Gaffneylania auricularis, Sterli & De La Fuente & Krause, 2015

Sterli, Juliana, De La Fuente, Marcelo S. & Krause, J. Marcelo, 2015, A new turtle from the Palaeogene of Patagonia (Argentina) sheds new light on the diversity and evolution of the bizarre clade of horned turtles (Meiolaniidae, Testudinata), Zoological Journal of the Linnean Society 174 (3), pp. 519-548 : 525-535

GAFFNEYLANIA AURICULARIS SP. NOV.

Type specimen: MPEF-PV 10556 , basicranium and other skull remains, almost complete lower jaw, carapacial and plastral remains, third cervical vertebra, four caudal vertebrae, complete left humerus, proximal end of right humerus, distal end of left ulna, femoral head, distal end of tibia, and several osteoderms .

Referred specimens: MPEF-PV 10557, carapacial remains; MPEF-PV 10558, carapacial remains; MPEF- PV 10559, carapacial remains; MPEF-PV 10560, 3rd cervical vertebra; MPEF-PV 10561, proximal end of right humerus; MPEF-PV 10571, osteoderm and shell fragment; MPEF-PV 1778-1, axis; MPEF-PV 1778-2, proximal caudal vertebra.

Derivatio nominis: auricularis , from auricle in reference to the half-moon shaped rim formed by the squamosal and quadratojugal that surrounds the cavum tympani of this species.

Locality: Rocas Gemelas, Cañadón Hondo, south-east Chubut Province, Argentina.

Horizon: Lower section of Sarmiento Formation, Casamayoran SALMA (Middle Eocene) ( Simpson, 1935; Schaeffer, 1947; Andreis, 1977).

Diagnosis: Gaffneylania auricularis is referred to the clade Testudinata because it has a complete shell formed by interlocking dermal bones. It is diagnosed as belonging to Meiolaniidae due to the presence of a synapomorphy of the clade, the intrapterygoid slit (Canalis caroticum F, character 98). Gaffneylania auricularis shares with other meiolaniids the presence of a foramen posterius canalis carotici interni formed by the pterygoid (Canalis caroticum G, character 99), a ventrally open sinus (= fenestra caroticus of Rabi et al., 2013) where the internal carotid artery splits into the cerebral artery (piercing the basisphenoid) and the palatine artery (entering through the intrapterygoid vacuity) (Canalis caroticum D, character 96), a very thick basisphenoid and basioccipital, absence of a foramen dentofaciale majus, ornamentation in the dermal bones of the skull, lower jaw and shell consists of many small pits, strongly anteriorly curved marginal sulci in the carapace, presence of formed cervical and caudal vertebrae (Cervical articulation A, character 186), cervical centra as long as high or slightly longer than high (Cervical vertebra H, character 195), tall neural arches, presence of cervical ribs (Cervical rib A, character 181), and opisthocoelous caudal vertebrae (Caudal C, character 203). Gaffneylania auricularis shares with Mei. platyceps the robust humerus with well-expanded ends, short shaft (Humerus E, character 219), closed ectepicondylar foramen (Humerus A, character 215), and the presence of osteoderms. It differs from Mei. platyceps by the absence of a premaxillar dorsal process, ventrally open sinus (= fenestra caroticus of Rabi et al., 2013) where the internal carotid bifurcates into the palatine artery and cerebral artery (Canalis caroticum D, character 96), by the dorsum sellae only slightly overhanging the sella turcica, by the thin bony wall between the anterior foramina of the cerebral artery, by a very close exit of both rami of the cerebral arteries at the base of the high dorsum sellae in the posterolateral corner of the sella turcica, and by the absence of the accessory ridge in the triturating surface of the lower jaw. It shares with Nio. argentina that the foramen posterius canalis carotici cerebralis is not covered in ventral view by the pterygoids (Pterygoid C2, character 60). It differs from Nio. argentina by the shape of the occipital condyle, the shape and orientation of the squamosal horn, the angle between the rami of the lower jaw, by the presence of a medial symphyseal hook formed by the labial ridge, and because the labial ridge of the triturating surface of the lower jaw is taller than the lingual ridge. It is characterized by the following autapomorphies: a half-moon-shaped, thickened rim that is formed by the quadratojugal and squamosal bones that surrounds the cavum tympani, the presence of three K scutes (K1, K2 and K3) covering the moon-shaped rim, the shape of the occipital condyle, an ovoid occipital platform pierced by a foramen that is placed on both sides of the ventral portion of the occipital condyle, and a pair of basioccipital foramina placed in the midline of the skull between the condylus occipitalis and a posterior basioccipital depression, and by an unenclosed canalis chorda tympani mandibularis.

DESCRIPTION

SKULL

The description of the skull is based on the holotype (MPEF-PV 10556). The skull bones are extremely ankylosed and therefore do not allow the recognition of several sutures. Some sutures are clearly seen along their full path (e.g. the prootic–quadrate), some other sutures are recognized in some parts (e.g. the pterygoid– quadrate), while other contacts are inferred from the presence of certain structures (e.g. the prootic– opisthotic suture in ventral view).

Cranial scutes: There are no remains of the bones from the skull roof, and consequently there is no preservation of the dorsal scutes. However, three scutes are preserved in the rim surrounding the cavum tympani ( Figs 5–8 ). The homology of these scutes with the scutes present in other meiolaniids is doubtful because in Mei. platyceps and Nin. oweni there are only two scutes in this region of the skull (scutes K and J from Gaffney, 1983). In Nio. argentina this area is damaged on both sides, but it is evident that it has two scutes J, J1 and J2, and only one scute K ( Gaffney, 1983; Sterli & de la Fuente, 2011b). In G. auricularis we recognize three scutes surrounding the cavum tympani as the scute K formed by three parts, K1, K2 and K3 ( Figs 5–8 ). Scute K1 is the most dorsal K scute and it is located entirely on the squamosal. Scute K2, by contrast, is located half on the squamosal and half on the quadratojugal. Scute K3 is the most ventral one and it is located in the quadratojugal.

Dermatocranium: No remains of prefrontal, nasal, frontal, jugal, postorbital or parietal are preserved.

Only the posterior portion of the left quadratojugal is preserved in the holotype ( Figs 5 , 6A , 7 , 8 ). As in Mei. platyceps the quadratojugal contacts the squamosal below the cavum tympani and it is recovered as a synapomorphy of Meiolaniidae in the cladistic analysis (Quadratojugal C, character 23). It is likely that this condition is present in other meiolaniids (i.e. Niolania argentina , Ninjemys oweni ). The quadratojugal also contacts the quadrate medially. The other contacts of the quadratojugal are not preserved. The quadratojugal forms the anterior portion of the halfmoon-shaped rim that surrounds posteroventrally the cavum tympani.

The left squamosal is preserved ( Figs 5–8 ). It forms the posterodorsal part of the half-moon-shaped rim that posteroventrally surrounds the cavum tympani and the horn (Squamosal C, character 26). The squamosal also forms the posterodorsal part of the cavum tympani. As in Mei. platyceps the squamosal contacts the quadratojugal below the cavum tympani. The squamosal also contacts the quadrate medially. The remaining contacts of the squamosal are not preserved.

The presence of horns in the squamosal is a synapomorphy of Meiolaniidae (Squamosal C, character 26). The horn core B ( Fig. 9 ) was found associated with the other cranial and postcranial remains herein described but its exact location on the skull cannot be assessed with certitude because it is broken at its base. Compared with Nio. argentina , the horn core B of this taxon is comparable in size and shape, but it is slightly smaller and curved slightly posterodorsally ( Fig. 9A–C ). The tip of the horn in this taxon is flat and blunt ( Fig. 9C ), while in Nio. argentina the horn ends in a pointed tip. In contrast to Mei. platyceps , but similar to Nio. argentina , the section of the horn is triangular ( Fig. 9D ). The triangular sections differ between Nio. argentina and G. auricularis . In the latter taxon the section is like an isosceles triangle with the short side facing dorsally ( Fig. 9D ), while in Nio. argentina is resembles a scalene triangle with its shortest side facing ventrally.

Palatal bones: There are no remains of the vomer or palatine. Only part of the right premaxilla is preserved ( Fig. 10 ). It contacts the other premaxilla medially and the maxilla laterally through an oblique suture. The posterior, horizontal process of the premaxilla is missing. The premaxilla forms the ventral border of the apertura narium externa. In contrast to Mei. platyceps , but similar to Nio. argentina , the premaxilla of MPEF- PV 10556 does not have a dorsal process. In ventral view, the premaxilla forms part of the triturating surface. Only the labial ridge is preserved in MPEF-PV 10556 and comparisons with Mei. platyceps , Nin. oweni or Nio. argentina are therefore limited.

A part of the right maxilla is preserved as well ( Fig. 10 ). The only preserved contact is the medial one with the premaxilla. Dorsally, the maxilla exhibits a sutural surface with the nasal or the prefrontal. Towards the posterior the maxilla is broken; possible contacts with the jugal or the nasal are not preserved. Conse- quently, it cannot be determined whether the nasomaxillary sinus was present. The maxilla forms the lateral border of the apertura narium externa. The portion of the maxilla that forms part of the triturating surface is broken in specimen MPEF-PV 10556.

Palatoquadrate bones: Both quadrates are preserved, the left one of which is more complete ( Figs 5–8 , 11 ). The quadrate contacts the prootic anteromedially, the pterygoid ventromedially, the quadratojugal lateroanteriorly, the squamosal posterior and posterolaterally, and the opisthotic posteriorly. The lateral aspect of the quadrate, as in most turtles, is funnel-shaped ( Fig. 5 ). The cavum tympani is deep (Quadrate B + C, character 49), but there is no distinct antrum postoticum (Antrum postoticum A,character 51) or precolumellar fossa ( Fig. 5 ) as in Mei. platyceps ( Gaffney, 1983) or in Warkalania carinaminor (Gaffney et al., 1992) . The anterior part of the quadrate forms the entire processus trochlearis oticum ( Figs 6 , 7A, 7 ; Quadrate G, character 54). The medial part of the quadrate forms the anterior wall of the canalis cavernosus and the lateral wall of the canalis stapedio-temporalis. The canalis stapediotemporalis ends dorsally in the foramen stapediotemporalis, which is formed by the quadrate, prootic and opisthotic ( Figs 7A , 8 ). This foramen is formed by the quadrate and prootic in Nio. argentina ( Sterli & de la Fuente, 2011b) and by the prootic and opisthotic in Mei. platyceps ( Gaffney, 1983) . The incisura columella auris is closed in its most lateral part by the squamosal and the quadratojugal, but the quadrate portion of the incisura is not completely closed posteriorly ( Figs 5 , 7B ). As in other meiolaniids (e.g. Mei. platyceps and probably in Nin. oweni and in War. carinaminor Gaffney, 1983, 1992 ; Gaffney et al., 1992), the incisura columella auris and the Eustachian tube are enclosed in bone in the external part of the cavum tympani (Quadrate F, character 52). In the anterolateral portion of the quadrate, the processus articularis ends in the condylus mandibularis ( Figs 6A , 7A ). The condylus mandibularis is rectangular, medio-laterally elongat- ed and the surface is almost flat, as in Mei. platyceps ( Gaffney, 1983) . It is divided in two parts, the medial and the lateral. The lateral part is located below the medial one.

The base of the right epipterygoid is preserved ( Figs 7A , 8 ), but the epipterygoid cannot be identified on the left side (Epiterygoid A, character 56). Due to the nature of the small fragment of the epipterygoid preserved on the right side, no detailed description is possible. The only preserved contact of the epipterygoid is with the pterygoid, ventrally ( Figs 7A , 8 ).

Both pterygoids are preserved, although the right one is more complete ( Figs 6A , 7A , 8 , 11 ), only missing its anterior part. The preserved contacts of the pterygoid are with the basisphenoid posteromedially, the basioccipital posteriorly, the prootic dorsally, the epipterygoid dorsally and the quadrate laterally. In MPEF-PV 10556 ( Figs 7A , 8A , 11A ) the right pterygoid shows the presence of an intrapterygoid slit, a characteristic of meiolaniids (Pterygoid C2, character 59). As a consequence, the pterygoid is located in a lower level than the basisphenoid in this area (Pterygoid M, character 70). In contrast to Mei. platyceps , but as in Nio. argentina , the pterygoids in G. auricularis ( Figs 6A , 11A ) do not cover the sinus (= fenestra caroticus of Rabi et al., 2013) ventrally where the internal carotid bifurcates into the palatine and cerebral arteries (Pterygoid C2, character 60). In this sinus (= fenestra caroticus), the cerebral branch pierces the basisphenoid ( Gaffney, 1983; Sterli et al., 2010; Sterli & de la Fuente, 2011b). In ventral view, at the level of the sinus (= fenestra caroticus), there is a dropshaped concavity pointing anteriorly ( Fig. 6A ). This concavity could have served for the attachment of the muscle adductor mandibulae internus Pars pterygoideus posterior (muscular unit number 27 of Werneburg, 2011). In the posterolateral part of the pterygoid, near its suture with the basioccipital and the prootic, the foramen posterius carotici interni (fpcci, Sterli et al., 2010; Canalis caroticum G, character 99) is preserved ( Figs 6A, B , 11 ). This foramen could also be recognized in Mei. platyceps ( Gaffney, 1983) and in Nio. argentina ( Sterli & de la Fuente, 2011b) . Posteriorly, the pterygoid forms the entrance of the canalis cavernosus ( Figs 7A , 11A ), which runs along the dorsal part of the pterygoid between the pterygoid (anteriorly) and the prootic (posteriorly). Through this canal the vena capitis lateralis leaves the skull.

Basicranial bones: Due to the nature of the sutures in MPEF-PV 10556, the sutures of the supraoccipital are not recognizable ( Figs 6B , 7 ). This bone might be fused with the exoccipitals. The characteristic contribution of the horizontal plate of the supraoccipital to the skull roof in meiolaniids is not preserved in MPEF- PV 10556; this area is broken.

Both exoccipitals are preserved ( Figs 7B , 11A ). The only clear suture of the exoccipital is the one with the opisthotic. It seems that the exoccipital and the basioccipital are fused. Perhaps the exoccipital is also fused with the supraoccipital. As in Nio. argentina , there are two large foramina nervi glossopharyngei in each exoccipital in G. auricularis ( Figs 7B , 11A ). Two large foramina and a third, much smaller, were described in Mei. platyceps ( Gaffney, 1983) . As is typical in turtles the exoccipital forms the lateral margin of the foramen magnum. As well, as in other turtles, the exoccipital probably contributes to the occipital condyle ( Gaffney, 1979). The exoccipital of G. auricularis furthermore forms the posterior wall of the recessus scalae tympani and the posterior margin of the foramen jugulare anterius that connect this portion of the cavum acusticojugulare with the cavum cranii ( Figs 7B , 11A ).

The basioccipital is a robust bone in G. auricularis and, together with the basisphenoid, is very thick in sagittal section ( Fig. 11C ). The basioccipital contacts the basisphenoid anteriorly, the pterygoid anterolaterally, the prootic dorsolaterally and anteriorly, the opisthotic dorsoposteriorly, and the exoccipital dorsally ( Figs 6A , 7B , 11A, C ). The basioccipital, together with the exoccipital, forms the condylus occipitalis. The occipital condyle has a triangular shape pointing ventrally, almost as wide as high ( Fig. 7B ). The outline and proportions of this condyle are different in other meiolaniids (e.g. it is subhexagonal two times wider than high in Nio. argentina and it is also subtriangular slightly wider than high in Mei. platyceps ). As in Mei. platyceps , the occipital condyle of G. auricularis has three articular surfaces, two located above and separated by a shallow concavity and one located below in the midline. The main differences between the occipital condyle of G. auricularis and Mei. platyceps are that the medial articular facet of G. auricularis not only has a posteri- or but also a ventral development and that G. auricularis lacks the presence of a well-delimited concavity in the middle of the condyle as is characteristic of Mei. platyceps ( Gaffney, 1983) . In posterior view, on each side of the ventral portion of the condyle, there is an ovoid platform pierced by a foramen ( Fig. 7B ). This platform is unique among turtles. The function of this platform and the identity of the foramina are unknown. In ventral view a deep, semicircular concavity is seen ( Figs 6A , 11A ). Between this concavity and the occipital condyle there is a pair of foramina of unknown function. These foramina are also unique for this taxon. In dorsal view at the level of the contact with the basisphenoid, the basioccipital bears the basis tuberculi basalis ( Gaffney, 1979) ( Figs 7A , 8 ).

Both prootics are preserved in G. auricularis ( Figs 6 , 7A , 8 , 11B, C ). The left one is complete, while the right one is missing the dorsal part. The prootic is a thick, quadrangular element. The prootic contacts the quadrate laterally, the pterygoid anteriorly, the opisthotic posteriorly, the basisphenoid medially and perhaps the parietal dorsally (this contact is missing in this specimen). The prootic forms part of several structures of the skull. The prootic forms the anterior part of the inner ear (cavum labyrinthicum), which is completed posteriorly by the opisthotic ( Fig. 11B, C ). The entire rim of the fenestra ovalis is ossified, the prootic being the bone that closes it anteriorly ( Fig. 11B, C ). By contrast, in Mei. platyceps a small notch is recognized in the ventral margins of the prootic, and it was probably filled with cartilage in life ( Gaffney, 1983). Dorsally the prootic forms the anterior rim of the foramen stapedio-temporalis ( Figs 6B , 8 ). The foramen stapedio-temporalis is framed by the prootic anteriorly, the quadrate laterally and the opisthotic posteriorly. In anterior view, the prootic forms the posterior border of the prootic foramen ( Figs 7A , 8 ). Due to breakage of the epipterygoid, the structure of the prootic foramen and the foramen nervi trigemini (V) cannot be assessed with certitude. In medial view the prootic forms the anterior wall of the hiatus acusticus, the wall separating the cavum cranii and the cavum labyrinthicum ( Gaffney, 1979). The hiatus acusticus is highly ossified in this taxon ( Fig. 11C ) as in Nio. argentina and Mei. platyceps ( Gaffney, 1983) . Neither the fossa acustico-facialis, nor the foramen aquaductivestibuli, foramen nervi acustici and foramen nervi facialis are seen. In inner view, the prootic houses the recessus labyrinthicus prooticus where the ampullae and the anterior and horizontal semicircular canal are located.

Remains of both opisthotics are present, but only the left one is complete ( Figs 6 , 7B , 8 , 11B, C ). The opisthotic contacts the exoccipital medially, the squamosal laterally, the prootic anteriorly, the quadrate anterodorsally and the basioccipital ventrally. Its contacts with the supraoccipital or parietal cannot be seen. The opisthotic together with the prootic forms part of the inner (cavum labyrinthicum) and middle (cavum acustico-jugulare) ears ( Figs 7A, 7 , 11A–C ). The recessus labyrinthicus opisthoticus is preserved in the opisthotic and houses the posterior ampullae and the posterior and horizontal semicircular canals ( Figs 7A , 8 , 11A ) ( Gaffney, 1979). The fenestra ovalis in this taxon is completely ossified ( Fig. 11A, B ). The processus interfenestralis of the opisthotic is a very thin strip of bone (Opisthotic D2, character 81) that reaches and fuses with the floor of the cavum acustico-jugulare ( Fig. 11A, B ). At the base, the processus interfenestralis of the opisthotic is pierced by the nervi glossopharyngei (IX) ( Fig. 11A ). The recessus scalae tympani and the cavum labyrinthicum are connected through the fenestra perilymphatica, which is located posterior to the processus interfenestralis of the opisthotic. In medial view, the opisthotic forms the posterior part of the wellossified hiatus acusticus ( Fig. 11C ). Posterior to the hiatus acusticus, between the exoccipital and the opisthotic the foramen jugulare anterius is visible ( Fig. 11C ). The vagus (X) and the accessory (XI) nerves and the vena cerebralis posterior leave the skull through this foramen. The processus paraoccipitalis of the opisthotic is well developed in this taxon ( Fig. 7B ) as in Mei. platyceps ( Gaffney, 1983) . The middle ear has a posterior wall, which is built up by the opisthotic ( Fig. 7B ). The foramen jugulare posterius and the fenestra postotica are coalescent and formed by the opisthotic ( Figs 7B , 11A ). In dorsal view, the opisthotic forms the posterior rim of the foramen stapediotemporale ( Figs 6B , 8 ).

The basisphenoid is almost complete, only lacking the rostrum basisphenoidale ( Figs 6 , 7A , 8 , 11A ). This bone contacts the basioccipital posteriorly, the prootic laterally and the pterygoid ventrolaterally. Similar to the basioccipital, the basisphenoid is a very thick bone and it appears that both bones are fused because no suture is recognized between them ( Fig. 11C ). On its dorsal surface, along the contact with the basioccipital, the basis tuberculis basalis is present ( Figs 7A , 8 ). As in Mei. platyceps , the dorsal surface of the basisphenoid is irregular with asymmetrical pits and grooves ( Figs 7A , 8 ). Together with the basioccipital, the basisphenoid forms the ventral rim of the hiatus acusticus ( Fig. 11C ). Ventrally, in the basisphenoid the sinus (= fenestra caroticus) where the inner carotid exits the skull and where it bifurcates into the cerebral and palatine arteries is present ( Figs 6A , 11A ). The cerebral artery enters the skull through the foramen posterius canalis carotici cerebralis in this sinus ( Sterli et al., 2010; Sterli & de la Fuente, 2011b; Rabi et al., 2013). The cerebral artery runs anteriorly through the basisphenoid and both branches exit very close to each other at the base of the high dorsum sellae in the posterolateral corner of the sella turcica ( Figs 7A , 8 ). In MPEF-PV 10556 the two foramina are separated by a thin wall of bone, in contrast to the thick wall of bone present in Mei. platyceps ( Gaffney, 1983) . The nervi abducentis (VI) also pierces the basisphenoid ( Figs 7A , 8 ). The entrance of the nervi abducentis to the basisphenoid is not seen, but the anterior exit is preserved. The nervi abducentis exits the basisphenoid laterodorsally to the foramen anterior canalis carotici cerebralis ( Figs 7A , 8 ). Both processus clinoideus are broken in the specimen ( Figs 7A , 8 ), so it is not possible to assess whether they were short as in Mei. platyceps . As in Mei. platyceps ( Gaffney, 1983) the dorsum sellae of MPEF-PV 10556 is high and delimited on either side by a ridge ( Figs 7A , 8 ). The dorsum sellae, in contrast to Mei. platyceps ( Gaffney, 1983) , overhangs the sella turcica by a small amount.

LOWER JAW

An almost complete lower jaw is available and only missed the right posterior part and both splenials and coronoids ( Fig. 12 ). The external surface of the bones of the lower jaw is highly ornamented with ridges, grooves and pits ( Fig. 12A, C–E ). This ornamentation is also present in Nio. argentina and Mei. platyceps , although, at least in the last taxon, the ornamentation is restricted to the dentary and the anterior part of the surangular.

Dentary: Both dentaries are preserved, with the exception of the tip of the left dentary ( Fig. 12 ). Both dentaries are fused at the symphysis ( Fig. 12A ; Dentary A, character 119). The dentary contacts the surangular posterolateraly, the angular posteroventrally, the coronoid posterodorsally, the prearticular posteromedially and the splenial medially ( Fig. 12B–F ). Although, both the splenial and the coronoid are missing in the specimen, the sutural surface is present on the dentary ( Fig. 12B, F ). The triturating surface of the lower jaw is formed entirely by the dentaries ( Fig. 12C, F ). As in Nio. argentina , there are only two ridges in the triturating surface, the labial and the lingual ridges. In Mei. platyceps , besides the labial and ligual ridges, an accessory ridge is described between them ( Gaffney, 1983). In contrast to Nio. argentina and Mei. platyceps , the labial ridge is taller than the lingual ridge. Both ridges are almost parallel along their entire length with the exception of the anterior part, near the symphysis, where both ridges slightly converge ( Fig. 12C ). Also, at the bottom of both ridges there are many small nutritive foramina located on the external surface in the labial ridge and on the lateral surface in the lingual ridge ( Fig. 12B ). The surface between both ridges is concave. In contrast to Nio. argentina , the labial ridge of this taxon forms a medial hook at the symphysis ( Fig. 12A ). The foramen dentofaciale majus, located on the outer surface of the dentary in most turtles, is absent in G. auricularis ( Fig. 12E ). This foramen is also not recognized in other meiolaniids such as Mei. platyceps , Nio. argentina or Nin. oweni . The sulcus cartilaginis Meckelii is open for a small distance, because the anterior border of the splenial ends near the symphysis ( Fig. 12B, F ). In the posterior part of the dorsal margin of the sulcus cartilaginis Meckelii the foramen alveolare inferius is present. The canalis alveolaris inferior extends anteriorly covered by a thin layer of dentary.

Angular: The left angular is complete, while just the anterior portion of the right one is preserved ( Fig. 12B, D, F ). The sutures of this bone are not clear, but the contacts with other bones can be inferred by the presence of certain structures and comparisons with other meiolaniids. The angular contacts the prearticular dorsally, the dentary anteroventrally, the splenial anterodorsally and the surangular laterally ( Fig. 12B, D, F ). The angular forms the ventral border of the large foramen intermandibularis caudalis ( Fig. 12B, F ). A large foramen intermandibularis caudalis is also present in Mei. platyceps ( Gaffney, 1983) .

Surangular: Both surangulars are preserved ( Fig. 12B– F ). The left one is complete, while the posterior part of the right one is missing. The surangular forms the posteolateral part of the lower jaw. It contacts the dentary anteriorly, the articular medially, the coronoid anterodorsally and probably the angular ( Fig. 12B– F ). The surangular forms the lateral rim of the fossa Meckelii ( Fig. 12B, F ). The foramen nervi auriculotemporalis is present at the level of the area articularis mandibularis ( Fig. 12E ). The ramus cutaneus recurrens of the branch of the mandibular nerve (V3) enters the surangular through this foramen. This nerve leaves this bone anteriorly along an opening located in the medial surface of the surangular in the posterior portion of the fossa Meckelii.

Coronoid: Both coronoids are missing, but their presence can be inferred by the sutural surface left on the dentary and surangular ( Fig. 12B, F ).

Articular: Just the left articular is preserved ( Fig. 12B, C, F ). Unfortunately the sutures of this bone are not discernible, probably because all the posterior bones of the lower jaw are fused (as in Mei. platyceps and other turtles). The area articularis mandibularis could be also formed by other bones (e.g. surangular) in this taxon, but we describe this surface here. The area articularis mandibularis is a rectangular area, mainly concave, slightly subdivided into two subareas ( Fig. 12B, C ). It faces dorsoposteriorly and it is slightly inclined laterally. The medial part is larger, and anteroposteriorly longer than the lateral one. Posterior to the area articularis mandibularis there is a small processus retroarticularis that is longer in its medial portion ( Fig. 12B ). This process could be also formed by the angular. In the dorsal part of the medial surface of the retroarticular process there is a groove, which continues anteriorly along the medial surface of this bone and the prearticular ( Fig. 12B, F ). We interpret this groove as the unenclosed canalis chorda tympani mandibularis ( Fig. 12B, F ). In Mei. platyceps and most turtles this canal is enclosed by the articular and prearticular.

Prearticular: The posterior and anterior portions of the left prearticular are preserved, as well as a small anterior portion of the right one ( Fig. 12B, F ). The prearticular contacts the articular posteriorly, the angular ventrally and probably the coronoid dorsally ( Fig. 12B, F ). The prearticular forms the dorsal border of the foramen intermandibularis caudalis and the inner rim of the fossa Meckelii. In the medial surface of this bone the groove of the unclosed canalis chorda tympani mandibularis is preserved ( Fig. 12B, F ).

Splenial: Both splenials are missing, but their presence can be inferred by the suture surface left on the dentary ( Fig. 12B, F ). As in Nio. argentina the splenial almost reaches the symphysis anteriorly ( Fig. 12B, F ).

Figures

Figure 5. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photograph and drawing of the skull in left lateral view.

Figure 6. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photographs and drawings of the skull in ventral (A) and dorsal (B) views.

Figure 7. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photographs and drawings of the skull in anterior (A) and posterior (B) views.

Figure 8. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Stereophotographs and drawing of the skull in dorsoanterolateral view.

Figure 9. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photographs and drawing of the horn core B in anterior (A), ventral (B), lateral (C) and medial (D) views.

Figure 10. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photographs and drawings of the right premaxilla and maxilla in anterior (A), posterior (B) and ventral (C) views.

Figure 11. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Stereophotographs and drawings of the skull in left ventroposterolateral (A) and right lateral (right quadrate removed) (B) views. Photograph and drawing of the skull in medial (C) view.

Figure 12. Gaffneylania auricularis gen. et sp. nov., MPEF-PV 10556 (holotype). Photographs and drawings of the lower jaw in anterior (A), posterior (B), dorsal (C), ventral (D), left lateral (E) and medial (F) views.