Bohra nullarbora Prideaux & Warburton, 2009

Prideaux, Gavin J. & Warburton, Natalie M., 2023, A review of the late Cenozoic genus Bohra (Diprotodontia: Macropodidae) and the evolution of tree-kangaroos, Zootaxa 5299 (1), pp. 1-95 : 49-59

Bohra nullarbora Prideaux & Warburton, 2009

Bohra sp. nov. 2: Prideaux (2006), p. 1524. Prideaux et al. (2007), p. 423, table 1.

Bohra sp. nov.: Warburton & Prideaux (2010), pp. 138–139, 143, 147, 149, figures 13.1, 13.5–13.6.

Holotype. WAM 05.4 .70, partial adult skeleton. Craniodental elements: fragmentary cranium (preserving left P3, left and right M1–4); partial left dentary (preserving base of i1, m1–3); right dentary preserving posterior half of m2, m3–4). Postcranial elements: vertebrae including atlas, axis, cervical 3–5, thoracic 1,?5–6,?10,?12, dorsal lumbar fragment, two mid-caudal and two distal-caudal elements; one mid-caudal chevron; left and right clavicles; six ribs; proximal portion of left humerus and distal fragments; partial diaphysis of right humerus; left ulna; left radius diaphysis fragment; right hamatum; left scaphoid; left metacarpal III; right metacarpal III; left metacarpals IV – V; manual phalanges, including those of digits I– IV proximal, digits III– V medial, digits III– IV distal; partial left innominates; fragments of right innominate; left epipubic; proximal portion of left femur; abraded distal fragments of right femur; fragments of left distal tibia diaphysis; right tibia diaphysis; distal portion of right fibula; left calcaneus; left talus; left navicular; right entocuneiform; right metatarsals IV – V, pedal phalanges including those of digits II, IV – V proximal, digits II – V medial, digits IV – V distal.

Type Locality. Leaena’s Breath Cave, Nullarbor Plain, southeastern Western Australia. The holotype was collected by Paul D. Devine and GJP in July 2002 from a tight space beneath an overhanging boulder atop the main boulder pile, adjacent to the ‘gypsum powder floor’. Fossils from the Leaena’s Breath Cave boulder floor, although previously inferred to be of early middle Pleistocene age ( Prideaux et al. 2007), are actually undated, but are associated with remains of other species known from dated middle and late Pleistocene sites elsewhere. At this point the type locality age is best considered conservatively as Pleistocene. The precise location from which the holotype was collected is recorded with the Department of Earth and Planetary Sciences , Western Australian Museum .

Referred specimens. Leaena’s Breath Cave (stratigraphic unit 3), Nullarbor Plain, southeastern Western Australia. WAM 2020.3.201, right cuboid.

RF 95 fissure fill, Curramulka Quarry, Yorke Peninsula, South Australia. SAMA P55204, left M2; SAMA P55205, left M2; SAMA P55206, right M2; SAM P55389, right M1; SAMA P55390, right M1; SAMA P55391, right M1; SAMA P55392, right M1; SAMA P55393, left M1; SAMA P55394, left M1; SAMA P55395, left M1; SAMA P55396, left M1; SAMA P55397, right M1; SAMA P55398, left M2, right M2 (these teeth are identical in morphology, wear and preservation, so are considered to belong to the same individual); SAMA P55400, right M3; SAMA P55407, right M1; SAMA P55411, left m2; SAMA P55412, left m2; SAMA P55413, left dP3; SAMA P55417, left m1; SAMA P55419, left m2 trigonid. These specimens were picked from concentrate sieved from sediment collected in 1997 by Jim McNamara (South Australian Museum).

Revised diagnosis. Bohra nullarbora is distinguished from B. illuminata in the following cranial features: a shallow buccinator fossa; a supraorbital crest that is more markedly projected laterally above the posterior end of the eye orbit; a less-domed dorsal neurocranial surface; a wider ectoglenoid process; a more distally narrowed postglenoid process. The cheek teeth are smaller relative to the dimensions of the palate than in B. illuminata . P3 is wider anteriorly than posteriorly, but narrow overall relative to M1, and it bears a small, low posterolingual cusp and narrow lingual cingulum. The dentary is characterised by a well-developed digastric eminence and sulcus, and a distinctly hooked mesial process on the postalveolar shelf. The dorsal and ventral enamel flanges on i1 are thinner than in B. illuminata . The lower molars are distinguished from those of other species of Bohra by having a short anterior portion of the trigonid, and a very low paracristid and cristid obliqua. The m4 has a very low parametacristid, which extends to centre of trigonid basin.

Bohra nullarbora is distinguished from B. illuminata in the following postcranial features. The clavicle is more robust and less flattened, with expanded articular facets and a more laterally positioned cranial inflection. The humerus is more robust with a stronger pectoral crest, deltoid ridge, bicipital groove and spinodeltoid insertion, but with a less pronounced teres major tubercle. The distal articular surface (especially the capitulum) of the humerus is relatively narrow. The ilium is relatively broader anteroposteriorly, and with a more sinuous medial border.A marked oval fossa is contiguous with a rugose muscle scar of the m. rectus femoris dorsal to the acetabulum. The epipubic is very large. The calcaneus is larger with partial separation of posterior talar facets, a very short anteroplantar sulcus, a more strongly developed plantar tuberosity, a wider sustentaculum tali, and a relatively narrow, less mesially tapered lateral talar facet. The talus is relatively longer with a higher lateral trochlear ridge. Metatarsal IV is more robust with a larger cuboid facet, a less medially constricted facet for metatarsal V, and a less rounded, less distally orientated sesamoid facet. Metatarsal V is more robust.

Bohra nullarbora is distinguished from B. paulae in the following pedal features: smaller absolute size ( Table 8 ); separation of the talar facets, less complete assimilation of the ventromedial cuboid facet with the dorsal cuboid facets, and very short anteroplantar sulcus on the calcaneus; higher trochlear crests (deeper trochlear groove) and a longer neck on the talus; more gracile metatarsals IV and V.

Bohra nullarbora is distinguished from B. planei by having a less laterally flared base of the greater trochanter, distinct posterior talar facets and more smoother cuboid step on the calcaneus, and higher trochlear crests on the talus, and from B. wilkinsonorum in its much smaller overall size and more complete assimilation of the ventromedial cuboid facet on the calcaneus.

Etymology. The species name refers to the Nullarbor Plain, the region whence the holotype was collected.

Description and comparisons. Cranium. Among the species of Bohra , only B. nullarbora ( Figure 27 ) and B. illuminata ( Figure 23 ) are known from parts of the cranium other than the tooth-bearing portion of the maxilla. The incisor-bearing portion of the premaxilla is slightly deeper in B. nullarbora than in B. illuminata . The buccinator fossa is shallower and less distinct than in B. illuminata . The supraorbital crest is markedly projected laterally above the posterior end of the eye orbit and underlain by a deep sulcus, whereas the supraorbital crest is more of a triangular swelling in B. illuminata . The zygomatic arch is relatively deeper in B. nullarbora than in B. illuminata , and the dorsal surface of the neurocranium is less domed. The ectoglenoid process is wider and the postglenoid process is more narrowed distally (ventrally).

Upper dentition. The upper cheek teeth ( Figures 27E , 28A–O ) are similar in size to those of B. planei and B. sp. cf. B. bandharr , but smaller than in B. illuminata , B. bandharr and B. bila ( Tables 1–7 ). Greater width of the P3 anteriorly compared with posteriorly ( Figure 27E ) is a condition unique to B. nullarbora . P3 is narrower relative to M1 than in any other species of Bohra . As in B. illuminata , there is no manifestation of a posterobuccal eminence on P3, whereas it is slight in B. bandharr and distinct in B. wilkinsonorum . The upper molars are most similar in morphology to those of B. illuminata , but differ by being slightly smaller overall and shorter relative to their width, and by having a more concave lingual margin of the crown adjacent to the interloph valley and a more protuberant lingual metaloph base. Absence of a stylar crest in the region of cusp C is a condition shared with B. bandharr , B. illuminata and B. wilkinsonorum , but not B. bila and B. planei , in which this crest is distinct.

Dentary. The well-developed digastric eminence and sulcus ( Figure 29A–C ), and distinctly hooked mesial process on the postalveolar shelf ( Figure 29G ) distinguish B. nullarbora from other species of Bohra . Although it is broken off, it is evident that the mandibular condyle was positioned at a higher level relative to the cheek teeth than in B. illuminata . The anterior insertion area for the internal superficial masseter muscle ( Figure 29A ) is larger than in B. illuminata , similar in proportions to B. sp. cf. B. bandharr (QM F4750), but smaller than in B. bandharr and B. bila .

Lower dentition. The i1 of B. nullarbora is similar in size to that of B. illuminata , but it has thinner dorsal and ventral enamel flanges. In overall size and morphology, the lower molars are most similar to those of B. sp. cf. B. bandharr (e.g., QM F4750, QM F58665), but they have a shorter anterior portion of the trigonid (precingulid + anterior portion of paracristid) than in any other species of Bohra , and the paracristid and cristid obliqua are also comparatively very low. The species is also distinguished by the presence, on m4, of a very low parametacristid, which extends to the centre of the trigonid basin, terminating against the paracristid ( Figure 29F ).

Clavicle. The clavicle is more robust and less flattened than in B. illuminata , with expanded articular facets and less-pronounced cranial curvature.

Humerus. The humerus is more robust than in B. illuminata , with a stronger pectoral crest, deltoid ridge, bicipital groove and spino-deltoid insertion. The teres major insertion is less protruding. The distal articular surface, in particular the capitulum, is relatively narrower than in B. illuminata .

Innominate. The base of the ilium is relatively broader in the craniocaudal axis, and the medial border is sinuous by comparison with the straight medial border in B. illuminata . An oval fossa contiguous with the rugose muscle scar of m. rectus femoris dorsal to the acetabulum is distinct and unique to B. nullarbora .

Femur. The femur of B. nullarbora is distinguished from that of B. illuminata in its more caudally positioned scars for the mm. adductores femoris, and from B. planei by having a less laterally projected base of the greater trochanter.

Calcaneus. Morphologically, the calcaneus of B. nullarbora is distinguished from those of B. illuminata , B. paulae and B. planei by having distinctly separate medial and lateral talar facets, and from B. wilkinsonorum and B. sp. indet. 1 by having a straight lateral edge to the medial facet, which extends both cranially and caudally from the facet margins. It shares with B. illuminata and B. paulae a less acute, more smoothed cuboid step than in B. planei , B. wilkinsonorum and B. sp. indet. 1. It shares with B. illuminata a ventromedial cuboid facet that is confluent with the dorsal facets, though the entire surface is not as smoothed as in B. paulae . The relatively very short anteroplantar sulcus between the rugose plantar surface and anterior plantar tubercle is unique to B. nullarbora .

Talus. The talus of B. nullarbora is distinguished from all other species of Bohra and Dendrolagus (e.g., Figure 9F–K ) in its relatively higher trochlear crests, and thus deeper trochlear groove, and in the distinct separation between the calcaneal facets. It also has a relatively deeper malleolar fossa, more projected malleolar tubercle, and longer neck than in other species of Bohra .

Metatarsals. Metatarsal IV and, in particular, metatarsal V of B. nullarbora are more robust than in B. illuminata , though this might be accounted for by the ontogenetically younger age of the holotype of B. illuminata versus that of B. nullarbora . The facet for metatarsal V is relatively smaller and the gap between this and the sesamoid facet is relatively wider in B. nullarbora compared with the conditions of B. illuminata and B. paulae , though this may be within the normal range of intraspecific variation given their differing ontogenetic ages. Metatarsal V of B. nullarbora is more gracile than in B. paulae , with a relatively narrower facet for metatarsal IV, a more elongate proximolateral process and a more deeply flexed cuboid facet.

Remarks. Our understanding of B. nullarbora is fundamentally as it was when it was named and first described in 2009, but the broader comparisons made here mean that the species is now better circumscribed. In addition, several loose molars referable to B. nullarbora have been identified in a Pleistocene assemblage from Yorke Peninsula, 1,000 km southeast of the Nullarbor type locality ( Figure 1 ). Whether the ancient DNA retrieved from Tunnel Cave in southwestern Australia ( Murray et al. 2013) belongs to B. nullarbora , B. illuminata or neither, remains to be verified with further molecular work.

Figures

FIGURE 1. Map of Australia and New Guinea showing localities that have produced fossils attributable, or potentially attributable, to species of Bohra.

FIGURE 9. Calcaneus and talus (right, adult) of Dendrolagus bennettianus (QM JM19863). Calcaneus (A–E). A: dorsal view. B: plantar view. C: medial view. D: cranial view. E: lateral view. Talus (F–K). F. plantar view. G: medial view. H: dorsal view. I: caudal view. J: lateral view. K: cranial view. AHN, head of talus (articular facet for navicular); APT, anterior plantar tuberosity; ATF, anteromedial facet for head of talus; CFA, articular facet for cuboid; CPS, calcaneal plantar surface; DMF, dorsomedial facet of calcaneal-cuboid articulation; DLF, dorsolateral facet of calcaneal-cuboid articulation; FGS, flexor groove of sustentaculum tali; FIB, fibular articular surface; FIL, tubercles for fibular ligaments; LCS, lateral calcaneal facet; LTF, lateral facet for talus; LTC, lateral trochlear crest; MCF, medial calcaneal facet; MFO, malleolar fossa; MMA, medial malleolus; MTC, medial trochlear crest; MTF, medial facet for talus; PVP, posteroventral process; STA, sustentaculum tali; TCA, tuber calcanei; TCE, epiphysis of tuber calcanei; TPS, transverse plantar sulcus; TRO, trochlea (talo-crural joint); VMF, ventromedial facet of calcaneal-cuboid articulation.

FIGURE 23. Cranium and partial dentaries of the holotype of Bohra illuminata (WAM 03.5.10). A: right lateral view. B: anterior view. C: dorsal view. D: palatal view. E: posterior view. F: posterior end of right dentary in lateral view. G: mesial view. H: partial left dentary in lateral view. I: mesial view.

FIGURE 27. Partial cranium (adult) of the holotype of Bohra nullarbora (WAM 05.4.70). A: dorsal view of neurocranium. B: ventral / internal view of neurocranium. C: anterior view of neurocranium. D: posterior view of neurocranium. E: stereo palatal view. F: posterior view of neurocranium.

FIGURE 28. Molars of Bohra nullarbora. SAMA P55395, left M1 (A–E). A: stereo occlusal view. B: lingual view. C: buccal view. D: posterior view. E: anterior view. SAMA P55204, left M2 (F–J). F: stereo occlusal view. G: lingual view. H: buccal view. I: posterior view. J: anterior view. SAMA P55400, right M3 (K–O). K: stereo occlusal view. L: lingual view. M: buccal view. N: posterior view. O: anterior view. SAMA P55417, left m1 (P–R). P: stereo occlusal view. Q: buccal view. R: lingual view. SAMA P55412, left m2 (S–W). S: stereo occlusal view. T: buccal view. U: lingual view. V: posterior view. W: anterior view.

FIGURE 29. Dentaries (adult) of the holotype of Bohra nullarbora (WAM 05.4.70). A: lateral view of left dentary. B: lateral view of partial right dentary. C: mesial view of left dentary. D: buccal view of i1. E: lingual view of i1. F: partial right dentary (partial m2, m3–4) in stereo occlusal view. G: left dentary (m1–4) in stereo occlusal view.