Bohra illuminata Prideaux & Warburton, 2008

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 : 42-49

Bohra illuminata Prideaux & Warburton, 2008

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

Bohra sp. indet.: Prideaux & Warburton (2008), pp. 463–464, figure 1 (partim). Prideaux & Warburton (2009), p. 166, figure 1 (partim).

Holotype. WAM 03.5 .10, partial adult skeleton including cranium, partial left and right dentaries. Minimal wear on P3 and M4 indicate that these teeth had only recently erupted. This reveals that the specimen is a young adult not yet fully grown as confirmed by the unfused epiphyses of vertebrae and limb elements. Postcranial elements: four cervical, four thoracic, five lumbar, and eight caudal vertebrae; numerous partial ribs; proximal fragments of right and left scapulae; left clavicle; right humerus (missing proximal epiphysis); right ulna; fragments of radius; triquetrum, hamatum; metacarpals; manual phalanges; innominate fragments, including partial left and right ilia with acetabular fossa; fragments of left femur and near-complete right femur; left and right tibiae; left calcaneus; right talus; right cuboid; partial left and right metatarsals IV; partial left metatarsal V; pedal phalanges, including left digits IV – V.

Revised diagnosis. Bohra illuminata is distinguished from B. nullarbora and the species of Dendrolagus in the following cranial features: a distinct buccinator fossa; a less distinct supraorbital crest above the posterior end of the eye orbit; a broad groove between the supraorbital crest and superior lacrimal rugosity, which produces a constriction of the frontals; a relatively shallow zygomatic arch; a strongly domed dorsal neurocranial surface; a distally broader, more anteriorly hooked postglenoid process. The cheek teeth are large relative to the dimensions of the palate. P3 bears a distinct posterolingual cusp, but only the slightest hint of a thin cingulum anterior to it, which distinguishes B. illuminata from all other species for which P3 is known. The dentary is shallower relative to the height of the lower molars than in all other tree-kangaroo species. The i1 of B. illuminata has thicker dorsal and ventral enamel flanges than in B. nullarbora . Lower molars bear a strongly developed premetacristid.

Compared with that of B. nullarbora , the clavicle of B. illuminata is more gracile and flattened, with less expanded articular facets and a more medially positioned anterior inflection. The humerus is more gracile with a weaker pectoral crest, deltoid ridge, bicipital groove and spinodeltoid insertion than in B. nullarbora , but with a higher m. teres major insertion. The distal articular surface of the humerus is relatively broad. The ilium is relatively narrower anteroposteriorly, with a straighter medial border compared with that of B. nullarbora . The distinct long adductor muscle grooves on the medial aspect of the femur distinguish B. illuminata from B. nullarbora and B. planei , and in this attribute resembles the species of Dendrolagus . The tibia of B. illuminata is smaller and more gracile than that of B. paulae , and the interosseous margin is less sinuous in cranial view. The talar articular surface on the calcaneus is wider and the medial malleolus is more obliquely orientated in distal view than in B. planei . The calcaneus has a longer anterior plantar sulcus than in B. nullarbora , and more confluent talar facets with a mesially tapered lateral talar facet. The cuboid facets on the calcaneus are smoothly confluent and the calcaneocuboid step is very shallow and smoothed. Metatarsal IV is less robust than in B. nullarbora , with a smaller cuboid facet, a more medially constricted facet for metatarsal V, and a more rounded, distally orientated sesamoid facet. Metatarsal V is less robust.

Type Locality. Metasthenurus Chamber, Last Tree Cave, Nullarbor Plain, southeastern Western Australia. Most of the holotype was collected from a small grotto on the north side of the chamber by John A. Long, Lindsay M. Hatcher and GJP in July 2002 and April 2003. However, the right femur and several non-descript postcranial fragments were collected by Lindsay M. Hatcher and GJP in April 2014. Fossils from the floor of Last Tree Cave , although previously inferred to be of early middle Pleistocene age ( Prideaux et al. 2007), are actually undated, but include specimens of several species known from well-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 .

Paratype. Main Chamber , Last Tree Cave . WAM 02.7 .16, partial juvenile skeleton. Craniodental elements: left P3, M1–2, right maxilla fragment (preserving M1); left i1, partial right dentary (preserving m 1–2 in occlusion, m 3 in crypt, isolated p3); Postcranial elements: fragments of numerous vertebrae including 14 caudal vertebrae; numerous rib fragments; proximal fragment of left scapula; proximal fragment of right humerus; numerous carpals and metacarpals; innominate fragments including left and right ilia with acetabula, right ischium and epipubic; proximal fragments of femora; distal epiphysis of right fibula; fragments of right and left proximal tibia epiphyses; distal fragment and epiphysis of right tibia; left and right calcanei (right with separate epiphysis); left talus; left cuboid; left navicular; left and right metatarsals IV; right metatarsal V (missing distal epiphysis); left proximal, left and right medial and distal phalanges of digit IV, plus several other distal phalanges. This specimen was collected by GJP on 7 July 2002 from beneath a boulder overhang on the east side of the southern end of the chamber, the deepest point in the cave at 40 m depth .

Referred specimens. RF 95 fissure fill, Curramulka Quarry, Yorke Peninsula, South Australia. SAMA P55401, right M4; SAMA P55402, right M4; SAMA P55403, left M4; SAMA P55406, left M3; SAMA P55408, left m1, right m1 (these teeth are identical in morphology, wear and preservation, so are considered to belong to the same individual); P55409, right m2; SAMA P55410, right m1; SAMA P55416, left M1. These specimens were collected by James A. McNamara (South Australian Museum) in the mid-1990s. The deposit is considered to be of Pleistocene age.

New Kalamurina, Warburton River, South Australia. SAMA P59526 , left i1. Collected by Neville S. Pledge ( South Australian Museum ), 9 March 1972. Middle to late Pleistocene .

Etymology. This refers to the insights provided by the holotype, the first-known specimen of a species of Bohra represented by associated hindlimb and cranial elements. This confirmed that Bohra paulae , known only from hindlimb elements, and B. wilkinsonorum , known only from one partial maxilla, were indeed congeneric, as argued by Dawson (2004a).

Description and comparisons. Cranium. Previously described in detail ( Prideaux & Warburton 2008). The incisor-bearing portion of the premaxilla ( Figure 23A ) is similar in proportion and relative depth to that observed in Dendrolagus bennettianus and D. inustus , but is shallower than in B. nullarbora and relatively longer than in most species of Dendrolagus .The narial aperture is slightly broader than deep( Figure23B ),as in B.nullarbora ,but the lateral margins are more concave than in species of Dendrolagus .The buccinator fossa is moderately deep( Figure 23A ),much more distinct than in B. nullarbora and species of Dendrolagus , in which there is only the barest hint of a concavity immediately above the diastema. The masseteric process is small, extending ventrally to about the level of the basal enamel margin of M2, as in species of Dendrolagus . Above the posterior extremity of the eye orbit, there is a swelling of the frontal, triangular in lateral view, that is bounded dorsally by a slight supraorbital crest ( Figure 23A ).Above the centre of the orbit, a broad groove ( Figure 23A, C ) separates the supraorbital crest from the superior lacrimal rugosity. This groove manifests itself in dorsal view as a constriction of the frontals. This combination of supraorbital features distinguishes B. illuminata from all other tree-kangaroo species. Posteriorly, the supraorbital crest is more markedly projected laterally in B. nullarbora , and much smoother and lower over its entire length in species of Dendrolagus .

The zygomatic process of the squamosal ( Figure 23A–B, E ) is shallower relative to the depth of the cranium than in all other tree-kangaroo species. The marked doming of the dorsal surface of the neurocranium, which is typically a feature of young juvenile macropodid individuals, is unique to B. illuminata among young adults or subadults of tree-kangaroo species. The relatively narrow ectoglenoid process ( Figure 23D ) and the manner in which the postglenoid process is broad at its distal extremity and curved anteriorly, providing the glenoid fossa with a semi-circular shape when viewed laterally ( Figure 23A ), are unique among tree-kangaroo species.

Upper dentition. Bohra illuminata is most easily distinguished from all other tree-kangaroo species by having larger cheek teeth relative to the overall proportions of the palate and a weakly developed lingual cingulum on P3, but with a distinct cuspule on the anterolingual corner of the crown ( Figures 23D , 24A ). In addition, the central cuspules of the P3 main crest are very small and only just distinguishable ( Figure 24A–B ). The upper molars of B. illuminata ( Figures 24A, C , 25A–J , Table 5 ) are most similar in size and morphology to those of B. bandharr , differing only by being marginally less flat-sided buccally. The upper molars are also similar to those of B. nullarbora , but differ by being slightly larger overall and longer relative to their width, by having a flatter lingual side of the crown base, and by having a low cingulum bordering the interloph valley lingually. They differ from those of B. bila by lacking any remnant cusp C region of the stylar crest, and by having a less incurved postparacrista.

Dentary. The horizontal ramus of B. illuminata ( Figure 23F–I ) is shallower relative to the height of the lower molars than in B. nullarbora , B. bila and the species of Dendrolagus , although this may be because the holotype is a subadult. The mandibular condyle is not positioned as high above the level of the molar row as in B. nullarbora . The digastric sulcus is less distinct in B. illuminata than in B. nullarbora and B. bila , and the anterior insertion area for the internal superficial masseter muscle is thinner and restricted to the rim of the masseteric fossa. The general profile of the posterior end of the dentary is otherwise similar between these three species.

Lower dentition. Although similar in size and overall morphology, the i1 of B. illuminata ( Figure 24I–K ) has thicker dorsal and ventral enamel flanges than that of B. nullarbora . The unerupted p3 of the paratype, WAM 02.7.16 ( Figure 24D ), although lacking its full complement of enamel, was clearly swollen posteriorly, but the posterobuccal eminence is not as large as in the holotype of B. bila . The lower molars ( Figures 24E–H , 25K–O ) closely resemble those of B. nullarbora , but they are larger and the premetacristid is more strongly developed, especially on m3–4, a morphology reminiscent of the condition seen in the species of Dorcopsis . The lophids of B. illuminata are slightly more swollen than in B. nullarbora , and the buccal and lingual sides of the interlophid valleys are less concave.

Clavicle. The clavicle is more gracile and dorsoventrally flattened than in B. nullarbora , with reduced articular facets and a less laterally positioned cranial inflection.

Humerus. The humerus is less robust than in B. nullarbora , with a weaker pectoral crest, deltoid ridge, bicipital groove and spino-deltoid insertion, and a higher teres major insertion.

Ilium. The ilium is relatively narrower craniocaudally than in B. nullarbora , with a less sinuous medial border.

Femur. The holotype right femur is abraded near its proximal epiphyseal margin, and the proximal and distal articular epiphyses are missing ( Figure 26 ). The distal end of the lateral trochanteric crest terminates craniad of the distal margin of the lesser trochanter ( Figure 26A ). The trochanteric fossa is relatively open ( Figure 26B ), as in species of Dendrolagus ( Figure 5A ). The shaft is cranially convex ( Figure 26C–D ), less robust than in B. nullarbora , and tending to ovoid in cross-section rather than circular, reminiscent of the species of Dendrolagus ( Figure 5A–D ). Highly distinct muscle scars – one on the proximocaudal surface immediately distal to the trochanteric fossa and two elongate, depressed scars on the medial surface of middle third of the femur – appear to correspond to the three portions of the mm. adductores femoris ( Figure 26C ). These are much more strongly marked than in B. nullarbora , which has no sign of the proximal one, and B. planei in which the adductor scars are more rugose than depressed and more caudally than medially positioned, but are similarly strongly developed in species of Dendrolagus ( Figure 7C ; Warburton et al. 2012). The quadratus femoris tubercle is more raised than in B. nullarbora and B. planei . The distal fossa for the medial gastrocnemius is very shallow, even shallower than in species of Setonix and Thylogale , and most similar to those of B. nullarbora and species of Dendrolagus ( Figure 7C ). This is also the case with the very shallow popliteal fossa. The distal epiphysis resembles that of the species of Dendrolagus ( Figure 7F ), but the fibular groove of the lateral condyle is less reduced and the cranial epiphyseal width is only slightly less than the caudal width in B. illuminata .

Tibia. The tibia of B. illuminata is smaller and more gracile than that of B. paulae ( Figure 11 ). The two species are similar in the relative size of the tibial crest, curvature of the shaft and length of fibular contact, but the proximal fibular facet of B. illuminata is less pronounced than in B. paulae . In cranial view, the interosseous margin of the tibia is less sinuous than in B. nullarbora , and particularly in B. paulae . From the distal view, the talar articular surface is wider and the medial malleolus set at a more oblique angle in B. illuminata than in B. planei ( Figure 32 ).

Calcaneus. The calcaneocuboid step is much shallower and more smoothed than in all other species of Bohra , with the possible exception of B. paulae . Compared with that of B. nullarbora , the calcaneus of B. illuminata is smaller (which in part is very likely due to its younger ontogenetic age), lacks a partial separation of the talar facets, and has a longer anterior plantar sulcus, a poorer developed plantar tuberosity, a narrower sustentaculum tali, and a relatively wider, more mesially tapered lateral talar facet. Distinguished from that of B. paulae by being smaller, with a relatively shorter and less barrel-shaped tuber calcanei, shorter and wider talar facets, a longer sustentaculum tali, a larger anteroplantar tuberosity, a relatively smaller ventromedial cuboid facet and relatively wider dorsolateral cuboid facet. The calcaneus of B. illuminata is distinguished from that of B. wilkinsonorum in being much smaller in absolute size ( Table 8 ), with much smoother and confluent talar and cuboid facets. The transversely wider, smoother, and more confluent cuboid facets similarly set the calcaneus of B. illuminata apart from that of B. planei ( Figure 33 ).

Talus. The holotypes of B. illuminata and B. nullarbora are very similar in talar morphology, but two clear differences are evident. The facets for articulation with the calcaneus on the ventral surface are smoothly conjoined in B. illuminata , whereas they are separated by a distinct groove in B. nullarbora . In addition, the malleolar fossa in B. illuminata is narrower than in B. nullarbora . Although the talus of B. illuminata is smaller and has a shallower trochlear groove, both of these differences may well be due to its younger ontogenetic age. All other differences evident between the two specimens appear to be superficial and the result of the incompleteness of several features due to post-depositional abrasion or breakage. By comparison, B. paulae ( Figure 12K ) and B. planei ( Figure 33I ) are characterised by a shorter talar neck and shallower malleolar fossa from the dorsal view, and a broader, less obliquely orientated navicular facet in cranial view.

Metatarsals. The metatarsal IV of the B. illuminata holotype is less robust than in B. nullarbora and B. paulae , and the metatarsal V facet is more medially constricted. In B. illuminata , the dorsolateral corner of the cuboid facet is more pointed than in B. nullarbora and B. paulae , while the ventral peninsula of this facet is intermediate in relative breadth between the conditions manifested in the other two species. The proximity of the plantar sesamoid and metatarsal V facets in B. illuminata is intermediate between that observed in B. nullarbora and B. paulae .

The metatarsal V of the B. illuminata holotype is less robust than that of B. nullarbora , but this may simply be because it is not fully grown. It also differs by having a relatively broader metatarsal IV facet. By comparison with B. paulae ( Figure 13 ), B. illuminata differs by having a less rounded medial end of the metatarsal IV facet. It differs from both B. nullarbora and B. paulae by having a more rugose interosseous ligament attachment.

Remarks. Most of what we know about B. illuminata is as it was in 2008, but the subsequent description of B. nullarbora , the belated 2014 discovery of the B. illuminata holotype right femur, and the allocation of pedal remains to other species have allowed the diagnosis and comparisons to be refined. Our understanding of the geographic distribution of B. illuminata has also been augmented through the referral to this species of loose molars from Curramulka Quarry, central Yorke Peninsula ( Figure 1 ). Ancient DNA that aligned best with that of a tree-kangaroo has been recovered from a late Pleistocene archaeological deposit in Tunnel Cave, southwestern Australia ( Figure 1 ; Murray et al. 2013), and may belong to B. illuminata or B. nullarbora , but confirmation of its tree-kangaroo identity must await 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 5. Humerus (right, adult) of Dendrolagus bennettianus (QM JM19863). A: cranial view. B: medial view. C: caudal view. D: lateral view. E: proximal view. F: distal view. CAP, capitulum; COF, coronoid fossa; DEL, deltoid crest; GRT, greater (lateral) tubercle; HHE, humeral head; ITG, intertubercular (bicipital) groove; LET, lesser (medial) tubercle; LEP, lateral epicondyle; MEP, medial epicondyle (missing epiphysis); MLD, insertion of m. latissimus dorsi; MPE, insertion of m. pectoralis superficialis; OLF, olecranon fossa; RAF, radial fossa; SCF, supracondylar foramen; SCR, (lateral) supracondylar ridge; TRO, trochlea.

FIGURE 7. Femur (right, adult) of Dendrolagus bennettianus (QM JM19863). A: cranial view. B: caudal view. C: medial view. D: lateral view. E: proximal view. F: distal view.AFO, fossa for m. adductors; FHE, femoral head; FTR, femoral trochlea; GTR, greater trochanter; ICF, intercondylar fossa; ITF, intertrochanteric fossa; LCO, lateral condyle; LEP, lateral epicondyle; LTC, lateral trochanteric crest; LTR, lesser trochanter; LSF, lateral supracondylar fossa (for m. flexor digitorum superficialis); MCO, medial condyle; MEP, medial epicondyle; MSF, medial supracondylar fossa (for m. gastrocnemius); TQF, tubercle for m. quadratus femoris.

FIGURE 11. Tibia of Bohra paulae. AM F62102, left adult tibia (A–F). A: cranial view. B: caudal view. C: medial view. D: lateral view. E: proximal view. F: distal view. AM F62101, partial left adult tibia (G–J). G: cranial view. H: caudal view. I: medial view. J: lateral view.

FIGURE 12. Calcaneus and talus (right, adult) of the holotype of Bohra paulae (AM F62099–F62100). Calcaneus (A–E). A: dorsal view. B: plantar view. C: medial view. D: lateral view. E: cranial view. Calcaneus and talus in articulation (F–I). F: dorsal view. G: medial view. H: cranial view. I: lateral view. Talus (J–O). J: cranial view. K: dorsal view. L: medial view. M: caudal view. N: plantar view. O: lateral view.

FIGURE 13. Metatarsals IV and V of Bohra paulae. AM F104075, left juvenile metatarsal IV (A–E).A: dorsal view. B: plantar view. C: lateral view. D: medial view. E: proximal (caudal) view.AM F104550, left juvenile metatarsal IV (F–J). F: dorsal view. G: plantar view. H: lateral view. I: medial view. J: proximal (caudal) view. AM F104092, right adult metatarsal V (K–N). K: dorsal view. L: plantar view. M: medial view. N: lateral view. AM F103802, right adult metatarsal V (O–R). O: dorsal view. P: plantar view. Q: medial view. R: lateral view.

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 24. Craniodental specimens of Bohra illuminata. WAM 03.5.10, holotype (A, G–J). A: left upper cheek-tooth row in stereo occlusal view. G: right m4 in stereo occlusal view. H: left lower cheek-tooth row in stereo occlusal view. I: left i1 in buccal view. J: left i1 in lingual view. WAM 02.7.16 (B–F). B: incomplete, unerupted right P3 in stereo occlusal view. C: left M1 in in stereo occlusal view. D: right p3 in stereo occlusal view. E: right m1 in stereo occlusal view. F: right m2 in stereo occlusal view. SAMA P59526, left i1 (K–L). K: buccal view. L: lingual view.

FIGURE 25. Molars of Bohra illuminata. SAMA P55406, left M3 (A–E). A: stereo occlusal view. B: lingual view. C: buccal view. D: posterior view. E: anterior view. SAMA P55401, right M4 (F–J). F: stereo occlusal view. G: lingual view. H: buccal view. I: posterior view. J: anterior view. SAMA P55408, left m1 (K–O) and right m1 (N). K: stereo occlusal view. L: lingual view. M: buccal view. N: posterior view. O: anterior view.

FIGURE 26. Right femur of the holotype of Bohra illuminata (WAM 03.5.10).A: cranial view. B: caudal view. C: medial view. D: lateral view.

FIGURE 32. Partial tibia (right, adult) of the holotype of Bohra planei sp. nov. (UCMP 70128).A: cranial view. B: lateral view. C: caudal view. D: medial view. E: distal view.

FIGURE 33. Calcaneus and talus (right, adult) of the holotype of Bohra planei sp. nov. UCMP 70128, holotype calcaneus (A–E). A: plantar view. B: dorsal view. C: cranial view. D: medial view. E: lateral view. NHMD 193283, partial right calcaneus (F–G). F: dorsal view. G: medial view. UCMP 70128, holotype talus (J–M). H: plantar view. I: dorsal view. J: medial view. K: lateral view. L: caudal view. M: cranial view.