Elseya (Elseya) flaviventralis, Thomson, Scott & Georges, Arthur, 2016

Thomson, Scott & Georges, Arthur, 2016, A new species of freshwater turtle of the genus Elseya (Testudinata: Pleurodira: Chelidae) from the Northern Territory of Australia, Zootaxa 4061 (1) : -

Elseya (Elseya) flaviventralis sp. nov.

Yellow-bellied Snapping Turtle ( Figure 1 )

Type data. HOLOTYPE: NTM 13512, adult female from Pine Creek Crossing, South Alligator River Drainage, Kakadu National Park, Northern Territory, Australia. 13° 30' S 132° 28' E ( Figure 2 ). PARATYPE and ALLOTYPE: NTM 13985, adult male from Pul Pul Billabong, South Alligator River Drainage, Northern Territory, Australia. 13° 34' S 132° 35' E ( Figure 3 ).

Referred specimens. AM 38325-26, 40181, 40278, 43532, 128001-02, 128004, 129342; ANWC 0531; NTM 5097, 13512, 13985, 34496; QM 59285-89; UC 0304; UU 14784-92, 17904-961, 18740-759.

Distribution. The Mary, South Alligator, East Alligator, Goyder and Mann River drainages of the north east of the Northern Territory, Australia ( Figure 4 ). It does not appear to be in sympatry with any other member of Elseya . It is, however, in sympatry with three species of Chelodina , at least two species of Emydura , Myuchelys latisternum and Carettochelys insculpta .

Diagnosis. Elseya flaviventralis is a large chelid turtle belonging to the Elseya (Elseya) subgenus. It can be distinguished from Elseya dentata and all other Australian members of the genus Elseya by the distinctive cream or yellow plastron, free of the dark streaking, blotches or suffusing present in other forms of Elseya ; bridge is extensive, with little or no abrupt angle between the bridge and the ventral surface of the plastron; a head shield that is broken up into a series of small plates rather than a single unit; flat uncornified temporal scales; and a narrower less robust skull. Osteologically, it can be distinguished from Elseya dentata by the contact of the vomer and the pterygoids. The carapace is typically a light to medium brown in color whereas the carapace of Elseya dentata is typically dark brown to almost black in color.

Etymology. The name flaviventralis comes from a combination of the Latin words flavus, meaning yellow, and ventralis, meaning ventral surface or belly. This is a reference to consistent cream or yellow coloring of the plastron in this species that distinguishes it from its nearest relative (both phylogenetically and geographically) Elseya dentata , which always has some degree of black coloration on the plastron.

Related taxa. Elseya flaviventralis is a member of the subgenus Elseya (Elseya) and is most closely related to Elseya dentata and Elseya branderhorsti .

Description. External Morphology.

Carapace. The carapace is broadly oval but narrowed at the anterior end. The most anterior points of the carapace are in the lateral third of the first marginal and the most posterior points are either side of the supracaudal notch. Marginals 4-7 are upturned in adults and marginals 8–11 are expanded and flared. There are no medial keels present in adults, but juveniles are slightly keeled medially. Adults do not have a serrated margin, but posterior marginals of juveniles are serrated from the posterior edge of marginal 7. Whereas Elseya dentata will show serrations from the posterior edge of marginal 4, Elseya albagula from marginal 1, Elseya irwini from marginal 9 and Elseya lavarackorum from marginal 2 (Thomson et al. 2006). Hence, similarly sized juveniles of Elseya flaviventralis can be distinguished from all other species of Elseya on this character. Spiny protrusions are absent from the posterior edge of marginals at all growth stages. The scute surface is not deeply fenestrated. Only one specimen examined had any degree of fenestration in the carapace ( AM 128004 ) but this appears to be an injury. The carapace is brown to dark brown, growth rings are often visible, but whether or not they are annual is unknown. The scutes of this species are often smooth and lustrous, as against the rough, matte, and textured scutes in other Elseya .

Plastron. Plastral formula using midline length is: pec> fem> abd> ana> int> hum> gul. The plastron is narrow with an axillary width approximately 40% of the carapace width. Bridge is extensive, little or no abrupt angle between the bridge and the ventral surface of the plastron; the posterior lobe of the plastron is longer than the anterior lobe. The anterior lobe is markedly narrower than in an Elseya dentata of equivalent size and this lobe is quite angular as against the more rounded shape seen in other species. Plastron color is yellow, cream or white and this species never has black streaking or mottling of the plastron, a feature that readily identifies this species from all other Elseya .

Head and Soft Parts. Head is large, but narrower and appears more delicate than its nearest relative, Elseya dentata , grey to brown on top white to cream below. The tomial sheath is yellow with no vertical barring, distinctive within the Elseya dentata group. The lateral sides of the head are covered in medium-sized scales but these are not raised or cornified. The parietal tubercles are rounded and small. A head shield is present which extends from the posterior of the nasals over the parietal and to the back of the skull but it does not extend down the parietal arch toward the tympanum. The head shield is fragmented, not entire as in all other Elseya . The dorsal surface of the neck is covered with medium sized pointed tubercles, though these are not as prominent as in Myuchelys latisternum . On the lower surface of the jaw there are two rounded barbels, which are larger than those in Elseya dentata but smaller than in the species from Queensland. The iris is green in color without a ring around the pupil and the sclera of the eye is brown. There are no dark spots on the iris anterior or posterior of the pupil. The rest of the skin is dark grey to brownish grey dorsally and cream to white ventrally. There are a series of enlarged scales on the thigh and shin region of the hind legs that form a skin flap that may assist in swimming. There are no pre-anal glands present.

Size and Sexual Dimorphism. Females grow to about 34 cm carapace length and males to about 27 cm. The largest animals measured in this study are a 325 mm female and a 265 mm male (Table 1).

TABLE 1. Selected measurements of Elseya flaviventralis examined in this study. CL = carapace length; CW#8 = carapace width at 7/8th marginal; CW#4 = carapace width at 4/5th marginal; PL = plastron length. All measurements are straight line and in mm.

Osteology. Skull. The skull of Elseya flaviventralis is large but delicate in structure, highly emarginated both from below and behind, to the extent that the parietal arch is narrow and hence cannot support the attachment of a head shield in this area ( Figure 5 ). The alveolar ridge begins laterally and adjacent to the foramen praepalatinum and the ridge does not exclude this foramen from view. The alveolar ridge extends posteriorly for the full extent of the triturating surface. The ridge is restricted to the maxilla and makes no contact with the palatines or premaxilla. Generally, this species is similar in alveolar ridge structure to Elseya dentata , but in similarly sized specimens the ridge is less distinctive. The lingual ridge of the triturating surface is serrated throughout its length and partially obscures the apertura nasalis interna. The lingual ridge extends posteriorly to almost make contact with the pterygoids. The lingual ridge begins on the premaxilla, unlike in Elseya dentata , and continues posteriorly along the maxilla to a point adjacent to the apertura nasalis interna where it continues onto the palatine bone. The degree of serration is less than in specimens of Elseya dentata of similar size, and far less than in the Queensland species.

The vomer is narrow throughout its length and contacts the pterygoids, separating the palatines. The canalis caroticus internus is closed over, but the foramen anterius canalis caroticus internus is absent. The supraoccipital is large in this species and it narrowly divides the parietals at the rear of the skull The crista supraoccipitalis is long and extends far beyond the occipital condyle, a feature absent in the Queensland forms but present to a lesser degree in the New Guinea species.

Cervicals. The centra all possess sagittal blades that are far less developed when compared to its sister species Elseya dentata . Each sagittal blade is concave in shape from the lateral view (flat in Elseya dentata ) and is narrow and concentrated at the anterior end. The transverse processes are large and triangular in shape and occupy the middle third of the centrum. They protrude horizontally from the neural arch whereas they angle downwards in Elseya dentata . The postzygophoses are large, almost join in the midline and are slimmer in overall structure than in Elseya dentata . The neural spine is completely absent in this species which distinguishes it from all other Elseya .

Shell. As a member of the Elseya (Elseya) subgenus this species has a prominent medial constriction in the anterior bridge strut suture, a feature shared with Elseya dentata . Exposed neurals have been observed in one specimen of this species (QM59285) as an individual variant; however, this animal is also aberrant in other shell features. This species has a less robust, thinner shell than Elseya dentata but much stronger buttressing, as evidenced by the stronger and more intricate anterior bridge struts.

Figures

FIGURE 1. Adult female Yellow Bellied Snapping Turtle (Elseya (Elseya) flaviventralis) from Pul Pul Billabong, Kakadu National Park, Northern Territory (13 ° 34 ' S, 132 ° 35 ' E).

FIGURE 2. Dorsal and lateral views of the holotype of Elseya (Elseya) flaviventralis NTM 13512, adult female from Pine Creek Crossing, South Alligator River Drainage, Kakadu National Park, Northern Territory, Australia. 13 ° 30 ' S 132 ° 28 ' E. The plastron has been disarticulated. Note the uniform coloration of the plastron, free from darker streaks and blotches, and the indistinct angle between the bridge and the plastron. Scale 10 mm.

FIGURE 3. Dorsal and lateral views of the Paratype (Allotype) of Elseya (Elseya) flaviventralis NTM 13985, adult male from Pul Pul Billabong, South Alligator River Drainage, Northern Territory, Australia. 13 ° 34 ' S 132 ° 35 ' E. Scale 10 mm. The plastron has been disarticulated.

FIGURE 4. Distribution of extant species in the genus Elseya. The ranges of Elseya rhodini and Elseya branderhorsti overlap to the west and including the Fly River drainage. Type localities are shown as red dots, with the exception of E. branderhorsti (green dot). The type locality for E. lavarackorum is outside range because it was described from a fossil from Riversleigh now outside its present range. E. rhodini occupies small streams and tributaries; E. branderhorsti occupies tidal regions, lower reaches and lakes, so the two are seldom found in microsympatry.

FIGURE 5. Lateral, Dorsal and Ventral views of the skull of Elseya flaviventralis. See Thomson et al. 2015; 2006 for comparative skulls of other Elseya species.