Elseya camfieldensis sp. nov.

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urn:lsid:zoobank.org:act:2F71950D-C7BC-4F58-B781-DA817D74B3ED

Holotype:- NTM P895-67 (Figure 1a, b), an articulated portion of the left anterior carapace, comprising the nuchal, left peripherals 1 – 3 and left costal 1, all relatively undamaged; excavated from the ‘Blast Site’, Camfield Station, Northern Territory (Latitude 17 00’S. Longitude 131 30’E.), Bullock Creek Local Fauna, mid-Miocene.

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Figure 1: Elseya camfieldensis sp. nov. Holotype individual. A, B, Fragment from anterior left portion of the carapace including nuchal, left costal 1 and left peripherals 1 to 3 (NTM P895-67) in A, dorsal and B, ventral views. C, D, left hypoplastron (NTM P895-66) in C, dorsal and D, ventral views. Scale bar = 100 mm.

Figure 2: Elseya camfieldensis sp. nov. NTM P923-7, isolated left costal 1. A, dorsal view. B, dorsal view with scute sulci marked. C, ventral view. D, ventral view with anatomical features marked. Note the semicircular notch on the posterior margin was caused by a drill during collection. Abbreviations: ass, axillary suture scar; P1, pleural scute 1; r1ss, sutural scar for first dorsal rib; V1, V2, vertebral scutes 1 and 2. Purple lines represent scute sulci; blue lines represent the outlines of other structures. Scale bar = 50 mm.

Figure 3: Elseya camfieldensis sp. nov. Isolated carapace elements. A-C, NTM P895-80, nuchal from small individual. A, dorsal view. B, dorsal view with scute margins marked. C, ventral view. D-G, NTM P927-4, isolated right costal 8. D, ventral view. E, dorsal view. F, ventral view with anatomical features marked. G, dorsal view with scute margins marked. Abbreviations: CE, cervical scute; ics, ilial-carapacial suture; M1, marginal scute 1; P1, 4, pleural scutes 1 and 4; V1, 4, 5, vertebral scutes 1, 4 and 5. Scale bar = 50 mm.

Figure 4. Elseya camfieldensis sp. nov. isolated plastron elements. A, B, NTM P925-6 and P87106-17, Left hyoplastron in A, dorsal and B, ventral views. C, D, NTM P9464-155, right hypoplastron with association fragment of right xiphiplastron in C, ventral and D, dorsal views. E, Close-up of medial end of hypoplastron sutural surface of NTM P925-6 and P87106-17. F, Close-up of medial end of hyoplastron sutural surface of NTM P895-66. Scale bar for A-D = 50 mm, scale bar for E,F = 20 mm. Note circular hole in Fig 4, a,b man-caused.

Figure 5 (left). Elseya camfieldensis sp. nov. isolated left hypoplastra. A, B, NTM P8692-23 in A, dorsal and B, ventral views. C, D, NTM P923-8 in C, dorsal and D, ventral views. Scale bar = 50 mm.

Figure 6 (right). Elseya camfieldensis sp. nov. isolated right xiphiplastra. A-C, NTM P87108-31. A, anterior view showing hypoplastral sutural surface. B, ventral view. C, dorsal view. D, E, NTM P87113-47 in D, ventral and E, dorsal views. Scale bar = 50 mm.

A mid-Miocene fossil species of short-necked turtle of the family Chelidae, assigned to the genus Elseya based on the morphology of the axillary buttress suture scar and overall scute sulci; distinguished from all currently known fossil and extant species by the following combination of characters: fully formed cervical scute; greatest width of the nuchal is at a point substantially posterior to half its length (Character N of Joseph-Ouni et al. 2023); vertebral 1 significantly wider than vertebral 2; contact of the V1-P1 sulcus with M1 at the mid-point (M2-V1 sulcus slightly shorter than M2-P1 sulcus); the distance from the medial extremity of the axillary buttress suture scar (ABSS) to the distal extremity of rib 1 is substantially more than half the length of the ABSS (Character G of Joseph-Ouni et al. 2023); the medial extremity of the ABSS lies lateral to the level of the conjunction of the nuchal, costal 1 and peripheral 1 (Character H of Joseph-Ouni et al. 2023); the posterior end of the suture between costal 1 and peripheral 2 lies within the ABSS (Character I’ of Joseph-Ouni et al. 2023); portion of the costal 1-peripheral 2 suture that lies anterior to the ABSS is substantially longer than the portion of that suture that is embedded within the ABSS (Character I of Joseph-Ouni et al. 2023); the medial extremity of the ABSS lies posterior to the level of the distal extremity of rib 1 (Character M of Joseph-Ouni et al. 2023); anterior lateral length of the nuchal (measured from the costal 1-peripheral 1-nuchal triple junction to the anterior end of the peripheral 1-nuchal suture) greater than the posterior length (measured from the posterior extremity of the nuchal to the costal 1-peripheral 1-nuchal triple junction) (Character N’ of Joseph-Ouni et al. 2023); the distance from the medial extremity of the axillary buttress suture scar (ABSS) to the distal extremity of rib 1 is subequal to the length of the suture between peripheral 1 and costal 1 (Character S of Joseph-Ouni et al. 2023); the length of the suture between peripheral 2 and costal 1 that is embedded within the ABSS is approximately half the distance between the medial extremity of the ABSS to the distal extremity of rib 1 (Character T of Joseph-Ouni et al. 2023); the length of the suture between peripheral 2 and costal 1 that is embedded within the ABSS is greater than the distance from the medial extremity of the ABSS to the level of the triple junction of the nuchal, costal 1 and peripheral 1 (Character U of Joseph-Ouni et al. 2023); and the width of the medial portion of the ABSS being so broad as to be contained only 2.5 x in the length (vs. ranging from 4x-10x in subgenus Elseya and ‘Pelocomastes’); medial end of the posterior sutural surface (that articulated with the hypoplastron) divided into an interdigitating dorsal part and a weakly rugose to smooth ventral part. These last two diagnostic features (broad axillary scar and horizontally divided articulating hyoplastral surface are unknown in any other Elseya or Emydura fossil or extant taxa. We tentatively refrain from assignment of this new taxon to a subgeneric Elseya level as it most likely represents an undescribed subgenus.

Description:- The holotype specimen consists of an articulated portion of the left anterior carapace, comprising the nuchal, left peripherals 1 – 3 and left costal 1, all relatively undamaged. All scute sulci are strongly preserved. The surface sculpture of the vertebral and pleural portions of the bones consists of long linear striations running anterior to posterior (Figure 1a), becoming finely striated on the marginal portions of the bone. However, these striations are weakly developed in P9612-171 (a costal 1 from Top Site) and are absent from NTM P923-7 and NTM P927-4 (costals 1 and 8 respectively, from the lower X-Y beds at Small Hills; Figures 2a, 3e), indicating that this characteristic may have varied from population to population. A fully formed cervical scute is present, well-delineated and unlike the infrequent aberrancy of cervical scutes seen in some modern Australian Elseya of the subgenus Elseya. Marginal 1 is wider than long. V1-Pl sulcus is strongly bowed convex exteriorly such that V1 is considerably wider than the prospective width of V2; contact of V1-P1 with M1 occurs at posterior 3/4th position. Regarding the nuchal, the anterior portion of the nuchal is 3x that of the posterior portion (character N).

Viscerally the suture of dorsal rib 1 and the entirety of the axillary suture scar (Figure 1b) are fully preserved. The axillary scar is a relatively short, robust and blunt structure that is markedly wide along its full length, showing no medial constrictions. The angle of declination from that of the midline of the carapace on the anterior portion of the scar is nearly 80 degrees, a sharp angle not seen in any currently known fossil or extant species. The terminus of dorsal rib 1 lies distal to the terminus of the axillary scar (character G), the spatial length being equal to the peripheral 1-costal 1 suture length (character S) such that the axillary terminus lies lateral to the level of the conjunction of the nuchal, peripheral 1 and costal 1 but is directly posterior to the conjunction of peripheral 1, peripheral 2 and 1st costal (character H). The terminus of the axillary scar lies slightly posterior of the dorsal rib 1 terminus (character M). The spatial distance between the termina of the dorsal rib 1 and the axillary scar is twice as long as the suture of peripheral 2-costal 1 embedded in the scar (characters T and U of Joseph-Ouni et al. 2023). The embedded suture is substantially longer than the exposed anterior suture of peripheral 2 (character I) and there is no exposed posterior suture (Character I’). The axillary scar base is as large or larger to the axillary terminus (character K). The axillary terminus is broadly rounded hemispherically (character L) and the base of the scar across the costal-peripheral sutures is broad (character O). The length of the axillary scar is shorter than the length of the nuchal-peripheral 1-costal 1 conjunction to the center base of the scar (Character P). The axillary scar length is much shorter than either of the lengths of the peripheral 1-2 and 2-3 sutures. The angle of the costal 1-peripheral 1-2 sutures is more than 130 degrees (character V). The overall shape of the axillary scar is an elongated oval with equally rounded ends, differing from all currently known fossil and extant Elseya species. The base of the axillary scar lies level to the posterior most portion of the nuchal (character J). As the first dorsal vertebra is not preserved, we cannot discern characters X, Y and Z.

Posteriorly, the iliac scar is centered upon costal 8, and crosses onto the suprapygal. The iliac scar only just crosses onto costal 7 along its dorsomedial margin (Figure 3f).

A unique and interesting detail is that the medial end of the posterior sutural surface (that articulated with the hypoplastron) is divided horizontally into an interdigitating dorsal part and a weakly rugose to smooth ventral part (Plate 1c). The same division is seen on the anterior sutural surface of P895-66 (Plate 1c- the hypoplastron referred to E. camfieldensis). This surface is completely interdigitating in all other known fossil and extant Elseya and Emydura.

Referred Specimens:- NTM P895-66 (Blast Site), left hypoplastron with hypoplastral bridge probably belonging to the holotype individual (Figure 1c, d); P895-80 (Blast Site), nuchal (Figure 3a, c); P907-38 (Top Site), partial right xiphiplastron; P923-7 (Site X), left costal 1 (Figure 2); P923-8 (Site X), left hypoplastron (Figure 5c, d); P927-4 (Site Y), right costal 8 (Figure 3d-g); P8692-23 (Blast Site), left hypoplastron (Figure 5a, b); P9464-155 (Top Site), right hypoplastron with anterior portion of xiphiplastron (Figure 4c, d); P9612-171 (Top Site), left costal 1; P87106-17 + P925-6 (Site Y), registered as a right hypoplastron but identified here as a right hyoplastron (Figure 4a, b); P87108-31 (Blast Site), right xiphiplastron (Figure 6a-c); P87113-47 (Site Y), right xiphiplastron (Figure 6d, e). Note that NTM P87106-17 and P925-6, both are separately registered parts that were later found to be the same specimen.

Figure 5 (left). Elseya camfieldensis sp. nov. isolated left hypoplastra. A, B, NTM P8692-23 in A, dorsal and B, ventral views. C, D, NTM P923-8 in C, dorsal and D, ventral views. Scale bar = 50 mm.

Etymology:- The species epithet is derived from the outcrops of origin, the Camfield Beds.

Comparison:- Elseya camfieldensis sp. nov. is assigned to the genus Elseya sensu lato on the basis of the broadly wide axillary suture scar (heavily constricted in extant Emydura and moderately wide in fossil Emydura), by the terminus of the axillary suture scar lying nearly level with the terminus of dorsal rib one (strongly posterior in fossil and extant Emydura), steeply angular declination of the scar (moderate to acutely angular in Chelodina, Pseudemydura; Rheodytes and Elusor); and by the base of the axillary scar lying on the conjunction of the costal 1-peripheral 2-3 sutures (sutures of 3-4 in Chelodina). Elseya camfieldensis sp. nov. is distinguished from all currently known fossil and extant Australian Elseya species by the following combination of characters: vertebral 1 much broader than 2; presence of a distinct fully-formed cervical scute (absent in extant taxa except as irregular vestigial or aberrant); the anterior portion of the nuchal being 3x that of the posterior (character N); the shape of the axillary being an elongated oval with equally rounded ends (spoon-shaped in subgenus Elseya; polygonal in subgenus ‘Pelocomastes’); the terminus of the axillary scar being hemispherical (clubbed in subgenus Elseya; tapered or fingered in subgenus ‘Pelocomastes’); and the width of the medial portion of the axillary scar being so broad as to be contained only 2.5 x in the length (more than 8x-10x in subgenus Elseya and ‘Pelocomastes’), a feature unknown in any other Elseya or Emydura fossil or extant taxa. The large size of the carapace bones clearly separates Elseya camfieldensis sp. nov. from the presumed sympatric dwarf genus Birlimarr. Separated from extant species by some 12 to 13 million years.

The axillary buttress suture scars of select fossil and extant Elseya and Emydura species are presented in Figure 12.

Comment:- This specimen was referred to as ‘Genus aff. Emydura/Elseya sp. indet.’ by Megirian & Murray (1999). Megirian & Murray were circumspect about referring the large hypoplastron NTM P895-66 to the same individual as NTM P895-67 because they perceived it as different from the hypoplastron of NTM P9464-134 which they regarded as the same species as NTM P895-67. We find that NTM P895-67 and NTM P9464-134 are different species and so the differences between the hypoplastra of NTM P895-66 and NTM P9464-134 are no impediment to uniting P895-67 with P895-66. Both are closely associated pieces that come from equally large chelids in a small deposit where there are no other chelid individuals of similar size, leaving little doubt they are parts of the same individual animal