same genus but in different species. UA 9748 is a nearly complete skull and can be appropriately employed to diagnose Kinkonychelys rogersi , but the incompleteness of FMNH PR 2446 precludes the naming of a new species, so we recognize it as Kinkonychelys sp. It will be difficult to assign new material to this taxon unless it has a well-preserved braincase.
RELATIONSHIPS AND BIOGEOGRAPHY OF KINKONYCHELYS
In order to determine the relationships of
Kinkonychelys , it was entered into the character matrix of Gaffney et al. (2006) and a new analysis was conducted. The results are shown in figure 9. The single cladogram contains 47 taxa and 175 characters, all characters are unweighted, the consistency index is 0.69, and the retention index is 0.81. The phylogenetic relationships of Kinkonychelys are strongly resolved with the Indian taxa Sankuchemys and Kurmademys , both of about the same age as Kinkonychelys . In fact, the phylogenetic resolution for the tribe Kurmademydini is ( Sankuchemys ( Kinkonychelys + Kurmademys )), indicating that Kinkonychelys is embedded within the tribe Kurmademydini , not simply a sister taxon to it. There are interesting biogeographic implications for these relationships.
Raxworthy (2003: 946) recently stated that, ‘‘Currently, there are no reptile groups in Madagascar that have well-supported phylogenies supporting a sister relationship with either the Seychelles or India.’’ As such, the extant Malagasy reptilian fauna shows no evidence of its former connections with the Indian subcontinent and the Seychelles block, the last major landmasses connected to Madagascar. The Indian subcontinent and Seychelles blocks are thought to have separat- ed, as a unit, from Madagascar approximately 88 Ma ( Storey et al., 1995, 1997; Torsvik et al., 2000; Reeves and de Wit, 2000; Raval and Veeraswampy, 2003). Separation began in the north, approximately 118 Ma, and spread southward over the next 30 million years, as the Indo-Madagascar landmass passed over the Marion mantle plume ( Seward et al., 2004). The Indian subcontinent and Seychelles blocks, in turn, separated from each other approximately 65 Ma, roughly contemporaneous with the intrusion of the Deccan basalts, or shortly thereafter (Ernst and Buchan, 1997; Pande et al., 2001; Chand and Subrahmanyam, 2003). There is growing consensus that the Indian subcontinent did not contact mainland Asia until at or near the Paleocene/Eocene boundary, roughly 55 Ma (e.g., Rowley, 1996; Clyde et al., 2003; Aitchison et al., 2007; Ali and Aitchison, 2008; Garzanti, 2008).
In this plate tectonic context, the phylogenetic hypothesis that Kinkonychelys is embedded within the Indian bothremydid tribe Kurmademydini as the sister taxon of Kurmademys ( Sankuchemys ( Kinkonychelys , Kurmademys )) indicates an even closer phylogenetic relationship than documented for other clades of Late Cretaceous vertebrates from Madagascar and the Indian subcontinent. Among gondwanatherian mammals, the Malagasy form Lavanify is more closely related to the Indian form Bharratherium (the senior synonym of Dhakshina Wilson et al., 2007) than it is to the South American forms Gondwanatherium and Sudamerica ( Gondwanatherium ( Sudamerica (Bharratherium, Lavanify ))) ( Krause et al., 1997, Wilson et al., 2007; Prasad et al., 2007). Similarly, among abelisaurid theropod dinosaurs, the Malagasy form Majungasaurus is phylogenetically closer to the Indian forms Indosaurus and Rajasaurus than it is to the South America genus Carnotaurus ( Carnotaurus ( Indosaurus , Rajasaurus , Majungasaurus )) ( Carrano and Sampson, 2008). As such, Kinkonychelys provides additional evidence of a close relationship among the latest Cretaceous terrestrial/freshwater vertebrate faunas of Madagascar and the Indian subcontinent but is the first taxon known from the Late Cretaceous of Madagascar that resides entirely within a clade previously known only from the Indian subcontinent.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.