Neural bones are median elements of the turtle carapace overlying the dorsal vertebrae. The ancestral condition is thought to be a series of eight relatively narrow, hexagonal neural bones with short sides anteriorly placed, forming a continuous series from the nuchal bone anteriorly to the first suprapygal posteriorly (Pritchard, 1988), a condition retained in many extant species of the Bataguridae, Emydidae and Cheloniidae, but frequently modified, e.g. by elimination of elements at the ends of the series, formation of one or more octagonal elements, or alteration to a series of hexagons with short sides posteriorly.

     Neural bones are probably structurally important for resisting downward pressure in high-domed species, but may be a disadvantage where lateral forces in flatter forms cause torsion among carapacial elements (Pritchard, 1988). Hence, strong swimmers that move by alternating thrusts of the rear limbs, and marine turtles that alternate strokes on land, tend to have reduced neural series with areas of median contiguity between opposing pleural bones (Pritchard, 1988). Neurals are often seemingly absent in Chelidae, where a fixed pelvic girdle and extensive plastral buttressing provide alternative structural resistances to downward pressure and lateral torsion caused by the sideways action of neck extension and withdrawal.

     Absence of neural bones was thought to be characteristic of all Australian chelid turtles (Boulenger, 1889; Waite, 1929; Williams, 1953; Zangerl, 1969) until neurals were reported as a consistent feature of Chelodina oblonga from Australia's southwest (Burbidge et al., 1974). Subsequently, neurals were also reported as inconsistant variations in five other Australian species (Chelodina novaeguineae, C. seibenrocki, C. longicollis, Elseya latisternum and Elseya sp.) (Rhodin and Mittermeier, 1977). In most cases, however, these neurals were few, small and rudimentary, not forming a contiguous series.

     In this note, we report a second Australian chelid characterized by the consistent presence of well developed neurals. This feature incidentally provides a morphological basis for separating what was previously a cryptic species pair (Georges and Adams, 1992). We also argue, on examination of sections through the vertebral region, that all chelids possess neural bone elements, but that in those species traditionally regarded as lacking neurals, these elements are so reduced as to be submerged beneath the dorsally medially contiguous pleurals.

     Specimens were obtained from various collections, skeletonized, and the scutes removed to reveal the arrangement of bony elements. Longitudinal and transverse sections of shell vertebrae and associated neurals and pleurals were prepared with a diamond saw for the chelid turtles Chelodina longicollis, C.oblonga, Emydura sp. aff. krefftii (Fraser Island), Emydura sp. aff. subglobosa (Sleisbeck) and Elseya dentata and for the trionychid Aspideretes hurum. Where exposed neurals were present, sections were arranged to transect one or more of them. Sections were examined under a microscope to ascertain the presence of sutures between the various elements.

Figure 1. Comparison of the neural region of the dorsal carapace of the sibling species pair Elseya sp. aff. latisternum (Manning) [a to d] and Elseya sp. aff. latisternum (Bellinger) [e to h]. Scale = 5 cm. a. AM 123042 b. QM 59290 c. QM 59289 d. AM 123040 e. AM 138387 f. AM 138388 g. UM 02016 h. UM 02017

     Specimens Examined.-All unregistered specimens that remained intact following examination were lodged with the Queensland Museum. The sectioned specimens remain in the collection of the University of Canberra. Names given to undescribed species follow those of Georges and Adams (1992). Abbreviations: AM, Australian Museum; QM, Queensland Museum; NTM, Museums and Art Galleries of the Northern Territory; UM, University of Michigan field series; UC, University of Canberra; PCHP, Peter C. H. Pritchard personal collection.

     Specimens Examined.-All unregistered specimens that remained intact following examination were lodged with the Queensland Museum. The sectioned specimens remain in the collection of the University of Canberra. Names given to undescribed species follow those of Georges and Adams (1992). Abbreviations: AM, Australian Museum; QM, Queensland Museum; NTM, Museums and Art Galleries of the Northern Territory; UM, University of Michigan field series; UC, University of Canberra; PCHP, Peter C. H. Pritchard personal collection.

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