Type Specimens

Holotype: QM J81785, adult female collected by Duncan Limpus on 24 October 2004 from the plunge pool at the downstream side of the Ned Churchwood Weir, Burnett River, Queensland, Australia (25°03′S, 152°05′E) (Fig. 2). Allotype: QM 28449, adult male from Nogoa River, Fitzroy River Drainage, Queensland (23°31′S, 148°01′E) (Fig. 3). Paratypes: QM 37933, adult male from Dawson River Crossing at Baroondah Station, Fitzroy River Drainage, Queensland (25°41′S, 149°13′E); QM 36041, 36044, two juveniles from Coondoo Creek, Tin Can Bay Road, Mary River Drainage, Queensland (25°59′S, 152°05′E). See Tables 2 and 3 for comparative measurements.

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Table 2. Relative measurements of the head for Elseya.^a

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Table 3. Relative measurements of the carapace and plastron for Elseya.^a

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Referred Specimens

QM 2966, 4501, 4505, 36036, 36039, 36042, 36045–7, 38533, 47987, 47998, 48002, 48010, 48012, 48026–27, 48029, 48039, 48046, 48052, 59269–71; UC 0305–6; UU 17086–102, 17274, 17874–903, 18514.

Diagnosis

The largest extant species of Elseya, reaching carapace lengths of 420 mm. Belongs to the E. dentata generic group, and as such can be distinguished from all members of the E. latisternum generic group by the following combination of characters: parietal arch narrow, much narrower than the otic chamber; head shield does not extend from the dorsal surface of the skull down the parietal arch toward the tympanum; alveolar ridge present on the triturating surfaces of the mouth; intergular scute narrow, maximum width less than that of the gulars.

Elseya albagula can be distinguished from species within the E. dentata generic group by the following combination of characters: skull robust but narrows acutely across the pterygoids behind the processus pterygoideus externus (Fig. 4); head shield deeply furrowed to the extent that osteologically there are also deep furrows in the dorsal surface of the skull of large adults; alveolar ridge on the triturating surfaces and underlying bone of the upper jaw very prominent, forming a complex with the equally prominent lingual ridge (Fig. 4). This complex corresponds with prominent ridges and cavities in the lower jaw to form shearing surfaces; lingual ridge of maxilla expanded such that, in older specimens, it obscures the foramen praepalatinum in ventral view.

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Anterior carapace blunt, with the first and second marginal scutes approximately equal in their anterior extent in large individuals (Fig. 5); carapace with serrated margin, most prominent in juveniles where serrations begin at the posterior edge of marginal 1 (Fig. 5); serrated margin persists into early adulthood; cervical scute absent (Fig. 5), except as a rare variant; anterior plastron broad, not oval in outline; posterior bridge strut articulates with the carapace posterior to the midline of pleural 5 or on the junction of pleurals 5 and 6, rarely on pleural 6 alone.

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Distribution

The major drainage basins of the Fitzroy, Burnett, and Mary rivers of southeast Queensland, Australia (Fig. 3), with records also from the minor Raglan, Kolan, and Gregory-Burrum drainages. Occurs in sympatry with Elseya latisternum, Chelodina longicollis, C. expansa, and Emydura macquarii krefftii in all three drainages that comprise its range; also with Elusor macrurus in the Mary River and Rheodytes leukops in the Fitzroy drainage.

Etymology

The name albagula is derived from the Latin adjective “alba” meaning white (feminine) and the noun “gula” for throat, which is also feminine. Hence the name means “white throat,” and refers to the white or cream throat commonly seen in adult females of this species.

Related Taxa

The affinities of E. albagula lie with a well-defined clade within the E. dentata subgeneric group comprising E. irwini, E. lavarackorum, an undescribed taxon from the Johnstone Rivers region of north coastal Queensland (Georges and Adams 1996), and possibly New Guinean E. branderhorsti (Thomson, unpub. data, 1996), but excluding E. dentata, E. novaeguineae, E. schultzei, an undescribed taxon from Arnhem Land, and a number of other undescribed species from the New Guinea region.

We consider the closest living relative to be an undescribed taxon from the Johnstone Rivers region near Cairns, but among described taxa, it is E. lavarackorum (White and Archer 1994) from the Nicholson Drainage, Queensland, not E. irwini (Cann 1998) from the Burdekin River, Queensland.

Carapace

Carapace broadly oval posteriorly, blunt anteriorly (Fig. 5). Marginals 2–6 upturned and marginals 7–11 expanded and flared laterally in adults. Adult carapace is dark brown to black in color, often also heavily stained. Surface smooth, with or without growth rings, and lacks luster.

Medial keels distinct on all vertebral and costal scutes of juveniles, forming a tricarinate ridged carapace; keels indistinct or absent in adults. Carapace of juveniles serrated from the posterior edge of marginals 1 (Fig. 6); young adults have a serrated margin from marginals 7. Spiny protrusions on the ends of marginals (Fig. 1) present to ca. 120 mm carapace length. These features are thought to derive from very rapid growth, and combine to make a very distinctive juvenile. Juvenile carapace tan, mottled with dull brown to black in small juveniles, changing to dark brown or black at variable size (in one case as small as 71 mm CL). Irregular mottling on each scute, concentrated as ragged blotches on and straddling the sulci.

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Plastron

Plastral formula (using midline length) of the holotype: fem > pec > abd > int > ana ≥ hum > gul (Fig. 5), with no variation among the adult plastra examined. Plastron narrow with axillary width ca. 50% of carapace width. Base of anterior lobe does not taper, its lateral margins roughly parallel for the length of the pectoral. Bridge extensive and posterior lobe longer than anterior lobe. Color of adult plastron often difficult to determine because of complete staining to black, but base color cream to yellow, with or without darker streaks and blotches. Axillary and inguinal scutes present.

Plastron yellow, mottled with indistinct black or brown, in some cases yielding a radial pattern in the direction of scute growth. Mottling concentrated on bridge and posterior half of the plastral surface. Inframarginal surfaces similarly mottled with irregular brown. Pale fields on inframarginals tinged with pinkish orange. Pattern becomes indistinct and inframarginal surfaces lose pale fields even in juveniles as small as 100 mm.

Head and Soft Parts

Head large, robust, but not to the extent of its nearest relatives within the E. lavarackorum group; dark brown above, cream, yellow, or white below in females; typically grey but occasionally cream below in males. Boundary between light ventral coloration and darker dorsal coloration of head and neck very irregular, forming large, distinctive patches that vary with age and among individuals (Fig. 7).

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Tomial sheath of upper jaw yellow, cream, or grey, sometimes with vertical barring (Fig. 7). Head shield entire, extending from immediately posterior to the nasals, over the parietal to the posterior extent of the skull; deeply furrowed, involving both scutes and the bone beneath in large adults. Head shield does not extend laterally to contact or approach the tympanum. Temporal region covered in medium rounded hard scales. Two very prominent barbels on chin, rounded (not pointed) terminally; cream, grey, and often suffused with pink in life; surrounded by small scales of low relief.

Boundary between pupil and iris indistinct (Fig. 7), occasionally with a vague lighter ring of gold flecks around the pupil. Iris dull brownish olive, not bright; sclera brown; leading and trailing eyespots absent. Upper eyelid with nine scales.

Dorsal surface of neck with medium rounded tubercles. Dark grey above, cream, yellow, or white below in females, typically light grey below in males but also may be cream, yellow, or white below as in females. As with head, boundary between light ventral coloration and darker dorsal coloration irregular and varies greatly among individuals.

Limbs and tail dark grey above, light grey below with or without irregular blotches (see allotype, Fig. 2). In some adult females, and rarely in males, the distinctive light coloration of the ventral and lateral surfaces of the head and neck may extend down the forelimbs. Five claws on the front feet; four on the rear. A series of enlarged scales present on the leading and trailing edges of the lower limb; may be present on the thigh. Pre-anal glands absent.

Dorsal color of the head and soft parts of juveniles follows that of the carapace. Ventral base color cream suffused vaguely with yellow or orange. Ventral surfaces of tail and hindlimbs noticeably brighter, forelimbs duller; no distinct striping on limbs or tail. Most neck tubercles are pale olive. A vague stripe extends from the angle of the mouth two-thirds of the way to the shoulder, including the lower tympanum. Ventral surface of head and neck cream or yellow, with a slight gold or orange suffusion on chin and gular region.

Size and Sexual Dimorphism

This species is among Australia's largest side-necked turtles, with possibly only Elusor macrurus attaining a larger size (J. Cann, pers. comm., 1997). Females grow to a larger size than males (females to 420 mm CL, Mary River [M. Dorse, pers. comm., 2004]; males to ca. 300 mm). Largest examples in this study were a 418-mm female and a 275-mm male. Males easily distinguished from mature females by a much larger tail (Figs. 1 and 2), as with all short-necked chelids, however, sex of animals up to 150-mm CL could not be determined with confidence.

Skull

Skull large and robust, emarginated both from below and behind (Fig. 4, n = 5), but to a much lesser degree than E. dentata (sensu stricto) (n = 12). Temporal emargination greater than in any other Queensland Elseya; parietal arch wider but not to the extent that it can support the attachment of a head shield. Alveolar ridge extensive, but not to the extent of E. lavarackorum (Fig. 8, n = 2), beginning adjacent to the premaxilla lateral to the foramen praepalatinum. Alveolar ridge extends back to the end of the triturating surface; does not contact the palatines. Lingual ridge of the triturating surface heavily serrated and widened throughout its length; almost obscures the apertura nasalis interna and completely obscures the foramen praepalatinum from ventral view. The ridge extends back to almost make contact with the pterygoids but does not obscure the anterior edge of the vomer, differentiating it from E. lavarackorum. The lingual ridge is on the premaxilla in the anterior skull and continues onto the maxilla but adjacent to the medial edge of the apertura nasalis interna it continues onto the palatine bone. The degree of serrating is moderate but second only to E. lavarackorum in its widening of the triturating surface. The maxilla and palatines are significantly thickened and the apertura nasalis internae are deeply recessed into the palatal surface of the skull.

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Vomer and the pterygoids not in contact; vomer not expanded posteriorly but separates the anterior two thirds of the palatines, a character that distinguishes this species from E. lavarackorum and E. sp. aff. dentata (Johnstone) (n = 4)—the vomer is expanded posteriorly in E. lavarackorum and only divides the anterior half of the palatines in E. sp. aff. dentata (Johnstone). Canalis caroticus internus closed. Foramen anterius canalis carociti interni absent.

Ventral surface of the skull below the foramen nervi trigemini constricted to the same width as the braincase. In other Elseya this section is significantly wider than the braincase. Supraoccipital is extremely small dorsally, does not divide the parietals but lies posteriorly to them at the rear of the skull. Crista supraoccipitalis short, extending beyond the occipital condyle, but not to the same extent as in E. dentata.

Cervicals

Articulation formula (Williams 1950) is the same as for all chelid turtles: (2(, (3(, (4(, (5), )6), )7(, (8). The atlas-axis complex (Hoffstetter and Gasc 1969) is made up of two neural arches and the first centrum ventrally and an intercentrum anteriorly, these units are fused as in the primitive condition for many turtle species. Centra of remaining cervicals have well-developed sagittal blades that are more prominent at the anterior end of the series and also at the anterior half of each centrum. Each sagittal blade straight in lateral view and narrow, except for the eighth cervical, which is markedly thickened. Transverse processes large, triangular, occupying the middle-third of the centrum and protruding horizontally from the neural arch; not angling downwards as in many other species. Postzygapophoses extremely large and almost joining in the midline; robust in overall structure. Prezygapophoses smaller and extending upwards to meet the postzygapophoses of the preceding vertebrae. Neural spine present but small.

Shell

Anterior bridge buttress poorly developed (n = 6). Anterior bridge strut suture with a widely spaced anterior and posterior component, a feature shared with E. lavarackorum (n = 4), E. sp. aff. dentata (Johnstone) (n = 4), and E. irwini (n = 1); no prominent medial constriction. Posterior bridge strut well developed, in significant contact with the fifth pleural. Exposed neurals absent.

Habitat

This species is widely distributed within the river systems it occupies, from the permanent waters of the uppermost spring-fed pools to the freshwater-brackish water interface (Hamann et al. 2004). It prefers flowing waters with complex subsurface structure in the form of log tangles, undercut banks, and irregular rocky substrata. It is typically absent or rare in standing waters impounded by dams or weirs, unless associated with free-flowing streams. It does not inhabit brackish waters.

Reproductive Cycles

The peak breeding season for males is between January and August. Females leave the water once per year between March and September to lay approximately 14 hard-shelled eggs (Hamann et al. 2004). The nest is constructed mostly on the front face and top of steep sloping banks with sand or soil substrates. Nest and hatchling predation by pigs, dogs, foxes, cats, monitor lizards, and water rats is intense. Many of these predators are exotic and their activity, coupled with habitat modification, is regarded as a major threat the persistence of the species in many parts of its range (Hamann et al. 2004).

Diet

Elseya albagula is primarily herbivorous, feeding on fruit and buds of riparian vegetation that falls upon the water, filamentous algae, and instream macrophytes. Animal material forms a small part of the diet of adults and includes freshwater sponges and carrion. Young may be more carnivorous. In captivity, the young feed readily on snails.

Conservation Considerations

Elseya albagula is widespread and locally abundant in three major drainage basins of southeastern Queensland (Hamann et al. 2004), and as such may currently be regarded as secure. The predominance of adults in all populations is a concern (Hamann et al. 2004) and possibly exacerbated by heavy predation by exotic predators. In addition, the species is intrinsically vulnerable by virtue of its specialized habitat requirements, namely a reliance on flowing waters and riffle, reinforced by its dual mode of respiration (Legler and Georges 1993; FitzGibbon 1998). Flowing waters are coming under increasing threat from water resource development, and particularly the development of new impoundments or redevelopment of existing impoundments to service the needs of agriculture, industry, and urban centres. Elseya albagula would be a good candidate for monitoring as a sensitive indicator of riverine health.