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Taxon name
Chelodina (Chelydera) nerophis
Figure citations
Fig. 5
Registration Number
urn:lsid:zoobank.org:act:B6D749A8-799A-47A5-A7A2-6A942F329B9D
Type statement
Holotype:. NTM P908-49 (Figure 5), a whole and undamaged right epiplastron; excavated from the ‘Blast Site’, Camfield Station, Northern Territory (Latitude 17 00’S. Longitude 131 30’E.), Bullock Creek Local Fauna, mid-Miocene.
Synonymy
Diagnosis
A mid-Miocene fossil species of long-necked turtle of the family Chelidae, assigned to the genus Chelodina based on the morphology of the shape of the epiplastron with clear intergular sulci showing the anterior border encapsulated by the presence of gular scutes (in medial contact), and further to the subgenus Chelydera based on the indicative placement of the conjunction of the humeral, pectoral and intergular sulci on the entoplastron as well as the proportionally smaller and narrower footprint of the intergular scute on the epiplastron; distinguished from all currently known fossil and extant species by the following combination of characters: presence of an autapomorphy amongst Chelodina (Chelydera), being the placement of the gular, humeral and intergular scute intergular scute sulcus conjunction well anterior of the level of the anteriormost portion of the epiplastral-entoplastral suture; relatively small portion of the epiplastral surface; humero-intergular scute sulcus longer than the gular-humeral scute sulcus, three times the length of the inter-gular scute sulcus and equal to the gular-intergular sulcus; humeral-intergular scute sulcus parallel to midline of plastron; the greater anterior occurrence of the humero-pectoral sulcus on the epiplastron and the indicative placement of the conjunction of the humeral, pectoral and intergular sulci on the entoplastron.
Description
The holotype specimen consists of a whole and undamaged right epiplastron. The ventral surface contains well-defined scale-like sculpture that is larger distally from the midline of the plastron and grading to a smaller size on the proximally portion, all conforming to Chelodina (Joseph-Ouni et al. 2023). It contains indications of the inter-gular scute sulcus, the entirety of the gular-intergular scute sulcus and gular-humeral scute sulcus. It also contains the humeral-intergular scute sulcus that normally occurs in subgenus Chelydera as well as the correct portion of the humeral-pectoral scute sulcus. This latter sulcus posteriorly crosses the epiplastral-hyoplastral suture at the mid-point; the epiplastral-hyoplastral sutural edge contains a posterior projection typically of Chelidae. The inter-epiplastral sutural edge is approximately 1.5 times the straight length of the epiplastral-entoplastral sutural edge. The humero-pectoral sulcus occurs almost entirely on the epiplastron, making this placement much more anterior than all other described taxa.
Specimens Examined
NTM P895-66 (Blast Site), a partial right epiplastron, here declared as paratype; P10858 (Blast Site), an almost complete left hyoplastron (Figure 5); NTM P8692-24 (Blast Site), a partial right 1st costal bone (Figure 5); NTM P908-48 (Figure 5), a complete and undamaged left 1st costal bone (Blast Site), all from Camfield Station, Northern Territory (Latitude 17 00’S. Longitude 131 30’E.), Bullock Creek Local Fauna, mid-Miocene.
Notes
Etymology. The species epithet is derived from the Greek, ‘nero’ = water and ‘ophis’ = snake, in reference to the long snake-like necks of Chelodina.
Remarks. Chelodina (Chelydera) nerophis sp. nov. is readily distinguished from all other described fossil and extant species of the subgenus Chelydera by the presence of an autapomorphy amongst Chelydera (gular, humeral and intergular scute intergular scute sulcus conjunction well anterior of the level of the anteriormost portion of the epiplastral-entoplastral suture) and the greater anterior occurrence of the humero-pectoral sulcus on the epiplastra (occurring posteriorly on all other species such that the majority of this sulcus occurs across the epi-hyoplastral suture) as well as by the following: from C. (C.) burrungandjii C. (C.) kuchlingi and C (C.) walloyarrina by a narrow, laterally straight-sided intergular scute, the humero-pectoral sulcus lying mostly anterior of the suture and by the conjunction of the intergular, humeral and pectoral sulcus conjunction lying anterior of the widest portion of the entoplastron (versus anteriorly wider intergular scute, the humero-pectoral sulcus lying along the epi-hyoplastral suture and the conjunction sulcus level lying at the widest point); from the C. (C.) rugosa group of taxa (C. rugosa, C. siebenrocki, and C. kurrichalpongo) by shorter lateral intergular scute sulci, the humero-pectoral sulcus lying mostly anterior of the suture and by the conjunction of the intergular, humeral and pectoral sulcus conjunction lying anterior of the widest portion of the entoplastron (versus longer sulci, the humero-pectoral sulcus lying along the epi-hyoplastral suture and the conjunction sulcus level lying at the widest point); from C. parkeri by the short, diverging lateral intergular scute sulci in C. parkeri (this latter taxon is the only member of Chelyderain which the conjunction of the humeral, pectoral and intergular sulci occurs on the epiplastron); and from the monotypic subgenus Chelodina (Macrochelodina) oblonga by the short lateral intergular scute sulci, the humero-pectoral sulcus lying mostly anterior of the suture and by the conjunction of the intergular, humeral and pectoral sulcus conjunction lying anterior of the widest portion of the entoplastron (versus longer intergular lateral sulci, the humero-pectoral sulcus lying along the epi-hyoplastral suture and the conjunction sulcus level lying at the widest point). Figures 6 – 7 illustrate comparative material of all pertinent Chelodina (Cheydera) and Chelodina (Macrochelodina) taxa.
We note that Kehlmaier et al. (2025) recently placed C. walloyarrinain the synonymy of C. kuchlingi and C. burrungandjii into the same synonymy as a valid subspecies, taxonomic acts with which we disagree (a forthcoming publication in preparation by the senior author that examines the osteology of all extant Northern Australian and New Guinea extant Chelyderaspecies will lay out the continued recognition of these taxa based on the strongly differential morphology of the skull, suture scars, coloration and scutation and bone sutures).
The Plio-Pleistocene fossil Chelodina (Chelydera) taxa C. (C.) taracreek, C. (C.) rugosa peregrina, C. (C.) expansa piscis and C. (C.) expansa flammafera all were described from non-overlapping material (Joseph-Ouni et al., 2023) with this new species. All of these latter taxa occur spatially and temporally separate (by millions of years) from C. (C.) nerophis sp. nov.
NTM P985-66, a referred specimen for C. (C.) nerophis sp. nov., a right epiplastron, also contains the observed autapomorphy and other characters confirming that the holotype epiplastron NTM P908-49 is not an aberrance.
The holotype specimen of Chelodina (Chelydera) nerophis sp. nov. NTM P908-49 was referred to as Chelodina sp. A by Megirian & Murray (1999), and it was the single specimen of all collected from Camfield Station attributed by them to that taxon. Those authors correctly observed the presence of two fossil Chelodina here, and noted that their Chelodina sp. A can be distinguished from their Chelodina sp. B (the taxon described here as Chelodina (Chelodina) aquanimare sp. nov.) by its “rounded as opposed to squared off marginal profile of the anterior plastral lobe in ventral view; proportionally long inter-epiplastral contact; and proportionally narrower intergular”.
A second fossil specimen, NTM P10858, a left hyoplastron, included as a referred specimen, offers further confirmation of the presence of the subgenus Chelyderaat Camfield Station. It can be identified as Chelodina by the absence of the humeral-pectoral sulcus on the anterior hyoplastron (present in Elseyaand Birlimarr, the only other species known) as well as by the reception pit on the epiplastral-hyoplastral sutural edge which receives the epiplastral process when in articulation. It can be further identified to Chelyderaby the proportion of the length of the inter-hyoplastral suture edge being 1.5 times the length of the epiplastral-entoplastral sutural edge (1 to 1 in the subgenus Chelodina and 3 times longer in Elseya/ Birlimarr – see Joseph-Ouni et al., 2023) for further description and illustration).
A third specimen, NTM P908-48, a complete and undamaged left 1stcostal bone is also referred here. Though this specimen is isolated and we cannot link it directly to the holotype, it is highly distinct and belongs to the subgenus Chelydera based on shared characters (see Joseph-Ouni et al., 2023 for these character states). We work from the assumption that only a single species of the subgenus Chelydera was present at this site and therefore confidently include it in the hypodigm of Chelodina (Chelydera) nerophis sp. nov. If so it helps strengthen the distinctiveness of this new species in that it differs from all known fossil and extant Chelodina in the following combination of characters: an autapomorphy in having the suture scar of the 1stdorsal rib laterally reach the anterior to posterior level of the joint nuchal-1st peripheral-1st costal suture conjunction; an axillary bridge buttress suture scar (ABBSS) not constricted but evenly broad along the length and becoming broader at the terminus into a rounded spoon head shape; ABBSS terminus ending anterior of the posterior bone suture edge of costal one (thereby being confined entirely to the 1st costal); ratio of the V1 scute surface present on the 1st coastal being more than 7 times that of the V2 scute surface.
Figure 5. Chelodina (Chelydera) nerophis sp. nov., hypodigm: a) NTM P908-49, holotype, complete right epiplastron; b) NTM P895-72, paratype, partial right epiplastron; c) NTM P908-48, referred specimen, complete left costal 1; d) NTM P8692-24, referred specimen, partial right costal 1; e) NTM P10858, referred specimen, partial left hyoplastron. All to scale.
Figure 6. Typically character states of Chelodina (Chelydera) plastral forelobes showing the size and shape of the epiplastra and entoplastron, bone sutures, surface bone texturing and scute sulci. Raw image in left column, interpretive sulci in blue and sutures in black in right column. All currently described species illustrated over Figures 6 and 7. Row A: C. (C.) nerophis sp. nov. holotype NTM P908-49; Row B: C. (C.) walloyarrina: Row C: C. (C.) kuchlingi: Row D: C. (C.) kurrichalpongo: Row E. C. (C.) burrungandjii. Images by authors, or courtesy of J.Cann and I.Smales.
Figure 7. 1) Typically character states of Chelodina (Chelydera) and Chelodina (Macrochelodina) plastral forelobes showing the size and shape of the epiplastra and entoplastron, bone sutures, surface bone texturing and scute sulci. Raw image in left column, interpretive sulci in blue and sutures in black in right column. Row A: C. (C.) parkeri: Row B: C. (C.) rugosa rugosa; Row C: C. (C.) rugosa siebenrocki (MCZ R153043); Row D:C. (C.) expansa: Row E: C. (M.) oblonga. Images by authors, or courtesy of J.Cann and I.Smales.
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